Taguchi design-based synthesis and structural analysis of Cassia galactomannan hydroxypropyl derivative

Hydroxypropylation is a significant industrial process for diverse applications of polysaccharides. In the present study hydroxypropylation of Cassia gum derived from ruderal Cassia tora species was investigated using Taguchi's L'16 orthogonal array design of experiments. The optimized reaction conditions comprised: reaction temperature 50 °C, time 240 min, sodium hydroxide (0.015 mol), propylene oxide (0.0755 mol) and 60% aq. propane-2-ol. The maximum hydroxypropyl content, 8.43 and 7.71% were achieved using chromic acid titration and 1H NMR spectroscopic analysis respectively in the optimized product. The chemical shift values of substituted hydroxypropyl groups for methyl, methine and methylene protons at 0.98, 3.87 & 3.41 ppm along with respective carbons at δ 18.23, 69.41 & 79.13, and other assignments, 1H and 13C signals, were confirmed by COSY and HSQC correlation spectral analysis. The substituted hydroxypropyl groups, C 6 of the β-D-1, 4-linked-Manp unit, were established at 66.18 ppm.