Reaction orders in the addition of methanol to chloral in 1,4-dioxan

Abstract

Reaction velocities are reported for the addition of methanol to chloral in dioxan at 25 °C. The reaction is first order with respect to chloral. In the absence of added catalysts the order with respect to methanol is three, indicating a cyclic transition state containing three methanol molecules, resembling that previously established for the addition of water to various carbonyl compounds. In the presence of carboxylic acids the catalysed reaction is first order with respect to catalyst, while the order with respect to methanol is between unity and 1·6. This indicates that the catalyst partially replaces methanol in the transition state, but a quantitative interpretation is complicated by association between methanol and carboxylic acids. Cryoscopic measurements show that methanol is only slightly associated in dioxan at the concentrations used in the kinetic experiments.