钴的羟胺酸类配合物催化对-二甲苯氧化反应研究

Studies on Selected Oxidation of p-Xylene Catalyzed by Hydroxamic Acid Cobalt Complexes

合成并表征了 3种羟胺酸类钴配合物 Co(OTPHA) 2 、Co(OTBHA) 2 和 Co(OTOHA) 2 ,并对比评价了它们催化对 -二甲苯均相液相氧化合成对 -甲基苯甲酸的活性和选择性 .考察了以纯氧为氧源 ,常压下反应温度、催化剂浓度、反应时间以及水对反应转化率和选择性的影响 .实验结果表明 ,不同分子结构的配体 ,可以通过其空间效应和电子效应对催化活性产生直接的影响 ,3种催化剂的活性顺序为 :Co(OTPHA) 2 >Co(OTBHA ) 2 >Co(OTOHA ) 2 .当反应温度为 110℃、催化剂浓度 1.0× 10 - 3mol/ L、反应 6 h时 ,催化剂 Co(OTPHA) 2 的对 -二甲苯转化率可达 33.9%、选择性为 86 .2 % .若提高反应温度和加大催化剂浓度 ,则会降低催化剂的活性 .反应中生成的水对氧化反应有抑制作用 。

Hydroxamic acid cobalt complexes Co(OTPHA)\-2 , Co(OTBHA)\-2 and Co(OTOHA)\-2 were synthesized and characterized. The catalytic properties of these complexes for the oxidation of p \|xylene have been studied under atmospheric pressure and 60～120 ℃ with oxygen as the oxidant. The results indicate that the catalytic activities and selectivities are high under mild reaction conditions without solvents. The molecular structure of hydroxamic acid ligands has influence on the catalytic activities of cobalt complexes by the electronic and steric factors. The catalytic activities of these three cobalt complexes are: \{Co(OTPHA)\-2\}>Co(OTOHA)\-2>Co(OTOHA)\-2. The conversions of p \|xylene and the selectivities to p \|toluic acid increase obviously if water is separated timely when it is formed in the oxidation.