Abstract:

Perioate oxidation of vicinal hydroxyls is a highly selective reaction which leads to the cleavage of the C—C bond and formation of dialdehyde groups. The reactions of periodate with guar gum(GG) and hydroxypropyl guar gum(HPG) were investigated at pH=4.3 and 25 ℃ and the oxidized products were characterized with IR and NMR. The results show that aldehyde groups in oxidized GG and HPG are in the form of hemiacetal structures like other polysaccharides such as starch and cellulose. The oxidation degree and the content of vicinal hydroxyls in GG and HPG were determined by the consumption of periodate(P_t) and the degree of substitution at the secondary hydroxyls(DS_S—OH)of HPG was calculated by probability analysis. The results of HPGs with different molar substitution of 0.04, 0.14, 0.36, 0.51, 0.78, 1.05 and 1.53 are 0.02, 0.09, 0.18, 0.30, 0.46, 0.59 and 1.03 respectively, which are in good agreement with the values found in the literature by other methods. Other polysaccharides, such as methyl cellulose also gave good results on the values of by the method of periodate oxidation.

Key words: Sodium periodate; Guar gum; Hydroxypropyl guar gum; Degree of substitution of secondary hydroxyl