Aromatic sulphonation. Part 54. Sulphonation of polyethylbenzenes. On the Jacobsen rearrangement of the tetraethylbenzenesulphonic acids

Abstract

The reaction of m- and p-di-, 1,3,5-tri-, and 1,2,3,5- and 1,2,4,5-tetra-ethylbenzene with concentrated aqueous sulphuric acid leads to clean sulphodeprotonation. m-Diethylbenzene in 95.2% H₂SO₄ at 25° gives 9% 2-, 90% 4-, and ⩽3% 5-substitution. The monosulphonic acids obtained from the di- and tri-ethylbenzenes are stable in the sulphonation media. In contrast the sulphonic acids obtained from 1,2,3,5- and 1,2,4,5-tetraethylbenzene are unstable in 98.4% H₂SO₄ and are eventually converted into 2,3,4,5-tetraethylbenzenesulphonic acid. The least stable acid is the 2,3,5,6-isomer which rearranges in part via the 2.3,4,6-isomer and in part directly to the 2,3,4,5-isomer by 1,2-ethyl shifts of the appropriately ring protonated arenesulphonic acids.