Preparation of Methyl and Benzyl Guar using Dimethyl Sulfoxide/Paraformaldehyde Solvent System

Abstract

Guar gum (GG) is a naturally occurring polymer extracted from the seeds of
Cyamopsiss tetragonaloubus plant, GG contains a minimum of 82%
galactomannan. The aim of this study is the etherification of GG under
homogeneous conditions using dimethyl sulfoxide/paraformaldehyde
(DMSO/PF) as a solvent system. Etherification of GG diversifies and enhances
its applications and functionality. GG was obtained and purified then dissolved
in DMSO/PF. The prepared GG ethers were methyl guar and benzyl guar, they
were prepared by the treatment of solubilised GG with dimethyl sulphate and
benzyl chloride in the presence of sodium hydroxide which acts as a reactant
and as a catalyst. Fourier transform infrared spectroscopy (FT-IR) shown new
peaks at 1114.78cm-1 and 1056.99cm-1 indicating (C-O) stretching vibration of
functional group of ether for methyl guar and benzyl guar respectively. The
degree of substitution (DS) was 0.97 for methyl guar and 0.3 for benzyl guar.
The results of thermal stability of purified GG and GG ethers by the thermal
gravimetric analysis (TGA) and differential scanning calorimetry (DSC) showed
that benzyl guar was more stable than the unmodified GG whereas methyl guar
was less stable. The solubility of methyl guar and benzyl guar in different organic solvents was different from the solubility of unmodified GG which only
soluble in water. This study recommends that further research should be carried
out to study the physical and biodegradable properties of the prepared guar
ethers.