Three types of acid catalysis in liquid phase of metal salts of 12-tungstophosphoric acid, Mn+xH3−nxPW12O40
Three types of acid catalysis in liquid phase of metal salts of 12-tungstophosphoric acid, Mn+xH3−nxPW12O40
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DOI：
10.1016/s0926-860x(98)00398-6
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发表时间：
1999-05
影响因子：
5.5
通讯作者：
G. Koyano;K. Ueno;M. Misono
中科院分区：
文献类型：
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作者：
G. Koyano;K. Ueno;M. Misono
12-钨磷酸及其酸性盐、H3PW12O40、CsxH3−xPW12O40（缩写为Csx；x=1、2、2.23、2.5、2.7和3）、BaxH3−2xPW12O40（缩写为Bax；x=0.5、1.25和） 1.5）和CexH3−3xPW12O40（缩写为Cex；x=0.33、0.66、0.87和1）作为酸催化剂应用于底物和溶剂极性差异很大的三个有机反应：（1）乙酸环己酯（在间二甲苯中）的分解，（2）苯甲酸与1-丁醇的酯化（无溶剂），和（3）苯频哪醇的重排（在甲苯中）。结果表明，这三个反应代表了杂多化合物液相酸催化反应中的三个典型反应场。反应（1）在固体催化剂的表面进行（表面型反应）。在这种情况下，催化活性主要由表面酸度决定。反应(2)主要在均相溶液中进行，催化活性与溶解在溶剂中的杂多酸的量相关。反应（3）观察到假液相催化，其中催化活性取决于催化剂固体块中吸收的底物的量。因此，杂多酸催化剂根据底物和溶剂的极性提供三种不同的反应场。反映反应场的催化活性的顺序有很大不同。这些结果表明，认识这些反应场对于理解和设计液相杂多酸催化非常重要。
12-Tungstophosphoric acid and its acidic salts, H3PW12O40, CsxH3−xPW12O40(abbreviated as Csx; x=1, 2, 2.23, 2.5, 2.7, and 3), BaxH3−2xPW12O40(abbreviated as Bax; x=0.5, 1.25, and 1.5), and CexH3−3xPW12O40(abbreviated as Cex; x=0.33, 0.66, 0.87, and 1), were applied as acid catalysts to three organic reactions which are very different in the polarities of substrates and solvents: (1) decomposition of cyclohexyl acetate (in m-xylene), (2) esterification of benzoic acid by 1-butanol (without solvent), and (3) rearrangement of benzopinacol (in toluene). It was demonstrated that these three reactions represent three typical reaction fields in the acid-catalyzed reactions of heteropoly compounds in the liquid phase. Reaction (1) proceeded on the surface of solid catalysts (a surface-type reaction). In this case, the catalytic activities were primarily determined by the surface acidity. Reaction (2) mostly took place in the homogeneous solution and the catalytic activities were correlated with the amount of the heteropolyacids dissolved in the solvents. Catalysis in pseudoliquid phase was observed for reaction (3), where the catalytic activities depended on the amount of substrates absorbed in the solid bulk of the catalysts. Thus, heteropolyacid catalysts provide three different reaction fields, depending on the polarity of substrate and solvent. The orders of the catalytic activity very much differed reflecting the reaction field. These results demonstrate that the recognition of these reaction fields is important for the understanding and the design of heteropolyacid catalysis in the liquid phase.