TEMPO (2,2,6,6-Tetramethyl-1-piperidinyloxy radical)-mediated oxidation of primary alcohol groups of galactomannan was studied at pH 10.2 and temperature of 0 ℃ with NaOCl as the primary oxidant. The high selectivity of reaction could be proved by using the FTIR and 13C NMR spectra and the end-point of oxidation process could be determined by the NaOH consumption. The oxidation process was investigated for a series of hydroxypropyl galactomannan with different molar degrees of substitution. It was shown that this oxidation could be used for the determination of the degree of substitution at C-6 position of the substituted galactomannan by comparing the difference of oxidation yields between substituted and natural samples. The formula for determination of the degree of substitution at C-6 position was established according to the consumption of NaOH during the oxidation process. Moreover, the hydroxypropyl reaction mechanism of galactomannan was investigated on the basis of determination of the degree of substitution at C-6 position.

Key words: galactomannan, degree of substitution, hydroxypropyl, TEMPO, selective oxidation