Sulfation of Chinese lacquer polysaccharides in different solvents

A branched ionic polysaccharide isolated from the sap of the Chinese lac tree (Rhus vernicifera) was chemically modified by sulfation using sulfur trioxide–pyridine (SO3·Py) complex as a reagent. Effects of molar ratio of SO3·Py complex to sugar unit, reaction time and reaction temperature on degree of sulfation (DS) and molecular weights of products were studied. Solvent was another important factor affecting sulfation reaction. In different solvents, when the other conditions remained constant, DS and molecular weights were in the following order: DMSO>DMF>FA (formamide) and DMSO<DMF<FA, respectively. The results depended on the nucleophilicity of the solvents used. The structures of sulfated polysaccharides were investigated by GPC, UV–Vis, FT-IR and FT-Raman spectroscopy. The results indicated that unsaturated bonds and anhydrogalactose residues were formed in lacquer polysaccharides due to the strong dehydration of SO3·Py complex. Based on these, we deduced that degradation of polysaccharide in the sulfation reaction process involved both dehydrolysis and hydrolytic degradation.