Distillative purification of 2,5-dioxo-1-oxa-2-phospholanes

摘要

2,5 DIOXO-1-OXA-2-PHOSPHOLANES OF THE GENERAL FORMULA: in which R1 stands for an alkyl radical having from 1 to 4 carbon atoms, or a phenyl radical, and R2 and R3 each stand for hydrogen or CH3, are distillatively purified. To this end the respective crude compound is preheated to 120 DEG to 160 DEG C and fed to the head of a distilling column provided with a plurality of individually heatable trays maintained at temperatures increasing from the upper-most tray to the lowermost, the uppermost tray in the column being maintained at 120 DEG to 160 DEG C and the lowermost tray being maintained at 160 DEG to 200 DEG C, the pressure at the head of the column being 20 to 200 mm Hg, preferably 50 to 120 mm Hg; an inert gas preheated to 160 DEG to 200 DEG C is introduced countercurrently at the base of the column; those impurities having a boiling point lower than that of the respective 2,5-dioxo-1-oxa-2-phospholane are withdrawn overhead together with the inert gas; the 2,5-dioxo-1-oxa-2-phospholane thus freed from low-boiling impurities is withdrawn from the base of the distilling column and passed to a film evaporator; and the 2,5-dioxo-1-oxa-2-phospholane is distilled off from higher-boiling impurities in the film evaporator under a pressure of 0.1 to 5 mm Hg.