GB462465A - Manufacture of methyl-aminonaphthalene-sulphonic acids - Google Patents

Abstract

1 - Methyl - 4 - aminonaphthalene - 2 - sulphonic acid and 1-methyl-4-aminonaphthalene-7-sulphonic acid are prepared by subjecting 1-methyl-4-aminonaphthalene to the action of a sulphonating agent and separating by fractional crystallization of the alkali salts the two sulphonic acids which are formed. The preferred sulphonating agent is concentrated sulphuric acid. In examples: (1) 1-methyl-4-amino-naphthalene is added slowly to strong sulphuric acid at 120 DEG C. and then heated for one hour at 150 DEG C. The product which is poured into ice water, filtered and dried, consists of 65 per cent of the -2-sulphonic acid and 35 per cent of the -7-sulphonic acid. If the heating is carried on for a longer time at a lower temperature, a larger amount of the -2-sulphonic acid is obtained; (2) the product of example (1) is neutralized with caustic soda, and the sodium salt of the 1-methyl-4-amino-naphthalene-7-sulphonic acid is precipitated by the addition of sodium chloride; (3) 1-methyl-4-aminonaphthalene is added to concentrated sulphuric acid so slowly that the temperature does not rise above 50 DEG C., whereupon fuming sulphuric acid is added slowly and the mixture heated at 100 DEG C. for one hour. The product is worked up as in example (1); (4) 1-methyl-4-aminonaphthalene is added to sulphuric acid as in example (3) and chlorosulphonic acid added slowly and heated to 100 DEG C. The product is worked up as in example (1). Both the sulphonic acids are crystalline. The -7-acid yields a blue colour with ferric chloride, whereas the -2-acid does not.