236. Mechanism of substitution at a saturated carbon atom. Part LIV. Kinetics of chlorine exchange between triphenylmethyl chloride and tetra-n-butylammonium chloride in benzene

Abstract

The kinetics are studied of the exchange of chlorine between triphenylmethyl chloride and tetra+butylammonium radiochloride in benzene at 26-46O.In these conditions the reaction is of first order in triphenylmethyl chloride, and of zeroth order in the salt at all concentrations up to saturation.This kinetic form and rate are practically unaffected by added tetra-nbutylammonium perchlorate, which undergoes no stoicheiometric reaction with triphenylmethyl chloride. But the kinetic form is changed, and the initial rate is reduced by added tetra-n-butylammonium azide, which concurrently produces the relatively inert substance, triphenylmethyl azide, though not rapidly enough to preclude observation of the strong initial retardation produced by the salt. This retardation is identified as the kinetic " mass-law effect " in an S,1-type reaction, as described in 1940 for unimolecular solvolysis and for other unimolecular substitutions.The rate of exchange is much increased by added nitromethane or nitrobenzene, without disturbance to the first-order form of the NIB. The initial rate of exchange is considerably increased by added pyridine, or tri-rr-butylamine, though now such a disturbance arises, apparently, from reversible interaction between the triphenylmethyl chloride and the amine. The initial rate of exchange is greatly increased by added methyl alcohol, benzyl alcohol, or phenol, which, as reaction continues, produce some kinetic disturbance arising from the concurrent, relatively slow, formation of an ether. All these catalytic effects, whether by non-reacting polar solutes, such as the nitro-compounds, or by reacting ones, such as the hydroxycompounds, have the common characteristic that, notwithstanding a contrary report by Swain and Kreevoy, they display no integral kinetic order which remains uniform over a significant concentration range. The number and