Kinetic and equilibrium studies on the esterification of monomeric and .MU.-oxo dimeric vanadium(V) complexes with butyl alcohols in chlorobenzene.

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概要

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• Kinetic and equilibrium studies were made on the esterification of the μ-oxo dimeric vanadium (V) complexes with monoanionic bidentate ligands(HL) such as 8-quinolinol, 5-chloro-8-quinolinol, 5,7-dibromo-8-quinolinol, and 4-isopropyltropolone by butyl alcohols (ROH) in chlorobenzene. The stoichiometry and the rate equation are expressed as follows:<BR>V<SUB>2</SUB>O<SUB>3</SUB>L<SUB>4</SUB>+2ROH\rightleftharpoons2VO(OR)L<SUB>2</SUB>+H<SUB>2</SUB>O:<I>K</I><SUB>DE</SUB>;<BR>−\fracd[V<SUB>2</SUB>O<SUB>3</SUB>L<SUB>4</SUB>]d<I>t</I>=\frac12×\fracd[VO(OR)L<SUB>2</SUB>]d<I>t</I>=(<I>k</I><SUB>1</SUB>+<I>k</I><SUB>2</SUB>[H<SUB>2</SUB>O])[V<SUB>2</SUB>O<SUB>3</SUB>L<SUB>4</SUB>][ROH].<BR>The more basic the bound ligand L<SUP>−</SUP>, the lower the water-independent rate constant <I>k</I><SUB>1</SUB> is. For less sterically crowded alcohols, <I>k</I><SUB>1</SUB> is higher, giving the reactivity order: <I>n</I>-><I>i</I>-><I>s</I>-><I>t</I>-. Water, presumably hydrogen bonded to the terminal oxo group of the complexes, <I>accelerates</I> the esterification(<I>k</I><SUB>2</SUB> path). The equilibrium constant <I>K</I><SUB>DE</SUB> is linearly correlated with the rate constant <I>k</I><SUB>1</SUB>. The esterification kinetics of the monomeric complex with 2-methyl-8-quinolinol(HL′), which corresponds to the proposed reactive intermediate in the esterification of the μ-oxo dimeric complexes, is also investigated and found the rate equation to be expressed as<BR>−\fracd[VO(OH)L′<SUB>2</SUB>]d<I>t</I>=\fracd[VO(OR)L′<SUB>2</SUB>]d<I>t</I>=<I>k</I><SUB>M,1</SUB>[VO(OH)L′<SUB>2</SUB>[ROH].<BR><I>k</I><SUB>M,1</SUB> is 5 times higher than the estimated for the corresponding dimeric complex. Large negative values of Δ<I>S</I><SUB>1</SUB><SUP>\neweq</SUP> and Δ<I>S</I><SUB>M,1</SUB><SUP>\neweq</SUP> point to an associative nucleophilic attack of alcohol to the vanadium center of both dimeric and monomeric complexes. The difference of the reactivity of complexes and alcohols and the detailed mechanism will be discussed.

• 公益社団法人 日本化学会の論文

著者

• Yamada Shinkichi

  Laboratory Of Analytical Chemistry Faculty Of Engineering Shizuoka University

• Tanaka Motoharu

  Laboratory of Analytical Chemistry Faculty of Science Nagoya University

• Yuchi Akio

  Laboratory of Analytical Chemistry, Faculty of Science, Nagoya University

• Yagishita Yumi

  Laboratory of Analytical Chemistry, Faculty of Science, Nagoya University

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