硝基苯催化还原羰基化为苯氨基甲酸乙酯

CATALYTIC REDUCTIVE CARBONYLATION OF NITROBENZENE TO N-PHENYLURETHANE

研究了几种含氮杂环配体的钯配合物或其相应的混合物在硝基苯还原羰基化为苯氨基甲酸酯反应中的催化性能。结果表明,钯-邻菲啰啉配合物在该反应中具有最高的催化活性,且钯配合物或钯盐的阴离子性质对生成苯氨基甲酸酯的选择性有很大的影响。从反应结果推测,在反应条件下可能形成两种不同价态钯的配合物,其中零价钯配合物是硝基苯的还原中心,而二价钯配合物为还原羰基化中心。电化学循环伏安法测试结果表明,吡啶、邻菲啰啉等配体对稳定Pd(Ⅱ)氧化态具有重要作用。

The reductive carbonylation of nitrobenzene to N - phenylurethane in ethanol medium catalyzed by a catalyst system comprised of either a mixture or a complex of pallaium salt and a nitrogen-containing compound, such as 4 - methylpyridine, 2,2'- bipyridine and phenathro-line has been investigated. Reductive carbonylation experiments were carried out in a 100ml stirred high pressure stainless steel autoclave, and the reaction was continued for a period of 2 h at 80-180℃ and 2.0-8.0 MPa pressure of CO, It was found that catalyst systems formed by a stable palladium salt and a bidentate chelating ligand, phenathroline ( or corresponding complexes ) shows highest catalytic activity and selectivity. It is interesting to note that the large effect of nature of palladium compounds on catalytic activity and selectivity is probably due to the formation of two types of catalytic active species, i.e., the Pd (Ⅱ) complexes and Pd ( 0 ) complexes in the reaction processes. It is generally believed that the former should be the catalytic species responsible for the urethane synthesis, and the later should be the main species responsible for the formation of reductive coupling products of nitrobenzene. Based on the results obtained in this investigation, a reaction mechanism of reductive carbonylation as well as the formation of byproducts has been suggested.