Aromatic sulphonation. Part 78. Behaviour of some α-chloro-substituted 9-methyl-, 9-ethyl-, 9-isopropyl-anthracenes, and of 1,4,9-trimethylanthracene in dioxan–sulphur trioxide complex in dioxan as sulphonating medium

Abstract

The reaction of some α-chloro-substituted 9-methyl-, 9-ethyl-, 9-isopropyl-anthracenes and of 1,4,9-trimethyl-anthracene (3a–j), with dioxan–SO₃ in dioxan has been studied at 25 °C. All the methylanthracene derivatives (3a–d) yield α-sulphonic acids (4a–d). 1,5-Dichloro-9-methyl- and 1,4,9-trimethyl-anthracene yield, in addition, the dimer (5c) and the sultones (6l and m) respectively.

1-Chloro- and 1,5-dichloro-9-ethylanthracene yield the dimers (5e) and (5f) respectively. 4-Chloro-9-ethylanthracene yields the two sulphonic acids (4g) and (7g). 4,5-Dichloro-9-ethylanthracene does not react. 1-Chloro- and 1,5-dichloro-9-isopropylanthracene yield besides the dimeric products (5) and the sulphonic acids (9), products corresponding with those obtained in the sulphonation of 9-isopropylanthracene [viz. sultones (8), 9-allylanthracene derivatives (10), and the sulphonic acids (11) and (12)]. A mechanism for the formation of the products is presented. It is proposed that the dimeric products (5) and the sultone (6d) result from initial attack of SO₃ at C-9 and C-1 respectively, whereas all other products result from attack of SO₃ at C-10. The behaviour of the substrates (3a–j) in the sulphonation is compared with that in their protonation.