A simple non-aqueous method for carboxymethylation of galactomannans

A simple non-aqueous method for the preparation of carboxymethyl (CM) derivatives of galactomannans and other biopolymers has been developed. Galactomannans such as guar, tara and locust bean gums were subjected to carboxymethylation using monochloroacetic acid under the catalytic influence of NaHCO3 in dry state. The ratios of reagent and catalyst as well as the temperature and duration of the reaction were varied to prepare CM derivatives of different DS values ranging from 0.065 to 0.675. The progress of the reaction was followed by FT-IR and 13C NMR spectral data. The reaction carried out in the presence of a small amount (<0.01%) of EtOH (just to surface wet the gum powder) gave CM derivatives having relatively a higher viscosity (3500 cps) than the unmodified gum. Being a mild alkali, removal of NaHCO3 was easier, and the possibility of alkaline degradation caused by strong NaOH and also the effect of elevated temperature could be minimized. Overall the described method adds to the cost effectiveness as well as eco-friendly characteristic of the reaction.