US2809088A - Process of retanning leather with a condensation product of sulfones of monohydric phenols, non-aromatic amines and formaldehyde - Google Patents

Description

PROCE 69F RETANNENG LEATHER WITH A CONDENSATEON PlRflD UCT F SULFQNES OF MQNUHYDRIC PHENGLS, NONARGMATIC AMINES AND FQRMALDEHYDE Martin Meister, Leverltusen-Vl iesdorf, and Gustav Maiithe, ()pladen, Germany, assignors to Farbenfabrilren Bayer Alrtiengesellschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Application duly 7, 1953, Serial No. 366,612

Claims priority, application Germany July 12, 1952 4 Claims. (Cl. 8-94.21)

The present invention relates to a new retanning process using salts of condensation products obtained from sulfones of monohydric phenols, non-aromatic bases and formaldehyde.

In our copehding application Ser. No. 295,558, filed June 25, 1952, and now U. S. Patent No. 2,733,977, we have described a new tanning process consisting inter alia in retanning and, if desired, neutralizing tanned leather or pretanned hides with condensation products of polyphencls, aromatic, non-aromatic amines orvammonia, as well as their salts, and aldehydes. These condensation products, which are obtained by condensation of more than 1 mol of polyphenols with 1 mol of amine or amine hydrochloride, are self-tannins with excellent tanning properties; they may be used to prepare commercial leather from animal hides and can be analysed by the hide powder analysis using 4 grams of pure tannin per liter.

The importance of the above retanning process consists in that the anionic tannins (the previously used tannins and auxiliary tannins of natural and/ or synthetic origin are of anionic nature), which are fixed in the leather or the hide substance, are converted to completely insoluble compounds by the cationic tannins of the invention. These cationic tannins impart to the leather an increase in weight and volume which could not be achieved up to the present. Furthermore, tanned leather of a poor filling effect is levelled up by said tannins. The substantially phenolic character of these tannins guarantees a uniform penetration into the hide and leather substance without the undesired case-hardening occurring.

In accordance with the invention we have found that the salts of the condensation products of the'sulfones containing monohydric phenols with primary and secondary non-aromatic bases and formaldehyde can be adopted to the process described in our copending application Ser. No. 295,558, filed June 25, 1952, now U. S. Patent No. 2,733,977. This eiiect is the more surprising since these condensation products show no capacity of precipitating gelatine or only to an immaterial degree, and their tanning effect on pelts prepared for tanning is poor.

The manufacturing process of the condensation products of sulfones and amine salts and the stability of these products to excess aldehyde and higher temperatures is described in our copending application Ser. No. 354,656, filed May 12, 1953. Higher molecular weight products with a lower diffusibility into the hide and leather are not formed during the process. The very low viscous solutions guarantee a rapid penetration into the leather substance.

The condensation products obtained from sulfones and amine salts are amphoteric in character, i. e. they are soluble in both alkalies and acids. They are generally insoluble around the neutral point. Strongly basic condensation products containing 2 amino groups in each nucleus are sometimes soluble upon addition of acids. Also organic acids may form salts. These condensation products, which Patented Oct. 8, 1957 are salt-like cationic compounds, precipitate anionic compounds such as tannings, auxiliary tannins, dyestuffs and sulfonated oils practically completely.

Leather is retanned with these condensation products obtained from sulfones and amine salts in quantities up to 25% in a usual tan liquor. Finally, the leather is neutralized with ammonia, especially when the bases are insoluble. This allows of exhausting the tan liquors completely and of incorporating higher percentages of retanhing agents into the leather whereupon an amazing increase in thickness of the leather is achieved. Light leather may be retanned by the brushing process, heavy leather by drurn-tanning or pit-tanning.

A marked increase in thickness can be ascertained after the usual processing and drying of the leather. Condensation products containing 1 amino group in each nucleus lead to an increaseof 20%, products containing 2 amino groups in each nucleus to a still higher increase. In spite of the increased filling effect the mellow handle of the leather is preserved, the color of the leather is lightened, the adsor'btive power for fats and the stability to light, in particular of leather tanned with vegetable tannins, is improved. The substantially improved dyeability or leather retanned by the herein described process is striking.

it is within the scope of the invention to retan leather tanned with mineral tannins, especially chrome leather, with the condensation products obtained from sulfones and amine salts. 1he filling effect of the leather is increased without the typical chrome character and the fine appearance of the grain being essentially altered. it is a remarkable feature of the invention that the chrome salts can be applied in combination with organic cationic condensation products. the salts, however, must be tested in advance for their compatibility since the sulfates of the organic cationic products are, in most cases, more dift'iculily soluble than the chlorides, and the chrome tanning salts sold on the marieet are suliates throughout. in such single bath tanning processes the chrome component is frequently masked.

'lhe condensation products of sulfones and amine salts employed according [O the invention for retanningleather can be admixed with the cationic tannins described in our copenoing applications Ser. NO. 241,093, hied August 13, 1951, now abandoned, and Ser. No. 351,460, riled January 15, i955, in all proportions; these condensation products improve the stability or said cationic tannins during tanning. We have surprisingly found that up to '/u2 u/o of these self-tannins can be replaced by the condensation products or sulfones and amine salts, which are contemplated originally for retanning processes, without the seii'ianning capacity of the mixtures as compared with the self-tannins being substantially aitected. Mixtures or the condensation products obtained troin sulfones and amine salts and the cationic tannins described in said copending applications, which may be used as sell-tannins, are exceiientiy suited for retanning leather tanned with organic and mineral tannins.

iiie following examples illustrate the invention, the parts being by weight, it not otherwise stated.

tsxzmzpte 1.luu parts (calculated on the shavers weight) of a chrome calf leather tanned in the usual manner with 3 parts of chrome oxide in the form of a commercial trivalent basic chrome salt and shaved to a thickness of 1.6 mm. are rinsed in flowing cold water for 30 minutes after accurately measuring the thickness of the leather at various places, and then milled in 200-250 parts of cold water.

A solution of 1 part of the dry substance of the cationic condensation product (hereinafter called retanning agent),

0 prepared by the process of our copending application Ser. No. 354,656, filed May 12, 1953, from 1 mol of 3 4.4'-dihydroxydiphenylsulfone, 2 mols of ethanol amine and 2 mols of formaldehyde and adjusted to a pH of about 3.5 with hydrochloric acid, in parts by volume of water is added in 2 portions at an interval of 5 minutes. [The retanning agent is prepared by mixing the 4,4- dihydroxy-diphenyl-sulfone, with stirring, with the ethanolamine, then slowly reacting the resulting warm mixture with the formaldehyde solution) as an exothermic reaction occurs. After heating the homogeneous mixture in a boiling water bath for 1 hour, the water insoluble base is dissolved in 120-130 cc. of concentrated hydrochl ric acid at about 70 C. If the addition compound of sulfone and amine crystallizes and solidifies prematurely. the mixture is nevertheless heated with the aldehyde whereupon dissolution occurs gradually] After milling for 30 minutes the tanning solution shows a pH of about 4.6. Upon addition of minor quantities of a dilute ammonia solution the t nning solution becomes slightly turbid due to precipit ting free portions of retanning agent. To exhaust the tanning solution in 23 portions ammonia solution (about 5%) is added in 2-4 portions un il the pH value of the tanning solution has increased to 5.86.0. The leather is subsequently milled for another 30-45 minutes. No turbidity occurs any longer in the tanning solution upon addition of further quantities of dilute ammonia. that means the retanning agent has been absorbed.

The leather is trestled over night and thereafter subjected to the usual aftertreatment. By drying a sample after normal fat-liquoring in this non-colored condition a leather is obtained which is distinguished from non retanned chrome leather by better filling properties, a softer handle and a character which could not be a hieved by a process using vegetable retanning agents in higher quantitics. The fine surface luster of the leather is especially striking. By dyeing the non-dried leather according to the methods usually applied in dyeing chrome leather with l part of a comm rcial acid leather dyestuff the leather subjected to aftertreatment with the retanning agent assumes a markedly deeper and more covered shade than a non-retanned chrrme leather which, otherwise, has been fat-liquored and dyed in equal manner and originates from a com arable position of the same hide. The dried, colored leather is measured with the caliper and the thus ascertained values are compared with the figures determined in the wet state after shaving the leather. The non-ret nncd leather shows a l ss of thickness of 2.35% whereas the leather treated with the retanning shows an increase of thicknessof 0.1%.

Examvle 2.100 p rts of the shaved chrome leather are treated with 3 parts of the above retanning agent (Example 1) in the manner described in Exam le 1. After dyeing with 1 part of a mixture of acid and substantive dyestuffs this leather showed an essentially deeper, more covered shade as compared with a non-retanned leather which originates from a comparable position of the same hide. In a diagonal cut it can be seen that the dyestu f penetrates into the retanned leather to an essentially lesser degree and is substantially fixed in the top layers of the grain and flesh side. By measuring the thickness of the leather as described above a loss of thickness of 2.0% is ascertained in the case of the nonretanned leather whereas the retanned leather shows an increase of thickness of 6.3%.

Example 3. 1O0 parts of chrome leather, as described in Example 1 are retanned in the manner described in Example 1 with a solution of 3 parts of the dry substance of a retanning agent (in 25 parts by volume of water), which was obtained as follows: 3 parts of the dry substance of'the tannin prepared by the process of our copending application Ser. No. 241,693, filed Aug st 13, 1951 (Example 33) fr m res rcin l. amm nium chl ride and formaldehyde. are mixed with 7 parts of a dry sub stance of the condensation product, described in Ex mnle 1, from 4.4-dihydroxy-diphenylsulfone, ethanol amine and formaldehyde, which was adjusted to a pH of about 3.5 with hydrochloric acid, and water is added to the mixture until a sirup capable of being easily poured has formed. Following is the procedure for preparing the tannins of Example 33, application S. N. 241,693:

102 cc. of formaldehyde solution 30% are added to the solution of 18 grams of ammonium chloride and 110 grams of resorcinol in 60 cc. of Water at room temperature. Within a few minutes the temperature rises above C.; the mixture is then heated for further 1% hours in the boiling water bath.

With 126 grams of pyrogallol the condensation proceeds likewise strongly exothermic. As the pyrogallol tends to crystallize prematurely, the aldehyde is added at 45 C.; the temperature rises to the boiling point of the reaction mixture. The mixture is heated for further 1% hours in the boiling water bath.

A mixture of e. g. 55 grams of resorcinol and 63 grams of pyrogallol shows quite a similar behaviour. The aldehyde can be added at 20 to 25 C.

The condensation of grams of catechol or grams of brenzoeF instead of the above-mentioned 110 I grams of resorcinol proceeds only weakly exothermic.

The aldehyde is added at 35 C., and the mixture is heated in the boiling water bath; there the reaction mixture comes to boil for a short time. It is heated for 2 /2 hours in the boiling water bath.

By decreasing the quantity of the ammonium chloride and using the same quantity of aldehyde more viscous, higher molecular, water-soluble condensation products are obtained.

The resorcinol condensation product, neutralized with a little ammonia, shows the following analytical values:

Concentration 47.8%. Tannins 34.3%. Percentage of pure tannin in dry substance 71.7.

Acid number pH value 6.25.

Weight of sample 12 grams=4.1 grams of pure tannin per liter.

With the corresponding quantities of ammonium bromide the condensation reactions proceed practically in the same way as those described above. The aldehyde is added at the temperature at which one of the reacting agents begins to separate, after complete dissolution had been effected at higher temperature. If necessary, the reaction may be restrained by shortly cooling with water. After fat-liquoring and dyeing the non-dyed leather is distinguished from a non-retanned chrome leather by a greater filling effect, a beautiful surface luster and a softer handle. The chrome leather color has disappeared, the leather has a yellowish brown appearance and a character like the leather retanned with vegetable tannins.

By dyeing with 1 part of an acid commercial dyestuif the retanned leather assumes an essentially deeper, more covered sh de than the non-retanned leather. The measuring of the thickness of the leather as described in Example 1 shows that the non-retanned leather has decreased in thickness by 2.0% where-as the retanned leather has increased in thickness by 19.4%.

Example 4.A piece of cow-hide tanned with a mixture of vegetable and synthetic tannins in a series of pits, which had not yet been subjected to the usual drum tanning, is set out well, rinsed with flowing cold water for 30 minutes, set out once more and divided into 2 approximately equally large pieces designated 1 and II. The weight of each of these pieces is determined and the thickness is accurately measured at various places with the caliper.

100 parts (referred to the sammied weight) of the piece designated l are milled in a solution of 1.2 parts of acetic acid (30%) in 300 parts by volume of water of 20 C. for 4O minutes. The pH value of the solution is atabout 4.0-4.2. The leather I is then tanned in 300 parts by volume of fresh solution of 20 C. containing 3 parts of the dry substance of the retanning agent named in Example 1, prepared from 4.4-dihydroxydiphenyl sulfone, ethanol amine and formaldehyde, by dissolving the said quantity of retanning agent in about 30 parts by volume of water and introducing the solution in two portions at an interval of minutes. After a running time of 45 minutes the tanning solution is adjusted to a pH of about 5.0 within 20 minutes by addition of dilute ammonia solution (about 5%) in portions. The leather is trestled over night, shortly rinsed the following morning and milled in 300 parts by volume of tanning solution of 45 C. containing 4 parts of a customary fat-liquoring mixture for 70 minutes. After drying a very fine, pliable and mellow leather of good feel and yellowish-brown color is obtained.

For comparison 100 parts of the leather designated H are retanned by the usual method as follows: The leather is fat-liquored in 300 parts by volume of water of 45 C. with 4 parts of the fat-liquoring mixture, which was employed for the leather 1, for 70 minutes and 3 parts of the pure tannin sumac extract dissolved in twice the volume of water is added to the same solution in two portions at an interval of 5 minutes. One hour after addition of the pure tannin the solution shows a pH of about 4.6.

Due to the poor exhaustion of the solution 0.2 part of formic acid (85%) is added to the tanning solution. After milling for 2 hours the solution has a pH of about 3.8. The leather is then removed from the solution and dried as usual. It is substantially harder, the feel is less good and rougher than the leather 1, the color is flatter and more reddish.

The following table shows comparative figures regarding the increase in thickness, the proportion of dry weight of the fully tanned leather to the shaved weight, the residual fat content of the liquoring solution and the content of substances capable of being washed out.

Example 5.100 parts (calculated on the sammied weight) of a vache sole leather tanned with vegetable and synthetic tannins at 12 B. which was shortly rinsed, set out, pressed off and suspended in the air, are preliminarily milled in the hot air-drum at about 35-40 C. for minutes.

1.5 parts of diluted technical acetic acid (1210) are added and the leather is milled at 35-40 C. for further 10 minutes. Thereupon a solution of 5 parts of the retanning agent described in Example 1 is added in the form of a solution in 10 times the quantity of water in 2 portions at an interval o-f 10 minutes and the leather is milled for 1 hour while cold air is introduced from time to time. After this time the tannin has penetrated into the leather. A solution of 0.5 part of sodium acetate dissolved in 10 times the quantity of water is added and a the solution is milled into the leather within minutes. The leather is then stored for 40 hours, fat-liquored with an oxidation inhibiting leather oil and carefully dried in a dark room.

The outside appearance of the leather is only slightly diferent from a non-retanned leather which has been oiled off and dried in the same manner and originates from the same hide.

In spite of the additional quantity of the retanning agent incorporated into the retanned leather the content of substances capable of being washed out totals to 10.3%

whereas the non-retanned leather shows a content of these substances of 13.6%. The content of organic substances capable of being washed out is 9.6% and 13.1% respectively.

Example 6.-l00 parts each (calculated on the sammied weight) of a goat skin tanned with 25 parts of pure tannin of a Vegetable mixture consisting of equal parts of pure tannin of cold dissolving quebracho extract and mimosa bark extract are retanned as follows:

Leather 1 with 5 parts of the dry substance of the condensation product, employed in Example 1 and adiusted with hydrochloric acid, which is prepared from 4.4-dihydroxy diphenyl sulfone, ethanol amine and formaldehyde.

Leather 2 with 10 parts of the dry substance of the aforesaid retanning agent.

Leather 3 with 20 parts of the dry substance of the aforesaid retaining agent.

Leather 4 with 5 parts of the dry substance of the retanning agent described in Example 3, which consists of a mixture of the condensation product prepared from 4.4'-dihydroxydiphenyl sulfone, ethanol amine and formaldehyde, and the condensation product prepared from resorcinol, ammonium chloride and formaldehyde.

Leather 5 with 10 parts of the aforesaid mixture.

Leather 6 with 20 parts of the aforesaid mixture.

Leather 7 with 10 parts of the dry substance of a vegetable mixture consisting of cold dissolving quebracho extract, mimosa bark extract, chestnut extract, myrabolatn extract and valex powder (30:30:30:5:5 parts of pure tannin).

Leather 8 with 30 parts of the dry substance of the aforesaid mixture.

Leather 9 is not retanned for comparison.

The pieces of leather 1-6 are retanned as follows: each piece of leather is shortly rinsed and well sammied. The thickness of each piece of leather is measured at 10 places. Each leather is then placed in a solution of about 250-300 parts of cold water.

The retanning agents are added at intervals of 15 minutes while continuously milling and the solution is circulated for totally two hours. After measuring the pH value of the solution is adjusted to about 5.8-6.2 by careful addition of ammonia (about 5%). This pH value is reached within about 30 minutes. After the ammonia has been added the solution is circulated for a further 30 minutes and the pieces of leather are then removed. After shortly rinsing each leather is sammied, oiled off from the grain with a suifonated commercial fatliquoring oil and dried. The leather 7 and 8 are retanned in the usual manner and rinsed, seat out, fat-liquored and dried as described above. Leather 9 is rinsed in the same manner without retanning, set out, fat-liquored and dried.

After oiling the thickness of the leather is measured at 10 places while still wet. The increase in thickness over the measurements in the wet state before retanning'is indicated in the following table:

Leather N o.

The pieces of leather Nos. 1-6 retanned according to the herein described process have a good filling effect and a uniform, beautiful, light color. The retanning agent is Well fixed, even when employed in very great quantities.

Leather 7 has essentially poorer filling properties, the fixation of the tannin is good. The filling effect of leather No. 8 is also markedly inferior to. that of the piecs 1-6. The fixation of the tannin is poor, the leather color has an unsettled appearance, especially at and near the margins. Leather No. 9-gives a markedly flat and dead impression.

Example 7.100 parts each of the goat skin tanned with the vegetable tannin employed in Example 6 are retanned in 250 parts by volume of water as follows:

Leather 1 is retanned with 2 parts of the dry substance of a mixture of retanning agents, which consists of equal parts of the dry substance of the retanning agent, employed in Example 1, consisting of 4.4-dihydroxydiphenylsulfone, ethanol amine and formaldehyde, and the retanning agent prepared from catechol, ethylene diamine and formaldehyde according to Example 23 of our copending application Ser. No. 241,693, filed August 13, 1951. Following is the procedure given in that example: 100 cc. of formaldehyde solution 30% are added to the solution of 110 grams of catechol, 80 cc. of water, 30 grams of ethylene diamine and 42 to 63 cc. of concentrated hydrochloric acid; the reaction is moderately exothermic; the smell of aldehyde soon disappears. The reaction mixture is heated for one hour in the boiling water bath.

Leather 2 is retanned with parts of the dry substance of the aforesaid mixture of retanning agents.

Leather 3 is retanned with 2 parts of the dry substance of a mixture of retanning agents consisting of equal parts of the dry substance of the retanning agents employed in Example 1, which is prepared from 4.4- dihydroxydiphenylsulfone, ethanol amine and formaldehyde, and the retanning agent prepared from catechol, morpholine and formaldehyde according to our copending application Ser. No. 241,693, filed August 13, 1951 (Example 26, third passage) by the following procedure: The solution of 44 grams of morpholine, 50 cc. of water, 41 cc. of concentrated hydrochloric acid and 110, grams of catechol which should show only weakly congo-acid reaction is mixed at 20 C. with 101 cc. of formaldehyde solution 30%. The temperature rises in the beginning slowly, afterwards more quickly towards 90 C. The reaction mixture is heated for 4-5 hours in the boiling water bath. The condensation product obtained is water-soluble in every proportion.

Leather 4 is retanned with 5 parts of the dry substance of the aforesaid mixture of retanning agents.

Leather 5 is not retanned.

The retanning process and further treatment is carried out as described in Example 6. After oiling off the thickness of the leather is measured at places while the leather is still wet. The increase in thickness over the measurements before retanning is indicated in the following table:

Increase in thickness, percent Leather N o.

by conventional methods. The pieces ofleather are rinsed in flowing water for some minutes and suspended in solu-' tions of the following composition for two days each (about 8 parts by volume of the solutions are employed per 1 part of leather (referred to the sammied weight) Leather 1 in a solution of 10 parts of dry substance of the mixture of retanning agents, described in Example 3, in 1000 parts by volume of water.

Leather 2 in a solution of 20 parts of the dry substance of the same retanning agent in 1000 parts by volume of water.

Leather 3 in a solution of 40 parts of the dry substance of the same retanning agent in 100 parts by volume of water.

Leather 4 in a solution of 40 parts of the dry substance consisting of 30 parts of the dry substance of cold dissolving quebracho extract, 30 parts of mimosa bark extract and 30 parts of chestnut extract and 5 parts of myrobalam extract and 5 parts of valex powder in 1000 parts of water.

Leather 5 in a solution of parts of pure tannin consisting of the aforesaid mixture in 1000 parts by volume of water.

Leather 6 was not retanned.

Leather 7 is suspended in a solution of 10 parts of the dry substance of the retanning agent, described in Example l, in 1000 parts by volume of water.

Leather 8 in a solution of 20 parts of the dry substance of the same retanning agent in 1000 parts by volume of water.

Leather 9 in a solution of 40 parts of the dry substance of the same retanning agent in 1000 parts by volume of water.

After standing for two days the pieces of leather are removed from the solution, shortly rinsed, pressed off, set out, oiled off from the grain with an oxidation inhibiting commercial tanning oil and slowly dried in a dark room.

The dry pieces of leather have the following appearance: Leathers 1, 2, 3 have a beautiful light color, are well flexible but nevertheless firm. Leather 6 (not retanned) is essentially darker and more brittle. The grain cracks upon more intensely bending. Leathers 4 and 5 are slightly lighter and have markedly better properties than leather 6 but do not reach the quality of leathers l, 2 and 3. Leathers 7 and 8 are approximately equal to leathers 1, 2 and 3.

The color and grain effect of leather 9 is markedly inferior to that of leather 3 but superior to that of leather 6.

According to analysis the following substances capable of being washed out were ascertained:

Percent Leather No. 1 5.36 Leather No. 2 6.10 Leather No. 3 6.05 Leather No. 4 7.25 Leather No. 5 8.55 Leather No. 6 10.5 Leather No. 7 4.70 Leather No. 8 5.28 Leather No. 9 6.02

Example 9.3 pieces of leather of about 10 x 15 cm. are taken from comparative positions of the same cow hide described in Example 8. The pieces of leather are rinsed in flowing water for some minutes. I

Leather No. 1 is oiled off from the grain after setting out well with oxidation inhibiting commercial tanning oil without further treatment and slowly dried in a dark room.

Leather No. 2 is retanned in 200 parts by volume of water of 40-45 C. (referred to the sammied weight) with a solution of 5 parts of the dry substance of the retanning agent described in Example 1, which is dissolved in 25 parts by volume fwater, Thesolution oftheretanning agent is added at once, the leather milled for 30 minutes and the pH value of the solution adjusted to 5.8 by careful addition of ammonia solution (about The leather is milled in the solution for a further 30 minutes, thereupon removed, shortly rinsed, pressed off and treated with oxidation inhibiting commercial tanning oil in the same manner as the comparative leather.

Leather No. 3 is treated in equal manner with 5 parts of the dry substance of the mixture of retanning agents, as described in Example 3, and the tanning solution adjusted to a pH value of 5.9 with ammonia in the same manner. The leather is further treated as leather No. 2.

After drying the pieces of leather have the following appearance:

Leather 1: Grey-brown color, rather firm leather of moderate grain effect.

Leather 2: The color is markedly lightened and displaced to yellow while the grain is of good appearance, the leather is somewhat mellower and more flexible, no crackiness of the grain.

Leather 3: The appearance is similar to that of leather 2, the flexibility slightly inferior to that of leather 2, the grain effect slightly poorer than leather 2 but markedly better than leather 1.

By analysing the leathers 1, 2 and 3 the following contents of substances capable of being washed out were ascertained:

Example 10.O parts of goat pelt are tanned according to the procedure described in Example 1 of our copending application Ser. No. 295,558, filed June 25, 1952 (now U. S. Patent No. 2,733,977), with parts of the dry substance of the tannin obtainable from resorcinol, ammonium chloride and formaldehyde as described in Example 33 of our copending application Ser. No. 241,693, filed August 13, 1951 (now abandoned). The leather is rinsed and set out. The thickness of the leather is measured at various places.

A solution of 5 parts of the dry substance of the retanning agent employed in Example 1 in about 40 parts by volume of water is added in two portions at an interval of 5 minutes into 250-300 parts by volume of water. The leather is milled for one hour and the solution adjusted to pH 5.8-6.0 as described in Example 1). The leather is shortly rinsed, set out on the table, the thickness measured and oiled oft" from the grain with a commercial sulfonated fat-liquoring solution. The increase in thickness attained in the retanning process averages 4%. After drying a leather is obtained which is distinguished from a non-retanned leather by a greater filling effect, better handle and a color which is displaced to yellow.

By carrying out the retanning process with 5 parts of the dry substance of a commercial, neutralized tannin the increase in thickness averages 3%. The filling effect of the dry leather is inferior to that of the leather retanned as above, the color is markedly more reddish.

Example ]].A piece of cow hide tanned with vegetable and synthetic tannins by conventional processes and dried is brushed on the grain side with a solution of 5 parts of the dry substance of the mixture of retanning agents, described in Example 3, in 1000 parts by volume of water. The tanning solution is applied to the leather by brushing twice; the leather is exposed to air for a short time before the second brushing operation. After hanging in the air for a short time the leather thus pretreated is brushed with an aqueous solution of acid leather dyestulfs according to the process generally adapted for the unilateral dyeing of cow hide leather. For comparison a leather wetted with water only is brushed with the aforesaid dyestutf solution under comparative con ditions. After drying the leather pretreated with the mixture of retanning agents is found to show a markedly deeper shade. On polishing this leather shows a more beautiful luster and greater brilliance. Furthermore, the pretreatment with the retanning agent results in inhibiting or preventing the dyestuffs from spewing on to the flesh side of the leather.

Example 12. parts of a leather (calculated as sammied Weight) tanned with 25 parts of the pure tannin of a vegetable and synthetic mixture consisting of 1 part of pure tannin of quebracho wood extract, 1 part of pure tannin of mimosa bark extract and 2 parts of pure tannin of a commercial synthetic tannin are well rinsed for 10 minutes, set out and shortly suspended in the air. After that the average thickness of the leather is measured at various places. The leather is retanned in 200250 parts by volume of water with 5 parts of the dry substance of a tannin obtainable from 4.4-dihydroxydiphenyl sulfone (1 mol), morpholine (4 mols) and formaldehyde (4 mols) according to the process of our copending application Ser. No. 354,656, filed May 12, 1953 (Example 3). [The retanning agent is prepared by mixing the crystalline 4,4'-dihydroxy-diphenyl-sulfone while stirring with the reaction product prepared from the morpholine and formaldehyde (30% solution). The reaction prodnot of morpholine and aldehyde is prepared by dropping the morpholine into the aldehyde with ice cooling then heating the mixture in a boiling water bath for 1 hour. The precipitated base dissolves upon addition of 140l50 cc. of concentrated hydrochloric acid] The retanning agent dissolved in about 10 parts by volume of water is added in 2-3 portions at intervals of 10 minutes each, the leather milled for a further 1 /z-2 hours and the solution adjusted to a pH value of about 5.5-6 by careful addition of a dilute ammonia solution, as more fully described in Example 1. The leather is milled in the clear solution for a further 30 minutes, removed and horsed up over night. The following morning the leather is shortly rinsed, set up well and exposed to air. The thickness of the leather is measured at the same places as before. The leather is oiled off from the grain with a commerical fatliquoring solution of sulfonated oils and dried. For comparison, a leather tanned with the above vegetable and synthetic mixture is retanned with 5 parts of the dry substance of a mixture of equal parts of quebracho wood extract and mimosa bark extract in the usual manner. The leather retanned with the retanning agents has an essentially greater filling effect and is of better handle than the leather retanned with the vegetable tannin, the color of the leather is slightly lightened and displaced to yellow. The leather retanned with the retanning agent shows an increase in thickness of 7.3% whereas the leather retanned with the vegetable mixture shows a loss of thickness of 2.8%.

Example J3.-l00-parts of the leather employed in Example 12 are retanned with 5 parts of the dry substance of the retanning agent obtainable from 4.4-dihydroxydiphenyl sulfone (1 mol), ethanol amine (4 mols) and formaldehyde (4 mols), as described in our copending application Ser. No. 354,656, May 12, 1953 (Example 10). Following is the procedure of that example:

200 cc. of formaldehyde solution (30 percent) is introduced in a thin stream into the mixture grams of 4.4 dihydroxydiphenyl-sulfone and grams of ethanol amine (94 precent) with stirring and water cooling and the mixture is heated in the boiling water bath or refluxed. The condensation product obtained is water soluble in all proportions in the form of its base, chloride, sulfate, nitrate and acetate. The tanned leather has an improved filling effect and is more mellow and pliable and of better handle, the color of the leather is lighter, more uniform and markedly displaced to yellow if compared with a leather retanned with 5 partsof the dry substance of a vegetable mixture of 11 equal parts of quebracho wood extract and mimosa barkextract.

By measuring the thickness of theleather asdescribedin Example 12 the leather treated with the retanning agent is found to shown an increase in thickness of 10.5% whereas the leather retanned with the vegetable tannin shows a loss of thickness of 2.8%.

Example 14.Two pieces of calf pelt of 50 parts each are tanned in 150 parts by volume of water as follows:

Pelt 1 is tanned in the usual manner with 4 parts of a 4/ 12 basic, commercial chrome tanning salt containing about 33% of chrome and about 3% of sodium sulfate and the pH value is adjusted near the neutral point..

Pelt 2 is tanned with a mixture of the following; composition: 9 parts of the dry substance of the mixture of retanning agents described in Example. 3 and 1.0 part of the above commercial trivalent chrome tanning salt, which is poor in salt, are dissolved in about 40 parts by volume of water. This solution is introduced into the tanning solution in two portions at aninterval of 1 hour and the pelt is milled for two days. After that the pH value is adjusted to about 5.8-6.0-by careful addition of ammonia solution (about 5% A tanning solution remains substantially clear until the tanning process is complete. Both pieces of leather are shortly. rinsed after tanning and greased with 1 part of'a commercial synthetic fat liquoring oil.

The pieces of' leather are dried and valuated as follows:

Leather 1 has the typical appearance of achrome leather with the soft handle and the color of normal chrome leather.

Leather 2 has a substantially greater filling effect and is more firm and shows a marked vegetable impression. The leather is of agreeable, yellowish-brown color and shows the green chrome color only in one part of the cutting place.

Example 15.A piece of East Indian cabretta is measured at various places with the thickness gauge and the average thickness is ascertained in dry condition. The leather is then well milled in cold water for 30 minutes, set out, the weight is determined and the leather is tanned as follows: 100 parts of this wet leather are milled in 250 parts by volume of water (referred to-the drained weight) and retanned with 5 parts of the dry substance of the mixture of retanning agents employed in Example 3 as described in the preceding examples. After a running time of 75 minutes the solution is adjusted to a pH value of about 5.8 by careful addition of ammonia solution (about 5%). After reaching this pH value the leather is circulated for a further 30 minutes, shortly rinsed in fiowing water, set out well and dried. The dried leather is measured again at various places and the average thickness calculated. The increase in thickness attained in.

the retanning process amounts to 24.5%.

Example 16.-In the same manner as is used in Example 15, 100 parts of moist East Indian cabretta are retanned with the retanning agent described in Example 1 and the tanning solution is adjusted to a pH near the neutral point. After drying the increase inthickness amounts to 28.0%.

Example 17.100 parts of moist East Indian cabretta are retanned in the same manner as is used in Example 15, in 25 parts by volume of tanning solution with parts of the dry substance of a retanning agent obtainable from 1 mol of o-cresol sulfone, ethanol amine and formaldehyde, as described in Example 4 of our copending application Ser. No. 354,656, filed May 12, 1953, and the pH of the tanning solutionis; adjusted near the neutral point; The procedure of reference. Example 4 is'as follows:

139 grams of crude cresol sulfone (prepared, from a crude cresol containing 57.2 percent of. o-cresol, 3.8. per- CGIJLOLIIlr-CIBSOI, 9.0.percent of. p-cresol and 19.8 percent.

of phenol in the form as it is obtained in the preparation after removing volatile ingredients at higher temperatures in vacuo), are mixed with 76 grams of ethanol amine (94 percent) at C. to form a homogeneous paste. By introducing 128 cc. of formaldehyde solution (30 percent) in a thin stream While stirring from 40 C. upwards and heating the mixture in the boiling water bath the reaction mixture becomes homogeneous after a short time. After heating for two hours the mixture is dissolved in about cc. of concentrated hydrochloric acid at 70-80 C. The reaction product is water soluble in all proportions and reacts weakly Congo-grey. After drying the increase in thickness amounts to 22.2%.

Example 18.As described above in Example 15, 100 parts of moist East Indian cabretta are retanned with 5 parts of the dry substance of a retanning agent obtainable by condensation of 1 mol of o-chlorophenol sulfone, 2 mols of morpholine and 2.2 mols of formaldehyde, as described in Example 5 of our copending application Ser. No. 354,656, filed May 12, 1953. Following is the procedure of reference Example 5:

44 grams of morpholine are added in drops to the suspension of grams of chlorophenol-sulfone and 50 cc. of formaldehyde solution (30 percent) with stirring and cooling from 20 C. upwards so that the temperature does not exceed 40 C. By heating in the boiling water bath the reaction mixture becomes first homogeneous and resinous after 1 hour. After heating for 5 hours the insoluble condensation product is dissolved in 50 cc. of hydrochloric acid 1:1 and 13 cc. of concentrated hydrochloric acid at 7080 C. Thereupon the product is water soluble in all proportions and reacts on Congo paper. weakly acid.

In the above reaction the morpholine is replaced by 45 grams of. dimethylamine solution (53 percent). The reaction mixture which is homogeneous from the start is heated first in the boiling water bath for 1 /2 hours and then refluxed for another hour. A portion of the nonconsumed aldehyde is removed by boiling and the evaporated water is replenished. The insoluble base is dissolved in about 25 cc. of concentrated hydrochloric acid. The product is water soluble in all proportions. After neutralizing and drying as usual the increase in thickness amounts to 34.0%.

Example 19.By retanning parts of moist East Indian cabretta with 5 parts of the dry substance of a retanning agent obtainable from 1 mol of o-chlorophenol sulfone, 2 mols of dimethylamine and 2.25 mols of formaldehyde as described in Example 5 of our copending application Ser. No. 354,656, filed May 12, 1953, an increase in thickness of 36.5% is determined after neutralizing and drying. By retanning 100 parts of moist East Indian cabretta for comparison with 5 parts of the pure substance of sumac extract an increase in thickness of 13.8% was found after drying.

All the pieces of leather produced as described in the examples by retanning with the cationic tannins are distinguished by extraordinarily beautiful and good filling properties which excel the filling effect of the leather retanned with sumac extract. The color of the leather is generally slightly lighter and clearer, the shade mostly displaced to yellow if compared with the East Indian cabretta.

retanned with sumac extract. Furthermore, leather retanned with the retanning agents shows especially beautiful surface luster.

We claim:

1. Retanning process which comprises retanning a previously tanned leather with a tanning liquor containing up to 25% of a salt of a condensation product obtained from sulfones of monohydric phenols with non-aromatic monoamines and formaldehyde at temperatures about 100 C.

2. The retanning process as claimed in claim 1 wherein thecondensation product isobtained from 4.4-dihydroxydiphenyl'sulfone, .ethanolamine'and formaldehyde.

3. The retanning process as claimed in claim 1 wherein References Cited in the file of this patent the condensation product is obtained from 4.4'-dihydroxy- UNITED STATES PATENTS diphenylsulfone, morpholine and formaldehyde.

4. The retanning process as claImed in claim 1 wherein g i the condensation product is obtained from 4.4'-dihydroxy- 5 2127O68 i 1938 Iitljddlchiorodlphenylsulfone, morpholine and formalde- 2,129,553 Russell Sept. 6, 1938 5. The retanning process as claimed in claim 1 wherein g the condensation product is obtained from 4.4'-dihydroxy- 2546946 g a 1951 dimethyl-diphenylsulfone, ethanolamrne and formalde- 10 ar Oug hyde. FOREIGN PATENTS 615,190 Great Britain Jan. 3, 1949

Claims (1)

1. RETANNING PROCESS WHICH COMPRISES TETANNING A PREVIOUSLY TANNED LEATHER WITH A TANNING LIQUOR CONTAINING UP TO 25% OF A SALT OF A CONDENSATION PRODUCT OBTAINED FROM SULFONES OF MANOHYDRIC PHENOLS WITH NON-AROMATIC MONOAMINES AND FORMALDEHYDE AT TEMPERATURES ABOUT 100*C.