Abstract: 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.degree. C. is reached and the 1-naphthylamine-4,8-disulphonic acid is separated from the mother liquor at a temperature not higher than 70.degree. 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 SO.sub.3 into sulphuric acid which has been introduced initially, a total of 1.5 to 3 mols of SO.sub.3 and 0.6 to 1.5 mols of alkali metal sulphate being employed per mol of 1-naphthylamine-8-sulphonic acid.

Abstract: 3-Hydroxybenzoic acid is obtained by reaction with an alkali metal hydroxide at a temperature of 220.degree. to 450.degree. C. and under a pressure of 1 to 120 bars, from a technical 3-sulphobenzoic acid mixture which contains sulphuric acid and/or sulphur trioxide and which contains at least 75% by weight of 3-sulphobenzoic acid, relative to the total organic constituents present, and not more than 35% by weight of sulphuric acid and/or SO.sub.3, relative to the total mass. For this purpose, this technical 3-sulphobenzoic acid mixture, if desired after dilution with an equal volume of water, is mixed with sufficient 50 to 100% strength by weight alkali metal hydroxide wherein the remaining 50 to 0% by weight consists essentially of water, for 2.5 to 8 mols of alkali metal hydroxide to be present per mol of 3-sulphobenzoic acid, after neutralization of the sulphuric acid and all the sulpho and carboxyl groups. In general, 10 to 45% by weight of water are present in the batch.

Abstract: A process for the preparation of an alkali metal salt of 3-hydroxybenzoic acid and the preparation of 3-hydroxybenzoic acid therefrom is disclosed wherein sulphophthalic acid or a salt thereof is reacted with an alkali metal hydroxide at a temperature in the range of 200.degree. to 300.degree. C. at a pressure of 10 to 30 bars.

Abstract: Improved process for the preparation of 1-naphthylamine-4,6-disulphonic acid wherein the sulphonation of the 1-naphthylamine-6-sulphonic acid is carried out by adding the oleum at a temperature of 10.degree. to 70.degree. C., either to initially introduce sulphuric acid simultaneously with the 1-naphthylamine-6-sulphonic acid or to 1-naphthylamine-6-sulphonic acid, which is dissolved or suspended in sulphuric acid, and by using such a molar ratio of sulphur trioxide to 1-naphthylamine-6-sulphonic acid that 1.2 to 3 mols of sulphur trioxide are present per mol of 1-naphthylamine-6-sulphonic acid. The sulphonation mixture formed in the preparation can be sulphonated in a second sulphonation stage to 1-naphthylamine-2,4,6-trisulphonic acid.