Aromatic sulphonation. Part 55. Reaction of polyisopropylbenzenes with concentrated aqueous sulphuric acid

Abstract

The reaction of a number of polyisopropylbenzenes, mainly with 98.4% H₂SO₄ at 25°, has been studied. m- and p-di-isopropylbenzene undergo sulphonation; no side reactions have been observed. 1,2,3-Tri-isopropylbenzene with ClSO₃H in CCl₄ at 0° yielded 80% 2,4,6-tri-isopropylbenzenesulphonyl chloride and small amounts of the 2,4,5-isomer. 1,3,5-Tri-isopropylbenzene with 98.4% H₂SO₄ led to the formation of 2,4,6-tri-isopropylbenzene-sulphonic acid which is rapidly converted into the 2,4,5-isomer and 3,5-di-isopropylbenzenesulphonic acid. The ratio of formation of these compounds is 0.53 ± 0.05; their eventual ratio in the reaction mixture was, however, 1.0 ± 0.1. 1,2,4,5-Tetraisopropylbenzene with 9 : 1 (v/v) 98.4% H₂SO₄–CF₃CO₂H at 25° yielded initially the corresponding tetraisopropylbenzenesulphonic acid, but eventually 2,4,5-tri- and 3,5-di-isopropylbenzenesulphonic acid in the ratio 6.0 ± 0.6. Mechanisms for the formation of the various products obtained with 1,3,5-tri- and 1,2,4,5-tetra-isopropylbenzene are proposed.