Patent Publication Number: US-4318705-A

Title: Process for improving the lightfastness of conventionally dyed leather

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a process for improving the lightfastness of dyed leathers by the use of alkane or chloroalkane sulfonamides. 
     Leather is dyed mainly by means of selected acid, substantive and metal-complex dyes and, to a minor extent, basic dyes. In the case of unfinished or just lightly finished leather, the lightfastness of the dye-leather union is a primary criterion of quality. This is so because when a dyed leather is exposed to light, what is measured is the fastness, not of the dyes used but of the dye-leather union. 
     For this reason, the lightfastness of identical dyes on leather usually is very much inferior to that on textile fibers. The lightfastness of dyes on leather depends in some measure on their structure and on the auxiliary materials used in the manufacture of the leather, such as tanning agents, lubricants, dyeing assistants, etc. (F. Grall and H. Gardere, &#34;Betrachtungen uber die Lichtechtheit des gefarbten Leders&#34; (Reflections on the lightfastness of dyed leather), a paper presented at the 15th IULTCS Congress, Hamburg, 1977; Das Leder 1978, 6, pp. 94 to 98.) 
     To achieve very good lightfastness, which on leather ranges from 4 to 5, measured in conformity with DIN 54 004, it is by no means enough to use only dyes, tanning agents and lubricants which are stable to light since unpredictable interactions may have a favorable or adverse effect on the lightfastness of the dye-leather union. 
     The fatliquoring agents used in the particular fatting operation have a decisive effect on the lightfastness of dyed leathers. They influence not only the hue, its depth, brilliance and uniformity, but also the lightfastness of the color imparted. With exacting requirements, so-called &#34;non-yellowing fatliquoring agents&#34; based on sperm oil, neatsfoot oil, synthetic triolein and similar raw materials are therefore used. Synthetic fatting agents based on alkane and chloroalkane sulfonates are regarded as possessing particularly good stability to light. (German patent applications DAS Nos. 1,142,833 and 1,494,828.) 
     However, for the reasons stated, the desired high lightfastness of the dyed leather, which has a decisive effect on the utility value of leather used in clothing or furniture, of aniline upper leather and suede, etc., is not or not fully achieved regardless of how carefully the auxiliary materials are selected. This is true also when the synthetic fatting agents mentioned are used. 
     French Pat. No. 866,256 and German Pat. No. 864,905 describe the preparation of sulfonamides by the reaction of chlorine and sulfur dioxide with saturated aliphatic hydrocarbons followed by reaction of the sulfohalides obtained with ammonia or primary and secondary amines. The sulfonamides obtained by this route are suited for use as oiling and fatting agents for materials of fibrous structure and also as lubricants for machinery. It is pointed out that sulfonamides are suited for the fatting and fatliquoring of leather, among other things. 
     In German Pat. No. 747,403 it is stated that emulsifiers which dissolve clear in mineral oils and fatty oils and exhibit improved effectiveness over long-chain paraffin sulfonates are obtained when these sulfonates are used jointly with sulfonamides, sulfoacylamides or disulfimides prepared by sulfochlorination of long-chain paraffin hydrocarbons followed by treatment with ammonia or its organic derivatives. The clear mixtures of the oils and these emulsifiers are water-soluble and are said to be suitable for use as drilling oils, leather stuffing materials, lubricating and cutting oils. 
     The use of sulfamides, sulfonamides or sulfimides such as obtained in the reaction of alkane sulfohalides with ammonia or its derivatives, in the fatting of leather in the amounts customary in leather fatting which, depending on the type of the leather and on the composition of the fatting agent, range approximately from 10 to 15 weight percent, based on the shaved weight of the leather, is then described. However, nowhere in the art of record are there any statements to the effect that such products have an effect on the lightfastness of dyed leather, and have such an effect even when used in small amounts. 
     Because of their insufficient solubility in water, these products cannot, however, be used alone in fatliquoring but must be combined for this purpose with other fatting agents or emulsifiers which assure that the overall combination of the fatting agent is soluble in water or at least gives an emulsion that is sufficiently stable in water. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to permanently improve the lightfastness of conventionally dyed leathers by simple yet effective means without the leather having to be subjected to a complicated separate treatment before, during or after dying, the improvement in lightfastness being achieved regardless of the type of dye, tanning agent, fatting agent or other leather dressing agent used and even when the leathers have been treated with fatting agents or other dressing agents which are not stable to light. 
     In accordance with the invention, this object is accomplished by treating the dyed leathers with alkane and/or chloroalkane sulfonamides. 
     The ability of these alkane and/or chloroalkane sulfonamides to markedly improve the lightfastness of the dyeleather union even when used in small amounts is surprising, especially since a pronounced improvement in lightfastness is observable also when the leather has been treated with auxiliary agents which are not stable to light, such as yellowed fatting agents, for example, sulfated fish oil. 
     The invention thus has as its object a process for improving the lightfastness of conventionally dyed leathers that is characterized in that the leathers are treated with alkane and/or chloralkane sulfonamides. The latter are used in amounts ranging from about 0.1 to 8 weight percent, and more particularly 0.3 to 6.0  weight percent, and preferably 0.5 to 2.5 weight percent, based on the shaved weight of the leather. Good results will be obtained with amounts of up to 4 or even 3 weight percent. 
     The treatment is preferably carried out together with the fatting, and more particularly the fatliquoring, in order to save an extra process step. However, the treatment may also be effected in a separate step before or after dyeing and fatting. Based on the total amount of fat used (the &#34;total fat&#34;), the proportion of the sulfonamides and/or chlorosulfonamides is between 0.2 and 50 weight percent, and more particularly between 0.5 and 40 weight percent, up to about 15% of fatting agent being generally used. However, the minimum amount is about 0.1 weight percent, based on the shaved weight of the leather. Good results will be obtained with for example a proportion of 17% sulfonamide and/or chlorosulfonamide, based on the total amount of fat. 
     The sulfonamides or alkanes or chloroalkanes having a chain length of about 10 to 30, and preferably 12 to 25, carbon atoms have proved best suited for the purposes of the invention. The chloroalkane sulfonamides preferably have a degree of chlorination ranging from 10 to 40 weight percent, and preferably from 15 to 30 weight percent, chlorine, based on the particular hydrocarbon. The alkanes on which the sulfonamides are based are predominantly straight-chain and thus are formed almost exclusively of n-paraffin, and have but a small content of branched isomers, usually due to the manufacturing process. 
     Depending on the manufacturing process, the alkane or chloroalkane sulfonamides may contain the corresponding sulfimides, apart from small amounts of sulfonic acid salts, the proportion of which is largely determined by the manufacturing process and by the manner in which the product is worked up. 
     When the alkane sulfonamides employed in accordance with the invention are used in fatliquoring, they are combined with fatting agents of varying composition which are either soluble in water or emulsifiable in water. 
     The alkane or chloroalkane sulfonamides are prepared by procedures patterned on methods known from the literature, paraffin sulfochlorides obtained by the sulfochlorination of paraffin or chloroparaffin being reacted with ammonia or primary and/or secondary amines: 
     F. Ansinger, Chemie and Technologie der ParaffinKohlenwasserstoffe (Chemistry and technology of paraffin hydrocarbons), Akademie-Verlag, Berlin, 1959, p. 465 et seq.; 
     FIAT Final Report No. 1141: Synthetic Detergents and Related Surface-Active Agents in Germany, by J. D. Brandner, W. H. Lockwood, R. H. Nagel and K. L. Russel, pp. 47 and 68; 
     U.S. Pat. No. 2,334,186; 
     French Pat. No. 878,971. 
     The amidation may be carried out with liquid, gaseous or aqueous ammonia or its organic derivatives. 
     Under industrial conditions, only partial sulfochlorination of the alkanes or chloroalkanes is usually effected. This is why the paraffin sulfochlorides or chloroparaffin sulfochlorides used as starting material contain a substantial proportion of neutral oil which remains in the resulting sulfonamides even when no special working-up and separating operations, such as extractions or distillations, are carried out. 
     The raw materials used in sulfochlorination and amidation in the examples which follow conform to the following specifications: 
     
         ______________________________________                                    
       Chloroparaffin:                                                    
______________________________________                                    
       Chlorine content:                                                  
                      19.4%                                               
       Specific gravity:                                                  
                      0.907                                               
       Index of refraction:                                               
                      1.4650                                              
       Pour point:    15° C.                                       
______________________________________                                    
 
    
     The product was obtained by chlorination of a paraffin having the following characteristics: 
     
         ______________________________________                                    
n-Paraffin content:    About 94%                                          
Isomers:               About 6%                                           
Average molecular weight:                                                 
                       304                                                
______________________________________                                    
 
    
     
         ______________________________________                                    
C 16             0.1%                                                     
C 17             1.2%                                                     
C 18             5.6%                                                     
C 19             12.2%                                                    
C 20             15.1%                                                    
C 21             14.6%                                                    
C 22             12.8%                                                    
C 23             11.1%                                                    
C 24             9.3%                                                     
C 26             5.3%                                                     
C 27             3.1%                                                     
C 28             1.4%                                                     
C 29             0.6%                                                     
C 30             0.2%                                                     
C 31             0.1%                                                     
C 32             0.1%                                                     
______________________________________                                    
 
    
     
         ______________________________________                                    
Paraffin:                                                                 
______________________________________                                    
n-Paraffin content:   98% min.                                            
Isomers:              2% max.                                             
Average molecular weight:                                                 
                      213                                                 
______________________________________                                    
 
    
     
         ______________________________________                                    
C 10             1%                                                       
C 11             3%                                                       
C 12             4%                                                       
C 13             6%                                                       
C 14             23%                                                      
C 15             25%                                                      
C 16             22%                                                      
C 17             15%                                                      
C 18             1%                                                       
______________________________________                                    
 
    
    
    
     EXAMPLE 1 
     A mixture of chlorine and sulfur dioxide gas is introduced in a volume ratio of 1:1:2 into chloroparaffin having a chlorine content of 19.4% at temperatures between 50° and 55° C. over a period of 3 h, with simultaneous exposure to ultraviolet light, until the hydrolyzable chlorine content is about 4%. 
     400 parts of the sulfochloride, expelled with nitrogen, is gradually introduced with stirring into a mixture cooled to -40° C. of 300 ml liquid ammonia and 200 ml petroleum ether. Stirring is then continued for 2 h with further cooling to -40° C. After heating to room temperature, the separated ammonium chloride is filtered off and the petroleum ether is separated from the reaction product by distillation. 
     The resulting yellow-brown, slightly turbid oil contains 
     19.4% chlorine 
     3.65% sulfur 
     1.56% nitrogen 
     and consists of 
     about 52% chloroparaffin sulfonamide and chloroparaffin sulfimide, and 
     about 48% chloroparaffin. 
     EXAMPLE 2 
     Analogously to Example 1, a sulfochloride containing about 6% hydrolyzable chlorine is prepared from a chloroparaffin having a chlorine content of 19.4%. 
     After being expelled with nitrogen, the sulfochloride is transferred to an autoclave equipped with an agitator into which gaseous ammonia is introduced at so rapid a rate that the reaction temperature can be maintained at between 15° and 25° C. through external cooling of the reactor. On completion of the exothermic reaction, agitation is continued for 1 h at an ammonia pressure of 4 bars. The reaction product is agitated for 1/2 h at 70° C. with the same weight of water and then allowed to stand for separation of the phases. After separation of the aqueous salt layer, washing is repeated with one-half the weight of water, the pH value of the solution being adjusted to 5 by the addition of hydrochloric acid. After the aqueous layer has been decanted, a yellow-brown, turbid product is obtained which contains 
     about 6.0% water, 
     about 0.1% ammonium chloride, and 
     about 93.0% of an organic substance 
     consisting of 
     about 74% chloroparaffin sulfonamide and chloroparaffin sulfimide, 
     about 20% chloroparaffin, and 
     about 6% chloroparaffin sulfonate and NH 4  salt. 
     EXAMPLE 3 
     Analogously to Example 1, a sulfochloride containing about 4.5% hydrolyzable chlorine is prepared from a chloroparaffin having a chlorine content of 19.4%. 
     847 parts of the chloroparaffin sulfochloride is introduced into 450 parts of a 10% aqueous ammonia solution with stirring. During the 3 h reaction time, the temperature rises to about 75° C. On completion of the reaction, a test is made to determine whether the solution is alkaline. After separation of the aqueous salt phase, there remains a yellow oil which at room temperature is clear and which contains 
     about 14% water 
     about 3% ammonium chloride and 
     about 83% of an organic substance composed of 
     about 23% chloroparaffin sulfonamide and chloroparaffin sulfimide, 
     about 35% chloroparaffin sulfonate and NH 4  salt, and 
     about 42% chloroparaffin. 
     EXAMPLE 4 
     In a sulfochlorination vessel, liquid n-paraffin having an average molecular weight of 213 is treated for 90 min. at temperatures between 50° and 55° C. with a gaseous mixture of chlorine and sulfur dioxide with a volume ratio of 1:1.2, with simultaneous exposure to UV light, until the hydrolyzable chlorine content is about 6%. The reaction is exothermic and appropriate cooling must be provided. On completion of the reaction, the reaction product is expelled with nitrogen. 
     The sulfochloride is charged to an autoclave equipped with an agitator into which gaseous ammonia is introduced at a rate permitting the reaction temperature to be maintained at between 15° and 20° C. by additional external cooling. On completion of the exothermic reaction, agitation is continued for 1 h at about 20° C. and an ammonia pressure of 3 bars. After the ammonia excess pressure has been relieved, the reaction product is mixed with one-fourth of its weight of water and agitated for 1/2 h at 60° C. and then allowed to stand at 60° C. for separation of the phases. After the aqueous salt layer has been decanted, a yellow, slightly turbid oil is obtained which contains 
     2.5% water, 
     0.5% ammonium chloride, and 
     97.0% of an organic substance 
     consisting of about 
     45% paraffin sulfonamide and paraffin sulfimide, 
     3% paraffin sulfonate and NH 4  salt, and 
     52% neutral oil. 
     The use made of the products will now be described in the examples which follow, all amounts being based on the shaved weight of the leather, and AS standing for active substance. 
     EXAMPLE 5 
     
         ______________________________________                                    
Stock:  Chrome-tanned cowhide                                             
        Shaved thickness: About 1.3 mm                                    
Rinsing                     35° C.                                 
                                     10 min.                              
Neutralization                                                            
200.0%                                                                    
      water                                                               
2.0%  Tanigan PC*                                                         
                               undissolved                                
                                       30 min.                            
1.0%  sodium bicarbonate                                                  
      pH of liquor about 7.0                                              
      Leather cross section against                                       
      Bromocresol Green: Blue                                             
Rinsing                   to 60° C.                                
Dyeing                                                                    
100.0%                                                                    
      water                60° C.                                  
1.0%  Supranol Fast Brown 5R         45 min.                              
      (an acid-substantive dye)                                           
      Colour Index Acid Orange 51                                         
      diluted 1:20, two portions                                          
      every 10 min.                                                       
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 8.5%   of a sulfated neatsfoot-sperm oil                              
           mixture,                                                       
           Na salts,                 45 min.                              
           ratio about 2:1                                                
           AS about 85%                                                   
           org. bound SO.sub.3 about 5.5%                                 
(b) 8.5%   sulfated neatsfoot-sperm oil                                   
           mixture as under (a)                                           
    2.0%   product according to Example 2                                 
                                     45 min.                              
Total fat:                                                                
       9.1%, of which sulfonamide 1.4%                                    
       = about 15.4% sulfonamide                                          
        about 84.6% residual fat                                          
(c) 8.5%   sulfated neatsfoot-sperm oil                                   
           mixture as under (a)                                           
    2.2%   product according to Example 4                                 
                                     45 min.                              
Total fat:                                                                
       9.3%, of which sulfonamide 0.97%                                   
         = about 10.4% sulfonamide                                        
           about 89.6% residual fat                                       
*Fast synthetic neutralization tanning agent of Bayer AG                  
Feed in all fatting operations:                                           
1.0% formic acid (85%), diluted 1:5                                       
                             15 min.                                      
All leathers hung on racks overnight to dry                               
at about 30° C. - moisten, stake and stretch.                      
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     Determination of lightfastness in conformity with DIN 54 004 Lightfastness: 
     (a) About 3 
     (b) About 4 
     (c) About 3.5 
     The concurrent use of chloroalkane sulfonamide in fatting resulted in an increase of the lightfastness from 3 to 4, which is particularly difficult to achieve in this application. The concurrent use of the alkane sulfonamide described also produced a half-step improvement in lightfastness. 
     EXAMPLE 6 
     Preliminary operations up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing                                                                    
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Olive LC2G 150%       45 min.                              
      (1:2 metal-complex dye)                                             
      Colour Index Acid Green 99                                          
      diluted 1:20, two portions every 10 min.                            
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 8.5%   of a sulfated neatsfoot oil-sperm oil                          
           mixture, Na salts,        45 min.                              
           ratio about 2:1                                                
           AS about 85%                                                   
org. bound SO.sub.3 about 5.5%                                            
(b) 8.5%   sulfated neatsfoot oil-sperm oil mixture                       
           as under (a)                                                   
    2.0%   product according to Example 2                                 
                                     45 min.                              
Total fat:                                                                
       9.1%,   of which sulfonamide 1.4%                                  
               = about 15.4% sulfonamide                                  
                 about 84.6% residual fat                                 
(c) 8.5%   sulfated neatsfoot oil-sperm oil                               
           mixture as under (a)                                           
    2.2%   product according to Example 4                                 
                                     45 min.                              
Total fat:                                                                
       9.3%,   of which sulfonamide 0.97%                                 
               = about 10.4% amide                                        
                 about 89.6% residual fat                                 
Feed in all fatting operations:                                           
 1.0% formic acid (85%), diluted 1:5                                      
                             15 min.                                      
All leathers hung on racks overnight to dry at about 30° C. -      
moistening, staking and stretching.                                       
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     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 2 
     (b) About 4 
     (c) About 3 
     Particularly impressive in this dyeing operation is the increase in lightfastness from 2 to 4 produced by the concurrent use of chloroalkane sulfonamide. The alkane sulfonamide also resulted in a decided increase in lightfastness from 2 to 3. 
     EXAMPLE 7 
     Preliminary operations up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing                                                                    
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Red CB                45 min.                              
      (an acid-substantive dye)                                           
      Colour Index Acid Red 154                                           
      diluted 1:20, two portions every 10 min.                            
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 8.5%   of a sulfated neatsfoot oil-                                   
           sperm oil mixture, Na salts                                    
           ratio about 2:1                                                
           AS about 85%                                                   
           org. bound SO.sub.3 about 5.5%                                 
(b) 8.5%   sulfated neatsfoot oil-sperm oil                               
           mixture as under (a)                                           
    0.5%   product according to Example 1                                 
                                     45 min.                              
Total fat:                                                                
       7.7%,   of which sulfonamide 0.25%                                 
               = about 3.3% sulfonamide                                   
                about 96.7% residual fat                                  
(c) 8.5%   sulfated neatsfoot oil-sperm oil                               
           mixture as under (a)                                           
    0.5%   product according to Example 4                                 
                                     45 min.                              
Total fat:                                                                
       7.7%,   of which sulfonamide 0.22%                                 
               = about 2.8% sulfonamide                                   
                about 97.2% residual fat                                  
Feed in all fatting operations:                                           
 1.0% formic acid (85%), diluted 1:5                                      
                             15 min.                                      
All leathers hung on racks overnight to dry at about 30° C.        
moistening, staking, stretching.                                          
______________________________________                                    
 
    
     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 2 
     (b) About 3 
     (c) About 3 
     Even small amounts of the chloroalkaneamide or alkaneamide used produce a decided increase in the lightfastness of the coloration. 
     EXAMPLE 8 
     Preliminary operations up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing                                                                    
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Brown LC5G            45 min.                              
      (a 1:2 metal-complex dye)                                           
      Colour Index Acid Brown 324                                         
      diluted 1:20, two portions every 10 min.                            
Fatting in the dye bath:                                                  
Feed                                                                      
(a) 8.5%   sulfated sperm oil, Na salt                                    
                                     45 min.                              
           AS about 82%                                                   
           Org. bound SO.sub.3 about 6%                                   
(b) 8.5%   sulfated sperm oil, as under (a)                               
    1.5%   product according to Example 2                                 
                                     45 min.                              
Total fat:                                                                
       8.4%,   of which sulfonamide 1.0%                                  
               = 11.9% sulfonamide, rest fat                              
(c) 8.5%   sulfated sperm oil as under (a)                                
    1.5%   product according to Example 4                                 
                                     45 min.                              
Total fat:                                                                
       8.5%,   of which sulfonamide 0.7%                                  
               = about 8.23% sulfonamide, rest fat                        
Feed in all fatting operations:                                           
 1.0% formic acid (85%), diluted 1:5                                      
                             15 min.                                      
All leathers hung on racks overnight for drying at about 30° C. -  
moistening, staking, and stretching.                                      
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     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 2 to 3 
     (b) About 3 to 4 
     (c) About 3.5 
     The concurrent use of a chloroalkane sulfonamide in fatting with a sperm oil regarded as having good stability to light results in an increase in the lightfastness of the coloration by 1 step, and the concurrent use of an alkane sulfonamide by about half a step. 
     EXAMPLE 9 
     Preliminary steps up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing                                                                    
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Olive LC2G 150%       45 min.                              
      (a 1:2 metal-complex dye)                                           
      Colour Index Acid Green 99                                          
      diluted 1:20, two portions every 10 min.                            
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 10.0%  sulfated fish oil, NH.sub.4 salt                               
                                     45 min.                              
           AS about 55%                                                   
           Org. bound SO.sub.3 about 2.7%                                 
(b) 10.0%  sulfated fish oil, as under (a)                                
     2.0%  product according to Example 1                                 
                                     45 min.                              
Total fat:                                                                
       7.5%,   of which sulfonamide 1.0%                                  
               = about 13.3% sulfonamide                                  
                 about 86.7% residual fat                                 
(c) 10.0%  sulfated fish oil as under (a)                                 
     2.0%  product according to Example 4                                 
                                     45 min.                              
Total fat:                                                                
       7.44%,  of which sulfonamide 0.88%                                 
               = about 11.8% sulfonamide                                  
                 about 88.2% residual fat                                 
1.0% formic acid (85%), diluted 1:5                                       
All leathers hung on racks overnight for drying at about 30° C. -  
moistening, staking, and stretching.                                      
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     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 2 
     (b) About 3 to 4 
     (c) About 3 
     The lightfastness of the dyed leather is substantially increased also in fatting with &#34;yellowing&#34; fatting agents such as sulfated fish oil. 
     EXAMPLE 10 
     Preliminary steps up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing                                                                    
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Brown LC5G            45 min.                              
      (a 1:2 metal-complex dye)                                           
      Colour Index Acid Brown 324                                         
      diluted 1:20, two portions every 10 min.                            
Fatting in the dye bath:                                                  
 Fatting with a fatting agent for soft leathers based on:                 
Feed:                                                                     
(a) 8.5% of a mixture of                                                  
40.0%      sulfated fish oil as in Example 9 (a)                          
45.0%      mineral oil                                                    
15.0%      chloroalkane sulfonate, NH.sub.4 salt                          
                                 45 min.                                  
           AS about 90%                                                   
           Org. bound SO.sub.3 about 2.0%, based                          
           on total mixture.                                              
(b) 8.0%   fatting agent as under (a)                                     
    1.0%   product according to Example 2                                 
                                     45 min.                              
Total fat:                                                                
       7.3%,   of which sulfonamide 0.7%                                  
               = about 9.6% amide                                         
                 about 90.4% residual fat                                 
(c) 8.0%   fatting agent, as under (a)                                    
    1.0%   product according to Example 4                                 
                                     45 min.                              
Total fat:                                                                
       7.4%,   of which sulfonamide 0.44%                                 
               = about 6% amide                                           
                 about 94% residual fat                                   
Feed in all fatting operations:                                           
1.0% formic acid (85%), diluted 1:5                                       
                             15 min.                                      
All leathers hung on racks overnight for drying at about 30° C. -  
moistening, staking, and stretching.                                      
______________________________________                                    
 
    
     Determination of lightfastness in conformity with DIN 54 004: 
     Lightfastness: 
     (a) About 3 
     (b) About 4 to 5 
     (c) About 4 
     The improvement in lightfastness due to the concurrent use of chloroalkane or alkane sulfonamides is substantial. This is all the more remarkable as the fatting agent contains substantial amounts of fish oil. 
     Finally, fatting agents based on alkane sulfonates and chloroalkane sulfonates, which are regarded as highly stable to light, were included in the test series. 
     EXAMPLE 11 
     Preliminary steps up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing:                                                                   
100.0%                                                                    
      water                  60° C.                                
1.0%  Supranol Fast Brown 5R         45 min.                              
      (an acid-substantive dye)                                           
      Colour Index Acid Orange 51                                         
      diluted 1:20, two portions every 10 min.                            
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 11.0%  alkane sulfonate, Na salt 45 min.                              
           Chain length: C.sub. 20 to C.sub.30                            
           AS about 60%                                                   
           Org. bound SO.sub.3 about 6%                                   
(b) 11.0%  alkane sulfonate, as under (a)                                 
     2.0%  product according to Example 2                                 
                                     45 min.                              
Total fat:                                                                
       8.56%,  of which sulfonamide 1.4%                                  
               = 16.4% sulfonamide                                        
                 83.6% residual fat                                       
Feed in all fatting operations:                                           
 1.8% formic acid (85%), diluted 1:5                                      
                             15 min.                                      
All leathers hung on racks overnight for drying at about 30° C. -  
moistening, staking, and stretching.                                      
______________________________________                                    
 
    
     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 3 
     (b) About 4 
     In this case, too, the concurrent use of chloroalkane sulfonamide resulted in a substantial improvement in the lightfastness of the coloration. 
     EXAMPLE 12 
     Preliminary steps up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing:                                                                   
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Olive LC2G 150%       45 min.                              
      (a 1:2 metal-complex dye)                                           
      Colour Index Acid Green 99                                          
      diluted 1:20, two portions every 10 min.                            
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 11.0%  alkane sulfonate, Na salt 45 min.                              
           Chain length: C.sub.20 to C.sub.30                             
           AS about 60%                                                   
           org. bound SO.sub.3 about 6%                                   
(b) 11.0%  alkane sulfonate, as under (a)                                 
     2.0%  product according to Example 2                                 
                                     45 min.                              
Total fat:                                                                
       8.5%,   of which 1.4% sulfonamide                                  
               = about 16.5% sulfonamide                                  
                 about 83.5% residual fat                                 
Feed in all fatting operations:                                           
 1.0% formic acid (85%), diluted 1:5                                      
                             15 min.                                      
All leathers hung on racks overnight to dry at about 30° C. -      
moistening, staking, and stretching.                                      
______________________________________                                    
 
    
     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 3 
     (b) About 4 
     In this dyeing operation, too, the chloroalkane sulfonamide produced a substantial increase in lightfastness, especially considering that the jump from step 3 to step 4 is big. 
     EXAMPLE 13 
     Preliminary steps up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing:                                                                   
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Brown LC5G            45 min.                              
      (a 1:2 metal-complex dye)                                           
      Colour Index Acid Brown 324                                         
      diluted 1:20, 2 portions every 10 min.                              
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 7.5%   chloroalkane sulfonate, Na salt                                
                                     45 min.                              
           Chain length: C.sub.16 to C.sub.22                             
           AS about 90%                                                   
           Chlorine content of alkane, about 20 wt. %                     
           Org. bound SO.sub.3 about 10%                                  
(b) 7.5%   chloroalkane sulfonate, as under (a)                           
    3.0%   product according to Example 3                                 
                                     45 min.                              
Total fat:                                                                
       9.25%,  of which 0.6% sulfonamide                                  
               = about 6.5% sulfonamide                                   
                 about 93.5% residual fat                                 
Feed in all fatting operations:                                           
 1.0% formic acid (85%), diluted 1:5                                      
All leathers hung on racks overnight to dry at about 30° C. -      
moistening, staking, and stretching.                                      
______________________________________                                    
 
    
     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 4 
     (b) About 5 
     In this dyeing operation, too, the concurrent use of chloroalkane sulfonamide resulted in an increase in lightfastness. 
     EXAMPLE 14 
     Preliminary steps up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing                                                                    
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Olive LC2G 150%       45 min.                              
      (1:2 metal-complex dye)                                             
      Colour Index Acid Green 99                                          
      diluted 1:20, 2 portions every 10 min.                              
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 10.0%  sulfated fish oil, Na.sub.4 salt                               
                                       45 min.                            
           AS about 55%                                                   
           Org. bound SO.sub.3 about 2.7%                                 
(b) 10.0%  sulfated fish oil, as under (a)                                
           Fresh liquor: 100%    60° C.                            
                                       45 min.                            
     1.0%  chloroalkane sulfonamide                                       
           according to Example 1 plus                                    
     2.0%  nonylphenol hydroxyethylate × 9                          
Total fat:                                                                
       8.5%,   of which sulfonamide 0.5%                                  
               = about 6% sulfonamide                                     
                 about 94% residual fat                                   
(a) 10.0%  sulfated fish oil, as under (a)                                
           Fresh liquor: 100%    60° C.                            
                                       20 min.                            
     1.0%  alkane sulfonamide according                                   
           to Example 4                                                   
Total fat:                                                                
       6.5%,   of which sulfonamide 0.44%                                 
               = about 7% sulfonamide                                     
                 about 93% residual fat                                   
Feed in all fatting operations:                                           
 1.0% formic acid (85%), diluted 1:5                                      
                             15 min.                                      
All leathers hung on racks overnight to dry at about 30° C. -      
moistening, staking, and stretching.                                      
______________________________________                                    
 
    
     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 2 
     (b) About 3 to 4 
     (c) About 3 to 4 
     This example illustrates the treatment with the additives in accordance with the invention which improve lightfastness in a separate stage following fatting, in other words, in a separate liquor. 
     EXAMPLE 15 
     Preliminary steps up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
Dyeing                                                                    
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Olive LC2G 150%       45 min.                              
      (a 1:2 metal-complex dye)                                           
      Colour Index Acid Green 99                                          
      diluted 1:20, 2 portions every 10 min.                              
Fatting in the dye bath:                                                  
Feed:                                                                     
(a) 10.0%  sulfated fish oil, NH.sub.4 salt                               
                                     45 min.                              
           AS about 55%                                                   
           Org. bound SO.sub.3 about 2.7%                                 
(b) 10.0%  sulfated fish oil, as under (a)                                
     2.0%  product according to Example 1                                 
                                     45 min.                              
Total fat:                                                                
       7.5%, of which 0.5% sulfonamide                                    
       = about 6.7% sulfonamide                                           
         about 93.3% residual fat                                         
(c) 10.0%  sulfated fish oil, as under (a)                                
     1.0%  product according to Example 1                                 
     1.0%  product according to Example 4                                 
Total fat:                                                                
       7.5%,   of which 0.94% sulfonamide                                 
               = about 12.5% sulfonamide                                  
                 about 87.5% residual fat                                 
Feed in all fatting operations:                                           
 1.0% formic acid (85%), diluted 1:5                                      
All leathers hung on racks overnight to dry at about 30° C. -      
moistening, staking, and stretching.                                      
______________________________________                                    
 
    
     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 2 
     (b) About 3 to 4 
     (C) About 3 to 4 
     This example illustrates the use of a combination of alkane sulfonamide and chloroalkane sulfonamide in the ratio of 1:1. 
     EXAMPLE 16 
     Preliminary steps up to the dyeing operation as in Example 5. 
     
         ______________________________________                                    
 (a) Dyeing:                                                              
100.0%                                                                    
      water                  60° C.                                
1.0%  Baygenal Brown LC5G                                                 
      (a 1:2 metal-complex dye)                                           
      Colour Index Acid Brown 324                                         
      diluted 1:20, 2 portions every 10 min.                              
                                      5 min.                              
Rinsing                      60° C.                                
100.0%                                                                    
      water                                                               
8.5%  of a sulfated neatsfoot oil-                                        
      sperm oil mixture, Na salts    45 min.                              
      as described in Example 6                                           
Feed:                                                                     
1.0%  formic acid (85%), dilute 1:5  15 min.                              
 (b) Dyeing:                                                              
As under (a)                                                              
Pretreatment in dye bath:                                                 
0,5%  chloroalkane sulfonamide according                                  
      to Example 1 plus                                                   
1.0%  nonylphenol hydroxyethylate × 9                               
                                 15 min.                                  
Total fat:                                                                
        8.7%,   of which 0,25% sulfonamide                                
                = about 3% sulfonamide                                    
                  about 97% residual fat                                  
Rinsing                  60° C.                                    
                                  5 min.                                  
Fatting:                                                                  
100.0%                                                                    
      water                  60° C.                                
8.5%  of a sulfated neatsfoot oil-                                        
      sperm oil mixture, Na salts    45 min.                              
      as described in Example 6                                           
Feed:                                                                     
1.0%  formic acid (85%), diluted 1:5  5 min.                              
All leathers hung on racks overnight to dry at about 30° C. -      
moistening, staking, and stretching.                                      
______________________________________                                    
 
    
     Determination of lightfastness in conformity with DIN 54 004: Lightfastness: 
     (a) About 3 
     (b) About 4.5 
     The lightfastness of the coloration is substantially improved when the leather is made to undergo a pretreatment with chloroalkane sulfonamide. 
     It will be appreciated that the instant specification, examples and claims are set forth by way of illustration and not limitation and that various changes and modifications may be made without departing from the spirit and scope of the present invention.