Unexpected roles of molecular sieves in palladium-catalyzed aerobic alcohol oxidation
Unexpected roles of molecular sieves in palladium-catalyzed aerobic alcohol oxidation
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DOI：
10.1021/jo052192s
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发表时间：
2006-03-03
影响因子：
3.6
通讯作者：
Stahl, SS
中科院分区：
文献类型：
--
作者：
Steinhoff, BA;King, AE;Stahl, SS
钯催化醇的好氧氧化方法通常得益于分子筛的存在。本文通过对存在和不存在分子筛时醇氧化的动力学研究，探讨了分子筛对Pd(OAC)(2)/吡啶和Pd(OAC)(2)/DMSO （DMSO =二甲亚砜）催化剂体系的影响。分子筛提高了Pd(OAC)(2)/吡啶催化醇的氧化速率，这一效应归因于分子筛作为Bronsted碱的能力。相比之下，Pd(OAC)(2)/ dmso催化的反应速率没有提高。两种催化剂体系在分子筛的存在下都表现出更好的催化剂稳定性，表现为更高的催化周转率。对照实验表明，这两种有益效果都与分子筛吸收水的能力无关，而水是这些反应的化学计量副产物。最后，利用同步气体吸收和原位红外光谱研究表明，分子筛抑制了H(2)O(2)的歧化，这一观察结果与之前的建议相矛盾，即分子筛的有益作用可能源于它们促进H(2)O(2)歧化的能力。
Methods for palladium-catalyzed aerobic oxidation of alcohols often benefit from the presence of molecular sieves. This report explores the effect of molecular sieves on the Pd(OAC)(2)/Pyridine and Pd(OAC)(2)/DMSO (DMSO = dimethyl sulfoxide) catalyst systems by performing kinetic studies of alcohol oxidation in the presence and absence of molecular sieves. Molecular sieves enhance the rate of the Pd(OAC)(2)/pyridine-catalyzed oxidation of alcohols, and the effect is attributed to the ability of molecular sieves to serve as a Bronsted base. In contrast, no rate enhancement is observed for the Pd(OAC)(2)/DMSO-catalyzed reaction. Both catalyst systems exhibit improved catalyst stability in the presence of molecular sieves, manifested by higher catalytic turnover numbers. Control experiments indicate that neither of these beneficial effects is associated with the ability of molecular sieves to absorb water, a stoichiometric byproduct of these reactions. Finally, the use of simultaneous gas-uptake and in-situ IR spectroscopic studies reveal that molecular sieves inhibit the disproportionation of H(2)O(2), an observation that contradicts a previous suggestion that the beneficial effect of molecular sieves may arise from their ability to promote H(2)O(2) disproportionation.