Synthetic Tannins, Their Synthesis, Industrial Production and Application

Chapter IX: Part II: Synthetic Tannins: Their Industrial Production and Application (2)

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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:--

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.

INDEX OF AUTHORS

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

Alcohol figure Algarobilla Alizarin Alizarin yellow, in paste Alkalies, reaction of, to Neradol D Alum-neradol tannage Alum tannage Aminobenzene Aminophenol, _p_- Aniline dyes Anthracene Anthraquinone Arylsulphaminoarylsulphonic acids Arylsulphoxyarylsulpho acids

Bakelite Bakelite solution Benzoylamino 6-chloranthraquinone Benzylsulphanilate sodium Bismuth salts Bleaching method for leather with Neradol D Bloom Bromo-[Greek: b]-naphthol Bromonitrophenol Bromophloroglucinol Bromosalicylic acid Bromotrinitrophenol

Carbazole Carbomethoxyhydroxybenzoic acid, Carbomethoxyhydroxybenzoic acid chloride, Catechine Catechol Cerium salts Ceruleoellagic acid Cesium salts Chestnut wood extract Chloronaphthalenesulphonic acid Chlorophenol Chrome-Neradol D tannage Chrome salts Chrome tannage Coal, bituminous Coffee tannin Combination tannage with Ordoval Combination tannage with Neradol D Condensation by heat Condensation methods Condensation with aldehydes Condensation with glycerol Condensation with phosphorus compounds Condensation with sulphur chloride Copper salts Corinal Cresol Cresol-_p_-sulphonic acid, _o_- Cresolsulphonic acid Cresotinic acid

Depsides Detannisation with hide powder Diaminoanthraquinone Diaminonaphthylmethanedisulphonic acid Dianilinoquinone Dibenzopyrrol Di-[Greek: b]-oxynaphthoic Di-[Greek: b]-resorcylic acid Dichloranthraquinone Dichloronaphthylmethanedisulphonic acid Dicresylmethanedisulphonic acid Dicresylmethanedisulphonic acid purified electro-osmotically Dicresylmethane sulphonate sodium Didepsides Didymium salts Diferulic acid Digallic acid Digallic acid, [Greek: b]- Digallic acid, inactive Digallic acid, _m_- Digalloylleucodigallic acid anhydride Digentisinic acid Dihydric alcohols, aromatic Dihydroxybenzene, _m_- Dihydroxybenzene, _o_- Dihydroxybenzene, _p_- Dihydroxybenzenes Dimethylaniline Dimethylellagic acid Di-_m_-oxybenzoic acid Dinaphthylmethanedisulphonic acid Dinitronaphthylmethanedisulphonic acid Di-_o_-cumaric acid Diorsellic acid, _o_- Diorsellic acid, _p_- Dioxyellagic acid Dioxynaphthylmethanedisulphonic acid Dioxytoluic acid Diphenylmethane Diphenylmethanedisulphonic acid Di-_p_-hydroxybenzoic acid Diprotocatechuic acid Disalicylic acid Disyringic acid Dithionaphthylmethanedisulphonic acid Dividivi Dividivi tannin Dixylylmethanedisulphonic acid

Electro-chemical behaviour of Neradol D Electro-osmosis of Neradol D Ellagic acid Ellagitannic acid Empirical formula of tannin Erythrine Esco-extract Ester formula of tannin Ethyl acetate figure

Fat-Neradol D tannage Feruloyl-_p_-oxybenzoic acid Flavellagic acid Fluorene Formaldehyde Formaldehyde tannage

G-acid Gallate ethyl Gallic acid Galloflavine Galloyl-_p_-hydroxybenzoic acid Galls, oak Gall tannin Generator tar Guaiacol

Halogens Hepta-[tribenzoyl-galloyl]-_p_-iodophenylmaltosazone Hexahydroxyaurinecarboxylic acid Hexoxyanthraquinone Hexoxydiphenyl Hexoxydiphenyldicarboxylic acid Hexoxydiphenylmethanedicarboxylic acid Humic acid Hydrolysis of tannins Hydroquinone Hydroxybenzoate sodium, _m_- Hydroxybenzoate sodium, _p_- Hydroxybenzoic acid, _p_- Hydroxybenzoic acid Hydroxy-cymenes

Indophenol reaction Iron, reaction of, to Neradol D Iron salts

Ketone formula of tannin

Lanthanum salts Lead salts Leather analysis in presence of Neradol D Lecanoric acid Leucodigallic acid Leucoellagic acid Leucotannin Lignite Luteic acid

Malletto tannin Mangrove tannin Melangallic acid Mercury salts Metellagic acid Methylamino-4-bromanthraquinone Methylenedinaphthol Methylenedisalicylic acid Methylenedisalicylic acid, brominated Methylenedisalicylic acid, iodised Methylisopropylphenanthrene Methylotannin Molybdenum figure Monochloro-_p_-dihydroxybenzene Mud Myrabolams Myrabolams, tannin

Naphthalenesulphonic acid, [Greek: b]- Naphthol, [Greek: a]- Naphthol, [Greek: b]- Naphthol-[Greek: a]-methanesulphonic acid Naphtholdisulphonic acid Naphtholmonosulphonic acid Naphtholsulphonic acid, [Greek: a]- Naphtholsulphonic acid, [Greek: b]- Neodymium salts Neradol D Neradol D tannin Neradol N Neradol ND Neradol ND, neutral Nitronaphthalenesulphonic acid Nitrophenol, _o_- Nitrosodimethylaniline Non-tannins Novolak

Oak bark Oak bark tannin Official method of tannin analysis Orcinol Ordoval G Orsellic acid Orsellinoyl-_p_-oxybenzoic acid Oxyanthraquinone Oxyazo reaction Oxybenzoyl-_m_-hydroxybenzoic acid Oxybenzoyl-_p_-hydroxybenzoic acid, _m_- Oxybenzoylsyringic acid Oxynaphthoyl-_p_-hydroxybenzoic acid, _a_- Oxynaphthylmethanesulphonic acid Oxyphenylmethanesulphonic acid Oxyquinoline

PATENTS-- _Austrian_ 58,405; 61,057; 61,061; 64,479; 66,895; 68,796; 69,194; 69,375; 69,376; 69,377; 70,162 _German_ 72,161; 111,408; 112,183; 132,224; 181,288; 184,449; 200,539; 206,957; 211,403; 262,558; 282,313; 286,568; 290,965; 291,457; 293,042; 293,640; 293,693; 297,187; 297,188; 300,567; 303,640; 305,516; 319,713; 320,613 _Swiss_ 78,282; 78,797; 79,139 _U.S.A._ 1,639,174 Peat Pelts Pelts, action on, of Neradol D Penta-[_p_-hydroxybenzoyl] glucose, Penta-[_p_-methyl-_m_-digalloyl]-glucose Penta-[pyrogalloylcarboyl]-glucose Pentacetylleucotannin Pentacetyl-_m_-digallic acid Pentacetyl tannin Pentadigalloylglucose Pentagalloylglucose Pentagalloylglucoside Pentamethyldigallic acid, methyl ester Pentamethyl-_m_-digalloyl chloride, Pentamethyl-_m_-digallic acid Pentamethyl-_m_-digallic acid methyl ester Pentamethyl-_p_-digallic acid Pentamethyl-_p_-digallic acid methyl ester Pentamethoxybiphenylmethylolide carboxylic acid methyl ester Pentoxybiphenylmethylolide Pentoxybiphenylmethylolide carboxylic acid Phenanthraquinone Phenolsulphonate sodium Phenolsulphonic acid Phenolsulphonic acid anhydride Phenol, tautomeric Phenylcarboxylic acid Phenylhydrazine derivatives of tannin Phenylhydrazine ellagic acid Phlobaphene Phlobaphene-solubilising action of neradols Phloroglucinol Phthalic acid Pickling Picric acid Platinum salts Polydepsides Polydigalloylleucodigallic acid anhydride Polyhydroxybenzenes Pomegranate Preparation of tannin infusion Properties of leather tanned with Neradol Protocatechuic acid Protocatechuyl-_p_-hydroxybemoic acid Pseudo-tannage Purpuro tannin Pyrogallol Pyrogallic acid Pyrogalloylcarboyl-_p_-oxybenzoic acid Pyruvic acid

Quinazarene Quinoline Quinone

R-acid Reaction, Procter-Hirst Reagents for Neradol D tannage Resites Resitol Resols Resorcinol Resorcylic acid, [Greek: b]- Retene

Rosins, acid Rosolic acid Rufigallic acid

S-acid Salicylic acid Salicylic acid phenyl ester Salicyl-_p_-hydroxybenzoic acid Salol Silver oxide Solution salt Solvenol Structure of tannin Sulphinic acid Sulphite cellulose extract Sulphite lye Sulphonamide Sulphonic acids, aromatic Sulphonic chloride Sulphur Sulphur tannage Sulphuric acid-free Neradol D Sulphuric acid in leather Syringoyl-_p_-hydroxybenzoic acid

Tannin Tannin action, real Tannin analysis Tanning matters Tannin molecule Tannin, pure Tannophor Test tannage Tetradepsides Tetragalloyl-[Greek: a]-methylglucoside Tetramethylellagic acid Tetroxydiphenyldimethylolide Thionaphtholsulphonic acid Thiosulphonic acid Thorium salts Thymol Toluidoanthraquinone, l-_m_- Total solids Total solubles Tribromophenol Tribromopyrogallic acid Tricarbomethoxygalloyl chloride Tridepside Trihydroxybenzenes Trinitrophenol Triphenylmethane

Valonea Vanadium salts Vanillic acid Vanilloyl-di-_p_-oxybenzoyl-_p_-hydroxybenzoic acid Vanilloyl-_p_-hydroxybenzoic acid Vanilloyl vanillin

Xanthenes

Zinc salts Zirconium salts

Comments

Synthetic Tannins, Their Synthesis, Industrial Production and ApplicationChapter IX: Part II: Synthetic Tannins: Their Industrial Production and Application (2)

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