GB826801A - Recovery of sucrose esters - Google Patents

Abstract

Esters of sucrose with aliphatic monocarboxylic acids are recovered from crude reaction mixtures containing such esters by removing at least 90% by weight of the reaction solvent, then contacting the remaining crude reaction mixture with water and a partially watermiscible ketone solvent or ester solvent to form an aqueous phase and a solvent phase, whereby the sucrose ester is extracted into the solvent phase, separating the solvent phase and recovering the sucrose ester therefrom. The process is preferably used to recover mono- and di-esters of sucrose and aliphatic acids containing at least 8 carbon atoms. The initial esterification suitably employs a solvent of relatively high boiling point such as dimethylformamide and the removal of at least 90% by weight of the solvent is preferably effected by distillation under reduced pressure. Suitable ketones are aliphatic and cycloaliphatic ketones containing up to 8 carbon atoms per molecule, methyl isobutyl ketone being preferred. Suitable esters are those containing at least 6 carbon atoms and derived from an aliphatic carboxylic acid and an aliphatic monohydric alcohol. The amount of water and ketone or ester solvent is suitably about twice the volume of the reaction mixture. The extraction may be effected at 40 DEG to 80 DEG C. and preferably while maintaining a neutral or slightly acid r H, e.g. 4-7, if necessary by adding acidic substances. The extraction may be carried out batchwise or continuously using a counter-current procedure. Preferably the solvent phase containing the sucrose ester is further contacted with water to form two phases, to remove the last traces of reaction solvent and sucrose into the aqueous phase. In a countercurrent system the outgoing solvent phase encounters a feed of fresh water shortly before leaving the system. The ester may be recovered from the solvent phase by distilling off the ketone or ester in the presence of water, leaving a solution or slurry of product which may be spray dried or drum dried. Alternatively, the water present in the solvent phase may be distilled as an azeotrope with the solvent using a decanting-type still head which continuously returns the solvent phase to the still. The ester may then be recovered by distillation of the solvent or by concentration and crystallization of the sucrose ester. Examples describe the preparation of sucrose esters by reacting sucrose with an alkyl ester of an aliphatic acid in dimethylformamide at elevated temperature in the presence of potassium carbonate as catalyst, and the recovery of the sucrose esters as described above.