Aromatic sulphonation. Part 57. Phenylsulphamic acid in sulphuric acid: solvolysis versus sulphonation

Abstract

Phenylsulphamic acid in a large excess of 86.8% H₂SO₄ at room temperature yields both the anilinium ion and a mixture of aniliniumsulphonic acids by solvolysis and sulphonation (followed by solvolysis) respectively. Both the higher ortho : para sulphonation ratio as compared with that for > 96% H₂SO₄ and the deviation of the sulphonation rate constant from the one estimated by extrapolation of the kinetics observed in > 97% H₂SO₄, are discussed in terms of medium effects, and a change in the reacting substrate species and the sulphonating entity. The solvolysis and sulphonation reactions of the o- and p-sulphophenylsulphamic acids in a large excess of weakly fuming sulphuric acid at 25° are controlled by the electronic and steric effects of the aromatic sulpho-group. Phenylsulphamic acid in 99.9% H₂SO₄ at 100° under heterogeneous conditions undergoes both sulphonation and solvolysis, whereas under homogeneous conditions, only sulphonation is observed.