GB771578A - Improvements in the preparation of aromatic sulphamic acids - Google Patents

Abstract

Aryl sulphamic acids are prepared by the action on a primary or secondary aromatic amine of a sulphonating agent consisting of the addition product of sulphuric anhydride, chlorsulphonic acid, an alkyl chlorosulphonate or pyrosulphuryl chloride and a pyridine base having at least one methyl group in the ortho position to the nitrogen atom or a mixture of such bases or a mixture of tertiary bases, the major proportion of which consists of one or more of the above-mentioned pyridine bases. Pyridine bases specified are 2-methyl- or 2 : 6-dimethyl-pyridine and mixtures thereof. The aromatic amines may be nuclearly substituted by halogen atoms or by alkyl, alkoxy, nitro, sulphonamido or carboxylic amide groups and those mentioned are 2 : 4- and 2 : 6-dinitro-aniline and 4-nitro-diphenyl. The effective sulphonating agent is stated to be the anhydrosulphonate of the pyridine base. The sulphonation may be conducted by adding the amine to the sulphonating reagent previously prepared by adding the sulphur-containing compound to the pyridine base. When the nitroarylamines mentioned are sulphonated the reaction may be conducted at slightly elevated temperatures, and the product is isolated by pouring the reaction mixture into aqueous sodium carbonate, steam distilling off the pyridine base, filtering off any unreacted amine and separating the sodium salt of the sulphamic acid by cooling or salting-out the filtrate. Examples are given.