单双核金属配合物选择性催化氧化对甲氧基苦杏仁酸

制备了以铜、钴、锰为中心离子的三种单核金属配合物L¹Cu、L¹Co、L¹Mn (L¹=N,N'-(2-羟乙基)丙二酰胺)和三种双核金属配合物L²Cu、L²Co、L²Mn (L²=N,N'-{2-(2-羟乙基氨基)乙基}丙二酰胺). 研究发现在缓冲溶液中六种金属配合物能将对甲氧基苦杏仁酸(4-MMA)高选择性地氧化成对甲氧基苯甲醛(AAD)以及少量对甲氧基苯甲酸(4-MBA), AAD的选择性(S)大于96%. 然而不同的催化体系在反应速率上表现了很大的不同: 铜金属配合物的催化活性最好; 双核配合物表现出更高的催化效率. 研究了酒石酸(TA)、磷酸(H₃O₄)、醋酸(HAc)三种缓冲溶液体系对L¹Cu催化H₂O₂氧化4-MMA反应的影响, 结果表明缓冲溶液种类对反应速率和选择性影响很大.研究了35℃时弱酸性条件(pH值从2.5到4.5的范围内)在酒石酸缓冲溶液中六种金属配合物催化H₂O₂氧化4-MMA的动力学, 计算出不同pH值条件下催化反应的表观反应速率常数k_obs, 并且讨论了pH值对催化反应的影响.

Selective Oxidation of 4-Methoxymandelic Acid Catalyzed by Mononucleonic and Binucleonic Metal Complexes

Three kinds of mononucleonic metal complexes of L¹Cu, L¹Co, and L¹Mn (L¹=N,N'-bis-(2-hydroxyethyl)-malondiamide), and three kinds of binucleonic metal complexes of L²Cu, L²Co, and L²Mn (L²= N,N'-bis{2-(2-hydroxyethylamino)ethyl}-malondiamide) were prepared. These complexes exhibited good catalytic performance for the selective oxidation of 4-methoxymandelic acid (4-MMA) by H₂O₂ in buffer solution, with >96% selectivity to anisaldehyde (AAD) and a small percentage to 4-methoxybenzoic acid (4-MBA). However, the reaction rates were quite different for these catalytic systems, in which the copper complex was the best candidate as the catalyst for the oxidation of 4-MMA. The binucleonic complexes displayed obviously better catalytic performance than the mononucleonic complexes. The effect of the applied buffers (tartaric acid (TA), H₃O₄, HAc) on the catalytic performance in terms of activities and selectivities for the oxidation of 4-MMA by H₂O₂ were investigated. The reaction kinetics of 4-MMA oxidation catalyzed by six complexes was studied in detail. The apparent first-order rate constants (k_obs) were obtained in the pH range of 2.5 to 4.5. The pHeffect on the catalytic oxidation was discussed in this paper.