卤素及取代效应对Cu系催化剂催化性能的影响

Effect of Halogen Anions and Substitution Effect on the Catalytic Performances of Cu Catalysts

摘要:

采用软硬酸碱理论，并结合离子半径和取代效应研究了铜系催化剂对甲醇氧化羰基化反应的影响。结果表明，交界碱Br-比软碱I-和硬碱Cl-更适宜与交界酸Cu2 和软酸Cu 配位，促进控制步骤CO对Cu-OCH3键插入的进行。在Cu(5-R-phen)Br2(R = 5-NH2、5-CH3、5-Cl、5-NO2；phen = 菲咯啉)中，弱给电子效应的甲基最有利于CO的活化和CO对Cu-OCH3键的插入反应，催化活性最高。同时在Cu(R?-phen)Br2 (R? = 2-CH3、4-CH3、5-CH3、2,9-dimethyl、4,7-dimethyl、5,6-dimethyl)中，含单甲基催化剂的活性比相应的含双甲基的高；邻近配位N原子的甲基空间位阻效应显著，且甲基越多，活性越低。以活性最高的Cu(5-CH3-phen)Br2为催化剂，在总压力4MPa，CO与氧气的分压比为19:1，反应时间4 h，反应温度130℃，催化剂浓度0.011mol/L的条件下的条件下，碳酸二甲酯的转化数和选择性分别为67.2和96.9%。

Abstract:

The catalytic performances of a series of Cu compounds in the oxidative carbonylation of methanol to dimethyl carbonate (DMC) were investigated by employing the soft-hard acid-base principle, the ion radius rules and the substitution effect. It has been found that it is the most appropriate for the border base Br- to coordinate with a border acid CuII and a soft acid CuI, improving the insertion of CO to the CuII—OCH3 bond, which is the rate-limiting step in DMC synthesis. Among a series of Cu(5-R-phen)Br2 catalysts (R = 5-NH2, 5-CH3, H, 5-Cl or 5-NO2, phen = 1,10-phenanthroline), the methyl substituent with the爓eakly electron-donating爀ffect is the most beneficial to the activation of CO and the insertion of CO to the Cu-OCH3 bond, and Cu(5-CH3-phen)Br2 exhibits the highest activity. For Cu(R?-phen)Br2 (R? = 2-CH3, 4-CH3, 5-CH3, 2,9-dimethyl, 4,7-dimethyl, or 5,6-dimethyl), the activity of the catalyst containing the mono-methyl group is higher than that of the corresponding catalyst with two methyl groups; the steric hinder effect is outstanding with the methyl close to N atoms, and the more the number of the methyl is, the lower the activity of the catalyst is. When Cu(5-CH3-phen)Br2 with the highest activity was used as the catalyst under the conditions of total pressure 4.0 MPa, ratio of partial pressure of CO to O2 19:1, reaction temperature 130 癈 and concentration of the catalyst in methanol of 0.011mol 稬-1, the turnover number and selectivity for DMC were up to 67.2 and 96.9%, respectively.