以空气为氧化剂Pd(OAc)2/HPMo/AcOH催化苯液相氧化偶联合成联苯

 研究了以Pd(OAc)2为催化剂,H3PMo12O40为助催化剂,空气为氧化剂,在乙酸溶液中于373 K条件下,在500 ml高压釜中由苯液相氧化偶联合成联苯. 结果表明,反应产物中联苯的选择性高达92%以上,并且只有少量的三联苯副产物生成. 分别考察了H3PMo12O40的加入量和O2分压对以空气或纯O2为氧化剂时Pd/HPMo/AcOH催化苯液相氧化偶联合成联苯反应催化性能的影响. 根据反应液颜色的变化以及文献结果推测,在反应过程中通过钯和钼物种的氧化和还原作用使苯氧化生成联苯.

Liquid-Phase Synthesis of Biphenyl by Oxidative Coupling of Benzene Using Pd(OAc)2/HPMo/AcOH Catalyst and Air Oxidant

Biphenyl is an important industrial material used as a heat transfer agent, anti-mildew agent and raw material of synthetic resins . Biphenyl derivatives are widely used as the monomers of various polymers and liquid crystal materials . Although the Ullmann reaction and Suzuki coupling are well-known methods for the preparation of biphenyl through aryl-aryl coupling, these reactions lead to undesirable by-products like copper iodide or boric salts. This is not satisfactory from the environmental and atom-utilization viewpoint. Biphenyl is presently manufactured by the vapor-phase dehydrogenation of benzene . A low-temperature liquid-phase synthesis of biphenyl such as the catalytic dimerization of benzene is interesting both academically and industrially. Hence, the development of biphenyl synthesis by the direct coupling of an aryl compound, such as benzene, is an important challenge in catalysis. Pd-catalyzed dimerization of benzene in a liquid phase has been investigated extensively . However, there are few literature reports on the selective synthesis of biphenyl by the oxidative coupling of benzene using a Pd/heteropoly acid/acetic acid catalyst and using air as the oxidant.