Received July 10, 1 9 S 5 EIZE J. STAMHUIS, HENK MAATMAN, HENK STINISSEN, and GEERT E. H. JOOSTEN. Can. J. Chem. 64, 1681Chem. 64, (1986. 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 [cp] and [ch] 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 a-carbon deprotonated in a rate-determining step. This step, which is catalyzed by the bases cp or ch, respectively, leads to the corresponding en01 as intermediate. The en01 is then chlorinated very rapidly. In addition to the chloro ketone, very reactive chloride anions are formed. A small fraction of these anions deprotonate a-or a'-carbon atoms of the oxygen-conjugate acid of the monochloro ketone. The remainder are captured by HCI to form energetically more favored CI--(HCl). 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 of more than three decades. Puisque le chlorure d'hydrogkne est un des produits, on doit classer la rCaction comme autocatalysique. Les effets isotopiques du deutCrium ainsi que les donnCes cinktiques suggerent fortement un mCcanisme impliquant, dans 1'Ctape qui dCtermine la vitesse, la dtprotonation du carbone-a d'une cCtone monorndre protonte par I'oxygkne. Cettc Ctape, qui est catalysee respectivement par les bases cp etch, conduit aux Cnols correspondants, comme intermtdiaires. L'Cnol est alors chlore tres rapidement. Une petite fraction de ces anions dCprotone les atomes de carbones-a et -a' de l'acide conjug6 de l'oxygbne de la cCtone monochlorCe. Le reste est capturC par le HC1 pour former des complexes C1--(HCI), ( n = 1, 2 et 3) qui sont plus favorists du point de vue CnergCtique. Ceci explique pourquoi, m&me a des taux de conversions en cCtones trbs faibles, il se forme des quantitCs substantielles de diverses cCtones dichlorCes aux cBtCs des produits monochlorCs. On a dCrivC une expression pour les vitesses qui dCcrit d'une f a~o n excellente les vitesses expkrimentales de chloration des cCtones cp et ch, a des taux de rCaction s'Ctalant sur trois ordres de grandeur.[Traduit par la revue]In polar media the acid-catalyzed halogenation of ketones of low dielectric constant appears to be significantly more usually proceeds by a rate-determining base-catalyzed a-carbon compl...
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