Sulphonation in non- or part-aqueous media

Most research workers have employed an aqueous sulphuric acid solution of the aromatic, but a few have used other solvent systems and sulphonating agents. Principal among these are Hinshelwood et a/.139, who measured the rates of sulphonation of aromatics by sulphur trioxide in nitrobenzene at temperatures between 0 and 100 °C, a minimum of about 40 °C being employed for each compound. The initial reaction rate was given by 

RATE COEFFICIENTS AND ARRHENIUS PARAMETERS FOR REACTION OF SO3 WITH ArH IN PhN02 at 40+0.1 °C139 

This mechanism does not, however, explain the fall-off in rate coefficients observed by Hinshelwood et al. 

Hinshelwood et a/.145 measured the rates of sulphonation of a wide range of aromatics by sulphuric acid in nitrobenzene, at temperatures between 5 and 100 °C (Table 32), and in particular the effect of adding up to 0.012 M water was determined. The reaction followed the complex rate law 

Further details relating to the mechanism of sulphonation under these con- 

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