消除法制备低氯漂白紫胶及机理

在漂白紫胶乙醇溶液中加入乙醇钠(一种亲核试剂),选择性与紫胶分子中结合氯的碳原子反应,脱除漂白紫胶中的氯,制备了低氯漂白紫胶。研究乙醇钠加入量、反应温度和反应时间对脱氯效果的影响。结果表明:100g漂白紫胶中加入4.2g的乙醇钠,在90℃反应90min脱氯效果最佳;最佳反应条件时,产品中氯的质量分数为0.28%,远低于脱氯前的2.6%。紫外光谱分析表明,漂白紫胶最大吸收峰的波长由236nm蓝移至222nm,脱除结合氯后最大吸收峰的波长值恢复。通过亲核消除反应,乙醇钠能脱除漂白紫胶的结合氯,漂白紫胶脱氯前后的结构不同。

Preparation and Mechanism of Low Chlorine Shellac by Means of Elimination Method

Sodium ethaxide,one kind of nucleophiles,was added into bleached seedlac alcohol solution as dechlorination agent.It can react selectively with the carbon atom connected with chlorine,as a re-sult the chlorine was removed by means of elimination reaction,and the products with low chlorine content was prepared.The effects of factors controlling the reaction on dechlorination efficiency were studied,such as dosage,temperature and time etc.,and the structure of seedlac,shellac and low chlorine shellac were characterized by ultraviolet spectrometer.The results show that the conditions routed as dosage of 4.2g sodium ethanol per 100g bleached shellac,temperature as 90℃ and time as 90min are the optimal,and that the content of chlorine in the final products is 0.28% which is far smaller than 2 .6%that of the products without dechlorination.Ultraviolet spectrometer analysis indi-cates the maximum adsorption wave of shellac is blue shifted to 222nm from 236nm,however it is recovered while the shellac is processed by dechlorination with sodium ethanol.As a result,the com-pacted chlorine of shellac can be eliminated by the process with the nucleophile,and the structure of shellac before and after elimination is different.