US3477801A

US3477801A - Water soluble synthetic tanning agent for producing shrunken grain leather

Info

Publication number: US3477801A
Application number: US729858*A
Authority: US
Inventors: Stanley A Lipowski
Original assignee: Diamond Shamrock Corp
Current assignee: Diamond Shamrock Chemicals Co; Diamond Shamrock Corp
Priority date: 1966-09-20
Filing date: 1968-04-08
Publication date: 1969-11-11
Anticipated expiration: 1986-11-11

Description

United States Patent 3,477,801 WATER SOLUBLE SYNTHETIC TANNING AGENT FOR PRODUCING SHRUNKEN GRAIN LEATHER Stanley A. Lipowski, Livingston, N.J., assignor to Diamond Shamrock Corporation, a corporation of Delaware No Drawing. Original application. Sept. 20, 1966, Ser. No. 580,616, now Patent No. 3,423,452, dated Jan. 21, 1969. Divided and this application Apr. 8, 1968, Ser.

Int. Cl. C14c 3/18 US. Cl. 8-94.24 4 Claims ABSTRACT OF THE DISCLOSURE This application is a divisional application of Ser. No. 580,616, Lipowski, filed Sept. 20, 1966, now Patent No. 3,423,452.

The present invention relates to synthetic tanning agents for producing shrunken grain leather as well as processes for producing and using such synthetic tanning agents.

Shrunken grain leather is a type of leather which has a pattern developed on the hide by the action of the tanning agent. The shrinking action is most pronounced on the grain of the leather which is the most sensitive part of the hide substance. The shrinking effect is visible on all of the corium of the hide and is characterized by a decrease in the total area of the hide. The shrunken grain pattern formed on the surface of leather by action of tanning agents is quite different from the pattern obtained by simple embossing. The pattern formed by shrinking the grain of the skin by tanning has a natural look contrary to the pattern obtained by simple embossing which has a definite artificial look and very little eye appeal. The principal problem in producing a shrunken grain efiect on the skins or hides which are to be used for manufacturing shoe leather or other fashion leathers is to obtain a natural looking pattern uniformly distributed over all of the surface area. Furthermore, such pattern should have sufficient depth and permanent features that the shrunken grain pattern will completely recover its appearance after the leather has been stretched and the stretch has been released. Snythetic tanning agents employed in producing shrunken grain leathers besides effecting the shrinking of the grain must be complete and satisfactory tanning agents for the leather and must not impair the generally required standards of good grade upper leather. Such standards mean that the shrunken grain leather must have good round feel, high tensile strength, high stitch tear strength and the like.

Numerous attempts have been made in the prior art to produce a synthetic shrunken gain tanning agent which will meet all of the above requirements. However, none of the synthetic tanning agents developed to date has been completely satisfactory. The principal reasons for the difiiculties which have been encountered in the development of synthetic tanning agents for producing shrunken grain leathers are that any good synthetic tanning agent under proper management of tanning processes can produce a shrinking effect on a skin or hide but none of the previously developed synthetic tanning agents has been able to satisfy all of the requirements that must be met in producing a satisfactory shrunken grain leather. Such agents generally produce shrunken grain leather having a wild coarse grain, that is, the grain is highly irregular. Furthermore, the shrunken grain pattern is not uniform and does not completely cover the entire surface area of the hide. The pattern has low depth and poor recovery on stretching which means that the shrunken grain leather may superficially look satisfactory but when it is exposed to the drastic action of shoe manufacturing machines and the like, the shrunken grain leather will partly or entirely lose its pattern. Since a shrunken grain leather must maintain its pattern during manufacture as well as during use, it is extremely important that the pattern has good recovery after stretching or use.

Production of satisfactory shrunken grain leather is highly advantageous in tannery operations where shoe leather or other fashion leathers are being produced. In every tannery producing smooth upper grade leather, some of the stock is of poor quality and produces second grade leather. Such second grade leather results from natural defects in the skins or hides such as barbed wire scratches, skin defects caused by insect bites, brand marks, other injuries or defects. These defects are clearly visible in the finished leather, limit the usefulness of the finished leather and represent a large loss in the cutting area. Obviously, second grade leather and products produced from second grade leather must be sold at much lower prices. For a long time, it has been a major problem of upper leather tanners to find more effective methods to utilize the defective hides more to their advantage. Such defective hides can be more effectively utilized when they are sorted from other hides at some intermediate step in the tanning operation such as either after liming or pickling or preferentially in the blue, that is, after chrome tanning when the defects in the hides become more apparent. If the defective hides are separated at such a point and then converted to shrunken grain leather with all of its desirable properties, the shrunken grain leathers can be sold as highly profitable fashion leathers. Furthermore, such defective hides are not converted to smooth upper leather with the attendant. losses in the cutting areas. It is to be understood that effective utilization of defective hides in the production of shrunken grain leathers can be accomplished only if the shrinking effect obtained is of such a nature that it provides extremely good coverage of all the defects in the hide and gives a leather which has a natural appearance, that is, distinctly different from the appearance of cheap embossed leather. Only a few of the synthetic tanning agents suggested by the prior art have shown promise in the production of shrunken grain leather. Although these agents have been able to produce more or less visible shrinking effects, none of these agents has been able to meet all of the rigorous requirements for shrunken grain leather outlined above.

For example, a synthetic tanning agent is disclosed in Us. Patent No. 3,010,779 as being useful in the production of shrunken grain leather. This synthetic tanning agent is based on a 4,4-dihydroxy diph-enyl sulfone resin condensed with naphthalene sulfonic acid and formaldehyde and is in a very strong acid form, that is, the agent contains free sulfuric acid and other strong acids which are extremely injurious to leather. This agent cannot be neutralized to the pH range of about 2 to about 5 which is normally used in tanning processes because the agent precipitates from solution during neutralization. The net result is that this agent produces a shrinking effect on leather which is of a very low quality and the pattern is coarse and not complete. The poor action of this synthetic tanning agent can be attributed to several factors. The agent lacks free methylol groups, that is, unreacted methylol groups which provide the astringency required to shrink the grain surface. The agent has low salt tolerance, that is, it precipitates in salt solutions containing low salt concentrations, that is, solutions containing as little as 1% by weight of sodium chloride. Thus, this agent on contact with pickled stock which contains appreciable quantities of salt will precipitate at an early stage during the tanning operation so that its shrinking action on the grain will be lost. Precipitation from salt solutions at these concentrations indicates that the agent is a polymeric material. Consequently, this agent is only able to act as a tanning agent because it does not have sufiicient astringency to cause proper shrinking of the grain surface. Similar results have been obtained with other synthetic tanning agents which are excellent tanning agents but do not have sufiicient astringency to cause rapid shrinking of the grain before further penetration of the synthetic tanning agent into the leather makes shrinking of the grain surface impossible.

It is an object of the present invention to provide synthetic tanning agents which will produce shrunken grain leathers which have deep, fine and uniform patterns, evenly distributed over the entire surface of the leather, have good recovery after stretching and have the other requirements of high fashion leathers. Another object of the present invention is to develop processes for producing synthetic tanning agents for use in the production of shrunken grain leathers. A further object is to produce tanning processes employing such agents in the production of shrunken grain leathers. Still another object is to produce shrunken grain leathers. Other objects of this invention will become apparent from the detailed description given hereinafter. It is intended that the detailed description and specific examples do not limit the present invention but merely indicate preferred embodiments thereof since various changes and modifications within the scope of the invention will become apparent to those skilled in the art.

The above as well as other objects of the present invention have been most unexpectedly and successfully achieved in the following manner. I have discovered a new and novel class of water soluble synthetic tanning agents which are useful in producing shrunken grain leathers for use in upper shoe leather and other high fashion leathers. Furthermore, I have discovered processes for producing such synthetic tanning agents. Additionally, I have found that use of these synthetic tanning agents in the tanning of hides and skins consistently produce high quality upper shrunken grain shoe leathers, fashion leathers and the like which far exceed the shrunken grain leathers produced in the past.

I have found that such synthetic tanning agents must contain at least 0.5 free methylol groups per mole of sulfone employed, that is, the unreacted methylol groups per mole of sulfone present in the synthetic tanning agent if all of the desirable properties are to be obtained with the agent in the production of shrunken grain leathers. Furthermore, I have discovered that it is essential for the synthetic tanning agent to be substantially in monomeric form and that synthetic tanning agents based on polymeric forms or resins are to be avoided. Such polymeric agents have poor shrinking action on leather. I have also found that such tanning agents when in solution should not precipitate on neutralization at pHs from about to about 7. Such tanning agents can be neutralized with alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide and the like, ammonium hydroxide low molecular weight amines such as monomethylamine, dimethylamine, monoethanolamine, diethanolamine, triethanolamine, n-ethylamine, n-propylamine, their isomers and the like. Likewise, such tanning agents should not contain strong acids such as free sulfuric acid or the like. Furthermore, such tanning agent should be soluble in tanning solutions or liquors containing at least 2.5% by weight of sodium chloride. The importance of such structural, chemical and physical requirements in synthetic tanning agents for use in the production of shrunken grain leathers was not appreciated or suggested by the prior art.

Briefly, the synthetic tanning agents disclosed in the present invention are the reaction products of one mole of a sulfone having a purity of from about to by weight such as 4,4'-dihydroxy diphenyl sulfone, 4,2- dihydroxy diphenyl sulfone, 2,2'-dihydroxy diphenyl sulfone or mixtures of these sulfones with from about 1.5 moles to about 5.0 moles of formaldehyde or formaldehyde liberating compositions per mole of sulfone and from about 0.5 mole to about 2.0 moles of 2-naphthalene sulfonic acid per mole of sulfone with the proviso that the final reaction product contains at least 0.5 free methylol groups per mole of sulfone, that is, unreacted methylol groups per mole of sulfone employed, is soluble in salt solutions containing at least 2.5% by weight of sodium chloride and when in solution does not precipitate on neutralization at a pH of from about 0 to about 7. Such synthetic tanning agents can also be the reaction products of (a) one mole of methylolated sulfone having a purity of from about 95 to 100% by weight such as methylolated 4,4'-dihydroxy diphenyl sulfone, methylolated 4,2-dihydroxy diphenyl sulfone, methylolated 2,2'-dihydroxy diphenyl sulfone or their mixtures wherein one mole of the sulfone contains from about 1.5 to about 4 free methylol groups and (b) from about 0.5 to about 2.0 moles of 2- naphthalene sulfonic acid per mole of sulfone with the proviso that final reaction product contains at least 0.5 free methylol groups per mole of sulfone employed, is soluble in salt solutions containing at least 2.5% by weight of sodium chloride and when in solution does not precipitate on neutralization at a pH of from about 0 to about 7.

These water soluble shrunken grain synthetic tanning agents can be prepared by reacting together at a temperature range of from about room temperature to about reflux temperature, an aqueous reaction mixture containing one mole of a sulfone having a purity of from about 95 to 100% by weight selected from the group consisting of 4,4'-dihydroxy diphenyl sulfone, 4,2'-dihydroxy diphenyl sulfone, 2,2'dihydroxy diphenyl sulfone or their mixtures, from about 1.5 moles to about 5.0 moles of formaldehyde or a formaldehyde liberating composition per mole of sulfone, from about 0.5 mole to about 2.0 moles of Z-naphthalene sulfonic acid per mole of sulfone and water with the proviso that the quantities of sulfone, aldehyde and Z-naphthalene sulfonic acid are selected within the molar range stated so that the final reaction product contains at least 0.5 free methylol groups per mole of sulfone, is soluble in salt solutions containing at least 2.5 by weight of sodium chloride and when in solution does not precipitate on neutralization at a pH of from about 0 to about 7. Such products should contain little, if any, unreacted naphthalene sulfonic acid. The temperature employed in this process may vary from about 20 C. to about C. and when pressure is employed may be as high as about C. The quantity of water employed is usually from about three to above five times the weight of the sulfone employed. The reaction mixture is relatively dilute and is sufficiently dilute to prevent any condensation of 2-naphthalene sulfonic acid with formaldehyde Which might lead to the formation of polymeric materials. The Z-naphthalene sulfonic acid in the initial stages of the reaction serves as a dispersant for the sulfone until methylolation of the sulfone begins. Once methylolation of the sulfone begins, a portion of the free methylol groups in the sulfone react with active hydrogen atoms on the naphthalene ring of the naphthalene sulfonic acid to form the desired synthetic tanning agent. The process is carried out by mixing the required quantities of reactants and Water at room temperature and heating the resulting mixture to the reflux point which is usually between 95 C. and 110 C. at atmospheric pressure. The mixture is refluxed until a clear solution is obtained and the product has the following properties. The final reaction product must contain at least 0.5 free methylol groups per mole of sulfone employed. Furthermore, substantially all of the naphthalene sulfonic acid should be condensed with the methylolated sulfone. The final product should be soluble in salt solutions containing at least 2.5% by weight of sodium chloride. Furthermore, the final product should not precipitate from solution on neutralization at pHs from about 0 to about 7. The final product should be sufficiently neutralized so that it does not contain strong acids such as free sulfuric acid or the like. When the final product has the above properties, it is then cooled to room temperature. The procedure described above avoids bridging between dihydroxy diphenyl sulfone molecules, other reactants or reaction product by reactions with formaldehyde which will produce polymeric materials. When desired, a solvent such as alcohol or any other solvent that does not interfere with the reactions involved in the process may be used in conjunction with water. Use of such solvent mixtures can be advantageous when higher or lower reflux temperatures are desired.

Alternatively, these water soluble shrunken grain synthetic tanning agents can be prepared by reacting together at a temperature range of from about 50 to about 150 C. an aqueous reaction mixture containing one mole of a methylolated sulfone having a purity of from about 95% to 100% by weight such as methylolated 4,4'-dihydroxy diphenyl sulfone, methylolated 4,2'-dihydroxy diphenyl sulfone, methylolated 2,2'-dihydroxy diphenyl sulfone or their mixtures wherein the sulfone contains from about 1.5 to about 4 free methylol groups per mole of sulfone employed, from about 0.5 mole to about 2.0 moles of Z-naphthalene sulfonic acid per mole of sulfone and water with the proviso that the quantities of methylolated sulfone and Z-naphthalene sulfonic acid are selected within the molar ranges stated so that the tanning agent contains at least 0.5 free methylol group per mole of methylolated sulfone employed, is soluble in salt solutions containing at least 2.5% by weight of sodium chloride and when in solution does not precipitate on neutralization at a pH of from about 0 to about 7. The quantity of water employed in this process may vary. Usually from about one and one-half to about two times the weight of sulfone of water is employed in the methylolation step and from about one-half to two times the weight of the sulfone of water is employed in the condensation process. The heating of the reaction mixture at the aforementioned temperatures, or preferably at reflux temperature, that 1s, about 95 C. to about 110 C. is carried out until a clear solution is obtained. If desired, the condensation can be carried out under pressure or in the presence of solvents at temperatures as high as about 150 C. The reaction product, that is, the water soluble shrunken gram synthetic tanning agent should have the following properties. The final reaction product must contain at least 0.5 free methylol group per mole of sulfone employed. Furthermore, substantially all of the naphthalene sulfonic acid should be condensed with the methylolated sulfone. The reaction product should be soluble in salt solutions containing at least 2.5% by weight of sodium chloride. Further, the reaction product should not precipitate from solution on neutralization at pI-ls from about 0 to about 7. The final product should be sufficiently neutralized so it does not contain strong acids such as free sulfuric acid or the like.

The number of free methylol groups per mole of sulfone in either the dimethylolated sulfone or the synthetic tanning agents described above can be determined by the De Jong method which is described in Rec. trav. chim. 72: 653, 654 (1953).

Methylolation of the sulfone Methylolation of the sulfone can be achieved in the following procedure which avoids bridging between dihydroxy diphenyl sulfone molecules during methylolation. When bridging occurs, the resulting polymeric materials are partially methylolated sulfone resins, which on acidification separate as gummy materials and are not crystalline solids which can be separated easily by acidification and washed by decantation. Prior to methylolation, the dihydroxy diphenyl sulfone is reacted with sodium hydroxide in such proportions that both of the hydroxyl groups in the phenol rings are converted to the corresponding sodium salts. At this point, the sulfone should be water soluble and have a pH of from about 9.5 to about 10.0. The disodium salt of the sulfone is then reacted with suificient formaldehyde to obtain the desired methylolated sulfone. Usually from about 1.5 moles to about 5.0 moles of formaldehyde or a formaldehyde liberating composition per mole of sulfone is employed. Methylolation takes place at moderate temperatures such as about 20 C. to about 55 C. over an extended period of time. For example, methylolation at about 45 C. to about 55 C. will require from about 16 hours to about 30 hours. The methylolation reaction mixture can be analyzed by determining the amount of formaldehyde remaining in the mixture by the method described in Example III below. This method determines the amount of formaldehyde remaining in the reaction mixture after methylolation. The methylolation reaction mixture can also be analyzed by the De Jong method described above. The De Jong method determines the number of free methylol groups present in the methylolated sulfone. When the De Jong method is employed, the unreacted formaldehyde should be removed from the reaction mixture before the number of methylol groups per mole of sulfone is determine. After methylolation is complete, the methylolated dihydroxy diphenyl sulfone is recovered in the form of a solid precipitate by precipitation with an acid such as hydrochloride, sulfuric or the like. The salts formed during the acidification are water soluble and can be easily removed from the methylolated dihydroxy diphenyl sulfone precipitate by simple decantation and washing. After the methylolated sulfone has been separated from the reaction mixture as a solid and washed free of salts, unreacted formaldehyde, formaldehyde liberating compositions and the like, it is reacted in aqueous solution with the required quantity of Z-naphthalene sulfonic acid at a temperature of from about 55 C. to about 150 C. to obtain a synthetic tanning agent having the properties described above. The methylolated sulfone to be useful in the present invention should have a purity of about by weight to by weight and should contain from about 1.5 to about 4 free methylol groups per mole of sulfone employed. The methylolated sulfone may be methylolated 4,4'-dihydroxy diphenyl sulfone, methylolated 4,2-dihydroxy diphenyl sulfone, 2,2'-dihydroxy diphenyl sulfone or mixtures thereof. The impurities in the methylolated sulfone include methylolated polymeric sulfone, methylolated phenol sulfonic acids, other byproducts and the like.

The dihydroxy diphenyl sulfone or mixture of sulfones employed in the processes disclosed in this invention must be of high purity. It should have a purity of about 95% to 100% by weight of 4,4'-dihydroxy diphenyl sulfone, 4,2-dihydroxy diphenyl sulfone, 2,2'-dihydroxy diphenyl sulfone or their mixtures and should not contain more than 5% by weight of impurities such as polymeric sulfones, phenol sulfonic acids, other byproducts or the like. A procedure for preparing a dihydroxy diphenyl sulfone having satisfactory properties is described in Example I below. It is to be understood that any known method which produces dihydroxy diphenyl sulfone isomers or mixtures thereof having purities from. about 95% by weight to 100% by weight can be employed in the present invention.

Formaldehyde or formaldehyde liberating compositions can be used in the preparation of the synthetic tanning agents and methylolated sulfones disclosed in the present invention. For example, formaldehyde can be used in the form of 10% to 40% aqueous solution, 30% to 55% alcoholic solutions with alcohols such as metha- I101, n-butanol, i-butanol or the like. Formaldehyde can also be used in the form of a formaldehyde liberating composition such as its polymeric forms such as paraformaldehyde, trioxane, or the like. It is also to be understood that such formaldehyde liberating compositions include any form such as an acetal which is capable of producing formaldehyde such as acetals and the like.

The synthetic tanning agents and their use The synthetic tanning agents produced by the processes described above are analyzed by the De Jong method referred to above to determine if they contain at least 0.5 moles of free methylol groups per mole of sulfone employed. When desired, the tanning agents may contain as may as 3 free methylol groups per mole of sulfone employed in the process. Furthermore, the tanning agent should be neutralized to the point where all of the free sulfuric acid present in the naphthalene sulfonic acid employed in the process is completely neutralized and any free, unreactul Z-naphthalene sulfonic acid remaining in the synthetic tanning agent is present only in an amount sufficient to give a pH of from about to about 7 in the finished synthetic tanning agent. For most purposes, about 90% of the Z-naphthalene sulfonic acid groups, after reaction of the naphthalene sulfonic acid with the methylolated dihydroxy diphenyl sulfone, are neutralized. The presence of unneutralized sulfuric acid or other sources of high acidity in the finished synthetic tanning agent is highly undesirable because such acidity contributes substantially to the coarseness of pattern produced when the synthetic tanning agent is employed in shrunken grain tanning. Furthermore, the synthetic tanning agents produced by the process disclosed in this invention should be soluble in water at any dilution, soluble in salt solutions containing at least 2.5% by weight of sodium chloride. Likewise, the tanning agent should not reci itate from solutions on neutralization to pHs of from about 0 to about 7.

The synthetic tanning agents disclosed in this invention are useful in producing shrunken grain effects on animal skins such as cowhides, calfskins, goatskins, horsehides, reptile skins, other animal skins or the like. The term skin is used to include any animal skin or hide which can be used in the production of shrunken grain leather. As examples of skins which may be employed in the production of shrunken grain leather, there may be mentioned skins of freshly killed animals, limed skins, pickled skins, partly tanned skins, partly dechromed skins, dechromed skins and the like. Generally from about by weight to about 50% by weight based on the Weight of the skins of the synthetic tanning agent is employed. By the term synthetic tanning agent is meant the solution of the solid reaction products, salts and the like obtained by the processes disclosed in this invention. The synthetic tanning agent generally contains from about 15% by weight to about 50% by weight of solid reaction products. Usually from about 30% by weight to about 100% by weight based on the weight of skins 0r hides of water is added to the synthetic tanning agent solution to prepare the tanning solution or liquor. Shrunken grain leathers are produced by drumming the synthetic tanning agent into the animal skin. The synthetic agent is used in form of a solution or liquor and is drummed into the skin at a temperature of from about 70 F. to about 90 F. for about two hours to about twelve hours. Exhaust of the synthetic tanning agent from the tanning solution or liquor at the end of the drumming process is essentially complete, that is, the tanning agent is absorbed in the skin and little if any of the tanning agent remains in the tanning solution or liquor.

Shrunken grain leather produced by synthetic tanning agents disclosed in this invention can be used in the manufacture of upper shoe leather, garment leather, handbag leather, high fashion leather and the like. When the synthetic tanning agents are used in connection with vegetable tannages, moccasin type leather can be produced.

The synthetic tanning agents of this invention can be combined not only with chrome tannages but with other tannages such as zirconium tannages and the like. When chrome stock is used in the production of shrunken grain leathers, the leather is dechromed prior to use. The dechroming process can be varied over wide limits by using chemicals and/or materials which complex easily with chromium and facilitate its removal from the chrome tanned leather. Materials useful in dechroming leather include complexing acids such as oxalic, tartaric, citric, phosphoric acid or salts of such acids, e.g., Rochelle salt and the like, chelating agents such as ethylenediaminetetracetic acid, hydroxamic acids, amidoximes or the like. Such dechroming agents are applied in sufficient quantities to dechrome the stock to the point where its shrinkage temperature in boiling water drops from about 212 F. to about 110 F. Processing conditions employed during dechroming .must be controlled carefully so that the internal structure of the leather is not damaged. After the leather is dechromed, the stock must be promptly washed with salt water to avoid acid swelling. The resulting washed dechromed stock is then used in the shrunken grain process in the same manner as pickled skins or other forms of stock.

When the tanning agents of the present invention are employed in the production of shrunken grain leathers, the mechanical action encountered in the drumming and other plant operations which promote the shrinking effect of the synthetic tanning agents must be controlled carefully. For example, the speed of the drums must not be exaggerated in order to prevent overheating of the stock. The temperature during the shrinking process must be carefully controlled and kept as low as possible. Usually temperatures in the range of from about F. to about F. are employed. The rotating drums .must be stopped at certain time intervals during the process so that they can be aired off and allowed to cool before the temperature of the stock reaches the critical upper temperature limit of about 90 F. Extensive damage can be done to the stock which will render it useless as leather unless these precautions are taken. The amount of synthetic tanning agent solutions employed in shrunken grain tanning will be from about 15% to about 50% by weight (as is) based on the weight of the stock.

Shrunken grain leather obtained by the processes disclosed in this invention shows undiminished strength after it is rechromed. The shrunken grain leather can be rechromed with from about 1 /2 to about 2 /2% chromic oxide based upon the weight of the stock. The starting basicity during rechroming can be as low as 33% to 50% Schlorlemmer degrees which corresponds to a basicity of 4/12 to 6/12. The lower basicity chrome liquors can be subsequently made more basic by the addition of alkalis such as sodium bicarbonate, ammonium bicarbonate or the like. Although higher basicity liquors do not require basicity adjustments, their action is more drastic and their use must be more carefully controlled. It is particularly important that care is taken not to overheat the stock during the rechroming process. The short floats and high basicity of the liquors in conjunction with the mechanical action of the rotating drums can easily cause severe damage to the hides in rechroming if the stock temperature is permitted to rise above temperatures of about 90 F. or higher. Generally, the shrunken grain stock is rechromed to a point where its shrinkage point is brought up to a minimum temperature of about 205 F. Generally, shrinkage temperatures of from about 210 F. to about 212 F. are the most desirable.

When stock such as pickled stock or dechromed stock is tanned with the synthetic tanning agents of this invention, complete exhaust of the synthetic tanning agent is observed. Complete exhaust demonstrates the high aflinity which the tanning agent has for the hide substance. Spent liquors from shrunken grain tanning processes in which the synthetic tanning agents of this invention are used contain little if any of the tanning agents. This is highly desirable as little if any of the agents are lost during the tanning processes. The concentration of synthetic tanning agents in the spent liquors can be determined by conventional methods such as the Oflicial Hide Powder Method and the like.

For a fuller understanding of the nature and objects of this invention, reference may be made to the following examples which are given merely to illustrate the invention and are not to be construed in a limiting sense. All weights, proportions and percentages are by weight unless otherwise indicated. Likewise all temperatures are C., unless otherwise indicated.

EXAMPLE I (A) Preparation of a dihydroxy diphenyl sulfone 1148 g. (12.2 moles) of phenol, 612 g. (6 moles) of sulfuric acid (96% by weight active) and 125 g. monochlorobenzene were charged into a reaction vessel equipped with an agitator and a water separation trap. The reaction mixture was heated to the reflux temperature which was about 140 C. The escaping vapors of chlorobenzene and water formed during the reaction were condensed in the condenser and were separated in the trap. The dry chlorobenzene was returned to the reaction mixture. Reaction temperature was gradually increased to a temperature between 165 C. and 170 C. After from about 210 cc. to 215 cc. of water had been separated by azeotropic distillation, the reaction mixture was titrated to determine its acidity. A 10 g. sample of the reaction mixture at this point should not require more than 19.00 cc. to 20.00 cc. of 0.5 N sodium hydroxide solution to neutralize the sample to a pH of 7.0 This titer showed that over 75 per cent of the reactants have been converted to dihydroxy diphenyl sulfone. Higher conversion would require higher temperatures and longer times with the resulting resinification of the sulfone. Titers in above mentioned range have been found to be satisfactory in that they avoid resinification and provide satisfactory conversion to dihydroxy diphenyl sulfones.

After the desired acidity was obtained, 500 cc. of water was added carefully to the reaction product. The reaction product was then neutralized to a pH between and 6 by the cautious addition of from about 120 g. to about 130 g. of 50% by weight sodium hydroxide solution. Approximately 1,000 cc. of Water was then added to the reaction product and the resulting mixture was azeotropical- 1y distilled to remove the chlorobenzene. The chlorobenzene was removed from the water and the water returned to the reaction mixture. After all of the chlorobenzene was stripped from the reaction mixture, an additional 1,000 cc. of water was added and the resulting solution of the reaction product was heated to its boiling point. A clear solution was obtained at the boiling point. The solution contained the reaction product dissolved in about 2,500 cc. of boiling water.

The clear solution was then transferred to a reaction vessel containing approximately 4,000 cc. of boiling water and the resulting diluted solution was allowed to cool slowly to room temperature with vigorous agitation. Dihydroxy diphenyl sulfone precipitated in the form of cream colored crystals from the solution on cooling to room temperature. The crystals were removed by filtration or centrifugation or were left in the crystallization vessel and were then washed several times with cold water until the crystals were free of residual salts. The resulting dihydroxy diphenyl sulfone crystals were then either dried or left in the form of a wet paste for use in further reactions. The dihydroxy diphenyl sulfone crystals were analyzed for isomer distribution by the procedure given in Example I of U .S. Patent No. 2,833,828-Sauls (May 6, 1958). The crystals were found to have a purity of 98% by weight and a weight ratio of 88% of 4,4-dihydroxy diphenyl sulfone isomer to 12% of 4,2'-dihydroxy diphenyl sulfone. The 2% by weight of impurities in the mixture consisted of polymeric sulfones, phenol sulfonic acids, other byproducts and the like.

(B) Recrystallization of dihydroxy diphenyl sulfone When desired or required, the crystalline dihydroxy diphenyl sulfone isomer mixture obtained in part (A) above was further purified by the following procedure. The crystalline material was suspended in twenty times its weight of water and heated to the boiling point. The crystalline material dissolved at the boiling point and a clear solution was obtained. 0.1% by weight of decolorizing carbon and 0.5% by weight of filter aid were added to the boiling mixture. The mixture was then stirred for about five minutes and filtered at its boiling point to remove the decolorizing carbon, filter aid and other impurities. The clear, decolorized solution of dihydroxy diphenyl sulfone isomers was then cooled slowly to room temperature with vigorous agitation. Crystals of the dihydroxy diphenyl sulfone isomers separated on cooling to room temperature and were removed by filtration. The recrystallized dihydroxy diphenyl sulfone isomer mixture was in the form of pure white crystals. It was approximately 100% by weight pure. The isomers were present in a weight ratio of 88% of the 4,4-dihydroxy diphenyl sulfone isomer to 12% of the 4,2-dihydroxy diphenyl sulfone isomer. It is to be understood that purification of the dihydroxy diphenyl sulfone by recrystallization is not generally required in the preparation of the synthetic tanning agents of this invention for most tanning processes.

EXAMPLE II Preparation of a Z-naphthalene sulfonic acid solution 128 g. (1 mole of naphthalene and 160 g. (1.6 mole) of sulfuric acid (98% by Weight active) were mixed together in a reaction vessel at room temperature. The resulting reaction mixture was heated rapidly to 150 C. and agitated for three hours at 150 C. The resulting reaction product which was a mixture of Z-naphthalene sulfonic acid and sulfuric acid was cooled to C. and sufiicient cold water was added to obtain a Z-naphthalene sulfonic acid-sulfuric acid mixture having an activity of about 75% by weight. This mixture was then cooled to room temperature. The mixture contained one mole of 2-naphthalene sulfonic acid and 0.6 mole of sulfuric acid.

EXAMPLE III Preparation of a synthetic tanning agent 159 g. of a dry crystalline dihydroxy diphenyl sulfone isomer mxture, containing 98% by weight of sulfones having an isomer weight ratio of 88% of the 4,4-dihydroxy diphenyl sulfone isomer to 12% of the 4,2'-dihydroxy diphenyl sulfone isomer and 2% by weight of impurities consisting of polymeric sulfones, phenol sulfonic acids, other byproducts and the like as described in part (A) of Example I above, 156 g. water and 100 g. (1.25 moles) of 50% by weight sodium hydroxide solution were mixed together and heated until a clear solution was obtained. The mixture of sulfone isomers used in this example weighed 156 g. (0.625 moles). The resulting clear solution was cooled to about 50 C. and 106 g. (1.307 mole) of form-aldehyde (37% by weight active) was added. The molar ratio of formaldehyde to dihydroxy diphenyl sulfone was 1.307/ 0.625 or 2.09. This reaction mixture was stirred at a constant temperature of 50 C. for 24 hours. As reaction proceeded, the initially clear solution became milky in appearance.

After reaction for 24 hours at 50 C. a sample of the reaction mixture was titrated by a modified sodium bisulfite method to determine its formaldehyde content. Briefly, this method involved addition of a 5 g. sample of the reaction mixture to 50 cc. of a 10% by weight sodium chloride solution. Sulfuric acid (98% by Weight active) was then added to obtain a pH of about 5. A precipitate formed and was removed by filtration. The filtrate was collected and then neutralized to a pH of 7.0. 50 cc. of a l M sodium sulfite solution was added. When formaldehyde was present in the filtrate, the pH of the filtrate was above 9. The filtrate was then back-titrated with 0.5 N hydrochloric acid solution to a pH of 9.0. When formaldehyde was not present, the pH of the filtrate after bisulfite addition was 9 and back-titration with 0.5 N hydrochloric acid was not required. The percentage of formaldehyde present in the filtrate was then calculated by the following formula Weight of sample wherein cc. HCl represents the quantity of 0.5 N hydrochloric acid required to back-titrate to a pH of 9. The formaldehyde content of the preparation described in this example was found to be 1.65% by weight. The concentration of formaldehyde present initially in the reaction mixture was 7.53% by weight which meant that 5.88% by weight of formaldehyde of 78.1% of the total formaldehyde employed initially in the reaction reacted. This formaldehyde usage meant that 1.02 mole of formaldehyde reacted with the phenolic rings present in the dihydroxy diphenyl sulfone, or in other words, the ratio of free methylol groups per mole of dihydroxy diphenyl sulfone was 163 free methylol groups per mole of dihydroxy diphenyl sulfone.

After the formaldehyde analysis, the reaction mixture was cooled to about 10 C. 250 cc. of cold water and 190 g. of sulfuric acid (33.5% by weight active) were added with cooling. The resulting mixture which contained a precipitate of methylolated dihydroxy diphenyl sulfone in a water and salt solution was decanted to remove the solution of water, unreacted formaldehyde and salt from the methylolated dihydroxy diphenyl sulfone crystals. The precipitated methylolated dihydroxy diphenyl sulfone crystals were then washed three times with 600 cc. portions of cold water and each cold water wash was removed by decantation. The formaldehyde content of the wash water obtained from the third wash and decantation was analyzed by the procedure described above and found to be 0.0% by weight. The pH of the third wash water was 5.4. After all of the formaldehyde had been removed by washing, the number of methylol groups per mole of sulfone in the methylolated sulfone crystals was determined by the De Jong method as described in Rec. trav. chim 72: 653, 654 (1953). The methylolated sulfone was found to contain 1.6 free methylol groups per mole of sulfone. The reaction mixture was 98% by weight pure and contained 2% by weight impurities. The weight ratio of isomers in the crystals was 88% of methylolated 4,4-dihydroxy diphenyl sulfone to 12% of methylolated 4,2'-dihydroxy diphenyl sulfone isomers. The 2% by weight of impurities included methylolated polymeric sulfones, methylolated phenol sulfonic acids, other byproducts and the like.

247.5 g. of Z-naphthalene sulfonic acid mixture (about 75% by weight active) which contained 0.71 mole of 2- naphthalene sulfonic acid and was prepared by the procedure in Example II above and 25 cc. of water were added to the wet, washed methylolated dihydroxy diphenyl sulfone crystals obtained above. The resulting reaction mixture was heated to reflux. Reflux temperature was about 110 C. After heating for five hours at reflux, 400 cc. of cold water was then added to the reaction mixture and the mixture neutralized under cooling by the addition of 105 g. of 50% by weight sodium hydroxide solution. The resulting neutralized solution was slightly hazy. 35 g. of isopropyl alcohol was added and the solution cleared immediately. The pH of the clear solution was 2.2 as is. The solution, which was a synthetic tanning agent, contained 34.5% by weight of solids. The pH of the solution when diluted with distilled water to 1% by weight solids was 4.4. The solution, which contained 34.5% by weight solids, was soluble at all proportions in water and was soluble in a 2.5% by weight sodium chloride solution. Furthermore,

the agent did not precipitate from solution on neutralization at pHs between about 0 and about 7. The number of free methylol groups in the synthetic tanning agent as determined by the above-mentioned De Jong method was found to be 0.6 free methylol groups per mole of sulfone employed in the agent.

EXAMPLE IV Preparation of a synthetic tanning agent 154 g. of a dihydroxy diphenyl sulfone paste mixture prepared by the procedure described in part (A) of Example I above was mixed with g. of water and 75 g. (0.94 mole) of 50% by weight sodium hydroxide solution and heated until a clear solution was obtained. 114 g. (1.41 mole) of formaldehyde solution (37% by weight) was added at 50- C. and the mixture was stirred at 50 C. for 24 hours. The sulfone parts employedv in this example contained 78% by weight of solids, the solids being 98% by weight of a mixture of pure sulfone isomers and 2% by weight of impurities. The mixture of sulfone isomers weighed 117.5 g. (0.47 mole). The sulfone isomers in the mixture were present in a weight ratio of 88% of the 4,4'-dihydroxy diphenyl sulfone isomer to 12% of the 4,2-dihydroxy diphenyl sulfone isomer. The 2% by Weight of impurities in the mixture consisted of polymeric sulfones, phenol sulfonic acids, other byproducts and the like. The molar ratio of formaldehyde to dihydroxy diphenyl sulfone in this reaction mixture was 3 moles of formaldehyde to 1 mole of dihydroxy diphenyl sulfone. After reaction for 24 hours at 50 C. a sample of the reaction mixture was titrated for its formaldehyde content by the procedure described in Example III above and found to contain 2.23% by weight of unreacted formaldehyde. The initial formaldehyde content of the reaction mixture was 9.95% by weight. In other words, 7.72% by weight of formaldehyde, which represented 77.6% of the total amount of formaldehyde used was consumed in the reaction. This formaldehyde usage represented reaction of 1.09 moles of formaldehyde with 0.47 mole of dihydroxy diphenyl sulfone, that is, the formaldehyde reacted with the phenolic rings present in the sulfone. The ratio of free methylol groups to moles of dihydroxy diphenyl sulfone was 2.32 free methylol groups per mole of dihydroxy diphenyl sulfone. After methylolation, 200 cc. of cold water was added to the reaction mixture and the reaction mixture was cooled to 10 C. A solution containing 50 g. of sulfuric acid (96% by Weight active) and g. of water was added to the reaction mixture with good cooling. The methylolated dihydroxy diphenyl sulfone separated from the reaction mixture on cooling to 10 C. and the resulting slurry contained crystals of the methylolated dihydroxy diphenyl sulfone and a solution of unreacted formaldehyde, salt and other impurities. The slurry was cooled to 10 C. and the crystals of dimethylolated sulfone allowed to settle. The solution containing the impurities was removed from the crystals by decantation. The crystals of methylolated dihydroxy diphenyl sulfone were then washed three times with 500 cc. portions of cold water. The slurry was externally cooled with ice during washing and decantation. After each addition of wash water, the crystals were slurried, allowed to settle and the wash water was decanted from the cooled slurry. The formaldehyde content of the last wash water was analyzed by the procedure described in Example III above and found to be 0.0%. The pH of the'last wash water was 3.8. The washed methylolated sulfone crystals were analyzed by the above described De Jong method and found to contain 2.32 free methylol groups per mole of sulfone. The crystals were found to be 98% by weight pure and to contain 2% by weight of impurities. The weight ratio of the isomers in the crystals was 88% of methylolated 4,4-dihydroxy diphenyl sulfone to 12% of methylolated 4,2-dihydroxy diphenyl sulfone. The 2% by weight of impurities in the crystals consisted of methylolated polymeric sulfones, methylolated phenol sulfonic acids, other byproducts and the like.

18.7.5 g. of Z-naphthalene sulfonic acid mixture (about 75% by weight active) which contained 0.54 mole of Z-naphthalene sulfonic acid and was prepared by the procedure given in Example II above, and 9 g. of water were added to the washed methylolated dihydroxy diphenyl sulfone crystals and the resulting reaction mixture was refluxed for hours at about 110 C. After refluxing for five hours, the reaction mixture was cooled to room temperature. 250 cc. of water was then added to the cooled mixture and the mixture was neutralized to a pH of 2.5 with 80 g. of 50% by Weight sodium hydroxide solution. The resulting product was a shrunken grain synthetic tanning agent in the form of a light yellow colored clear syrupy solution. This solution contained 36% solids. The solution was clear and soluble when it was mixed with a 3% by weight sodium chloride solution. The tanning agent did not precipitate from solution on neutralization at pHs of from about 0 to about 7. The synthetic tanning agent was analyzed by the De Jong method and found to contain 1.1 free methylol groups per mole of sulfone employed.

EXAMPLE V An alternate procedure for producing a shrunken grain synthetic tanning agent 204 g. of dihydroxy diphenyl sulfone paste prepared by the procedure described in part (A) of Example I above was charged into a reaction vessel. The paste contained 78% by weight of solids, the solids being 98% by weight of a mixture of pure sulfone isomers and 2% by weight of impurities. The mixture of sulfone isomers weighed 156 g. (0.625 mole). The sulfone ismoers in the mixture were present in a weight ratio of 88% of the 4,4- dihydroxy diphenyl sulfone isomer to 12% of the 4,2- dihydroxy diphenyl sulfone isomer. The 2% by weight of impurities in the mixture consisted of polymeric sulfones, phenol sulfonic acids, other byproducts and the like. 407 g. of water, 250 g. of Z-naphthalene sulfonic acid mixture (about 75% by weight active) which contained 0.71 mole of Z-naphthalene sulfonic acid and was prepared by the procedure described in Example II above and 101 g. (1.25 mole) of formaldehyde solution (37% by weight active) were then charged into the reaction vessel and were mixed at room temperature. The molar ratio of formaldehyde to dihydroxy diphenyl sulfone isomers in the mixture was two moles of formaldehyde per mole of dihydroxy diphenyl sulfone. The reaction mixture was heated to the reflux point, that is, about 102 C. and became a clear solution immediately. The reaction mixture was refluxed at 102 C. for 15 hours, cooled to room temperature and neutralized with cooling by the addition of 106.5 g. of 50% by weight sodium hydroxide solution and 50 g. of water. The product of the reaction was about 1100 g. of a clear syrupy liquid containing 35% solids by weight. The clear syrupy liquid was the desired synthetic tanning agent. The properties of the synthetic tanning agent were comparable to those of the agent obtained in Example III above. That is, the tanning agent was soluble in salt solutions containing at least 2.5% by weight of sodium chloride and the agent did not precipitate from solution on neutralization at pHs from about 0 to about 7. Analysis of the synthetic tanning agent by the De Jong method showed that it contained 1.0 free methylol groups per mole of sulfone employed.

EXAMPLE VI A synthetic tanning agent was prepared according to the procedure described in Example I of US. Patent No. 3,010,779, was synthesized and evaluated in the following manner.

255 g. of a dry 98% by weight pure crystalline dihydroxy diphenyl sulfone isomers mixture prepared by the procedure given in part (A) of Example I above, 150 g. of water and 35 g. of 45% by weight sodium hydroxide solution were charged into a reaction vessel and mixed. The sulfone isomer mixture contained 98% by weight of sulfone isomers and 2% by weight of impurities. The mixture of sulfone isomers weighted 250 g. (1.0 mole). The sulfone isomers in the mixture were present in a weight ratio of 88% of the 4,4'-dihydroxy diphenyl sulfone isomer to 12% of the 4,2'-dihydroxy diphenyl sulfone isomer. The 2% by weight of impurities in the mixture consisted of polymeric sulfones, phenol sulfonic acids and the like. 87.5 g. (0.88 mole) of formaldehyde solution (30% by weight active) was then charged into the reaction vessel and the resulting reaction mixture was heated at its boiling point for 3 hours "to obtain a condensation product. The resulting condensation product was then mixed with 275 g. (1.12 mole) by weight of the naphthalene sulfonic acid obtained by the procedure described in US. Patent No. 1,972,754 and the mixture was reacted by heating at 120 C. for 1.5 hours. When an attempt was made to neutralize the reaction product of this mixture with 50% sodium hydroxide solution, the synthetic tanning agent precipitated. Analysis of the synthetic tanning agent by the De Jong method showed that it contained 0.0 free methylol groups per mole of sulfone employed.

This example demonstrated that synthetic tanning agent prepared in accordance with this procedure could not be satisfactority neutralized to a pH in range of about 0 to about 7 so that the free sulfuric acid was completely neutralized and the naththalene sulfonic acid was partially neutralized. During the neutralization when only a fraction of the free sulfonic acid was neutralized, precipitation of the tanning agent began and became increasingly heavy as the pH was raised gradually above 0. Further, the agent was not soluble in a salt solution containing 0.1% by weight of sodium sodium chloride.

EXAMPLE VII This example demonstrates the preparation of a synthetic tanning agent from a crude and impure dihydroxy diphenyl sulfone.

162 g. (1.72 mole) of phenol, 87 g. (0.85 mole) of sulfuric acid (967 by weight active) and 50 g. of monochlorobenzene were mixed together in a reaction vessel and heated to a maximum temperature of about 168 C. The water formed during reaction was removed by azeotropic distillation. After the dihydroxy diphenyl sulfone was formed, the reaction mixture was neutralized with a solution containing 110 g. of 50% by weight sodium hydroxide solution and 300 g. of water. Monochlorobenzene remaining in the reaction mixture was removed by azeotropic distillation. After all of the monochlorobenzene had been removed, the reaction mixture was cooled to 20 C. and a suspension of white crystals in a pink mother liquor was obtained. The suspension of crystals in mother liquor was then used directly without any purification or removal of mother liquor. This suspension was found to contain 0.6 mole of sulfone isomers, that is, it contained 70% by weight of a mixture of 4,4-dihydroxy diphenyl sulfone and 4,2'-dihydroxy diphenyl sulfone isomers. The 30% by weight of impurities in the mixture included polymeric sulfones, phenol sulfonic acids, other byprodnets and the like.

g. (1.23 mols) of formaldehyde (37% by weight active) was added to the suspension of the crystals in the mother liquor and the resulting mixture stirred for 1 hour and 25 minutes at 24 C. The reaction temperature was then gradually raised to 55 C. The mixture was then reacted at 50 C. to 55 C. for 24 hours. The formaldehyde content of the reaction mixture was determined by the procedure in Example III above and found to be 1.02% by weight. The reaction mixture was then reacted at 50 C. to 52 C. for 17 additional hours. The formaldehyde content was found to be 0.01% by weight. The mixture was then cooled to room temperature and 70 g. of sulfuric acid (96% by weight active) and 70 g. of water were added. The reaction product was a suspension of solids in salt water. The solids were allowed to settle and the salt Water removed by decantation. The solids were then washed three times with 500 g. quantities of water cooled to 10 C. After the third wash, the formaldehyde content of the third wash water was determined and found to be 0.01% by weight. After the methylolated crude sulfone mixture was washed free of formaldehyde, it was analyzed by the De Jong method and found to contain 1.8 free methylol groups per mole of sulfone.

230 g. of Z-naphthalene sulfonic acid mixture, which contained 0.66 mole of Z-naphthalene sulfonic acid and was about 75% by weight active, was added to the washed methylolated sulfone solids and the resulting reaction mixture refluxed at 110 C. for hours. The reaction mixture was then cooled to 30 C. and 375 g. of Water and 95 g. of 50% by weight sodium hydroxide solution were added. The resulting product was a clear solution of a synthetic agent which contained 44% by weight solids and had a pH of 2.2 as is. Analysis of the tanning agent by the De Jong method showed that it contained 0.4 methylol groups per mole of sulfone employed instead of the expected 0.7 methylol groups per mole of sulfone. The unaccounted free methylol groups had reacted with the byproducts present in the crude sulfone mixture. Such byproducts included polymeric sulfones, phenolic sulfonic acids an the like. The agent precipitated from 2% by weight sodium chloride solution.

EXAMPLE VIII This example demonstrates the preparation of a synthetic tanning agent from a dihydroxy dimethyl diphenyl sulfone prepared from ortho cresol.

A dihydroxy diphenyl sulfone was prepared from ortho cresol by using the procedure given in Example I(A) above and substituting an equirnolar quantity of ortho cresol for phenol. The resulting dihydroxy dimethyl diphenyl sulfone was washed, filtered and dried. 139 g. (0.5 mole) of the dihydroxy dimethyl diphenyl sulfone obtained from this preparation was mixed with 400 cc. water, 81 g. (1 mole) of formaldehyde solution (37% by weight) and 300 g. (0.86 mole) of Z-naphthalene sulfonic acid solution (75% by weight active) prepared according to the procedure in Example II above. The resulting reaction mixture was refluxed at 102 C. for hours in a reaction vessel, cooled to 30 C. and neutralized to a pH of 2.8 by the addition of 171 g. of 50% by weight sodium hydroxide solution. The mixture was cooled at 30-4 0 C. during neutralization. The neutralized product was a synthetic tanning agent in the form of a clear solution containing 38.4% by weight of synthetic tanning agent. The product was analyzed by the De Iong method and found to contain 0.3 free methylol groups per mole of sulfone employed.

EXAMPLE IX Evaluation of the synthetic tanning agents prepared in Examples III through VIII.

300 g. of drained pickled stock gauging 3 oz. and having a pH of 2.0 was floated in 300 cc. of a 4% by weight salt solution for 30 minutes to rewet and soften the stock. The solution was drained. 150 g. of water and 90 g. of the synthetic tanning agent obtained in Example III above was added. The stock was rotated for 4 hours in the synthetic tanning agent and water solution. After 4 hours of rotation, exhaust of the synthetic tanning agent was complete. Exhaust was determined by the Oflicial A.L.C.A. Method A2S. The exhausted solution was drained and a new float of 300 cc. of water and 24 g. of a chrome liquor containing 25% chromium oxide of 33% basicity were added. The sample of stock was rotated in this liquor for 12 hours. Then cc. of a 10% by weight sodium bicarbonate solution was added and the sample was rotated for an additional two hours. The sample was taken out of the drum, horsed for 48 hours, then washed in fresh water, dyed and fat liquored in the usual manner. After fat liquoring, the sample was taken out of the drum, dried, staked and toggled on frames. After drying, the leather sample was finished in the usual manner. The leather sample produced by this procedure had a round feel and was soft and strong. The pattern developed on the grain of the leather by the above tanning procedure was carefully examined. The pattern was found to be highly uniform, spread evenly over all of the surface of the leather with high depth. N0 coarseness whatsoever in the pattern was noted and the pattern gave an overall picture of a natural, uniform, fine pattern. On strong stretching of the leather sample, the sample immediately recovered the same pattern after the stretch was released.

The same test procedure was used to evaluate samples of the synthetic tanning agents obtained in Examples IV through VIII. The following results were obtained. Stock tanned with the products of Examples IV and V by this procedure showed the same favorable results as obtained with the product of Example III. The leather obtained with Example IV was superior to that obtained With the product of Example III and the properties of the leather obtained with the product of Example V were closest in quality and properties to that obtained with the product of Example IV. Leather tanned with the product of Example VI showed a very poor and non-uniform shrinking pattern having low depth, poor surface coverage by the pattern and was inferior in feel and strength. The leather obtained'with the product of Example VII was slightly better in appearance to that obtained with the product of Example VI but was very inferior to the leather obtained with the product of Examples III, IV and V. Leather obtained with the product of Example VIII had a very poor non-uniform pattern. When the product of Example VI was neutralized to a pH of 2.2 as is and the precipitated mixture was used in the evaluation on leather, equally poor results were obtained as with the unneutralized product. It was noted that the precipitated tanning agent dissolved gradually during the tanning procedure but that the gradual solution of the precipitated tanning agent did not improve the shrunken grain leather pattern. As pointed out above, the grain must be shrunken during the initial phase of the tanning process.

EXAMPLE X Shaved chrome tanned stock was partly dechromed with a 5% by Weight oxalic acid solution, washed thoroughly and then retained in a 50% float by the procedure described in Example IX above with 30% by Weight of each of the synthetic tanning agents described in Examples III through VIII above. When the samples of finished shrunken grain leather were examined, the same results as those obtained in Example IX above were noted and the only distinction was that the differences between the various tanning agents were more pronounced. This meant that the synthetic tanning agents produced in Examples IV and V were superior to all of the others. The leather obtained with the synthetic tanning agent of Example III was good and of excellent quality. Leather obtained from Example VI was extremely poor. Leather obtained with the synthetic tanning agents of Example VII and VIII respectively were also extremely poor.

EXAMPLE XI 500 g. of shaved chrome calf leather was dechromed with an oxalic acid solution containing 25 g. oxalic acid in 500 g. water. When the shrinkage temperature of the stock dropped from an original value of 212 F. to F. the dechromed leather was washed thoroughly and then treated in a tanning liquor containing 250 g. water with g. of the synthetic tanning agent of Example IV. The leather samples were rotated in this liquid for 5 hours. The tanning liquor was drained, the samples reflected with 500 g. water and 40 g. of a chrome liquor containing 25% chromium oxide of 33% basicity was added. After 8 hours of rotation, 50 g. of a 10% solution 17 of sodium bicarbonate was added as the leather rotated for an additional half hour. The shrunken grain leather samples were washed, dyed, fat-liquored and finished in the usual way. A very deep, fine and uniform pattern resulted, evenly distributed over the entire area of the calf skin. The same procedure was repeated with the synthetic tanning agent of Example V with equally good results.

EXAMPLE XII 100 lbs. of pickled cowhides were floated in 200' lbs. of a 4% by weight salt solution for one hour to soften the stock. The salt solution was drained and 50 lbs. of water and 30 lbs. of the synthetic tanning agent produced according to Example V above were added as a tanning liquor. The hides were rotated for six hours until the exhaust of the synthetic tanning agent was complete. Subsequently, the tanning liquid was drained and the hides refloated in 100 lbs. water. 9 lbs. of a chrome liquor containing 25% by weight chromium oxide of 40% basicity was added. The hides were'rotated in this liquor for 12 hours. Then 0.8 lb. of sodium bicarbonate dissolved in 8 lbs. water was added over a period of one-half hour and the hides rotated for an additional 2 hours. The hides were taken out from the drum, horsed for 48 hours, then washed in water, neutralized with sodium bicarbonate solution, dyed and fat-liquored in the usual Way. After this procedure was finished, the hides were taken out, dried, staked and toggled on frames. After drying, they were finished in the usual way. The appearance of the shrunken grain leather produced by this procedure was examined. The leather had a round feel and was soft and strong. The shrunken grain pattern on the leather was examined and found to show a uniform picture with no difference in the pattern formed on the middle parts, neck parts, tail parts or flanks of the hides. The pattern was deep, very uniform, fine and natural looking. Even the most powerful stretching of the hides did not make the pattern disappear and recovery of the pattern after release of the stretch was complete.

EXAMPLE XIII 10 lbs. of shaved chrome tanned side leather were partially dechromed by treatment with a by weight oxalic acid solution. The partially dechromed hides were washed thoroughly and the wash water was drained. 5 lbs. of water and 3 lbs. of the synthetic tanning agent of Example IV above were added as a tanning liquor and the hides were rotated in this liquor for 5 hours. The tanning liquor was drained and a float of lbs. of water and 3 lbs. of a chrome liquor containing chromium oxide of 33% basicity was added. The hides were rotated in this liquor for 12 hours. Then 0.12 lb. of sodium bicarbonate dissolved in 1.2 lbs. water was added and the hides rotated for two additional hours. The float was drained and 10 lbs. water and 1 lb. of a 35% quebracho extract were added. The hides were rotated for five additional hours, then washed and finished in the usual way. The finished shrunken grain leather was examined and showed very high depths of the pattern form distributed uniformly over the entire area of the hides. The feel of the leather was round. The shrunken grain pattern on the leather recovered completely after release of stretching. The finished leather was soft and strong.

EXAMPLE XIV This example demonstrates the preparation of a shrunken grain synthetic tanning agent using 95% by weight pure dihydroxy diphenyl sulfone isomer mixture.

(A) Preparation of 95% by Weight pure dihydroxy diphenyl sulfone isomer mixture.

1148 g. (12.2 moles) of phenol, 612 g. (6 moles) of sulfuric acid (96% by weight active) and 125 g. monochlorobenzene were charged into a reaction vessel equipped'with an agitator and a water separation trap. The reaction mixture was heated to the reflux temperature which was about C. The escaping vapors of chlorobenzene and water formed during the reaction were condensed in the condenser and were separated in the water trap. The dry chlorobenzene was returned to the reaction mixture. Reaction temperature was gradually increased to a temperature between C. and C. After from about 210 cc. to 215 cc. of water had been separated by azeotropic distillation, the reaction mixture was titrated to determine its acidity. A 10 g. sample of the reaction mixture at this point should not require more than 19.00 cc. to 20.00 cc. of 0.5 N sodium hydroxide solution to neutralize the sample to a pH of 7.0.

After the desired acidity was obtained, 500 cc. of water was added carefully to the reaction product. The reaction product was then neutralized to a pH between 5 and 6 by the cautious addition of from about 120 g. to about 130 g. of 50% by weight sodium hydroxide solution. Approximately 1,000 cc. of water was then added to the reaction product and the resulting mixture was azeotropically distilled to remove the chlorobenzene. After all of the chlorobenzene was stripped from the reaction mixture, an additional 1,000 cc. of water was added and the resulting solution of the reaction product was heated to its boiling point. A clear solution was obtained at the boiling point. The clear solution was then transferred to a reaction vessel containing approximately 4,000 cc. of boiling water and the resulting dilute solution was allowed to cool slowly to room temperature with vigorous agitation. Dihydroxy diphenyl sulfone precipitated in the form of cream colored crystals from the solution during cooling.

The precipitated crystals were filtered off on a filter press without washing and dried at 105-110 C. The dry product was analyzed for its actual sulfone content and found to contain 95 by weight of pure dihydroxy sulfone isomers and 5% by weight of impurities. The isomers in the mixture consisted of 4,4'-dihydroxy diphenyl sulfone and 4,2-dihydroxy diphenyl sulfone. The 5% by weight of impurities in the mixture included polymeric sulfones, phenol sulfonic acids, other byproducts and the like.

(B) Preparation of a shrunken grain synthetic tanning agent by using a 95 by weight pure dihydroxy diphenyl sulfone isomer mixture.

164.5 g. of the 95% by weight pure sulfone isomer mixture obtained in part (A) and containing 156 g. (0.625 mole) of dihydroxy diphenyl sulfone isomers, 426 g. of water, 248 g. of 2-naphthalene sulfonic acid solution containing 0.653 mole of sulfonic acid, 0.394 mole of sulfuric acid and the balance being water, and 101 g. aqueous formaldehyde solution containing 1.25 mole of formaldehyde were mixed together and heated to reflux. The molar ratio of formaldehyde to sulfone was 2 moles of formaldehyde to 1 mole of sulfone. The reflux temperature of the mixture was 101.5 C. The refluxing solution was slightly hazy in appearance. After 15.5 hours of reflux, the reaction mixture was cooled to 40 C. and neutralized with 106 g. of 50% by weight sodium hydroxide solution and 50 g. of water. No precipitate formed during the neutralization but the solution had a faint haze. 10 g. of filter aid was added and the solution was filtered through a Knieger pressure filter. It was then brilliantly clear. Analysis of the shrunken grain synthetic tanning agent showed that it contained 0.9 molev of free methylol groups per 1 mole of sulfone employed in the reaction. The properties of the tanning agent were comparable to the synthetic tanning agent of Example V above.

EXAMPLE XV This example demonstrates preparation of a shrunken grain synthetic tanning agent by using a 100% by weight pure dihydroxy diphenyl sulfone isomer mixture. 2

The procedure given in Example IV above was repeated with the exception that 117.5 g. (0.47 mole) of 100% by weight of a pure crystalline dihydroxy diphenyl sulfone isomer mixture prepared by the procedure given in part (B) of Example I above was employed instead of 154 g. of sulfone paste. The sulfone isomers in the mixture were present in a weight ratio of 88% of the 4,4'-dihydroxy diphenyl sulfone isomer to 12% of the 4,2-dihydroxy diphenyl sulfone isomer. The properties of the synthetic tanning agent were comparable to those of the synthetic tanning agent produced in Example IV.

The foregoing examples demonstrate that the synthetic tanning agents of the present invention produce shrunken grain leathers having deep, uniform patterns which completely recover after stretching and release of the stretch.

The examples given below, that is, Examples XVI through XVIII further demonstrate that synthetic tanning agent solutions prepared by procedures outside the scope of the invention do not produce shrunken leathers having satisfactory properties.

EXAMPLE XVI This example is directed to preparing a tanning agent from an impure, crude sulfone.

200 g. of a crude dihydroxy diphenyl sulfone isomer mixture was prepared according to the procedure given in Example VII above, the only difference being that the reaction was carried half way to completion. The crude sulfone contained 80% by weight solids, was about 40% pure by weight and contained 80 g. (0.32 mole) of dihydroxy diphenyl sulfone isomers. The 60% by weight of impurities in the mixture included polymeric sulfones, phenol sulfonic acid, other byproducts and the like. This quantity of sulfone represented a 37% yield instead of the expected 75% yield. The crude sulfone was mixed with 100 g. of water and 95 g. (1.17 mole) of aqueous formaldehyde solution 37% by weight active). The ratio of formaldehyde to sulfone was 3.66 moles of formaldehyde to 1 mole of dihydroxy diphenyl sulfone. The mixture was heated to 50 C. and held at 50 C. with agitation for 12 hours. After heating 12 hours at 50 C., a gummy product precipitated from the solution. The water layer was decanted from the gummy resinous precipitate and the precipitate washed three times with 500 cc. quantities of cold water. Analysis showed that the third 500 cc. water wash was free of formaldehyde, that is, the precipitate did not contain any free or unreacted formaldehyde. The crude methylolated sulfone mixture contained 1.4 free methylol groups per mole of sulfone employed.

125 g. (0.33 mole) of naphthalene sulfonic acid mixture (about 75% by weight active) prepared by the procedure described in Example II above was added to the washed resinous precipitate and then 50 g. of water was added. The resulting mixture was heated to reflux and refluxed for 2 hours. No solubilization of the reactants occurred during the 2 hours that the reactants were refiuxed. Further, no appreciable solubilization of the reactants were refiuxed. Further, no appreciable solubilization of the reactants occurred on prolonged refluxing of the reaction mixture. After cooling the reaction mixture, the major portion of the reaction product formed a gummy resinous mass, which was insoluble in water. Neutralization of the reaction product to a pH of 3.5 by the addition of sodium hydroxide solution did not solubilize the resinous reaction product. Further, the reaction product was not soluble in a salt solution containing 0.1% by weight sodium chloride. The resinous product contained 0.0 free methylol groups per mole of sulfone employed. The product was not in suitable form for use as a synthetic tanning agent in producing shrunken grain leather.

This example demonstrated the use of a crude dihydroxy diphenyl sulfone mixture which had a purity of about 40% by weight and was outside the purity limit of this invention did not give a satisfactory shrunken grain tanning agent even though the quantities used, that is, one mole of the dihydr xy diph nyl sulfone mixture,

20 3.66 moles of formaldehyde and 1.06 moles of 2-naphthalene sulfonic acid, were within the limits of this invention.

EXAMPLE XVII This example is directed to the preparation of a tanning agent from a crude sulfone.

(A) 188 g. (2 mole) phenol, 102 g. (1 mole) sulfuric acid 98% by weight and 25 cc. chlorobenzene were heated to reflux and the water formed during the reaction was removed azeotropically. After refluxing the reaction mixture for 75 minutes, the reflux temperature was 175 C. and a total of 37 cc. of water had been removed by azeotropic distillation. The reaction mixture was neutralized with 13.5 g. of sodium hydroxide and 94 g. of water. The neutralized crude sulfone dissolved when the mixture was heated to its boiling point. 200 cc. cold water was added to the crude dihydroxy diphenyl sulfone. The crude sulfone isomer mixture was 75% pure by weight. The 25% by Weight of impurities in the mixture included polymeric sulfones, phenol sulfonic acids, other byproducts and the like.

(B) 128 g. (1 mole) naphthalene was reacted with 160 g. (1.6 mole) sulfuric acid (98% by weight) for 1 hour at 155 C. The reaction mixture was cooled to C. and 100 g. of ice was added to the reaction mixture at room temperature. The reaction mixture was a mixture containing about 75% by weight of 2-naphthalene sulfonic acid plus excess free sulfuric acid, that is, 1.0 mole of 2-naphthalene sulfonic acid and 0.6 mole of sulfuric acid.

(C) The crude dihydroxy diphenyl sulfone mixture, which represented 0.75 mole of 100% by weight pure dihydroxy diphenyl sulfone isomers obtained in part (A) above was mixed with the solution of Z-naphthalene sulfonic acid (1.0 mole) obtained in part (B) above and 296 g. of water added. A total of 162 g. (2 moles) of aqueous formaldehyde solution (37% by weight active) was added and the resulting reaction mixture heated to reflux. The reaction mixture contained 0.75 mole of sulfone and 2.00 moles of formaldehyde and had a molar ratio of formaldehyde to sulfone of 2.67. The reactants in the reaction mixture did not dissolve in the reaction mixture but remained insoluble even after the reaction mixture had been refluxed for 14 hours. When the reaction mixture was cooled and neutralized, a gummy precipitate was obtained. The reaction product was insoluble over the entire neutralization range, that is, from a pH of about 0 to about 7. Further, the final product was insoluble in salt solutions containing as little as 0.1% by weight sodium chloride. The final reaction product contained 0.0 methylol groups per mole of sulfone employed. This product was not in suitable form for use as a synthetic tannin-g agent in producing shrunken grain leather.

This example demonstrated that use of a crude dihydroxy diphenyl sulfone isomer mixture which had a purity of 75% by weight and was outside the purity limits of this invention did not give a satisfactory shrunken grain synthetic tanning agent even though the quantities used, that is, one mole of the dihydroxy diphenyl sulfone mixutre, 2.67 moles of formaldehyde and 1.33 moles of Z-naphthalene sulfonic acid, were within the limits of the present invention.

EXAMPLE XVIII This example is directed to preparing a tanning agent with a molar quantity of formaldehyde outside the limits of the present invention.

127.5 g. of a dry, crystalline dihydroxy diphenyl sulfone isomer mixture of 98% purity by weight as described in Example I(A) above, g. (0.5 mole) of 2-naphthalene sulfonic acid mixture as described below, 500 g. of water and 55 g. (0.68 mole) of aqueous form-. aldehyde solution (37% by weight active) were mixed and heated to reflux. The mixture of sulfone isomers 21 weighed 125 g. (0.5 mole). The sulfone isomers in the mixture were present in a weight ratio .of 88% of the 4,4'-dihydroxy diphenyl sulfone isomer to 12% of the 4,2'-dihydroxy diphenyl sulfone isomer. The 2% by weight of impurities included polymeric sulfones, phenol sulfonic acids, other byproducts and the like. The naphthalene sulfonic acid was prepared by the procedure given in Example XVII(B) abovewith the exception that ice was ,not added and the sulfonic acid was substantially anhydrous. After 18 hours at reflux, the mixture was neutralized with 86 g. of 50% .by weight sodium hydroxide solution and 100 g. of water to obtain a synthetic tanning agent solution having a pH of 2.5. The solution contained 30% by. weight solids. The molar ratio of formaldehyde to sulfone was 1.35:1 and the synthetic tanning agent contained 0.36 free methylol groups per moleof sulfone employed, that is, the tanning agent contained about 0.4 methylol groups per mole of sulfone employed. The tanning agent wasevaluated as a shrunken grain tanning agent for leather. The agent did not profew scattered patterns on the leather and none of the patterns had depth. e

This example demonstrated that use of less than 1.5 moles of formaldehyde per mole of sulfone did not give a satisfactory shrunken grain tanning agent because the agent contained less than 0.5 methylol groups per mole of sulfone employed and was outside'the limits of the present invention. i

What is claimed is:

1. A process of producing shrunken grain leather from a skin selected from the group consisting of animal skins, pickled skins, partially tanned skins, partially dechromed skins and dechromed skins comprising (I) introducing from about by weight to about 50% by weight based on the weight of said skin of a water soluble shrunken grain synthetic tanning agent in substantially monomeric form comprising the reaction product of (a) one mole of a sulfone having a purity of from about 95% to 100% by weight selected from the group consisting of 4,4'-dihydroxy diphenyl sulfone, 4,2-dihydroxy diphenyl sulfone, 2,2- dihydroxy diphenyl sulfone and mixtures thereof, (b) from about 1.5 moles to about 5.0 moles of formaldehyde per mole of said sulfone, and (c) from about 0.5 mole to about 2.0 moles of 2- naphthalene sulfonic acid per mole of said sulfone, said (a), (b) and (0) being mixed at about room temperature, and thereafter reacted at temperatures of from about 20 C. to about 150 C. in aqueous solution until a clear solution is obtained with the proviso that pressure is employed at temperatures between about 110 C. and about 150 C. and water being present in an amount of from about three to about five times the weight of said sulfone, and with the further proviso that said reaction product contains at least 0.5 free methylol groups per mole of said sulfone, is soluble in salt solutions containing at least 2.5% by weight of sodium chloride and when in solution does not precipitate on neutralization at a pH of from about 0 to about 7, and from about by weight to about 100% by weight based on the weight of said skin of water, and thereafter (II) drumming said skin with said agent at a temperature of from about 70 F. to about 90 F. for about 2 hours to about 12 hours so that said agent is exhausted into said skin. 2. A process of producing shrunkent grain leather from a skin selected from the group consisting of animal skins, pickled skins, partially tanned skins, partially dechromed skins and dechromed skins comprising 2.0 duce satisfactory shrinking effects, that is, there were 22 I (I) introducing from about 15% by weight to about 50% by weight based on the weight of said skin of ,a water soluble. shrunken grain synthetic tanning agent in substantially monomeric form comprising the reaction product of (a) one mole of a methylolated sulfone having a purity of from about 95 to 100% by weight selected from the group consisting of rnethylolated 4,4'-dihydroxy diphenyl sulfone, methylolated 4,2-dihydroxy diphenyl sulfone, methylolated 2,2-dihydroxy diphenyl sulfone and mixtures thereof wherein said sulfone contains from about 1.5 to about 4 free methylol groups per mole of said sulfone, said methylolated sulfone I being prepared by reacting about one mole of a disodium salt of dihydroxy diphenyl sulfone having a purity of from about 95% to 100% by 1 Weight selected from the group consisting of the disodium salt of 4,4'-dihydroxy diphenyl sulfone, the disodium salt of 4,2' -dihydroxy diphenyl sulfone, the disodium salt of 2,2'-dihydroxy diphenyl sulfone and mixtures thereof, and from about 1.5 moles to about 5 moles of formaldehyde at about 20 C. to about 55 C. in water present in an amount of from about one and onehalf to about two times the weight of said diphenyl sulfone and at a pH of about 9.5 to about 10, thereby forming the disodium salt of said methylolated sulfone. and thereafter precipitating said methylolated sulfone by acidification of said disodium salt of said methylolated sulfone, and (b) from about 0.5 mole to about 2.0 moles of 2- naphthalene sulfonic acid per mole of said sulfone, said (a) and (b) being mixed at about room temperature, and thereafter reacted at temperatures of from about 50 C. to about 150 C. in aqueous solution until a clear solution is obtained with the proviso that the pressure is employed at temperatures between about 110 C. and about 150 C. and water being present in an amount of from about one-half to about two times the weight of said sulfone, and with the further proviso that said reaction product contains at least 0.5 free methylol groups per mole of said sulfone, is soluble in salt solutions containing at least 2.5% by weight of sodium chloride and when in solution does not precipitate on neutralization at a pH of from about 0 to about 7, and from about 30% by weight to about 100% by weight of said skin of water, and thereafter (II) drumming said skin with said agent at a temperature of from about 70 F. to about F. for about 2 hours to about 12 hours so that said agent is exhausted into said skin.

3. Leather treated with a water soluble shrunken grain synthetic tanning agent in substantially monomeric form comprising the reaction product of (a) one mole of a sulfone having a purity of from about to by weight selected from the group consisting of 4,4'-dihydroxy diphenyl sulfone, 4,2'-dihydroxy diphenyl sulfone, 2,2'-dihydroxy diphenyl sulfone and mixtures thereof,

(b) from about 1.5 moles to about 5.0 moles of formaldehyde per mole of said sulfone, and

(c) from about 0.5 mole to about 2.0 moles of 2- naphthalene sulfonic acid per mole of said sulfone,

said (a), (b) and (c) being mixed at about room temperature, and thereafter reacted at temperatures of from about 20 C. to about 150 C. in aqueous solution until a clear solution is obtained with the proviso that pressure is employed at temperatures between about C. and about C. and water being present in an amount of from about three to about five times the weight of said sulfone, and with the further proviso that said reaction product contains at least 0.5 free methylol groups per mole of said sulfone, is soluble in salt solutions containing at least 2.5% by weight of sodium chloride and when in solution does not precipitate on neutralization at a pH of from about to about 7 wherein said reaction product is drummed into said leather at a temperature of from about 70 F. to about 90 F. for about 2 hours to about 12 hours so that said reaction product is exhausted into said leather.

4. Leather treated with a water soluble shrunken grain synthetic tanning agent in substantially monomeric form comprising the reaction product of (a) one mole of a methylolated sulfone having a purity of from about 95% to 100% by Weight selected from the group consisting of methylolated 4,4-dihydr0xy diphenyl sulfone, methylolated 4,2-dihydroxy' diphenyl sulfone, methylolated 2,2-dihydroxy diphenyl sulfone and mixtures thereof wherein said sulfone contains from about 1.5 to about 4 free methylol groups per mole of said sulfone, said methylolated sulfone being prepared by reacting about one mole of a disodium salt of dihydroxy diphenyl sulfone having a purity of from about 95% to 100% by weight selected from the group consisting of the disodium salt of 4,4-dihydroxy diphenyl sulfone, the disodium salt of 4,2-dihydroxy diphenyl sulfone, the disodium salt of 2,2'-dihydroxy diphenyl sulfone and mixtures thereof, and from about 1.5 moles to about 5 moles of formaldehyde at about 20 C. to about 55 C. in water present in an amount of from about one and one-half to about two times the weight of said diphenyl sulfone and at a pH of about 9.5 to about 10, thereby forming the disodium salt of said methylolated sulfone and thereafter precipitating said methylolated sulfone by acidification of said disodium salt of said methylolated sulfone, and (b) from about 0.5 mole to about 2.0 moles of 2- naphthalene sulfonic acid per mole of said sulfone, said (a) and (b) being mixed at about room temperature, and thereafter reacted at temperatures of from about C. to about 150 C. in aqueous solution until a clear solution is obtained with the proviso that pressure is employed at temperatures between about 110 C. and about 150 C. and water being present in an amount of from about one-half to about two times the weight of said sulfone, and with the further proviso that said reaction product contains at least 0.5 free methylol groups per mole of said sulfone, is soluble in salt solutions containing at least 2.5% by weight of sodium chloride and when in solution does not precipitate on neutralization at a pH of from about 0 to about 7 wherein said reaction product is drummed into said leather at a temperature of from about F. to about F. for about 2 hours to about 12 hours so that said reaction product is exhausted into said leather.

References Cited UNITED STATES PATENTS 1,901,536 3/1933 Shafer.

FOREIGN PATENTS 750,143 6/1956 Germany.

LEON D. ROSDAL, Primary Examiner M. HALPERN, Assistant Examiner US. Cl. X.R. 260-512; 8-94.33