Oleoylation of sugarcane bagasse hemicelluloses using N-bromosuccinimide as a catalyst

Conditions for the preparation of esters of sugarcane bagasse hemicelluloses with oleoyl chloride using N-bromosuccinimide (NBS) as a catalyst in the N,N-dimethylformamide/lithium chloride system under mild conditions were studied comparatively. The oleoylation was followed in terms of yield and degree of substitution (DS). The parameters optimised included oleoyl chloride concentration as the molar ratio of oleoyl chloride/anhydroxylose units in native hemicelluloses (1:1-8:1), NBS concentration (0.5-3.0%), reaction time (20-100 min) and reaction temperature (30100 °C). Results were also compared with those for other catalysts such as H2SO4 and four tertiary amine catalysts, pyridine, 4dimethylaminopyridine, N-methyl pyrrolidine and N-methyl pyrrolidinone. An oleoyl chloride/hemicellulose molar ratio of 3:1 was found to be necessary for the reaction to proceed smoothly and to yield a product with a low DS. The new materials were characterised by FT-IR and 1H and 13C NMR spectroscopies as well as thermal analysis. The thermal stability of the oleoylated hemicelluloses decreased slightly upon chemical modification, but no significant further decrease in thermal stability was observed for DS >= 0.29.