GB777481A - Process for the preparation of aromatic sulphamic acids - Google Patents

Abstract

A process for the preparation of 4-aminodiarylamino-N4-sulphonic acids comprises reacting a 4-nitroso-diarylamine with one or more salts of sulphurous acid in the absence of caustic alkali and in a medium capable of dissolving at least partially one of the said starting materials. The medium is considered to be free from caustic alkali if the totality of salts and other ionizable products which it contains includes fewer basic chemical equivalents in weight coming from alkali metals than acid chemical equivalents in weight, the initial nitroso derivative not being reckoned as an acid. Where alkali metal salts of sulphurous acid are used it is advantageous to use a trisulphite eventually mixed with a sulphite to change the pH of the medium or another alkali metal salt may be added provided caustic alkalinity is not introduced. Sulphurous acid salts of nitrogenous bases which may be used are those of ammonia, aliphatic, primary, secondary or tertiary amines such as mono-, di- and trimethylamine, diethylamine, aromatic amines such as aniline, heterocyclic bases such as pyridine, its homologues or technical mixtures thereof. Nitrogenous compounds may be added to the reaction medium such as the above bases and amides such as formamide. A mixture of an alkali metal and a salt of a nitrogenous base with sulphurous acid may be employed. Organic solvents such as methyl, ethyl, propyl and butyl alcohols may be employed in the reaction medium and water and an organic solvent either miscible or substantially immiscible with water may be employed. p-Nitrosated diaryl-amines mentioned as starting materials include 4-nitrosodiphenylamine, 4 - nitroso - 3:31 - dimethyl - diphenylamine, 4-nitroso-3-methoxy diphenylamine and 4-nitroso-41-methoxy-diphenylamine. In examples: the sodium salt of 4-amino-diphenylamino - N4 - sulphonic acid is obtained by heating 4-nitroso-phenylaminobenzene with an aqueous ethanol solution of ammonium sulphite, treating the product with sodium carbonate and distilling off the alcohol and part of the water and salting out the product; a similar result is obtained using diethylamine sulphite (I); the sodium salt of 4-amino-diphenylamino-N4-sulphonic acid is obtained by heating 4 - nitroso - phenylamino - benzene with an aqueous solution of sodium bisulphite, ammonia and pyridine and isolating the desired product as in (1); sodium salts of 4-amino-3: 31-dimethyl - diphenylamino - N4 - sulphonic acid, 4 - amino - 3 - methoxy - diphenylamino - N4-sulphonic acid and 4 - amino - 41 - methoxy - diphenylamino-N4-sulphonic acid are similarly obtained, the products being hydrolysed and acetylated to obtain 4-acetylamino derivatives of 3:31-diphenylamine, 3-methoxy-diphenylamine and 41-methoxydiphenylamine (2); 4-amino - diphenylamino - N4 - sulphonic acid is obtained as the sodium salt by heating 4-nitrosodiphenylamine with an aqueous ethanol solution of sodium bisulphite (3); the sodium salt of 4 - amino - diphenylamino - N4 - sulphonic acid is obtained by heating 4-nitroso-diphenylamino with an aqueous solution of ammonium sulphite and pyridine or formamide and working up the product as above (4); and the sodium salt of 4 - amino - diphenylamino - N4 - sulphonic acid is obtained by heating 4-nitroso-diphenylamine with a boiling suspension of ammonium sulphite monohydrate in absolute alcohol or an azeotropic mixture of water and alcohol and working up the product as before (5). The products are employed in preparing oxidation dyestuffs on the fibre.