GB573723A - Improvements in or relating to the manufacture of polymerisable unsaturated acids - Google Patents

Abstract

In the production of unsaturated acids by oxidation with molecular oxygen of acrolein and its a -substitution products, a diluent is added before distillation of the product in such quantity as to reduce the concentration of the acid that at the distillation temperature polymerization of the acid is substantially prevented. When a solvent is used in the oxidation, it may be distilled off before the distillation, or the solvent and the diluent may be the same substance. Preferably the diluent is not more volatile than the acid to be made; if the diluent is more volatile, it may be made to entrain the acid without allowing its quantity in the still to fall below the necessary amount. Suitable diluents are anisol, phenetol, diamyl ether, acetic, chloracetic, butyric and isobutyric acids, amyl propionate and acetate, ethylidene diacetate, xylene, isopropyl benzene, tetrachlorethane, chlortoluene, pentachlorethane, and ketones. Alcohols such as cyclohexanol, methyl cyclohexanol and furfuryl, tetrahydrofurfuryl and amyl alcohols may be used if the temperature is below the esterification temperature. Preferably the distillation is effected at reduced pressure. Any unoxidised aldehyde or low-boiling solvent present may be distilled off before the acid or together with the acid. In examples: (1) and (2) acrolein dissolved in acetic acid is oxidized with molecular oxygen in presence of vanadium pentoxide; the unchanged acrolein is removed by gaseous oxygen, the mixture diluted with anisol or acetic acid, filtered and distilled; (3) a mixture of acrolein, anisol and acrylic acid is oxidized, more anisol is added and distillation is effected in vacuo at 42 DEG C.; (4) a mixture of acrolein and ethylidene diacetate is oxidized, more ethylidene diacetate is added and the mixture distilled. Specification 560,166 is referred to.