Kinetic analysis of homogeneous acid catalysis in the chloromethylation of toluene

Abstract

The catalytic activity of acids in the chloromethylation of toluene has been studied in a complex mixture of toluene, paraformaldehyde, hydrochloric acid, acetic acid and zinc chloride. A relation between the Hammett acidity function and the initial reaction rate has been found: r 0 = h mf(k,C) m = 1.25 where: h = 10 − H 0; H 0 being the Hammett acidity function. This relation describes the influence of three acids, acetic acid, hydrochloric acid and zinc chloride, on the initial reaction rate in the investigated range of variables C T 0 = 0.075 M, C F 0 = 2.5 M; 30% ⩽ C HAc ⩽ 50%, 5% ⩽ C ZnCl 2 ⩽ 15% and 2 M ⩽ C HCl ⩽ 4 M. These results are useful in the evaluation of the reaction rate for the chloromethylation of toluene as a function of the proton activities. Finally, some mechanistic implications are discussed.