SYNTHESIS AND CHARECTERIZATION OF AUTOCHTHONIC GUAR GUM DERIVATIVES

Abstract

The objective of this research is to introduce new green, nontoxic, cost effective derivatives of guar gum (GG-1). Guar gum is one of the important naturally occurring non-ionic polysaccharide which has incredible applications due to its rheological modifying properties in medicinal, pharmaceutical, food, textile, cosmetics, water treatment, mining, drilling, explosives, confectioneries and scores of other industrial and commercial sectors. Guar gum, also called guaran, is a galactomannan. It is primarily the ground endosperm of guar beans. The guar seeds are dehusked, milled and screened to obtain the guar gum. It is typically produced as a free-flowing, off-white powder.The adaptation of physical properties of GG-1 & GG-2 can improve and diversify its commercial applications. GUAR GUM x In this project, novel and efficient synthesis of five different new derivatives (120-124) of guar gum were done by insitu activation of cinnamic acid, ferulic acid, caffeic acid, coumaric acid and hydrocinnamic acid by coupling with dicyclohexylcarbodiimide (DCC) and N, N-dimethylaminopyridine (DMAP). Effect of temperature, concentration of reactants and time interval plays important role for determining DS value of guar esters. Reaction conditions were optimized for each reaction. Antioxidant potential was examined by DPPH method. A rapid method for protecting the hydroxyl group in sterically hindered gum has been developed by using microwave assisted synthesis (MAS). A novel and efficient synthesis of different guar gum derivatives (126-133) such as acetate, butyrate propionate, maleate, succinate, phthalate, citraconate and glutarate have been developed by microwave irradiation. The maximum ester formation was successfully achieved in 15minutes at 600W by using iodine and DMAP as a reaction promoter. Gum ester formation was obtained by concentration variation at different time intervals. The products were characterized by IR and NMR spectroscopy and SEM. Moreover, degree of substitution was also calculated for each experiment by titration method. First time fatty acid esters (C5-C18) were formulated (136-145) via acid chloride route. Reaction proceeded in two steps. First step involves conventional synthesis of fatty acid chlorides (135a-135j) by reacting corresponding acid with slight excess of thionyl chloride (134). Second step involves esterification of free hydroxyl group of GG-2 with acid chloride; as a result novel derivatives (136-145) with fascinating thickening and emulsifying properties were obtained which might be promising candidate for cosmetic and food industry. Physical properties were examined like solubility, surface morphological study, swelling behavior, gelation index etc. Different spectroscopic techniques were used for structure elucidation. In situ hydrolysis of guar esters were done in DCl during NMR experiments due to the poor solubility of guar derivatives. Guar derivatives with variable degree of substitution (DS) were prepared and were confirmed by FT-IR spectroscopy, presence of carbonyl signal confirmed the formation of guar ester. Further structural elucidation was done by 1H-NMR .Surface morphological study of guar esters was done by scanning electron microscopy (SEM) which showed networking in guar derivatives which xi enhanced when degree of substitution increased. Degree of substitution was determined quantitatively by titration method for each derivative.