Aromatic sulphonation. Part XLVI. Isomer distributions in the sulphonation of acenaphthene and its 3- and 5-sulphonic acids with sulphuric acid

Abstract

The sulphuric acid sulphonation of acenaphthene and its mono- and di-sulphonic acids has been investigated. The kinetic isomer distribution for sulphonation in 95·2% H₂SO₄ at 25° is for acenaphthene 68 ± 14% 3- and 32 ± 14% 5-substitution, for acenaphthene-3-sulphonic acid 6 ± 2% 5-, 66 ± 4% 6-, and 28 ± 3% 8-substitution, and for acenaphthene-5-sulphonic acid 28 ± 3% 3- and 72 ± 3% 8-substitution. The relatively high degree of substitution adjacent to the ethylene bridge is explained in terms of an electrostatic proximity effect. The pseudo-first-order rate constants for sulphonation of the 3,5-, 3,6-, and 3,8-disulphonic acids in the reaction mixtures, i.e. in ca. 94% H₂SO₄, at 25° are (6 ± 2)× 10³, (1·9 ± 0·2)× 10³, and (2·4 ± 0·3)× 10³ s^–1, respectively.