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...
EIZE J. STAMHUIS, HENK MAATMAN, and GEERT E. H. JOOSTEN. Can. J. Chem. 64, 1690 (1986). The kinetics of the direct chlorination of 2-chlorocyclopentanone (2-mccp) and 2-chlorocyclohexanone (2-mcch) in carbon tetrachloride, catalyzed by hydrogen chloride, were studied. Reaction products are all the possible 2,2-, 2,5-, and 2,6-dichloro compounds. The ratios depend on the concentrations of the monochloro compound and hydrogen chloride. Surprisingly, even at conversions of the monochloro compound as low as 2%, 2,2,5-trichlorocyclopentanone and 2,2,6-trichlorocyclohexanone, respectively, are also formed. The chlorination reaction of both monochloro ketones shows zero order in chlorine. The order in hydrogen chloride is 1.3. The order in 2-mccp and 2-mcch varies somewhat with the concentration of the ketone and was found to be roughly 1.7. The variation in reaction order is explained by a partial self-association of the ketones. The ketones act as substrates as well as basic catalysts in the rate-determining a -or a'-carbon deprotonation. General base catalysis is clearly demonstrated by a strong increase in the rate of chlorination of 2-mccp upon addition of cyclopentanone (cp) to the reaction mixture, which agrees with the mechanism as presented in a previous paper. Kinetic equations derived from the reaction models for the "separate" and "mixed" ketone chlorinations accurately describe the observed rates of the chlorination of 2-mccp and 2-mcch in the concentration range of 0.04-1.0 M. EIZE J. STAMHUIS, HENK MAATMAN et GEERT E. H. JOOSTEN. Can. J. Chem. 64, 1690 (1986). OpCrant dans le tCtrachlorure de carbone, on a CtudiC la cinCtique de la chloration directe, catalysCe par le chlorure d'hydrogkne, des chloro-2 cyclopentanone (2-mccp) et cyclohexanone (2-mcch). Les produits de la reaction correspondent a tous les produits possibles pour les disubstitutions en -2,2, -2,5 et -2,6. Les rapports varient avec les concentrations initiales de composC monochlorC et de chlorure d'hydrogttne. I1 est surprenant de noter, a des taux de transformation du dCrivC monochlorC aussi bas que 2%, qu'il y a aussi formation, selon le cas, de trichloro-2,2,5 cyclopentanone ainsi que de trichloro-2,2,6 cyclohexanone. Par rapport au chlore, l'ordre de la rCaction de chloration des deux cCtones monochlorees est Cgal i zCro. Par rapport au chlorure d'hydroghe, il est Cgal a 1,3. Par rapport aux cCtones 2-mccp et 2-mcch, l'ordre varie en fonction de la concentration des cCtones; il s'Ctablit approximativement 2 1,7. On explique cette variation de I'ordre par rapport aux cCtones en fonction d'une auto-association partielle des cCtones. Les cCtones agissent comme substrats ainsi que comme catalyseurs basiques dans la deprotonation des carbones a et a ' qui dCtermine la vitesse de la rCaction. On a facilement mis en Cvidence une catalyse gCnCrale des bases en notant la grande augmentation de la vitesse de chloration de la 2-mccp par addition de cyclopenta?one (cp) au milieu reactionnel; cette observation est en accord avec le mCcanisme proposC...
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