Kinetics of nuclear chlorination of toluene and some substituted toluene by trichloro-isocyanuric acid

Abstract

Nuclear chlorination of toluene and substituted toluenes by trichloroisocyanuric acid is first order each in [trichloroisocyanuric acid] and [substrate]. The observed second order rate constants increase with increase in [H⁺] in solvent mixtures containing less than 50% HOAc. The <em>k</em>₂ values increase with an increase in the proportion of HOAc, reach maximum at 50% HOAc above which the rate constants have a diminishing trend. At higher proportion of HOAc, the rate constants are insensitive to change in [HClO₄]. Added Cl^- ions enhance the rate. Based on the observed results a plausible mechanism has been proposed which envisages a positive ion dipole reaction between H<img src='http://www.niscair.res.in/jinfo/plustwo.gif' border=0>OCI generated from hydrolysis of TCICA and the substrate molecules at low proportions of HOAc. At high proportion of HOAc, chlorine acetate has been suggested to be the electrophile. Molecular chlorine as well as H<img src='http://www.niscair.res.in/jinfo/plustwo.gif' border=0>OCl are the chlorinating species in the presence of C1^- ions. The Hammett plot is linear with a <em>ρ</em> value -5.55. The activation parameters have been computed.