A simple methylation method for obtaining water-soluble O-methyl glucomannan derivatives

Water-soluble O-methyl glucomannan derivatives (O-MGs) with various degrees of substitution were obtained by direct alkylation reaction of an insoluble glucomannan with methyl iodide without any organic solvent including methanol and dimethyl sulfoxide. The structure of O-MGs was characterized by 1H, 13C, 1H 13C NMR-HSQC, and 1H 13C NMR-HMBC spectra. The reactive conditions for synthesizing of O-MG derivatives were also evaluated. The results shown that the optimal conditions for methylation of glucomannan were pH 10, temperature of 40 °C for 3 h. The degree of substitution (DS¯) of O-substitution increased from 0.09 to 0.175 since the ratio (w/v) of glucomannan/methyl iodide changed from 1/3 to 1/15.