GB538266A - Manufacture of azo pigments - Google Patents

Abstract

538,266. Organic pigments. TWITCHETT, H. J., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. Oct. 24, 1939, No. 28577. [Class 2 (iii)] The azo pigment, 3-nitro-4-aminotoluene # #-naphthol, is modified to obtain a product of a yellower shade of scarlet and of a greater tinctorial strength by effecting the coupling under such conditions that the azo pigment, 2-chloro-4-nitroaniline - #-naphthol is present in the alkaline coupling medium either during the coupling or immediately thereafter, the second diazo component being used in an amount of 5 to 40 per cent. of the total amount of the two diazo components. In examples, (1) a mixture of the two diazo solutions is added slowly to a solution at 5‹C. of #-naphthol in a dilute solution of sodium hydroxide and sodium carbonate and, after stirring, the precipitate is filtered off, washed and dried; (2) a solution of diazotized 3-nitro-4-aminotoluene is added slowly to a similar solution of #-naphthol, immediately thereafter a solution of diazotized 2-chloro-4-nitroaniline is added slowly and, after stirring, the precipitate is filtered off, &c. as in (1) ; (3) the order of the addition of the two diazo solutions in (2) is reversed ; (4) the solutions of diazotized 3-nitro- 4-aminotoluene and diazotized 2-chloro-4-nitroaniline are added separately and simultaneously to 85 and 15 per cent. respectively of the #- naphthol solution, the resulting suspensions are immediately mixed and stirred and the precipitate is filtered off, &c. as in (1) ; (5) the two diazo components are mixed, the mixture is diazotized, the mixed diazo solution is added slowly to the #-naphthol solution and after stirring, the precipitate is filtered off, &c. as in (1), Specification 517,456 is referred to.