GB778081A - Improvements in or relating to separation of acid alkyl phosphates - Google Patents

Abstract

A method of separating the mono- and dialkyl phosphates of an alkyl alcohol in a mixture thereof or of increasing substantially the concentration of one of the acid alkyl phosphates with respect to the other comprises treating the mixture with two substantially immiscible solvents, one of which is a glycol and/or water and the other is an aromatic or an alicyclic hydrocarbon to bring about partition of the acid alkyl phosphates between the solvents, allowing the resulting phases to settle and separating the phases. The separated phases may be washed each with a quantity of the solvent immiscible therewith to improve the degree of separation and the washed phases may then be treated, e.g. by distillation, to remove the more volatile component. The partition may be brought about by dissolving the mixed alkyl phosphates in the aromatic or alicyclic hydrocarbon and intimately mixing an equal volume of a glycol and/or water with the solution until equilibrium is reached, allowing the mixture to settle and then separating the phases. In examples: (1) a commercial n-octyl phosphate containing 56.7 per cent of mono-n-octyl phosphate and 27.0 per cent of di-n-octyl phosphate is agitated with equal volumes of benzene and ethylene glycol and the phases allowed to separate, the distribution ratio into the benzene phase being 0.264 for the monoester and 4.43 for the diester. Other solvent pairs referred to for use with the same phosphate mixture are xylene/ethylene glycol, xylene/diethylene glycol, mesitylene/ethylene glycol, cyclohexane/ethylene glycol, tetrahydronaphthalene/ethylene glycol and decahydronaphthalene/ethylene glycol; (2) commercial 2-ethyl hexyl phosphate containing 43.2 per cent of the monoester and 52.7 per cent of the diester is treated as in (1) with the following solvent pairs: benzene/ethylene glycol, xylene/ethylene glycol, cyclohexane/ethylene glycol, tetrahydronaphthalene/ethylene glycol and decahydronaphthalene/ethylene glycol; (3) commercial 3,5,5 - trimethylhexyl phosphate containing 35.9 per cent of the monoester and 61.7 per cent of the diester is treated as in (1) with the following solvent pairs: benzene/ethylene glycol, toluene/ethylene glycol, xylene/ethylene glycol, cyclohexane/ethylene glycol, tetrahydronaphthalene/ethylene glycol and decahydronaphthalene/ethylene glycol. Equal volumes of the hydrocarbon and glycol are employed in each case and the distribution ratios of the mono- and diester into the hydrocarbon phase are given. In the cases of Examples (2) and (3) two washes of the separated phases with equal volumes of the solvent immiscible therewith result in substantially complete separation of the esters. On removal of the solvent a small amount of the monoester remains in the diester fraction. For the separation of dibutyl phosphate and monobutyl phosphate water is preferably employed instead of a glycol. The process is stated to have particular application to the separation of acid alkyl phosphates having up to 10 carbon atoms in the alkyl group.