Polysaccharide derivatives and preparation thereof

A m- or p-sulphobenzoyl ester of a polysaccharide or a polysaccharide derivative containing free hydroxyl groups is made by reaction of the polysaccharide, in presence of a tertiary organic base, with a m- or p-halogenosulphonylbenzoic acid. The benzene nucleus of the acid may be substituted by groups inert to reactants and reaction products, e.g. nitro or alkyl groups, or halogen atoms. The polysaccharide may be e.g. cellulose, starch, amylose, amylopectin, alginic acid and partially esterified and/or etherified derivatives thereof, e.g. cellulose acetate, ethyl-, benzyl- and hydroxyethyl celluloses. Specified acids are m- and p-chlorosulphonyl benzoic acids. Specified tertiary organic bases are anhydrous pyridine, dimethyl-and diethyl aniline, trimethylamine and triphenylamine. Reaction is carried out at room temperature for e.g. 24 hours or at 60-80 DEG C. for e.g. 4-6 hours, the product is a salt of the tertiary base, and may be converted to free acid ester by known methods. In a typical example, hydroxyethyl cellulose (D.S. 0.85) and p-chlorosulphonyl benzoic acid are added to anhydrous pyridine. After reaction at 80 DEG C. for 24 hours, hydroxyethyl cellulose-p-sulphobenzoate is precipitated in dilute HCl. The esters, as free sulphonic acids or as alkali metal, ammonium or tertiary base salts, are used as binding and thickening agents in photographic materials (see Division G3).