Aromatic sulphonation. Part XLVII. Reaction of 1,2-dihydrobenzocyclobutene with sulphonating reagents

Abstract

Reaction of 1,2-dihydrobenzocyclobutene (DHBCB) with sulphur trioxide addition complexes leads to the formation of DHBCB-3- and DHBCB-4-sulphonic acid and the sultone of 2-(o-sulphophenyl)ethanol. The ipso : 3- : 4-substitution ratio is (25 ± 5) : (5 ± 3) : (70 ± 4) for CH₃NO₂–SO₃ in nitromethane at 0° and (32 ± 6) : (7 ± 4) : (61 ± 5) for dioxan–SO₃ in trichlorofluoromethane at 0–20°. DHBCB on reaction with concentrated sulphuric acid is mainly converted (ca. 90%) into polyxylylene. At 90% H₂SO₄ the terminal group is the 4-DHBCB system; below 90% H₂SO₄ it is in part replaced by the 2-(p-phenylene)ethyl sulphate group. The ethylene bridges in the polymers have mainly the meta-orientation. In addition the sulphuric acid soluble 2-(p-sulphophenyl)ethyl sulphate (3) and 5-[β-(p-sulphophenyl)ethyl]DHBCB-4-sulphonic acid (4) are formed. The ratio of (3) to (4) decreases strongly with increasing sulphuric acid concentration. Mechanisms for the formation of the polymers and (3) and (4) are proposed.