The kinetics of chlorination of aliphatic, aralkyl and alicyclic ketones by 1-chlorobenzotriazole (cbt) have been studied in aqueous acetic acid media. In the presence of a mineral acid (HClO4), the order of the reaction with respect to [ketone] is one and that with respect to [cbt] is zero, suggesting the enolisation of ketone as the slow step, followed by a fast attack of the halogenating species. A primary kinetic isotope effect (kH/kD=6·6) is also noticed, when acetone and acetone-d6 are used as the substrates. Initial addition of chloride ion leads to a first order dependence on [cbt] and a fractional order (0·6) on [acetone]. Thermodynamic parameters for the reaction have also been reported. A negative Hammett reaction constant (ρ=−0·57) has been obtained for the halogenation of substituted acetophenones bycbt.
Volume 134, 2022
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