the invention comprises a bunte salt azo dye compound capable of causing coloration of fibers such as textile fibers and animal fibers such as wool , leather , and animal hair ( excluding human hair ), and a dye composition containing the bunte salt azo dye compound . although bunte salt dyes have been employed in dyeing fibers , the use of such dyes , particularly for dyeing animal hair has required the pretreatment of the material to be dyed in order for the dye to perform effectively . examples of combining such reducing or mordanting steps with application of bunte salt dyes to fibers can be found in u . s . pat . no . 5 , 071 , 641 . unlike the prior art bunte salt azo type dyes which are generally employed to dye fibers such as animal hair , the bunte salt group of the present invention is in a para position relative to the azo bond , attached directly to a connecting benzene ring of a phenylamino radical without an intervening carbon or oxygen atom . it is believed that the proximity of the para - bunte salt group to the azo bond is a critical factor in eliminating the requirement for the mordanting or reducing step . in addition , such conventional bunte salt azo dyes generally have at least one carbon atom between the bunte salt group and the benzene ring adjoining the azo bond . the bunte salt azo dyes of the present invention are prepared by diazotization of the s -( 4 - amino phenyl ) thiosulfate by reacting the primary aromatic amine with sodium nitrite in the presence of a mineral acid such as hydrochloric acid to form a diazonium salt , followed by a coupling of the diazonium salt under alkaline conditions ( at a ph from about 8 to about 10 ) with a salt of an aryl amino hydroxy naphthalene sulfonic acid , such as phenyl j - acid or phenyl gamma - acid . phenyl j - acid is a term of the dye art referring to a compound having the molecular formula c 16 h 13 no 4 s such as 2 - phenylamino - 5 - naphthol - 7 - sulfonic acid , or 6 - phenylamino - 1 - naphtol - 3 - sulfonic acid . phenyl gamma - acid is a term of the dye art referring to a compound having the molecular formula c 16 h 13 no 4 s such as 2 - phenylaminonaphthalene - 8 - hydroxy - 6 - sulfonic acid . the critical aspect of the process of the present invention is to provide a bunte salt azo dye which includes an azo group having at least one bunte salt group in a para position on a benzene ring relative to the azo group attached to that benzene ring . the use of the sodium s -( 4 - amino - phenyl )- thiosulfate as the starting material results in the bunte salt group being para to the azo bond in the molecule . the invention further comprises a method for coloring keratin fiber such as animal hair including wool and other animal fur comprising directly applying an aqueous based hair dye composition comprising a bunte salt azo dye compound , without a reducing agent , to animal hair for a period of time sufficient to cause coloration of the animal hair . it was surprisingly discovered that a reducing agent was not required to assist the dye in bonding to the animal hair . the composition is applied to the animal hair and allowed to remain on the hair for about 5 to 50 minutes , depending on the type and texture of the animal hair . the animal hair is then rinsed well with water to remove the composition . the compositions of the present invention are very gentle to the animal hair because they do not require the use of reducing agents to pre - treat the animal hair before the dye is applied . this application method is similar to that described in u . s . pat . no . 3 , 415 , 606 ( example 1 ), but without the mordanting pretreatment with thioglycolic acid solution . it was noted in u . s . pat . no . 3 , 415 , 606 that hair which had not been subjected to the mordanting pretreatment only dyed very slightly in this manner . the invention will be further described in connection with the following examples which are set forth for the purposes of illustration only . in an 800 ml beaker , 20 . 5 grams of sodium s -( 4 - aminophenyl ) thiosulfate ( prepared as described in u . s . pat . no . 3 , 562 , 246 ) was diazotized in the conventional manner by adding sodium s -( 4 - aminophenyl ) thiosulfate to 325 ml of 2 . 8 % hydrochloric acid , cooling the mixture to & lt ; 5 ° c . by the direct addition of ice , then adding 18 . 1 grams of a 40 % aqueous solution of sodium nitrite . the resulting diazo slurry was then added to the solution made in a 2000 ml beaker from 400 ml of water , 37 . 7 grams of phenyl j - acid , and 9 . 2 grams of sodium carbonate . the addition of the diazo slurry was made while maintaining the temperature at about 7 ° c . by the direct addition of ice , and maintaining the ph of the composition at about 8 by the addition of 20 % aqueous sodium carbonate . the composition was then stirred 16 hrs , while allowing the temperature to rise to about 20 ° c . the dye was salted out with about 90 grams of sodium chloride , filtered , washed with about 1000 ml of 20 % aqueous sodium chloride , dried , and ground , yielding about 34 g of dye powder . was prepared as described in example 1 , except that 37 . 7 grams of phenyl gamma - acid was substituted for the phenyl j - acid . the dye prepared in example 1 was applied to virgin yak hair in the manner described below : a bundle of virgin yak hair ( weighing about 3 grams ) was immersed in a 150 ml beaker containing 75 ml of a 3 % slurry of the dye in water , which had been adjusted to ph 9 with aqueous ammonia . the immersion was carried out for 30 minutes at ambient temperature . the yak hair bundle was removed and rinsed thoroughly with ambient temperature water , then dried . the yak hair was dyed a strong red color ( cielab de = 50 . 11 vs . the originally undyed yak hair ). the cielab de is the total color difference between the dyed sample and a standard , in this case the undyed hair or fiber , as measured by a datacolor spectraflash 600 reflectance spectrophotometer . the cielab de reading provides a measure of the dye uptake on the fibers . the dyed yak hair prepared in example 3 was washed at 25 ° c . with a 1 % solution of a generic shampoo containing ammonium lauryl sulfate and ammonium laureth sulfate ( suave , a trademark of helene curtis , naturals fresh mountain strawberry ), then rinsed thoroughly with water at a temperature of 25 ° c . this was repeated 5 times . a minor amount of color loss was seen ( reflectance strength = 86 % compared to the dyed hair of example 3 ). the dye prepared in example 1 was applied to cotton in the manner described below : a swatch of mercerized cotton fabric ( weighing about 3 grams ) was immersed in a 400 ml beaker containing 200 ml of a 3 % slurry of the dye in water and about 0 . 05 g of sandopan dtc - 100 . this mixture was heated to 90 ° c . for 5 minutes , after which time the mixture was cooled to 50 ° c . the fabric was removed and rinsed thoroughly with water at ambient temperature . the cotton had been dyed a strong red color ( cielab de = 75 . 8 vs . the originally undyed cotton fabric ). the dye prepared in example 1 was applied to nylon in the manner described below . a swatch of nylon fabric ( weighing about 3 grams ) was immersed in a 400 ml beaker containing 200 ml of a 3 % slurry of the dye in water , 2 . 0 g of acetic acid , and 4 . 0 g of sodium acetate . this mixture was heated to the boil for 10 minutes , after which time the mixture was cooled to 50 ° c . the fabric was removed and rinsed thoroughly with water at ambient temperature . the nylon had been dyed a strong red color ( cielab de = 83 . 8 vs . the undyed nylon fabric ). the dye prepared in example 1 was applied to wool , in the manner described below . a swatch of wool fabric ( weighing about 3 grams ) was immersed in a 400 ml beaker containing 200 ml of a 0 . 03 % solution of the dye in water , 6 . 0 g of sulfuric acid , and 20 . 0 g of sodium sulfate . this mixture was heated to the boil for 10 minutes , after which time the mixture was cooled to 50 ° c . the fabric was removed and rinsed thoroughly with water at ambient temperature . the wool had been dyed a strong red color ( cielab de = 73 . 6 vs . the undyed wool fabric ).
the invention relates to a bunte salt azo dye composition comprising an azo dye containing at least one bunte salt group . the resulting dye is water soluble material which is useful in the rapid dying of natural and synthetic fibers . the bunte salt azo dye of the present invention can be used without requiring a mordanting step or a concurrent or pre - reducing step to condition fibers of animal hair to accept the dye to achieve strong color performance .