Aromatic sulphonation. Part 72. Behaviour of some 9-alkylanthracenes containing 2 α-hydrogens and 0–3 β-hydrogens in the side-chain with dioxan–sulphur trioxide in dioxan as sulphonating medium; mechanism for alkyl side-chain reduction and subsequent sulphonation

Abstract

The reactions at 17 °C of seven 9-alkylanthracenes, with two alkyl α-hydrogens, with dioxan–SO₃ in dioxan has been studied. With the exception of 9-ethyl- and 9-neopentyl-anthracene these substrates yield products having a side-chain structure with (i) the sulphonate group at C-α(α-sulphonic acids) and/or (ii) a double bond at C-α with the sulphonate group at C-γ(α-alkene-γ-sulphonic acids). 9-Ethylanthracene yields, besides the α-sulphonic acid, an α-alkene-β-sulphonic acid, whereas 9-neopentylanthracene leads to sulphonation of the anthryl group at the 10- and 4-positions. It is proposed that the α-sulphonic acids are formed as suggested for the formation of 9-anthrylmethanesulphonic acid from 9-methylanthracene, and that the α-alkene-γ-sulphonic acids are produced by sulphonation of 9-(alk-1-enyl)anthracenes, which intermediates result from a redox reaction between the 9-alkylanthracenes and SO₃.