Aromatic sulphonation. Part LI. Sulphonation of 1,3,5-tri- and m- and p-di-t-butylbenzene, the three t-butylbenzenesulphonic acids, and 3,5-di-t-butylbenzenesulphonic acid

Abstract

The reaction of t-butylbenzene (T), m- and p-di- and 1,3,5-tri-t-butylbenzene (MDT, PDT, and 1,3,5-TT), the three t-butylbenzenesulphonic acids (OTS, MTS, and PTS), and 3,5-di-t-butylbenzenesulphonic acid with a number of sulphonating reagents has been studied at 25°. T with 98.5% H₂SO₄ gives 82 ± 2%para- and 18 ± 2%meta-sulphonation. MDT and PDT in 98.5% H₂SO₄ both yield the same mixture of mainly (insoluble) MDT-5-sulphonic acid † and p-T-sulphonic acid. MDT in 103% H₂SO₄ gives 20 ± 10% 4- and 80 ± 10% 5-sulphonation. PDT with 103% H₂SO₄ yields 8 ± 1% t-butylbenzene-2,4-disulphonic acid, 6 ± 2% MDT-5-sulphonic acid, 67 ± 2% PTS, and 19 ± 2% T-3,4-disulphonic anhydride and T-3,5-disulphonic acid. Reaction of PDT with SO₃ in CCl₃F yields 42 ± 2% PDT-sulphonic anhydride and 58 ± 2% PTS anhydride. 1,3,5-TT in 102% H₂SO₄ yields predominantly MDT-5-sulphonic acid. PTS with 107% H₂SO₄ yields 70 ± 2% T-3,4-disulphonic anhydride and 30 ± 2% T-2,4-disulphonic acid. The latter acid is the only initial product of OTS in 107% H₂SO₄. T-2,4-disulphonic acid in 107% H₂SO₄ slowly yields 2,3-dihydro-3,3-dimethyl-1,1-dioxobenzothiophen-6-sulphonic acid. MTS in 107% H₂SO₄ yields 86 ± 2% T-3,5-disulphonic acid and 14 ± 2% T-3,4-disulphonic anhydride. OTS in 98.5% H₂SO₄ yields mainly MTS and PTS in the ratio 0.40 ± 0.04. MDT-5-sulphonic acid in 107% H₂SO₄ yields 16 ± 2% T-3,4-disulphonic anhydride and 84 ± 2% T-3,4-disulphonic acid. The formation of the several initial and eventual sulphonic acid products from the various substrates is explained in terms of sulphodeprotonation, protio- and sulpho-de-t-butylation, isomerization by alkyl migration, and isomerization by desulphonation and subsequent resulphonation or intramolecular sulpho-migration. The results illustrate that, in addition to the sulphonation, isomerization and dealkylation take place. The relative importance of these reactions and the reaction mechanisms are discussed.