SYNTHETIC TANNINS: THEIR INDUSTRIAL PRODUCTION AND APPLICATION
With regard to their industrial production, but few synthetic tannins
are, to-day, of practical and commercial interest. In addition to
simplicity in the method of manufacture a certain degree of purity of
the raw materials constitutes the criterion of their suitability. The
methods of manufacture, of which nearly all are the property of the
B.A.S.F., have been so worked out that the production of synthetic
tannins presents no difficulties on a practical scale. Cresols,
naphthalenes, and higher hydrocarbons are used as starting materials in
the production of synthetic tannins; the former substances or their
oxidation products are sulphonated by means of concentrated sulphuric
acid, and the tanning matter produced by condensing the sulphonic acids
with formaldehyde. The crude synthetic tannin thus obtained has yet to
be diluted and partly neutralised before it can be applied in practice,
and this is carried out by mixing the crude product with strong caustic
lye. By these means the high acidity is reduced to a suitable degree
learned from experience on the one hand; on the other hand, the salts of
the sulphonic acids form valuable components of the commercial synthetic
tannins.
The first product placed on the market was named Neradol D; this
represents the condensation product of cresolsulphonic acid. The second
synthetic tannin was Neradol N, which represents the condensation
product of naphthalenesulphonic acid; when diluted and neutralised to
the same extent as is done in the case of Neradol D, the product is
named Neradol N D. The latest synthetic tannin has been called
Ordoval G, the starting material of which is a still higher
hydrocarbon.
The tannoid-chemical properties of these synthetic tannins have been
exhaustively determined by the author, who employed Neradol D, which is
most suitable for such a purpose, and the investigations relating to it
will now be treated fully in the following chapters. The two other
synthetic tannins exhibit very similar properties, but their few
characteristics shall be shortly dealt with.
The condensation product obtained by the method described on p. 55 forms
a viscous, dark coloured mass, the analysis of which by the shake method
gives the following figures:-
Tanning matters 62.6 per cent.
Non tannins 6.4 "
Insolubles 0.0 "
Water 31.0 "
———————-
100.0 per cent.
Acidity: 1 gm. = 40 c.c. N/10 NaOH.
According to its chemical constitution, this product may
be considered to be dinaphthylmethanedisulphonic acid.
Samples of this crude, strongly acid material were partly
neutralised, and the following figures obtained on analysis:—
Acidity. Tanning Soluble Water.
Matters. Non-tans.
Per Cent. Per Cent. Per Cent.
1 gm. = 35 c.c. N/10 NaOH 61.8 7.0 31.2
1 " = 30 " " 58.9 7.1 34.0
1 " = 25 " " 50.1 7.9 42.0
1 " = 20 " " 42.2 8.9 48.9
1 " = 15 " " 37.4 10.4 52.2
1 " = 10 " " 31.6 13.6 54.8
1 " = 5 " " 26.3 16.6 57.1
Experimental tanning tests which were carried out with the various
partly neutralised samples yielded leathers which, on an average, were
nearly white, but which in comparison with a leather tanned with Neradol
D appeared rather more greyish and were much harder.
A solution of the half-neutralised substance (1gm. = 20 c.c.
N/10 NaOH) gives the following reactions:—-
Gelatine—Precipitate, partly soluble in excess tannin solution.
Ferric chloride——-No coloration.
Barium chloride——-Precipitate, insoluble HNO_3.
Bromine water——-No reaction.
Silver nitrate——-No reaction.
Aniline hydrochloride——Precipitate, dissolves when solution
is heated.
This condensation product is very soluble in water, but insoluble in
most solvents, excepting methyl and ethyl alcohols. The above reactions
show the similarity of this dinaphthyl derivative to the dicresyl
derivative, and the absence in the former of characteristic reactions
with iron salts is mainly accounted for by its lack of phenolic groups.
The absence of this reaction does not, of course, influence the tannoid
character of dinaphthylmethanedisulphonic acid in the least, and is of
no importance in practice, since the various stages of tannage may be
demonstrated by means of a solution of indigotine.
From a technical point of view the absence of this reaction is
advantageous to this extent, that it eliminates the exceedingly great
care to avoid the contact of tan liquors and tanned pelt with iron
particles which has to be observed when tannins of phenolic character
are employed.
In a chemical and technological evaluation of this tanning matter, all
those details apply which will be described when discussing Neradol
D. The most important advantage possessed by this tanning matter, from a
commercial point of
view, is the lower price which it owes to the greater ease with which
naphthalene may be obtained.
By treating the non-condensed crude product with barium chloride, a
product completely devoid of sulphuric acid is easily obtained; the
contents of sulphuric acid calculated as BaSO_4 is about 9.5 per
cent. This value is higher than that found by Neradol D, and may be
explained by the fact that a slight excess of sulphuric acid is
necessary for the preparation of [Greek: b]-naphthalenesulphonic acid.
Comparative tanning tests using products containing sulphuric acid and
products free from sulphuric acid (neutralised to the same degree of
acidity) yielded leathers which were very similar; the liquor containing
no sulphates yielded slightly softer leather than that obtained from a
liquor containing sulphates.
An experiment was also carried out, using a liquor containing the tannin
completely neutralised with caustic soda and subsequently acidified with
acetic acid till the acidity of 1 gm. = 10 c.c N/10 NaOH; here, again,
no essential difference could be detected in the leather as compared
with that from a liquor containing sulphates.
One of the most striking properties of this tanning matter is its
solubilising effect on natural tannins and the phlobaphenes; this
property may mainly be compared to the similar one of other condensed
sulphonic acids in their behaviour towards natural tannins.
If, therefore, natural tannins are mixed with this product and the
solution used for tanning purposes, the resultant leather will possess a
dark colour owing to the presence of solubilised phlobaphenes; if, on
the other hand, a dark coloured leather, which has been tanned with
natural tannins, is washed over with a 5° Bé solution of this synthetic
tannin, or immersed for some time in the solution, the leather assumes a
lighter colour owing to the phlobaphenes being dissolved and removed
from the leather by the synthetic tannin.
The presence of Neradol ND in leathers is detected by methods to be
described under Neradol D (cf. p. 108). The oxyazo reaction only
succeeds when the solution has been boiled with a few drops of
hypochlorite solution, quickly cooled and excess of ammonia added. When
applying the indophenol reaction, the solution must be treated as
follows: 3-4 drops of hypochlorite solution is added, and the solution
heated for a short time; or 5-6 drops hypochlorite solution may be
added, and the solution left for some time, in which case the heating
may be omitted. The solution is then made distinctly ammoniacal, 1-2
drops of dimethyl-p-phenylenediamine solution and a layer of alcohol
poured on the top. In most cases a blue coloration will appear; the
addition of 1-2 drops of potassium ferricyanide solution with formation
of a blue coloration indicates the presence of Neradol ND without fail.
The fact that a product possessing tanning properties may be obtained by
condensing [Greek: b]-naphthalenesulphonic acid makes it interesting to
investigate the behaviour of a non-condensed [Greek:
b]-naphthalenesulphonic acid towards pelt. The following solutions were
allowed to act upon pelt for twelve days:—
(1) Concentrated solution of [Greek: a]-naphthalenesulphonic acid (10° Bé).
(2) " " [Greek: b]- " " (6° Be.)
(3) " " 2,7- " " (18° Bé.).
Solution 1 swells the pelt to a considerable extent without, however,
solubilising it. Solution 2 produces a similar effect. Solution 3
dissolves the pelt appreciably on the first day; after six days,
solubilisation is complete. The reason of this different behaviour of
the mono- and disulphonic acids is mainly to be sought in their
difference of solubility; the monosulphonic acids are not very soluble,
and are only capable of giving solutions measuring 10° and 6° Bé,
respectively, whereas the disulphonic acid yields an 18° Bé solution, in
addition to which the much higher acidity of the latter quickly
gelatinises the pelt.
As regards the capability of the naphthalenesulphonic acids of
dissolving phlobaphenes, the following results were obtained:—solid
Argentine quebracho extract was mixed with—
5 percent, [Greek: a]-naphthalenesulphonic acid: opaque sol.,
large quantity of insolubles.
10 " " " lesser " "
20 " " " no insolubles.
30 " " " "
5 " [Greek: b]-naphthalenesulphonic acid: opaque sol.,
lesser quantity of insolubles.
10 " " " "
20 " " " clear solution, no insolubles
30 " " " "
5 " 2,7-naphthalenedisulphonic acid: opaque sol.,
large quantity of insolubles.
10 " 2,7 " " as above.
20 " 2,7 " " slightly opaque, some insolubles.
30 " 2,7 " " nearly clear solution, no insolubles.
It is hence clear that the [Greek: b]-sulphonic acid possesses
phlobaphene-solubilising qualities greater than those of the [Greek:
a]-sulphonic acid or the disulphonic acid; the Greek: b]-sulphonic acid
was therefore made the subject of Ger. Pat., 181,288 (8th February
1917).
The synthetic tannin, Ordoval G, is the formaldehyde condensation
product of higher hydrocarbons (mainly retenes), and is a partly
neutralised product containing no sulphuric acid. The author's analysis
gave the following figures:—
Tanning matters 10.7 per cent.
Soluble non-tannins 16.4 "
Insolubles 0.0 "
Water 73.0 "
Acidity: 1 gm. = 4 c.c. N/10 NaOH.
Density: 23° Be.
Ordoval G is completely soluble in water and glacial acetic acid. Only
its organic constituents are soluble in alcohol, ethyl acetate, and
acetone, whereby a dark coloured crystalline mass separates. Ordoval G
is insoluble in benzene.
The aqueous solution of Ordoval G gives the following reactions:—
Gelatine Moderate flocculent precipitate.
Ferric chloride Darkish coloration.
Potassium dichromate No reaction.
Aniline hydrochloride Dark brown precipitate.
Formaldehyde hydrochloric acid No precipitate.
Bromine water No reaction.
Zinc acetate Very slight opalescence.
Barium chloride Slight opalescence.
Its capability of solubilising and consequent saving of natural tannins
is shown by the fact that 100 kilos of vegetable tanning material may be
substituted by 40 kilos of Ordoval G and the material in question in
order to obtain the entire tanning intensity of the latter.
In one respect—that of its salts—Ordoval G differs from the Neradols;
whereas the chromium and aluminium salts of the latter possess no such
tannoid properties as will make the resultant leather exhibit any of the
characteristics of either tannage, it is possible to carry out combined
tannage with a mixture of Ordoval G and metallic salts. Tanning
experiments carried out with the chromium, iron, aluminium, and calcium
salts of Ordoval G yielded leathers which possessed proportionate
characteristics of either kind of tannage to the extent to which either
material was present. This combination tannage seems to be assured of a
great future; especially may a combination tannage of iron salts and
Ordoval G eventually entirely replace chrome tannage.
The detection of Ordoval G in leather is carried out as follows: 10
gm. of leather are boiled with 150 c.c. of acetic acid, a solution of 25
gm. of CrO_8 in 25 c.c. of a 50 per cent, solution of acetic acid
gradually added, and the mixture boiled for three hours, till the
leather is decomposed and the solution has assumed a brown instead of
the original light yellow colour. The solution is then evaporated, the
residue dissolved in 600 c.c. hot water, and the chromium precipitated
with a 40° Bé. solution of caustic soda. The solution is filtered and
cooled, and a little hydrosulphite is added to 20 c.c. of the cold
alkaline filtrate; in the presence of Ordoval G, a red colour will
appear (oxanthranolsulphonic acid).
Brief mention must be made of the so-called Corinal [Footnote: Swiss
Pat, 78,282, 78,797, 79,39.] a synthetic tannin placed upon the market
by Chem. Fabrik Worms A.-G., in Worms-on-the-Rhine. It is a viscous,
brown fluid, containing the aluminium salts of the tannoid acids. The
latter are formaldehyde-condensation products of sulphonated tar oils,
or the hydroxylated derivatives of the latter. The density being 33° Bé,
it contains 28.1 per cent. tanning matters, 13 per cent. soluble
non-tannins, and 10.8 per cent. inorganic matter (3.2 per cent. Al_2O_3
and 7.6 per cent. Na_2SO_4.
A similar product, containing chrome salts as base, is the so-called
ESCO-EXTRACT, [Footnote: Schorlemmer, Collegium, 1917, 124]
manufactured by the Chem. Fabrik Jucker & Co. in Haltingen
(Baden). This product is a dark, reddish-brown fluid, possessing acid
reaction, which strongly precipitates gelatine. Analysed by the filter
method it contains 12-15 per cent. tanning matters, 17-20 per cent.
soluble non-tannins, and 18 per cent. ash, of which 3 per cent. is
Cr2O_3. This synthetic tannin may be employed alone or in conjunction
with other tannins, and yields a leather similar to that obtained by
chrome tannage.
A. Condensation of Free Phenolsulphonic Acid
In practice, the results of condensing phenolsulphonic acid with
formaldehyde are manifold, according to whether these materials are used
in their concentrated or dilute state; whether they interact in the cold
or when heated; or whether their interaction is gradual or rapid.
1. If a moderately dilute solution of phenolsulphonic acid (1:1) is
mixed with one-sixth of its volume of a dilute formaldehyde solution (1
part 30 per cent. HCHO solution plus 3 parts of water) in the cold, with
continuous stirring, the solution remains clear and assumes a brown
colour. When left several hours, a light, white flocculent precipitate
deposits, which increases in quantity on diluting with water. The
solution precipitates gelatine; the flocculent precipitate is easily
soluble in hot caustic soda solution, and, when subsequently neutralised
with acetic acid, precipitates gelatine.
If equal parts of dilute phenolsulphonic acid and dilute formaldehyde
(concentrations as above) are gradually mixed in the cold, whilst
stirring, the mixture soon becomes opalescent, and a flocculent deposit
separates after eighteen to twenty-four hours.
These experiments carried out on the water bath immediately yield
opalescent liquids, from which an insoluble, brown, gluey, and very
sticky mass separates after twenty-four hours; the latter is sparingly
soluble in alkalies, partly so in organic solvents.
2. If a moderately dilute solution of phenolsulphonic acid (1:1) is
gradually mixed with one-sixth of its volume of a concentrated (30 per
cent.) formaldehyde solution in the cold, whilst stirring, slight
opalescence immediately results, and a flocculent deposit separates
after about twenty minutes, which gradually increases in quantity during
the next few hours. If the volume of formaldehyde is increased to the
same as that of phenolsulphonic acid solution, the flocculent deposit
immediately separates, and after twenty-four hours a brown, gluey, and
very sticky mass—of the same solubility as that described in the
previous experiment—is to be found at the bottom of the vessel used.
It should be noted that in both these experiments with concentrated
formaldehyde solution a slight increase in temperature occurs
concurrently with the process of condensation. If the experiments are
carried out on the water bath, a gelatinous mass is instantly formed,
which assumes the colours of grey, dirty light violet and dark violet,
in the order named, and which, whilst left several hours—or when heated
on the water bath—is suddenly converted into the insoluble, brown,
gluey mass above referred to.
3. If, for the purpose of condensation, phenolsulphonic acid to which 10
per cent, of water has been added, is employed, the reaction proceeds
very quickly and energetically. If one-sixth of its volume of
formaldehyde (1:3 of the 30 per cent. solution) is added drop by drop to
a cold solution of phenolsulphonic acid, a reddish, milky solution
results, which assumes a slightly lighter colour on addition of more
formaldehyde and deposits an insoluble flocculent precipitate. If the
solution is kept below 45° C., by artificial cooling, the light colour
is maintained, but a gelatinous precipitate is soon formed, the
viscosity of which increases on stirring, and finally is converted into
an insoluble, tough, gummy mass. If, on the other hand, the mass is
heated at the beginning of the reaction, or if the amount of
formaldehyde is increased and the mass cooled during reaction,
effervescence occurs, and a cheesy, dirty-coloured mass results, which,
on cooling, rapidly becomes solid and yields a very firm, elastic,
rubbery mass, which is absolutely insoluble in water.
4. The condensation proceeds exceedingly violently when concentrated
phenolsulphonic acid is acted upon by one-sixth of its volume of
formaldehyde. If the latter is firstly added drop by drop to the
phenolsulphonic acid, a gel immediately results, the temperature of
which quickly increases on further addition of formaldehyde and suddenly
boils over, yielding a reaction product which, when cooled, forms a
dirty violet, firm, elastic, and rubbery mass, insoluble in alkalies and
hardly affected by organic solvents.
Finally, if the amounts of concentrated phenolsulphonic acid and
formaldehyde stated above are mixed, strong effervescence occurs and
heat is evolved, and a dirty blackish-violet mass is instantly formed
which, on cooling, yields a rather brittle, hard product insoluble in
water.
5. Totally different end-products are, however, obtained when the
addition of formaldehyde (30 per cent.) in the proportion of one-sixth
of the volume of dilute phenolsulphonic acid (1 plus 9 aq.) to the
latter is extended over several hours. In this case a slightly
opalescent liquid is obtained which, when left twelve hours, is
transformed into a brown mass soluble in water, which strongly
precipitates gelatine and possesses tanning properties. Hence direct
tannoid substances are obtained by this method of condensation.
Whereas no direct tanning experiment can be carried out with the
insoluble compact mass obtained in the preparations described above on
account of their absolute insolubility, it is still possible to carry
out tanning experiments with opalescent colloidal solutions in the
following ways:—
(a) If a bated pelt is immersed in a liquid containing a condensation
product obtained by gradually mixing a moderately dilute solution of
phenolsulphonic acid and a dilute solution of formaldehyde, the pelt is
rapidly tanned on the surface. Complete penetration of the substance
does not occur even after several days, since the strong acidity of the
solution causes a strong swelling of the pelt.
(b) If a pelt is shaken for six hours in a shaking apparatus containing
the liquid mentioned under (a), tannage again only takes place on the
surface, penetration being impeded by the strong swelling effect of the
liquid. Repetition of the latter two experiments, with the addition of
15 per cent, common salt, increases the tanning effect to some extent;
the pelt, however, is not tanned through, but the non-tanned layers may
be clearly seen to be pickled.
The tanning effects described above are only exhibited when the
colloidal tan-liquor is present in great excess over the pelt, since the
former obviously only contains small amounts of tanning matter, and even
the presence of common salt does not bring about complete tannage of the
pelt.
In order to prove the presence of "tanning matters" in the liquid
described above, several freshly prepared samples of the latter were
analysed by the shake method of analysis without being first filtered
and the following figures obtained:—
1. 2. 3. 4.
Per Cent. Per Cent. Per Cent. Per Cent.
Tanning matters 6.4 7.7 8.2 9.1
Soluble non-tannins 15.2 17.4 14.5 11.8
These condensation products suspended in water all precipitate gelatine
strongly and leave behind a perfectly clear liquid. In all cases, an
intense blue colour was obtained on adding ferric chloride, a slight
precipitate only was obtained with aniline hydrochloride, and bromine
was rapidly absorbed with the separation of an insoluble white deposit.
The condensation products obtained by the interaction of dilute
solutions of phenolsulphonic acid and formaldehyde at moderately high
temperature, which form slimy masses and are insoluble in water, are
soluble in alcohol. An alcoholic solution of such a product was used in
a tanning experiment, and a piece of pelt immersed in the solution was
tanned through in a few days; the resultant leather being rather firm,
springy, and slightly hard, and the colour was a light brownish-grey.
All those condensation products which are easily or partly soluble in
alcohol dissolve in caustic soda, sodium carbonate, in some cases also
in borax and sodium sulphite. They are rendered soluble with greater
ease when the freshly prepared solution is heated on the water bath
with the alkali; the alkaline solution, neutralised as far as is
possible with acetic acid, yields light brown coloured solutions, the
tanning effects of which have proved very satisfactory. Leathers tanned
in such solutions, however, are rather empty and hard, possess but
little resilience and an uneven, dirty greyish-brown colour.
A sample of such a product, as nearly as possible neutralised with
acetic acid, contained 14.8 per cent. tanning matters, by the shake
method of analysis.
B. Condensation of Partly Neutralised Phenolsulphonic Acid
Attempts were made at condensing partly neutralised phenolsulphonic
acid; the latter was obtained by mixing equal quantities of
phenolsulphonic acid and sodium phenolsulphonate (prepared by exactly
neutralising phenolsulphonic acid with a concentrated solution of
caustic soda).
The consequent dilution and decrease in acidity, however, considerably
diminished the velocity of the reaction. Hence, if the half-neutralised
Solution A1 (cf. p. 98) is diluted with water, taking equal volumes,
and one-sixth of the volume of dilute formaldehyde (1:3) gradually added
in the cold, condensation is not induced. When heated several hours an
opalescent liquid results from which, however, no flocculent deposits
separate when left for some time. Using a concentrated solution of
formaldehyde (Experiment A2, p. 98) in the cold produces no reaction,
but after heating for a time an opalescent liquid is obtained. Both
liquids give only slight precipitates with gelatine. Excess formaldehyde
does not influence the reaction.
A repetition of Experiment A3 (cf. p. 99), using the above
half-neutralised phenolsulphonic acid, similarly required heat to induce
condensation, when a milky liquid of light reddish colour resulted.
Whereas the addition of formaldehyde to non-neutralised concentrated
phenolsulphonic acid caused violent reaction, this proceeded very slowly
in the case of half-neutralised phenolsulphonic acid, resulting in the
formation of a semi-solid mass, which on heating became more viscous,
and finally, when left twenty-four hours, became a solid, compact,
insoluble mass possessing a dirty light violet colour.
Tanning experiments with these opalescent solutions proved them to exert
a rapid penetration on the surface, complete tannage, however, taking
place after eight days only, when a flat, greyish-coloured and rather
hard leather resulted.
C. Condensation of Completely Neutralised Phenolsulphonic Acid
If concentrated phenolsulphonic acid is gradually neutralised with
concentrated caustic soda solution till the former is faintly alkaline,
the sodium salt thus obtained is not so easily condensed with
formaldehyde as is the case with the free acid.
1. If formaldehyde is gradually added to the neutralised phenolsulphonic
acid in the cold, opalescence immediately results; on addition of water,
the liquid assumes a milky appearance. On adding gelatine to this
liquid, a slimy precipitate is thrown down, leaving a slightly
opalescent liquid.
2. If formaldehyde is added to neutralised phenolsulphonic acid whilst
it is heated on the water bath, a slimy mass instantly separates, which
on cooling solidifies and forms a greyish-blue brittle mass, insoluble
in water and but sparingly soluble in alcohol; the alcoholic solution is
capable of converting pelt into leather.
The filtrate from the solidified mass strongly precipitates gelatine,
whereas the insoluble condensation product is soluble in caustic soda;
this alkaline solution also precipitates gelatine and the addition of
acetic acid transforms the mixture into the gel state.
If the insoluble condensation product is dissolved in warm concentrated
sulphuric acid, the solution remains clear upon the addition of water,
but does not precipitate gelatine. If, finally, this solution is
neutralised with caustic soda, the solution remains clear and
precipitates gelatine strongly.
D. Condensation of Cresolsulphonic Acid
Experiments were carried out with the object of condensing o-, m-,
and p-cresolsulphonic acids with formaldehyde in various ways; no
essential differences could be detected as regards the mode of reaction
or the properties of the intermediary and end-products as compared to
those of phenolsulphonic acid. Similarly, condensation of different
samples of crude cresol containing varying quantities of o-, m-, and
p-cresol did not yield end-products sufficiently different to justify
describing them in detail.
E. Relative Behaviour of an Alkaline Solution of Bakelite and Natural
Tannins
Phenolsulphonic acid was condensed with a little formaldehyde, and the
reddish pasty condensation product dissolved in caustic soda. This
alkaline solution of bakelite was exactly neutralised with acetic acid
and mixed with strong solutions of an untreated quebracho extract. It
was observed that the solubility of the quebracho extract was not
increased by this treatment, but the faintly acidic character of the
natural tannin caused the bakelite to be thrown down as an insoluble
precipitate.
Crude phenolsulphonic acid, when added to a solution of the quebracho
extract referred to, does not increase the solubility of the latter,
which even deposits considerable amounts of insoluble tannin particles.
Quite different properties are exhibited by sodium phenolsulphonate,
which completely converts quebracho tannin into a water-soluble
substance, the aqueous solution of which deposits no insolubles. The
partly neutralised condensation product of phenolsulphonic acid and
formaldehyde exhibits similar properties [Footnote: Grasser, Collegium,
1913, 521, 478.] (see later).
F. Dicresylmethanedisulphonic Acid (Neradol D) [Footnote: Ger, Pat.,
291, 457; Austr. Pat., 61, 057.]
Neradol D is a viscous liquid, measuring about 33° Bé., which is similar
to extracts of natural tannins. One of its characteristics is its
phenolic odour; it is completely soluble in water, forming a clear,
semi-colloidal solution, but is insoluble in all organic solvents with
the exception of alcohol, glacial acetic acid and ethyl acetate, which
dissolve all but its inorganic constituents. The latter owe their
presence to the neutralisation of the crude Neradol with caustic soda,
and are composed of sodium salts of the sulphonic acid in addition to
Glauber salts.
The aqueous solution of Neradol D shows properties similar to those
exhibited by solutions of natural tannins and reacts as
follows:—[Footnote: Grasser, Collegium, 1913, 520, 413.]
Methyl orange Acid reaction.
Barium chloride White precipitate, insoluble in HNO_3.
Ferric chloride Deep blue coloration.
Silver nitrate Slight opalescence.
Bromine water No precipitate.
Formaldehyde hydrochloric acid No precipitate.
Gelatine Complete precipitation.
Aniline hydrochloride Strong precipitate.
The reactions with ferric chloride and gelatine should be especially
noted, since they are analogous to those given by natural tannins. On
the other hand, the reactions with BaCl_2, bromine water and formaldehyde
hydrochloric [Footnote: Stiasny carries out the reaction with
formaldehyde-hydrochloric acid as follows:—50 c.c. of the tannin
solution, plus 5 c.c. concentrated hydrochloric acid and 10
c.c. formaldehyde (40 per cent.) are heated under reflux condenser for
ten minutes; most natural tannins are completely precipitated
(Collegium, 1906, 435; 1907, 52 et 188).] acid prove the different
chemical composition of Neradol D as compared to that of the natural
tannins.
The fact that a positive reaction is given with aniline
hydrochloride [Footnote: This reaction is carried out as follows:—5
c.c. of the tannin solution to be examined (about 4 gm. tanning matter
per litre) are shaken violently in a test tube with 0.5 c.c. aniline and
2 c.c. concentrated HCl added. All natural tannins are unaffected by
this treatment, ligninsulphonic and other sulphonic acids cause
opalescence. Note.—Employing formic acid in lieu of hydrochloric
acid (Knowles) renders the reaction no more reliable.—Transl.] is
very puzzling; none of the natural tannins are precipitated by this
reagent, but only sulphite cellulose on account of its content of
ligninsulphonic acid. One is justified in assuming that there is at
least some connection between the constitution of ligninsulphonic acid
and that of dicresylmethanedisulphonic acid.
Stiasny [Footnote: Collegium, 1913, 516, 142.] recommends the
following reaction for the detection of and differentiation between
Neradol D and wood pulp extract:—10 c.c. of a 5 per cent. solution of
the extract to be analysed are violently shaken with 1-2 drops of a 1
per cent. alum solution and about 5 gm. of ammonium acetate. If only
Neradol D is present no precipitate separates even after twenty-four
hours, but if wood pulp be present, a precipitate is thrown down in a
quantity corresponding to the amount of wood pulp present.
The official analysis gives the following figures:
[Footnote: Grasser, loc. cit.]
Tanning matters 32.5 per cent.
Soluble non-tannins 33.0 "
Insolubles 0.0 "
Water 34.5 "
——————-
100.0 per cent.
Ash 17.0 "
Acidity: 1 gm. = 10 c.c. N/10 NaOH.
Density: 33º Bé.
A comparison of its quantitative analysis to that of a natural tanning
extract is illustrated by the following figures of a chestnut and a
quebracho extract of same density (26º Bé):—
Chestnut Quebracho
Per Cent. Per Cent.
Tanning matters 32.0 34.0
Soluble non-tannins 12.0 8.0
Insolubles 1.5 2.0
Water 54.5 56.0
——- ——-
100.0 100.0
Ash 0.4 2.0
This comparison shows that extracts of natural tannins firstly contain
certain amounts of "insolubles," whereas Neradol is completely soluble
in water, forming a clear solution; secondly, natural tanning extracts
contain smaller quantities of soluble non-tannins, consisting of
colouring matter and sugars, in addition to small quantities of mineral
matters (ash). Neradol D contains considerable amounts of soluble
non-tannins, derived from salts of sulphonic and sulphuric acids, again
offering a satisfactory explanation of the high ash. If, therefore, a
mixture of Neradol D and a natural tanning extract was submitted to a
quantitative analysis, the higher non-tannins and the high ash would
indicate the presence of Neradol D, provided that wood pulp or a highly
sulphited extract were not components of the mixture.
The chemical reactions taking place in the preparation of
Neradol D may be expressed thus:-
OH OH OH OH
H ^ H___O_____H ^ H H ^ H__CH_2__H ^ H
| | || | | = | | | | + H_2O
| | CH_2 | | | | | |
H v CH_3 CH_3 v H v CH_3 CH_3 v H
HSO_3 HSO_3 HSO_3 HSO_3
1. Neradol D Reactions
1. The quantitative determination of phenols introduced by Bader,
[Footnote: Bull. soc. scient., Bucarexi, 1899, 8, 51.] which consists
in precipitating them as oxyazo compounds, has been modified by Appelius
and Schmidt [FootNote: Collegium, 1914, 597.] for the purpose of
detecting Neradol D:—To 50 c.c. of the tannin solution (analytical
strength) 15 c.c. of diazo solution are added, the mixture filtered, if
necessary, and the filtrate made alkaline with caustic soda; in the
presence of Neradol D in sufficient quantity, a blood-red coloration
results. If but little Neradol D be present, the procedure is altered as
follows:—The tannin solution, to which the diazo solution has been
added, is filtered, and the filtrate poured on a piece of filter paper
which is then dried; a solution of caustic soda is spotted on the paper,
when, if Neradol D be present, a red-edged spot will appear.
According to Tschirch and Edner, [Footnote: Archiv. d. Pharm., 1907,
150.] the diazo solution is prepared as follows:—5 gm.p-nitraniline
are introduced into a 500 c.c. measuring flask, 25 c.c. of water and 6
c.c. concentrated sulphuric acid added, the mixture shaken and a
solution of 3 gm. of sodium nitrite in 25 c.c. of water plus 100 c.c. of
water added, and the whole then filled up to 500 c.c. The solution
should be stocked in the dark.
2. A less sensitive reaction for Neradol and wood pulp extract
constitutes that of Appelius and Schmidt employing cinchonine,
[Footnote: Collegium 1914, 597.] while the presence of the substances
in question yields characteristic precipitates.
3. Seel and Sander [Footnote: Zeits. f. ang. Chem., 1916, 333.]
recommend the following method of detecting Neradol D:—
(a) Oxyazo Reaction.—About 5 c.c. of the tannin solution are rendered
alkaline with caustic soda; after cooling with ice, about half the
volume of alcohol is added. 3-4 drops of diazo solution are then
added. Frequently, this results in the solution assuming a blue
coloration. If not, the solution is acidified with hydrochloric acid,
ether added, and the mixture well shaken. The water is now separated
from the mixture, fresh water added, together with some caustic soda
solution, when, if Neradol D be present, the salt of the colour acid
formed dissolves in the water with a beautiful green or bluish-green
colour. At the place of contact of the water and the ether a
bluish-green ring appears.
The diazo solution is prepared by dissolving p-aminophenol or its
hydrochloric in a little dilute hydrochloric acid, cooling in ice and
carefully diazotising in the cold till a slight excess of nitrous acid
is present. It is essential that this solution should be tested before
use, and this is carried out by coupling it with an alkaline phenol
solution; if a dark blue oxyazo colour is formed, the solution may be
used. It must be kept cool by surrounding it with ice.
(b) Indophenol Reaction.—To 5 c.c. of the solution to be tested, a
drop of a solution of dimethyl-p-phenylenediamine is added, the
solution rendered alkaline with caustic soda and 1-2 drops of a 5 per
cent. solution of potassium ferricyanide added. If Neradol D be present,
a blue colour appears, either immediately or after some time. The
reaction is rendered more sensitive if alcohol is carefully poured on
the solution after it has been rendered alkaline, and potassium
ferricyanide is then added. At the place of contact a blue layer is
formed, which ultimately diffuses into the alcohol.
According to Lauffmann [Footnote: Collegium, 1917, 233.] the presence
of natural tannins as well as that of wood pulp diminishes the
sensitiveness of the reactions described above; [Footnote:
Zeits. f. ang. Chem., 1916, 333.] this investigator recommends a
modification of these reactions.
2. Electro-Chemical Behaviour of Neradol D
The author's investigations of the electro-osmosis of an aqueous
solution of Neradol D [Footnote: Collegium, 1920, 597, 24.] proved
that dicresylmethanedisulphonic acid exhibits anodic migration; hence
this product possesses negative charge and acidic character. The
impurities accompanying the synthetic tannin, i.e., salts, free
sulphuric acid, and some phenols, migrated anodic and cathodic
respectively, according to their charges. A Neradol D purified by
electro-osmosis finally yielded a pure solution of
dicresylmethanedisulphonic acid, which precipitated gelatine and
exhibited pronounced tanning effects, but gave a greenish-black
coloration with iron salts. This conclusively proves that the blue
coloration given by Neradol D with iron salts is no characteristic
feature of the pure synthetic tannin, but is caused by the phenolic
impurities accompanying the latter. Especially the first stage of the
electro-osmosis produces a cathodic migration of the phenols, which may
then be detected at a cathode by means of the iron and bromine
reactions.
It is characteristic of a dicresylmethanedisulphonic acid purified by
electro-osmosis that it does not precipitate aniline hydrochloride. It
appears, therefore, that this reaction—which is characteristic of most
synthetic tannins—is again caused by the presence of impurities.
3. The Influence of Salts and Acid Contents on the Tanning Effect of
Neradol D
Chemical analysis of crude Neradol revealed a natural
dicresylmethanedisulphonic acid (the tanning agent) contents of about 68
per cent, which agrees fairly well with the calculated amount. Like
other "strong" and "weak" acids this sulphonic acid exercises a strongly
swelling influence on pelt. Whereas the effect of acid present in
solutions of Neradol D of medium concentration and its tanning effect
both influence the pelt and are fairly well balanced, this is not the
case as regards highly concentrated and very dilute solutions. If, for
instance, a very dilute solution of crude Neradol (about 0.25° Bé.) is
used, the tanning effect of this solution is exceedingly small and does
not show itself till after several hours. The relatively high
dissociation of the acids at this high degree of dilution causes an
extremely rapid and strong swelling of the pelt, which has therefore
absorbed its maximum amount of water (maximum swelling) before the
tanning effect of the sulphonic acid comes into play and by fixing the
surface of the pelt is enabled to prevent the excessive swelling effect
of the acids.
The addition of neutral salts to the tan liquor diminishes the effect of
the acids on pelt (dehydrates the pelt) and prevents "drawing" of the
grain. If, for instance, common salt be added to a solution of crude
Neradol, the original quantity of sulphonic acid present would remain
constant, but the presence of salt would diminish the degree of
dissociation and consequently the swelling. This effect is still more
pronounced when the absolute amount of free sulphonic acid is
diminished. Hence, if crude Neradol is treated with increasing amounts
of caustic soda, a series of products containing increasing quantities
of salt and decreasing concentrations of sulphonic acid is obtained.
The acidity of the Neradols may be determined by titration with N/10
caustic soda; this procedure hence establishes a means of determining
the (unknown) acidities which may be expressed in terms of c.c. N/10
NaOH. The acidity of crude Neradol was found to be—
1 gm. = 50 c.c. N/10 NaOH
i.e., 1 gm. of crude Neradol requires 50 c.c. N/10 NaOH for complete
neutralisation; the decrease in acidity causes a decrease in contents of
tanning matters and the quantities of salts increase. The following
table gives the figures obtained by differently neutralised neradols:—
Acidity. Tanning Matters. Na_2SO_4.
Per Cent. Per Cent.
1 gm. = 50 c.c. 68 …
1 gm. = 40 c.c. 59 4
1 gm. = 30 c.c. 50 8
1 gm. = 20 c.c. 41 12
1 gm. = 10 c.c. 33 17
1 gm. = 5 c.c. 28 20
1 gm. = 0 c.c. 20 …
Tanning experiments with these different neradols (employing solutions
of 1° Bé. strength) demonstrated that neradols of acidity 50°, 40°, and
30° exerted strong swelling and gave comparatively hard leathers;
neradols of acidity 20°, 10°, and 5° exert no swelling, yield quick
tannage and soft leather. The swelling (hardening) effect of the acid
and the dehydrating (softening) effect of the salts in this case,
therefore, are well balanced, and this fact affords an explanation of
the rapid change from hardening to softening effects exhibited by partly
neutralised Neradol where less acid and a greater quantity of salts
respectively are present.
It may finally be noted that the acidity of Neradol D, 1 gm. = 10
c.c. N/10 NaOH, has been found to be the most suitable one for practical
purposes. The author has, however, successfully employed some neradols
of considerably higher acidities. The acidity above mentioned is
possessed by a Neradol D containing 17 per cent. ash and 30 per cent.
sodium sulphonates and Glauber's salts crystals respectively. This
large quantity of salts present on the one hand effects the rapid pickle
and tanning effect exhibited by Neradol D, on the other hand it also
effects the softness in the leather resulting from its use either alone
or in admixture with natural tannins.
4. Phlobaphene Solubilising Action of Neradols
A special feature of Neradol D is its property of solubilising
phlobaphenes, which may be ascribed to its contents of sulphonic acids
or their salts. In order to demonstrate whether the sulphonic acids and
their salts are capable of solubilising the insoluble or sparingly
soluble anhydrides of the tannins (the phlobaphenes) before and after
condensation, the following experiments were carried out:—
Crude Argentine solid quebracho extract was converted into a highly
viscous liquid by treating it for several hours with water at 100° C.,
and the anhydrides rendered insoluble by diluting the liquid with a
large volume of cold water. The precipitate formed, consisting of
quebracho phlobaphenes, was separated from the liquid by decantation,
and purified by washing it several times with water. Each 10 gm. of this
moist paste were treated in the cold with (a) free phenolsulphonic
acid; (b) sodium phenolsulphonate; (c) crude Neradol and (d)
Neradol D, 20 c.c. of water at 45° C. added, and the mixture allowed to
cool slowly; the following solutions resulted:—
(a) Opalescent solution, much deposit,
(b) Clear solution, no deposit.
(c) Nearly clear solution, very little deposit.
(d) Clear solution, no deposit.
This clearly proves that free and condensed phenolsulphonic acids as
such are not capable of completely solubilising phlobaphenes, whereas
the sodium salts of free and condensed phenolsulphonic acids possess
this property. The salt contents of Neradol D, therefore, constitute an
advantage in this respect, that not only may Neradol D be mixed with
solutions of any natural tannin without insolubles being thereby
deposited, but it may also be added in large quantities to a tannin
solution with the result that the sparingly soluble and wholly insoluble
constituents (phlobaphenes) are completely brought into solution.
The practical importance of the solubilising effect of Neradol D
relating to solid Argentine quebracho extract is demonstrated in the
following series of investigations carried out by the author:—
[Footnote: Collegium, 1913, 478; Austr. Pat., 68, 796.]
Solid Neradol Matters Tanning Abs. Increase
Argentine D. Calc. of Mixture Increase per
Quebracho Found. in Tanning 100 gms.
Extract. Matters. Extract.
Gm. Gm. Per Cent. Per Cent.
100 0 66.0 66.0 … …
0 100 32.5 32.5 … …
90 10 62.7 64.7 2.0 2.2
80 20 56.1 58.7 2.6 3.3
60 40 52.6 56.9 4.3 7.1
50 50 49.3 55.2 5.9 11.8
30 70 42.6 47.3 4.7 15.6
20 80 39.2 42.3 3.1 15.5
The maximum solubilising effect is exhibited in the mixture of 70 parts
of Neradol and 30 parts of quebracho, with an additional percentage of
tanning matters in the mixture of 15.6 per cent.—a figure which is very
nearly identical with that of the insolubles present in the original
Argentine quebracho extract.
The phlobaphene-solubilising property of Neradol D is closely connected
with the influence of the latter on the colour of leathers tanned with
natural tannins. If, on the one hand, a pelt is tanned with natural
(i.e., non-treated) quebracho extract, a rather light coloured leather
results, the fleshy colour of which is characteristic of quebracho. The
dark coloured phlobaphenes present, on account of their insolubility,
will have no influence on the colour of the leather. If, now, the
quebracho extract be treated with sulphite and bisulphite in the usual
way, the phlobaphenes are solubilised, but the reducing effect of the
bisulphite tends to brighten the colour of the otherwise dark coloured
phlobaphenes as well as that of the soluble tannins, and a
reddish-yellow coloured extract results, imparting its own colour to the
pelt. When, on the other hand, the quebracho extract is solubilised by
means of Neradol D, the phlobaphenes are brought into solution without
reduction taking place, and a dark brownish-red extract results, which
imparts a similar colour to the finished leather. This darkening effect
of Neradol D is most conspicuous in the case of mangrove, maletto, and
chestnut, but is absent in the case of algarobilla, dividivi, gambir,
sumac, and valonea. The varying phlobaphene contents of the tannins
easily afford an explanation of the different properties above alluded
to: the mangrove phlobaphenes are dark coloured bodies, those of mimosa,
maletto, and chestnut are of lighter colour, and the last-named tanning
materials enumerated above are either devoid of phlobaphenes or possess
them only as very light coloured bodies. Algarobilla, sumac, gambir,
dividivi, and valonea, on the other hand, are associated with large
amounts of sparingly soluble ellagic acid, known as "bloom" or "mud"
which imparts a light colour to the finished leather, and conveniently
covers the dark colour imparted to the leather by other tanning
materials; for this reason the former are often used in the lay-aways or
in the finishing processes.
Similar effects to those of Neradol D are exhibited by other salts of
sulphonic acids, e.g., sodium benzylsulphanilate (Solvenol B.A.S.F., or
solution salt ("Solutionsalz") Hoechst); the author prepared mixtures of
such salts and untreated quebracho extract in order to determine their
solubilising effects, and arrived at the following results:—
30 parts Solvenol plus 70 parts quebracho extract: clear solution,
no deposit.
25 parts Solvenol plus 25 parts quebracho extract: clear solution,
very little deposit
20 parts Solvenol plus 80 parts quebracho extract: nearly clear solution,
very little deposit.
15 parts Solvenol plus 85 parts quebracho extract: slightly opaque solution
some deposit.
Leathers tanned with these mixtures were more or less dark coloured
according to the amounts used of solvenol and the consequent
solubilisation of the phlobaphenes.
A similar effect, though of opposite nature from a tanning standpoint,
is exhibited by sulphonates on certain colloidal dark coloured
substances. A phenolsulphonic acid, which had been overheated during
sulphonation and subsequently condensed (crude Neradol), imparted a
conspicuous greyish-brown colour to the leather; samples of this crude
product were then partly neutralised with varying amounts of alkali, and
these samples (containing increasing quantities of salts) tested for
tannin and colour effects. It was found that the more highly neutralised
samples imparted a darker colour to the solutions, but these dark
products did not deposit the dark impurities on the pelt. One may
therefore assume that tannoid substances are colloidally suspended, and
when converted into true solutions are incapable of being fixed in
insoluble form by the pelt.
Just as, by adding Neradol D to a tanning extract, the phlobaphenes are
solubilised and a dark coloured extract results, it is also possible to
remove the mechanically deposited phlobaphenes and oxidised tannins from
the finished leather, and, as a consequence, lighten the colour of the
leather. For practical purposes, bleaching with Neradol D is carried out
by brushing over the darkly coloured leather with a 2°-3° Bé. solution
of Neradol D, and then rinsing well with water, in order to remove the
solubilised tannin. A lighter colour may also be obtained by immersing
the leather in a liquor of the strength mentioned above for several
hours, and then rinsing with water, but by this procedure not only the
surface tannin is removed, but also tannin from the leather substance
itself; this method is therefore not suitable for heavy leathers which
are sold by weight.
The advantage of employing Neradol D as a bleach in this way is to be
found in the fact that, on the one hand, the bleaching sulphonic acid
attacks the leather to a much slighter extent than is the case with
inorganic acids usually employed for this purpose; on the other hand,
the method of brushing the sulphonic acid on the leather only introduces
small amounts of sulphonic acid in the leather, thus lessening the
harmful effects of acids upon leather. Furthermore, the common methods
of using alkalies as tannin-solubilising agents with the consequent
running off and waste of alkaline tan liquors are here substituted by a
method leaving liquors rich in tannin and Neradol, and which may be used
in the ordinary procedure of tannage.
Since Neradol D contains neutral sodium sulphate (about 3 per cent.),
and the latter, by precipitating colouring matters present in tan
liquors, may slightly bleach these, it was of interest to determine
whether the sodium sulphate plays any part in the bleaching effected by
Neradol. Mixtures of chestnut and quebracho extracts were prepared, to
which were added:—
(1) 5 per cent. Neradol D.
(2) 5 per cent. Neradol D. free from Na_2SO_4.
(3) ° 15 Per cent. sodium sulphate (corresponding to above
Neradol D).
These mixtures were allowed to act upon pelt alongside of comparison
tests using quebracho and chestnut extracts only, the strength of the
liquors in all cases being 1.5° Bé; the pelt was left in the solution
till tanned through. The following results were obtained:—
(1) Quebracho tanned leather was darker; no difference in
colour by chestnut extract.
(2) Similar to (I).
(3) Same colour as given by the original extracts.
This experiment demonstrates that absence of sodium sulphate in the
mixture is without influence on the colour of the resulting leather, and
that an addition of sodium sulphate to natural extracts does not affect
the colour imparted by them to pelt
5. Effect of Neradol D on Pelt
Being a sulphonic acid derivative, the chemical constitution of Neradol
is obviously considerably different from that of the natural tannins,
and the question has been asked: Will Neradol D, in its concentrated
form, attack the hide substance?[Footnote 1: Collegium, 1913, 521,
487.] Bearing in mind that concentrated extracts of vegetable tannins
in some circumstances effect a "dead" tannage (cf. case-hardening) and
hence reduce their practical value, and that for this reason it is
impossible to allow either concentrated extracts or concentrated Neradol
D to act upon pelt, the author still decided to carry out some
experiments in this direction. Concentrated Neradol D (33° Bé.) and
strong aqueous solutions of this material in strengths of—
30° 25° 20° 15° 10° 5° 3° 1° Bé.
were therefore allowed to remain in contact with pelt for a period of
ten days, when the pelts were taken out and washed in running water for
twenty-four hours, and then dried. The resultant leathers possessed the
following properties:—
33° Bé. solution: completely gelatinised.[Footnote 2]
30° " " " [Footnote 2]
25° " two-thirds gelatinised; surface tanned.
20° " one third gelatinised; surface "dead" tanned.
15° " pelt was glassy throughout.
10° " rather cracky leather, but well tanned.
5° " normal tannage.
3° " " "
1° " " "
[Footnote 2: Impossible to subject the pieces to a proper washing out.]
The interiors of the leathers obtained from the 25° and 20°
Bé. solutions were completely gelatinised; this may be accounted for by
assuming that the surface was "dead" tanned, and that hence the free
dissociated sulphonic acid diffused into the leather, towards which it
exhibited hydrolysing rather than a tannoid effect with the consequent
result described above. Above 10° Bé. the effect is more that of an acid
with concentrations below 10° Bé.—the only ones of technical
importance—however, no ill-effects may be observed.
For tanning purposes, Neradol D solutions of 2° Bé. are quite
satisfactory, and it has been found [Footnote 1: Technikum, 1913, 80,
324.] that solutions of this strength do not dissolve out any protein of
the hide. [Footnote 2: The translator cannot agree with the author on
this point. He has, for instance, found that solutions of analytical
strength dissolve considerable amounts of hide substance, and his
practical experience confirms results arrived at in the laboratory.]
A purely Neradol D tanned leather may be produced by immersing a bated
pelt, free from lime, in a 2° Bé. Neradol D liquor for about four days;
the resultant leather being nearly white and otherwise very similar to a
leather tanned with vegetable tanning materials.
The main application of Neradol D is in admixture with vegetable tanning
materials; especially in the early stages of tannage is this substance
of value, since by its use not only a light coloured leather surface is
obtained, but its presence prevents a subsequent dead tannage when
strong vegetable tan liquors are applied, and it also imparts strength
to the grain layer. It is thus possible to shorten the time consumed by
the tanning process by employing Neradol D in the manner described.
A further explanation as to why the tanning process is considerably
hastened by using Neradol D, either alone or in conjunction with natural
tannins, is afforded by the fact that though Neradol D quickly
penetrates the grain, it is but "loosely" fixed by the latter, i.e.,
it is not deposited to such an extent that it would prevent penetration
of the vegetable tannins. In the case of a mixture of Neradol D and
vegetable tannins, the former quickly diffuses into the pelt and fixes
the fibres, thus facilitating penetration of the vegetable tannins.
This assumption is justified in view of the speed with which Neradol D
completely penetrates and tans the pelt, since Neradol D containing
acids and salts exhibits effects similar to those of a pickle.
6. Reactions of Neradol D with Iron and Alkalies
A special characteristic of Neradol D tannage is the sensitiveness of
the latter to the action of iron and alkalies. The active principle of
Neradol D being free dicresylmethanedisul-phonic acid, which is easily
neutralised by lime, ammonia, and amino-acids and hence rendered
inactive for tanning purposes, it is essential that the pelt prior to
tannage with Neradol D should be completely delimed, bated, and freed
from all constituents possessing alkaline reaction. It is, however,
possible to regenerate Neradol D liquors contaminated with alkali or
partly neutralised by the addition of small quantities of organic
(formic, acetic, lactic, and butyric) or inorganic (hydrochloric or
sulphuric) acids,i.e., the dicresyl-methanedisulphonic acid is again
partly liberated, and this procedure is always preferred where the
tanning process does not allow of a complete deliming of the pelt prior
to introducing the latter into a Neradol D liquor. If, on the other
hand, such liquors are kept properly, and the addition of acid referred
to kept up, they will remain active for weeks and need only
strengthening up with the requisite quantity of Neradol prior to
introducing fresh pack.
The sensitiveness to alkalies of Neradol D is considerably greater than
in the case of natural tannins, and it appears that a vegetable tan
liquor neutralised with lime will not even surface-tan when acting upon
pelt and will neither impart a dark colour to the leather nor remove
from it any appreciable amount of protein. Similarly, a Neradol D liquor
neutralised with lime exerts no tanning action, but in contradistinction
to the vegetable tan liquor similarly treated, will impart a blue or
blackish-blue colour to the pelt, from which it removes larger
quantities of protein. The author examined two such liquors relating to
their contents of tanning matters and protein and obtained the following
results:—
Reaction. Bark. Tans. Non-Tans Insol. Proteins
Per Per Per Per
Cent. Cent. Cent. Cent.
Vegetable Slightly 12° 0 2.93 0.35 0.01
tan alkaline
liquor
Neradol " " 10° 0 4.43 0.17 0.17
These figures do not only show the higher protein contents of the
Neradol D liquor, but do also show higher contents in soluble
non-tannins, which consist mainly of lime (2.12 per cent.) and sodium
salts (1.8 per cent.), thus establishing the fact of the sensitiveness
of Neradol D to alkalies in addition to its lime-solubilising effects.
The sensitiveness towards alkalies is also noticeable on a large scale
where the tanpits have been built of cement; though the pelt may be
quite free from lime, the Neradol D is quickly neutralised by the
cement, with results similar to those enumerated above.
The blue coloured soluble compound of Neradol D and iron salts, to which
frequent reference has been made, is very important from a practical
standpoint. Whereas the catechol tannins (i.e., fir, gambir, hemlock,
cutch, mangrove, and quebracho) are coloured black, those of the
pyrogallol class (i.e., algarobilla, dividivi, valonea, gallotannic
acid, myrabolams, and sumac) bluish-black, and the "mixed" tannins
(i.e., canaigre, oak, and mimosa bark) bluish-purple by iron alum,
Neradol D is coloured a pure blue. How sensitive this reaction is, the
following comparative analyses illustrate: to each litre of tan liquor
containing 4 gm. tanning matter prepared from (a) quebracho extract
and (b) Neradol D, 10 c.c. of a 10 per cent. iron alum solution were
added, the solutions heated to 100° C., cooled and filtered, and the
colour of the filtrates and the weight of the precipitates determined:—
(a) Quebracho solution: light reddish-brown filtrate, 3.22 gm.
precipitate.
(b) Neradol solution: deep blue filtrate, 0.02 gm. precipitate.
Hence, on adding a soluble iron salt to a solution of a natural tannin,
most of the tanning matter is precipitated; the colour of the filtrate,
however, is much the same as that of the original solution. A Neradol D
liquor similarly treated gives no precipitate, but is coloured blue
throughout. The filtrates from the above solutions were allowed to act
upon pelt, and the following observations were made:—
(a) The light reddish-brown filtrate from the quebracho liquor
exhibited no well-defined tanning effect on pelt, to which it imparted a
light brown colour.
(b) On the other hand, the deep blue filtrate from the Neradol D
liquor exhibited well-defined tanning effects, and imparted a deep blue
colour to the pelt.
For practical purposes, the sensitiveness of Neradol D to iron is not
only remarkable because any contact with iron particles will colour the
liquor (and hence the pelt) blue, but also because the slight amount of
iron always present in cement renders the use of cement pits prohibitive
where Neradol D liquors are used.
This intense blue coloration might have made possible a colorimetric
estimation of Neradol D. The author has investigated this possibility,
using different concentrations of Neradol D liquors to which a solution
of iron ammonium alum was added, and found that when, at certain
concentrations, the maximum blue colour had been obtained, it was still
possible to increase the quantity of Neradol without the intensity of
the colour being affected. Addition of a little alkali tends at first to
darken the blue colour, more alkali changes the blue colour to brown and
yellow, successive additions of a weak organic acid (e.g., acetic
acid) rapidly lighten the blue colour. Since industrially used Neradol
D liquors always contain varying quantities of acid and may be neutral
or even slightly alkaline, it must be considered impossible to make any
use of such a colorimetric estimation for practical purposes.
7. Reagents Suitable for Demonstrating the Various Stages of Neradol D
Tannage
The extent to which tannage with Neradol D proceeds on the surface and
within the pelt may be judged from the feel of the skin, but such a
method is totally unsuited to any but a practical tanner. A suitable and
reliable reagent is indigotine (B.A.S.F.), which clearly distinguishes
tanned and untanned layers of the pelt. If, for instance, a 1-2 per
cent, solution of indigotine is brought into contact with a fresh cut on
a pelt, and the latter subsequently washed with warm water, the
indigotine is only retained by the untanned parts; a leather tanned with
Neradol D is therefore only coloured by indigotine to the extent to
which it has combined with the Neradol. [Footnote: According to Seel
and Sander (Zeits. f. ang. Chem., 1916, 333), basic dyestuffs are also
very suitable for demonstrating tanned parts of the pelt.]
Another reagent is constituted by iron ammonium sulphate; the extent of
the penetration of Neradol D, which gives an intense blue coloration
with iron salts, into the leather may be determined by washing the pelt
treated with Neradol D, making a cut, again washing and treating the cut
with a few drops of a weak solution of iron ammonium sulphate. Those
parts of the pelt which have been converted into leather then appear
deep blue; on the other hand, those which have been in contact with
Neradol D, but have not yet been converted into leather, are light
blue. Those parts which have not yet been in contact with Neradol D
appear pure white; the results of this reaction are therefore opposite
to those obtained by the use of indigotine.
8. Combination Tannages with Neradol D
Whereas mixtures of Neradol D and vegetable tannins impart properties to
the leather consistent with the proportions in which these materials are
present, it is not possible to combine Neradol D with mineral tanning
agents or fats (e.g., fish oils, etc.) in such a way that a leather
characterised by the properties of either material is
obtained. Experiments were carried out using (1) chrome salts plus
Neradol D; (2) aluminium salts plus Neradol D; and (3) oils plus Neradol
D, and the following conclusions were arrived at:—
1. CHROME-NERADOL D liquors, containing comparatively larger amounts of
Neradol D, act too rapidly on the pelt and draw the grain; smaller
amounts of Neradol D seem without influence on the finished leather,
which possesses pronounced characteristics of chrome leather. Another
disagreeable factor is the following: the chrome salts must possess a
certain degree of basicity in order to produce good leather; the Neradol
D must, on the other hand, possess a certain acidity to produce the
optimum results, and it is hence impossible to balance practically the
basicity of the chrome salts and the acidity of the Neradol in order to
justify the presence of both. If one of the two is used separately
before the other, a leather always results possessing the
characteristics of the material first employed, provided the time of
action has been sufficiently extended. If insufficient time has been
allowed, the characteristics imparted by the main tanning agent are not
altered.
2. ALUMINIUM SALTS AND NERADOL require practically the same basicity and
acidity respectively, and when combined always yield a leather
possessing mainly the properties of one of the components. In addition
to this fact, leathers tanned with aluminium salts possess great
softness and stretch, those tanned with Neradol D greater firmness and
less stretch, and these opposing qualities completely compensate one
another and render nil the value of such mixtures.
In addition to this, the presence of aluminium salts produces no better
fixation on the leather fibre of basic coal-tar dyes, so that in this
respect also a combination of aluminium salts and Neradol D is of no
value.
3. FAT NERADOL D TANNAGE: Just as aluminium salts impart special
characteristics to leather, this property is exhibited by fatty matters,
especially so as regards stretchiness and softness. Both of the latter
are not apparent to the same extent in an oil tannage into which Neradol
D and oil enter as constituents. It is, however, not excluded that, in
view of the fact that the combination of oils and Neradol D appear to
produce the most promising results of the three from a technical point
of view, such combination would yield products possessing less stretch
and greater softness which, by occupying an intermediary position, might
possess certain advantages and be useful for certain technical purposes.
9. Analysis of Leather Containing Neradol D
Chemical examination of leathers tanned with Neradol D or with mixtures
of natural tannins and Neradol D often involve a determination of the
materials employed in tannage. In most leathers exclusively tanned with
vegetable tanning materials, it is usually possible to determine at
least the nature of the main tanning agent, whereas the attempts at
determining those tannins which are only present in minor quantities
rarely succeed. Since Neradol D usually is employed in comparatively
small quantities, it has been imperative to find a method which also
permits of the detection of smaller quantities of Neradol D. Provided
the presence of not less than 5 per cent. (on the weight of the leather)
of Neradol D, the following method yields reliable results:—20-30
gm. of the leather are ground or sliced as finely as possible and the
powder (or the slices) treated in the cold with a sufficient volume of
dilute ammonia solution (5 c.c. ammonia plus 95 c.c. of water) for
eight to twelve hours. The object of this is to dissolve the tannins,
but no protein should go into solution. The solution is filtered and
the filtrate evaporated on the water bath till it occupies a volume of
about 30 c.c. A few c.c. of aniline hydrochloride are now cautiously
added, when it should be carefully noted if a precipitate is thrown down
which might be either completely or only partly soluble in excess of
aniline hydrochloride. A precipitate is always thrown down when Neradol
D or wood pulp is present; only the Neradol D precipitate is soluble in
excess of aniline hydrochloride. Partial solubility of the precipitate
therefore indicates the presence of both wood pulp and Neradol D.
The quantitative determination of sulphuric acid—the detection and
estimation of which in leather is important—is considerably influenced
by the presence of Neradol D. Practically all methods in vogue dealing
with its determination were based on the estimation of the sulphur
introduced into leather by sulphuric acid. The presence of Neradol D,
the main constituent of which is dicresylmethanedisulphonic acid,
renders it impossible by such methods to determine whether the combined
sulphur owes its origin to sulphuric or sulphonic acid. It remains yet
to be determined whether the sulphonic acid influences the leather
substance to the extent that sulphuric acid does; it must, however, be
borne in mind that Neradol D in addition to free sulphonic acid also
contains sulphonates and sulphates, which may enter into the leather and
thus increase the sulphur contents of the latter. A method must hence be
devised which estimates the free acid only and provides the means of
distinguishing this from all other acids of organic and inorganic
acids. Paessler, [Footnote: Collegium, 1914, 527, 126; 531, 509; 532,
567.] by extracting the leather and dialysing the filtrate, has
effected a separation of the acids and the tanning and colouring matters
and quantitatively estimated the sulphuric acid in the dialysate.
Immerheiser [Footnote 1:Collegium, 1918, 582, 293.] devised a method,
based upon the property of sulphuric acid of combining with ether, for
the purpose of determining free sulphuric acid in leathers:—10 gm. of
the leather, cut into small pieces, are extracted three times with 200
c.c. distilled water at room temperature, the time of each extraction
being ten to twelve hours, and the combined extracts evaporated to
dryness on the water bath, 5 gm. of quart sand being added. The dry
residue is now powdered, introduced into an Erlenmeyer flask provided
with a glass stopper, and 200 c.c. of anhydrous ether [Footnote 2: To be
tested for water by shaking with anhydrous copper sulphate.] added.
After about two hours, during which the flask is occasionally shaken,
the ether is poured through a filter, the residue washed with a little
ether, and the operation repeated twice with each 40 c.c. anhydrous
ether, using the same filter. To the combined ether extracts (about 200
c.c.) HCl and [Greek: b]aCl_2 are added, the ether distilled off and the
residue evaporated on the water bath, in order to decompose the
ether-sulphuric acid compound. 50 c.c, of hot water acidified with HCl
are now added, the precipitate allowed to settle, filtered, washed,
dried, and weighed. The sulphuric acid thus estimated was present in the
leather as free sulphuric acid. That present as sulphates soluble in
water is estimated in the residue on the filter: the residue is
extracted with hot water, the sand filtered off, the filtrate acidified
with HCl, boiled for one quarter hour and filtered if necessary. The
clear filtrate, which may be coloured, is brought to boil and
[Greek: b]aCl_2 is added. The barium sulphate indicates the sulphuric
acid present in the leather as water-soluble sulphates.
Whether the latter be sulphates or bisulphates may be indicated by the
aqueous extract of the above residue, since neutral reaction would
indicate the absence of bisulphates, acid reaction their presence in
addition to possible normal sulphates; the quantitative estimation of
the metals would decide this point definitely.
10. Properties of Leathers Tanned with Neradol D
Whereas the colour of leathers tanned with Neradol D only is nearly a
pure white, those tanned with mixtures of Neradol D and vegetable
tanning materials are more or less light coloured according to the
quantity of Neradol D present, as has been explained when discussing the
phlobaphene-solubilising action of Neradol D. In any case, all leathers
tanned with Neradol D possess fibre of remarkable length, which explains
their increased tensile strength and elasticity. The tensile strength
of a leather tanned with a mixture of Neradol D and vegetable tannins
was 3.7 per cent, as compared to 3 per cent when no Neradol was used;
the extension was 56 per cent, when tanning with Neradol D as against 36
per cent, without the latter.
The sensitiveness to light of leathers tanned with Neradol D may be
mentioned. Exposed to direct sunlight, the surface of the leather
assumes a yellowish colour after two days' exposure, and assumes a pure
yellow colour after a further three days. A further fifteen days'
exposure only darkens the leather slightly, the final colour being very
little different from the one obtaining after five days' exposure.
In passing, it may be remarked that this yellow colour is observed on
the surface only, the grain otherwise possessing that pure white colour
characteristic of Neradol D tanned leather. Further, it may be noted
that leathers tanned—with Neradol D fix basic coal-tar dyes
excellently, whereas acid and substantive dyestuffs are fixed with other
than their natural shades.
The author has analysed a leather exclusively tanned with Neradol D, and
has obtained the following results:—[Footnote: Collegium, 1913, 521,
478.]
Moisture - - - - - 15.53 per cent.
Ash - - - - - - 0.93 per cent.
Fats- - - - - - 1.26 per cent.
Extraneous matters - - - 0.00 per cent.
Leather Substance |Tanning matters- 36.92 per cent.
Leather Substance |Hide substance - 45.36 per cent.
———————-
100.00 per cent.
[Footnote: Sp. gr., 0.642.]
From these figures, those of "degree of tannage" and "yield"
(pelt—>leather) are calculated as 81.4 and 220 respectively.
These figures correspond closely to those obtained by the analysis of
leathers tanned with vegetable tanning materials, and this proves the
similarity between the Neradol D tannage and a vegetable tannage in
their chemical aspects.
11. Neradol D Free From Sulphuric Acid
In order to prepare phenol and cresulphonic acids, such quantities of
technical sulphuric acid are used as do not allow of the assumption of
complete utilisation of the sulphuric acid; hence it was of theoretical
interest to remove eventual traces of free sulphuric acid from the
product. For this purpose, the author diluted crude Neradol to 20°
Bé. and gradually added small quantities of milk of lime; the
precipitates were freed from the liquid by suction and washing, and a
Neradol free from sulphuric acid resulted, which was then brought to the
acidity of Neradol D with the calculated amount of alkali. From the
calcium sulphate precipitate, the amount of sulphuric acid originally
present was calculated, and was found to be only 4 per cent.
The acid-free sample of Neradol was tested with regard to its
suitability as a tanning agent; leather tanned with this sample differed
from one tanned with an untreated sample (Neradol D) by being harder and
possessing a pronouncedly greyish colour. This difference, however, may
not be due to the absence of sulphuric acid but to the presence of the
slightly soluble calcium sulphate in the sample treated with milk of
lime. To prove this point, another way of preparing Neradol D free from
sulphuric acid was looked out for. Sodium acetate was added to a
solution of crude Neradol until the latter was no longer acid to
congo-red; at this point no free sulphuric acid can be present in the
solution. The product, partly neutralised till the acidity of Neradol D
was reached (part of the acidity then being due to liberated acetic
acid), yielded a leather which neither in colour nor in feel differed
from the usual Neradol D tanned leather. This proves that the grey
colour and the hardness of the leather described in the former
experiment is due to the presence of calcium sulphate.
If the crude Neradol treated with sodium acetate is not partly
neutralised, the analysis gives the following figures:—
Tanning matters 67.3 per cent.
Soluble non-tannins 8.6 "
Insolubles 0.0 "
Water 24.1 "
————-
100.0 per cent.
Acidity: 1 gm. = 46 c.c. N/10 NaOH.
Compared to the analysis of crude Neradol containing sulphuric acid, the
figures show that, on the one hand, the presence of the comparatively
small quantity of sodium acetate but slightly influences the contents of
non-tannins and water, but, on the other hand, reduces the contents of
tannins and also the acidity. The tanning intensity of this product,
however, is considerably increased, and using a 1° Bé. solution a
leather is obtained in a very short time very similar to that yielded by
ordinary Neradol D, but considerably harder; the latter property is due
to higher acidity and almost complete absence of salts in the product
treated with sodium acetate.
The author finally attempted to partly neutralise crude Neradol with
various hydroxides and carried out tanning tests with samples containing
the different metals. Hardly any difference in the finished leathers
could be observed as regards colour or quality; the tannage could by no
means be described as that of a combination of Neradol D and the
respective metals.
12. Neutral Neradol
Crude Neradol, completely neutralised with caustic soda, yields a
product of the following composition:—
Tanning matters 19.8 per cent.
Soluble non-tannins 37.9 "
Insolubles 0.0 "
Water 42.3 "
——————
100.0 per cent.
The qualitative reactions of this product differ from those of
non-neutralised Neradol to the extent that gelatine is not precipitated
and iron salts are not coloured blue, but dirty brown, by the aqueous
solution of this product.
The completely neutralised product, diluted to various concentrations
(of 1°, 2°, 3°, and 5° Bé.) and tested as to tanning properties,
revealed the surprising fact that the pelts were not even surface
tanned, and were coloured evenly blue throughout by indigotine.
It might have been anticipated that sodium dicresylmethanedisulphonate
would be as devoid of tanning powers as is a neutralised vegetable
tannin, but it is difficult to explain the fact of the sodium salt being
adsorbed by hide powder as "tanning matters" in the Official Method of
Analysis. Brought to a logical conclusion, the figure 19.8 per cent,
should be deducted from 32.5 per cent, obtained in the analysis of a
partly neutralised Neradol D, which comparatively large quantities of
the sodium sulphonate also adsorbed by hide powder, leaving the "tanning
matters" of Neradol D at 13.5 per cent.
This diminished figure, however, does in no way reduce the value as a
tanning agent of Neradol D; it merely shows how inadequate is the hide
powder method of analysis when applied to substances of the composition
of Neradol D. This is further confirmed by the Loewenthal permanganate
method, which yields the following figures:—
Tanning matters 7.2 per cent.
Soluble non-tannins 59.1 [Footnote: Collegium, 1913, 521,487.]
If, on the other hand, completely neutralised Neradol is acidified with
an organic acid, such as acetic acid, till the acidity, (1 gm.= 10
c.c. N/10 NaOH) is reached, the resulting product is in all respects
similar to Neradol D and yields a corresponding leather.
It is permissible to assume that the irregularity exhibited by Neradol D
as regards the analytical estimation of its tannin contents is connected
with the low molecular weight of the tanning principle. Whereas all
tannins so far isolated from the natural tanning materials possess
rather high molecular weights, that of Neradol D deviates considerably
from this rule, as is shown by the following table:—
Neradol D tannin Cl_5H_16S_2O_8 358
Mangrove " C_24H_40O_2l 670
Oak bark " C_28H_28O_23 840
Myrabolam " C_54H_48O_35 1256
Dividivi " C_54H_46O_35 1270
Malletto " (C_4lH_50O_20)_2 1724
This low molecular weight may mainly account for the figures obtained by
the incorrect oxymetric estimation with permanganate; the apparent
tannoid property of the tannoid-inactive neutral salt of
dicresylmethanedisulphonic acid may be explained by assuming that though
it is, probably, in the colloidal state, and as such adsorbed by hide
powder, it is still devoid of astringent properties.
G. Different Methods of Condensation as Applied to Phenolsulphonic Acid
In addition to formaldehyde, many other substances may, theoretically,
induce condensation of phenolsulphonic acid; condensation takes place
either with the elimination of water or, in addition to this, with the
introduction of methane group.
So far, the following condensing agents have been investigated:—
(1) Heating in vacuo.
(2) Sulphur chloride.
(3) Phosphorus compounds.
(4) Aldehydes.
(5) Glycerol.
1. Condensation Induced by Heat
If phenolsulphonic acid is heated in vacuo at 130° C. for twenty
hours, condensation takes place [Footnote: Austr. Pat., 64,479.]
without the addition of any condensing agent, and an anhydride of the
^ __O__ ^
| | | |
| | | |
v v
HSO_3 HSO_3
composition is formed. This product is a viscous liquid, possessing a
very corrosive action. Added to a solution of gelatine, a light, fine
flocculent precipitate is thrown down. Analysed by the shake method of
analysis, the tannin content of the product equals about 46 per
cent. Its strongly acidic and hence swelling character does not express
qualities consistent with the conception of suitability for tanning
purposes: a sample of the product was therefore partly neutralised to
the acidity of Neradol D, when the shake method of analysis yielded the
following figures:—
Tanning matters 21.5 per cent.
Soluble non-tannins 48.3 "
Water 30.2 "
———————
100.0 per cent.
This partly neutralised sulphonic acid represents a white, pasty mass,
which is not particularly easily soluble in water, yielding a solution
of milky appearance. Treated with the usual tannin reagents, it exhibits
the following characteristics:—
Gelatine Light Flocculent precipitate.
Bromine water Compete fixation.
Ferric chloride Cherry-red coloration.
Lead acetate Very slight Percipitate, insoluble HNO_3.
Aniline hydrochlonde Slight percipitate.
Solutions of this product in concentrations from 1°-8° Bé. exerted no
tanning action whatever, whereas more concentrated solutions (15° Bé.)
converted pelt in eight days into a leather very similar to a Neradol D
leather in colour and feel, but considerably harder.
In order to determine its phlobaphene-solubilising effects, samplesof
the product were mixed with concentrated quebracho extract in the
proportions 5,10, 20, and 30 per cent. on the weight of extract, and the
following observations made:—5 and 10 per cent. were without effect,
20 and 30 per cent. showed some solubilising tendency, but on diluting
the mixture with water the quebracho was completely thrown out of
solution. Apparently this anhydride is, in this respect also, quite
different from the partly neutralised diphenylmethanedisulphonic acid.
2. Condensation with Sulphur Chloride
When sulphur chloride is allowed to act upon phenolsulphonic acid whilst
heat is applied, a yellowish-grey mass results, which dissolves in
water, forming a reddish-yellow solution. Neutralised to acidity 10, it
exhibits the following reactions:—
Gelatine————————Precipitate.
Ferric chloride————-Deep blue coloration.
Lead acetate——————White precipitate, insoluble HNO_3.
Aniline hydrochloride—-Precipitate.
Bromine water—————-No reaction.
The partly neutralised 2° Bé. solution of this product yielded a
reddish-grey coloured leather, the qualities of which were very similar
to that yielded by Neradol D.
3. Condensation with Phosphorus Compounds
Schiff's well-known synthesis, [Footnote: Liebig's Ann., 178, 173.]
in which phosphorus oxychloride interacts with phenolsulphonic acid,
yields a product which exhibits some tannin reactions, but which, when
acting on pelt, converts the latter into a leather which, when dried, is
very cracky. If, on the other hand, cresolsulphonic acid is condensed
with phosphorus oxychloride by heating the two together, products
eminently suitable for tanning purposes result. These products are
non-crystalline bodies easily soluble in water, and are coloured
bluish-violet by ferric chloride and precipitate gelatine. Solutions of
the free acids and acidified solutions of the salts convert pelt into
firm and white leathers possessing great softness and
pliability.[Footnote: Austr. Pat, 66,895.]
4. Condensation with Aldehydes
By treating phenolsulphonic acid with acetaldehyde in the usual way, a
viscous brown mass is obtained, which is very soluble in water, the
solution being of a brown colour. When brought to acidity 10, the
following reactions are exhibited by the product:—
Gelatine - - - Precipitate.
Ferric chloride - - Deep blue coloration.
Aqueous ammonia - - Cherry-red coloration.
Lead acetate - - - Yellowish precipitate, insoluble
HNO_3.
Aniline hydrochloride - - Yellow precipitate, soluble excess
aniline.
Bromine water- - - No reaction.
Tanning experiments with this substance yielded, even after extended
tannage, an undertanned leather, the surfaces being coloured brown, the
inner layers, however, white. Further neutralisation reduces the
tanning intensity of the product; the addition of sodium sulphate to the
original partly neutralised product hastened tannage, the leather,
however, possessing dark colour and being undertanned. The following
constitution may be ascribed to this product:—
OH OH
^ —-CH_2—-CH_2—- ^
| | | |
| | | |
v v
HSO_3 HSO_3
If benzaldehyde is used in lieu of acetaldehyde for condensing
phenolsulphonic acid, a water-soluble product results, exhibiting
reactions similar to those of the acetaldehyde-condensation product. The
former product is more suitable as a tanning agent and yields a
reddish-brown rather firm and hard leather; it possesses the
constitution—
H
OH || OH
^ ____C____ ^
| | ^ | |
| | | | | |
v | | v
HSO_3 v HSO_3
For the purpose of condensing phenol with formaldehyde, it is not
essential to first convert the phenol into the water-soluble
phenolsulphonic acid, since it is possible to convert the condensation
products of phenol and its derivatives, which are soluble in alkali,
into water-soluble form by either heating the condensation products with
concentrated solutions of formaldehyde and neutral sulphites, or by
dissolving the condensation products in alkali and inducing reaction by
means of formaldehyde bisulphite. [Footnote: Collegium, 1913, 518,
324.] Highly concentrated solutions result, which may be concentrated
either as such or after the alkali present has been neutralised. The
sulphurous acid formed prevents oxidation of the product on
evaporation. A special advantage of this method of preparation is the
fact that sulphuric acid, which is but difficultly removed from the
end-product, is not employed at all.
The product thus obtained is a yellowish-white crumbly mass, which is
very soluble in water, forming a clear solution. The latter exhibits
the following reactions:—
Gelatine———————-Precipitate.
Ferric chloride————Deep blue coloration.
Aqueous ammonia————Cherry-red coloration.
Lead acetate—————-White precipitate, insoluble in
HNO_3.
Aniline hydrochloride—Precipitate.
Bromine water—————No reaction.
The product brought to acidity 10, yielded on analysis the
following figures:—
Tanning matters————————— 25.2 per cent.
Soluble non-tannins——————— 56.3 "
Insolubles———————————- 0.0 "
Water—————————————— 18.3 "
——————-
100.0 per cent.
Tanning experiments with this substance yielded white and soft leathers,
which were indistinguishable from those tanned with Neradol D.
A characteristic feature of this synthetic tannin is its behaviour in
concentrated form towards pelt, which is not attacked by it, but is
readily tanned even at such high concentrations. An explanation of this
is to be found in the large quantity of salts present in the product. A
disadvantage of this synthetic tannin is its complete incapability of
dissolving phlobaphenes, which is even so far extended as to precipitate
otherwise easily soluble tannins when adding it to solutions of the
latter in comparatively large proportions; here, again, the salts are
responsible for this behaviour, their large quantities effecting a
salting out of the natural tannins.
The class of aldehyde condensations also comprises that of inducing
condensation by means of sugars; if phenolsulphonic acid is heated with
glucose, a reddish-brown liquid results, which is soluble in water. The
solution exhibits reactions similar to those of Neradol D. It is,
however, not possible, by this method of condensation, to prepare as
highly concentrated products as is possible in the case of Neradol D,
since employing sugars as condensation agents means liberation of a
large volume of water. Analysis of this product, using the shake method,
gives a tannin content of 16.2 per cent; tanning experiments
demonstrated that the time of tannage, using a 2° Bé. solution, was the
same as that required by Neradol D, and yielded a leather, the surface
of which was reddish-grey, the inner layers being white, but which is
otherwise very similar to Neradol D tanned leather. [Footnote:
Austr. Pat, 69,375, 69,376, 69,377.]
Relatively to its capability of solubilising phlobaphenes, this product
exhibits similar properties to that obtained by merely heating
phenolsulphonic acid, to a slight extent only solubilising quebracho
extract, which, on diluting the mixture, is completely thrown out of
solution.
5. Condensation with Glycerol
Phenolsulphonic acid, when heated with glycerol, undergoes the process
of condensation, and forms a brown fluid, which, when brought to acidity
10, exhibits the following reactions:—
Gelatine————————-Precipitate.
Ferric chloride—————Brown-black coloration.
Lead acetate——————-White precipitate, insoluble in
HNO_3.
Aniline hydrochloride——Slight precipitate.
Tanning experiments with this partly neutralised product resulted in a
very gradual conversion of the pelt into a greenish-grey coloured
leather; the colour, however, does not penetrate the pelt and is hence
caused by colloidally suspended impurities. If the solution is filtered
through a filter candle, a somewhat clearer solution results, but the
latter also tans very slowly and yields a brown coloured leather.
Analysis of the partly neutralised product reveals a tannin content of
17.6 per cent. A 2° Bé. solution of the non-neutralised product showed a
rapid tanning effect at first, when brought into contact with pelt, on
which it had a strong swelling effect, and to which it imparted a
greenish colour; the tanning effect, however, slowed down considerably,
after a few days, and the solution penetrated the pelt only very
gradually; this is probably due to the presence of large quantities of
colloidally suspended impurities, which, when the substance is partly
neutralised with the formation of salts of the sulphonic acids, are
brought into true solution and hence penetrate the pelt with greater
rapidity.
Adler
Appelius
Ashmore
Bader
Badische Anilin u.(German abbreviation for "und") Soda-Fabrik
Baekeland
Baeyer
Berzelius
Biginelli
Boehringer & Sons
Bottinger
Braconnot
Buff
Caro
Chem. Fabrik Jucker & Co.
Chevreul
Dekker
Deutsch-Koloniale Gerb u. Farbstoff Gesellschaft
Deyeux
Dizé
Drabble
Edner
Elberfelder Farbenfabriken
Fahrion
Feist
Fischer, E.
Freudenberg
Froda
Gerhardt
Gesellschaft f.(German abbreviation for "für") Chem. Industrie, Basle
Graebe
Graham
Grasser
Hatchett
Heinemann
Herzig
Herzog
Hönig
Iljin
Immerheiser
Jennings
Kahl
Kauschke
Klepl
König
Kostanecki
Krafft
Krauss
Kunzemüller
Lauffmann
Liebig
Lipp
Lloyd
Löwe
Manning
Mauthner
Meunier
Michael
Mielke
Mitscherlich
Nierenstein
Paessler
Paternò
Payne
Pelouze
Perkin
Proust
Rapoport
Raschig
Reinsch
Resch
Russanow
Sabanajew
Sander
Scheele
Schiff
Schmidt
Schorlemmer
Seel
Seyewetz
Sisley
Skey
Stiasny
Strauss
Thuau
Tschirch
Vogel
Walden
Webster
Weinschenk
Wohl
Zacharias