GB722594A - Improvements in the manufacture of cellulose esters - Google Patents

Abstract

A dicarboxylic acid ester of cellulose or of a cellulose derivative is obtained by treating the cellulosic material under substantially anhydrous conditions with a dicarboxylic acid anhydride in the presence of a lower aliphatic carboxylic acid, containing 1-4 carbon atoms in the molecule, as solvent and of an acid-soluble salt which exhibits basic properties in non-aqueous solution. The cellulosic material may be cellulose, a cellulose ether or a cellulose ester. The anhydride may be phthalic, nitrophthalic, succinic or maleic anhydride, and the acid-soluble salt may be an acetate of an alkali metal, alkaline-earth metal or organic amine. It may be sodium, potassium, ammonium, calcium, magnesium, methylamine or pyridine acetate, or trisodium phosphate. The proportion of the salt may be within the range of 5-350 per cent by weight of the cellulosic starting material. The esterification may be carried out at 60 DEG C. up to the reflux temperature of the reaction solvent. Precipitation of the ester may be effected by adding sufficient water to the reaction mass to cause precipitation at 55-95 DEG F. The solution may be neutralized, before precipitation, by the addition of an acid such as hydrochloric or sulphuric acid. In an example, regenerated cellulose is soaked in water and then the water is removed by means of glacial acetic acid. The cellulose impregnated with acetic acid is introduced into a bath containing acetic acid, pyridine acetate and phthalic anhydride. The mixture is maintained at 100 DEG C. until the cellulose has dissolved. The cellulose phthalate formed is precipitated by pouring the solution into acidulated water. In another example, cellulose acetate containing free hydroxyl groups is mixed with phthalic anhydride, sodium acetate and propionic acid. The mass is heated on a steam bath for 6 hours and the product is precipitated from the solution by the addition of water. Butyric acid or acetic acid may be used as solvent instead of propionic acid. In other examples, the starting material is ethyl cellulose containing free hydroxyl groups and it is reacted with nitrophthalic anhydride, succinic anhydride or maleic anhydride in presence of sodium acetate and acetic acid.