6932-77-0Relevant articles and documents
Reactions of alicyclic ketones in carbon tetrachloride. I: The kinetics of the chlorination of cyclopentanone and cyclohexanone catalyzed by hydrogen chloride
Stamhuis, Eize J.,Maatman, Henk,Stinissen, Henk,Joosten, Geert E. H.
, p. 1681 - 1689 (2007/10/02)
The kinetics of the direct chlorination of cyclopentanone (cp) and cyclohexanone (ch) in carbon tetrachloride, catalyzed by hydrogen chloride, was studied.The rate of chlorination, measured by flow and stopped-flow techniques, is zero order in chlorine; the order in cp and ch increases from 1 at and of 0.01 M concentration to 2 at concentrations of 1 M.This is explained by self-association of the ketones in carbon tetrachloride solutions.The order in hydrogen chloride is 1.Since this compound is one of the products, the reaction is autocatalytic.Deuterium isotope effects and the kinetic data strongly point to a mechanism in which the oxygen-protonated monomeric ketone is α-carbon deprotonated in a rate-determining step.This step, which is catalyzed by the bases cp or ch, respectively, leads to the corresponding enol as intermediate.The enol is then chlorinated very rapidly.In addition to the chloro ketone, very reactive chloride anions are formed.A small fraction of these anions deprotonate α- or α'-carbon atoms of the oxygen-conjugate acid of the monochloro ketone.The remainder are captured by HCl to form energetically more favored Cl--(HCl)n complexes with n = 1, 2, or 3.This explains why, even at low conversions of the ketones, substantial amounts of the various dichloro isomers are formed in addition to monochloro products.A rate expression is derived, which excellently describes the experimentally obtained rates of chlorination of cp and ch over a range of reaction rates more than three decades.
