Aromatic sulphonation. Part 77. Sultone and 1,3,2,4-dioxadithian 1,1,3,3-tetraoxide formation in the sulphonation of 3-phenylpropan-1-ol

Abstract

Reaction of 3-phenylpropan-1-ol (1) in concentrated sulphuric acid leads initially to the formation of mainly 3-(p-sulphophenyl)propyl hydrogensulphate (3a) and ca. 12% of the ortho-isomer (3b). Compound (3a) is slowly converted into the geometrically isomeric dioxadithian tetraoxides (6a) and (7a) which eventually yield (E)-1-(p-sulphophenyl)prop-1-ene-2-sulphonic acid (4a). Compound (3b) eventually yields via the sultone (8), a detectable and isolable intermediate and the dioxadithian tetraoxides (6b) and (7b). Reaction of (1) with SO₃ in nitromethane leads to the formation of the para-sulpho isomer (3a) which is slowly converted into (6a) and (7a) as stable products in the reaction system. Mechanisms for the formation of the various products in the two sulphonating systems are proposed, and the differences in mechanism discussed.