高分子多糖载体对四苯基金属卟啉催化性能影响

在壳聚糖四苯基金属卟啉中, 氨基或羟基可能对金属卟啉的稳定性和催化活性起重要作用. 为探索这两类基团的作用效果差异, 并调查具有类似壳聚糖结构的纤维素作为载体, 对金属卟啉的保护以及羟基的协助催化作用, 制备了纤维素四苯基铁、钴和锰卟啉. 研究了纤维素四苯基铁、钴和锰卟啉催化空气氧化环己烷的能力, 并与相应的壳聚糖金属卟啉比较. 在418 K和0.8 MPa的空气压力下, 纤维素四苯基铁(钴或锰)卟啉均只能作一次性催化而耗尽; 所获得的醇酮选择性均低于相应的壳聚糖四苯基金属卟啉. 研究结果表明: 纤维素对四苯基铁、钴和锰卟啉没有明显的保护作用, 羟基对其催化环己基过氧化氢的协助分解作用也比较小. 壳聚糖对金属卟啉有很强的保护作用, 氨基有较强的协助金属卟啉催化环己基过氧化氢分解的能力, 使醇酮选择性提高.

Effect of Polysaccharide Supports on Catalytic Performance of Metal Tetraphenylporphyrin

The amino groups or the hydroxyl groups on the chitosan-supported metal tetraphenylporphyrins may play a key role in improving the stability and the catalytic activity of metalloporphyrins. To investigate the different effect produced by two kinds of groups, the situation of metalloporphyrins protected by cellu-lose from destruction and the cocatalysis of hydroxyl groups, three supported metalloporphyrins were pre-pared by adsorbing iron, cobalt and manganese porphrin onto chitosan-structure-like cellulose. The amount of metalloporphyrin adsorbed on cellulose was measured by UV-vis spectroscopic technique. The catalysis of the three supported catalysts for aerobic oxidation of cyclohexane was studied in absence of any solvents and reductants, and compared with those of the three chitosan-supported metalloporphyrins accordingly. Under the reaction condition of 418 K and 0.8 MPa air pressure, three cellulose-supported metalloporphyrins were used to perform catalysis for aerobic oxidation of cyclohexane once and exhausted respectively. The selectivity of alcohol and ketone acquired from the three catalysts respectively was lower than those from the corresponding chitosan-supported metalloporphyrins. The results indicate that cellulose has not any pro-tection of them from destruction by oxygen, and the hydroxyl groups in the two kinds of supports have weak cocatalysis of metalloporphyrins for decomposing cyclohexyl hydrogen peroxide into ketone and alcohol. Inversely, chitosan has stronger protection of metalloporphyrins from destruction and the amino groups on it have stronger cocatalysis of metalloporphyrins for decomposing cyclohexyl hydrogen peroxide into productsneeded. Therefore, the acquired selectivity of alcohol and ketone was higher.