Alpha- naphthol prodn. from naphthalene - by sulphonation with sulphuric acid in the presence of acetic anhydride, reaction with molten alkali, and neutralisation with mineral acid

摘要

In a new process for the prodn. of alpha-naphthol, (a) naphthalene is sulphonated with conc. H2SO4 at 30-85 degrees C for 60-120 mins. in the presence of acetic anhydride in an amount of 0.5-1.5 mol per mol naphthalene; (b) the resulting 1-naphthalenesulphonic acid is melted 10-30 mins. at 180-285 degrees C with 3-4 molar proportions of alkali; (c) the resulting melt (consisting of alkali alpha-naphthalate and alkali sulphite) is mixed with a polar solvent and the resulting mixture is acidified with a mineral acid in an amount equivalent to the alkali alpha-naphthalate; and (d) alpha-naphthol is separated off from the resulting suspension. alpha-Naphthol is useful as an antioxidant for mineral and vegetable oils. It is also useful as an intermediate for azo dyestuffs and for the insecticide 1-naphthalyl N-methyl-carbamate. The yield of crystalline alpha-naphthol of 99.5% purity is 0.7-0.8 mol per mol naphthalene. The content of beta-naphthol is is not >0.5wt.%. Working up of the mother liquor gives further alpha-naphthol of purity 95-98% (contg. 2-5wt.% beta-naphthol) giving an overall yield of 95-98%. All steps of the process are carried out in homogeneous phase, and H2SO4 and alkali consumption are minimised.