中等分子量的κ-卡拉胶乙酰化方法的筛选

Screening of methods for acylating κ-carrageenan with middle molecular weight

选择常规直接酰化、相转移催化酰化和离子交换-酰化共3种方法对3万中等分子量的κ-卡拉胶进行了乙酰化反应.气相色谱分析表明,采用常规直接酰化时反应难以进行;以四丁基溴化铵为催化剂的相转移催化酰化法因第一步的固液离子交换较难进行而只能稍许提高酰化度,也无实际应用价值;离子交换-酰化法却因能显著增强κ-卡拉胶在有机溶剂中的溶解性而大大提高了κ-卡拉胶的酰化度.红外光谱分析结果指出,只有离子交换-酰化法所获得的酰化κ-卡拉胶具有典型的乙酸酯吸收特征峰.研究集中揭示了中等分子量的κ-卡拉胶选择先经离子交换转型后酰化的方式较适宜.

Three methods （conventional direct acylation, acylation by phase transfer catalyst （PTC）, and ionexchange - acylation） were selected for the purpose of acetylating κ- - carrageenan with 30kDa molecular weight. The gas chromatograph （GC） analysis shows that, the first method is nearly impossible ; in comparison, the second method fails to distinctively improve the acylation substitution degree when tetrabutylammonium bromide, the common PTC was used ; the third method can greatly increase the substitution degree. Thus, only the third method has the practical value. The IR analysis confirms that only the IR spectrum of acylated carrageenan from the third method bears the typical characteristic absorption peak of acetate. As compared with the GC analysis for acylated carrageenan, which must follow a complicated and unstable pretreatment process of samples, the IR analysis can work as a qualitative analysis means for screening the methods for acylating carrageenan.