【摘要】 本文探索了表征羟乙基瓜尔胶(HEG)中羟乙基摩尔取代度(MS)以及取代位置的化学方法。当反应温度为110℃,时间为14hr,HEG中羟基与混酐比例为1:2.5时,用混酐化学法可准确测定HEG的羟乙基MS,测定结果与计算值的相对误差小于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,由此可表征羟乙基链段的取代位置。在瓜尔胶醚化生成羟乙基瓜尔胶的过程中,醚化反应并不是完全发生在伯羟基上。伯羟基的反应活性是仲羟基的6-10倍。随着MS的增大,连接在仲羟基上羟乙基链段占所有羟乙基链段的比例逐渐增大,当MS=0.4时该比例基本不再变化,为40%左右。更多还原

【Abstract】 An improved chemical method for the determination of the molar substitution degree and substitution position of hydroxyethyl guar gum has been described.The hydroxyethyl groups are totally cleaved from modified guar gum at 110℃ in the presence of excess mixed p-toluenesulfonic-acetic anhydride for 14 hours,and then the products entirely hydrolyzed into ethylene glycol at pH=11 in an hour.Quantifying the mass of reaction products derived from the hydroxyethyl group,the molar substitution degree of the low-substituted hydroxyethyl guar gum can be exactly estimated,and the relative error of the method is less than 10%.When TEMPO-mediaed was used for the oxidation of guar gum,only primary hydroxyl groups in guar can be selectively oxidized to carboxyl groups.The resaults indicate that the activity of the primary hydroxyl groups is 6-10 times of that of the secondary hydroxyl groups.And etherification mainly occurs on the primary hydroxyl groups when the molar substitution degree of the guar gum is low,the percentage of hydroxyethyl groups increases with molar substitution degree,which link to secondary hydroxyl groups,however,it is up to a stable value(about 40%) when the molar substitution degree equal to 0.4.更多还原