羟丙基瓜尔胶中羟丙基摩尔取代度以及取代位置的表征

本文探索了表征羟丙基瓜尔胶(HPG)中羟丙基摩尔取代度(MS)以及取代位置的化学方法.当反应温度为110℃、反应时间为14h以及HPG中羟基与对甲苯磺酸-乙酸酐摩尔比为1:3.5时,用对甲苯磺酸-乙酸酐化学法和气相色谱法可准确测定HPG的羟丙基MS,与1H-NMR测定结果相对误差小于10%.在pH=10.30和0℃的条件下,瓜尔胶的伯羟基被2,2,6,6-四甲基哌啶氮--氧化物(TEMPO)-NaClO-NaBr体系选择性氧化成羧基,由此可表征羟丙基链段的取代位置.

Determination of the molar substitution degree and substitution position of hydropropyl guar gum

An improved chemical method for the determination of the molar substitution degree and substitution position of hydropropyl guar gum has been described.The hydropropyl groups are totally cleaved from modified guar gum at 110℃ in the presence of excess mixed p-toluenesulfonic-acetic anhydride for 14 hours,and the products entirely hydrolyzed into 1,2-dihyroxypropane at pH=11 in an hour.Quantifying the mass of the reaction products derived from the hyropropyl groups,the molar substitution degree of the substituted-hydropropyl guar gum can be exactly estimated,and the relative error of the method is less than 10% compared with the result of the 1H-NMR.Only primary hydroxyl groups can be oxidized to carboxyl groups by use of TEMPO-mediated oxidation,and that is applied for characterizing the substitution position of hydropropyl guar gum.