Process for the isolation of 1-naphthylamine-4,8-disulphonic acid

摘要

Process for the isolation of 1-naphthylamine-4,8-disulphonic acid from sulphonation mixtures containing it according to which process the sulphonation mixture is introduced into preheated water in such a manner that, at the start of crystallization, a temperature of at least 100 DEG C. is reached and the 1-naphthylamine-4,8-disulphonic acid is separated from the mother liquor at a temperature not higher than 70 DEG C. The process is applied particularly advantageously for the isolation of 1-naphthylamine-4,8-disulphonic acid from sulphonation mixtures which have been obtained by introducing in turns alkali metal sulphate, 1-naphthylamine-8-sulphonic acid and SO3 into sulphuric acid which has been introduced initially, a total of 1.5 to 3 mols of SO3 and 0.6 to 1.5 mols of alkali metal sulphate being employed per mol of 1-naphthylamine-8-sulphonic acid.