Mesitylene-a-sulphonate anion

When the concentration of 2-phenylethanesulphonate anion was >0-5 mol 1, or when 2-mesitylethanesulphonate anion (v), " mesitylene-a-sulphonate anion, or iso-durene-a -sulphonate anion were nitrated, the initial part of the reaction deviated from a first-order dependence on the concentration of the aromatic towards a zeroth-order dependence. 

The rates of nitration of mesitylene-a-sulphonate anion (iii) and iso-durene-a -sulphonate anion (iv) in mixtures of aqueous nitric and perchloric acid followed a zeroth-order rate law. Although the rate of exchange of oxygen could not be measured because of the presence of perchloric acid, these results again show that, under conditions most amenable to its existence and involvement, the nitric acidium ion is ineffective in nitration. 

The kinetics of desulphonation of sulphonic acid derivatives of m-cresol, mesitylene, phenol, p-cresol, and p-nitrodiphenylamine by hydrochloric or sulphuric acids in 90 % acetic acid were investigated by Baddeley et a/.701, who reported (without giving any details) that rates were independent of the concentration of sulphuric acid and nature of the catalysing anion, and only proportional to the hydrogen ion concentration. The former observation can only be accounted for if the increased concentration of sulphonic acid anion is compensated by removal of protons from the medium to form the undissociated acid this result implies, therefore, that reaction takes place on the anion and the mechanism was envisaged as rapid protonation of the anion (at ring carbon) followed by a rate-determining reaction with a base. 

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