壳聚糖担载树状大分子锡配合物催化性能研究

A study on the catalysis of chitosan-supported dendritic tin complexes

通过固相合成方法将各代聚酰胺一胺树状大分子担载于壳聚糖上,外围分别用不同配体进行修饰,再与SnCl_2·2H_2O反应形成两类树状大分子金属锡配合物.对配体和配合物的结构用IR,ICP和XPS进行了表征.此类配合物作为非均相催化剂,对低浓度双氧水氧化环酮和链酮的Baeyer-Villiger反应,在较短反应时间内显示出较好的反应活性.除2-金刚烷酮外,环戊酮、环己酮、4-甲基环己酮、4-叔丁基环己酮、3-甲基-2-戊酮和4-甲基-2-戊酮分别在不同溶剂中,在50～70℃条件下转化为相应的酯和内酯,底物的转化率(67%～99%)和产物的选择性(>99%)均较高.配体(4-羟基苯甲醛、2,4-二羟基苯甲醛和邻羟基苯甲醛)对配合物的锡担载量和催化活性具有一定的影响,其中邻羟基苯甲醛修饰的配合物因具有最高的金属担载量而成为最佳的催化剂.此催化氧化体系以天然高分子壳聚糖为载体,原料来源丰富,廉价.运用固相合成法,使催化剂的制备方法简单.以低浓度H_2O_2为氧化剂,避免了传统B-V反应中使用过酸带来的有害副产物.此催化氧化体系既适用于环酮的氧化,也适用于链酮的氧化,并可回收并重复使用.

Different generations of PAMAM were successfully supported on chitosan by solid phase synthesis. The peripheral amino groups on these dendrimers were modified by 2,4-dihydroxybenzaldehyde and salicylaldehyde; then the ligands reacted with SnCl_2·2H_2O to obtain chitosan-supported dendritic Sn complexes. The ligands and the complexes were well characterized by IR,ICP and XPS.The complexes showed promising catalytic activities for the Baeyer-Villiger oxidation of cyclic and acyclic ketones with environmentally friendly 30%hydrogen peroxide as a heterogeneous catalyst in a shorter time.2-adamantanone,cyclopentanone, 4-methylcyclohexanone,4-tert-butylcyclohexanone,3-methyl-2-pentanone and 4-methyl-2-pentanone were all oxidized in a reaction catalyzed by these complexes at 50～70℃in different organic solvents,affording the corresponding lactones or esters with a high conversion（67%～99%） and selectivity（99%）.The complexes with different ligands（4-Hydroxybenzaldehyde,2,4-dihydroxybenzaldehyde and salicylaldehyde） had different tin loadings and different catalytic activities for Baeyer-Villiger oxidation of ketones.Among them,salicylaldehyd modified Sn complexes were found to be the optimum catalysts as they have the highest tin content.The catalysts could be obtained in a simple and efficient manner and by using natural product chitosan as the supporter, which can be obtained on a large scale with a low cost.This oxidation procedure is promising both for cyclic and acyclic ketones and is much cleaner than those of the traditional B-V oxidation as it is carried out without the use of peracids which would produce harmful by-products.And the catalyst can also be recycled.