Patent GB-1015201-A (GB)
Title: Process for the preparation and recovery of trimethyl phosphite and derivatives thereof
IPC: C07F9/16
Filed: 1961-12-11
Abstract: A mixture containing trimethyl phosphite contaminated with reactants from which it was made and with by-products of the reaction in which it is made, and methanol is distilled to yield a vapour phase consisting of a mixture of trimethyl phosphite and methanol and substantially pure trimethyl phosphite is recovered from the mixture by distillation.  The mixture containing the trimethyl phosphite may be that obtained by reacting phosphorus trichloride with methanol in the presence of a hydrogen chloride acceptor, e.g. triethylamine, but is preferably that obtained by transesterifying an aryl-substituted phosphite selected from aryl dimethyl phosphites, diaryl methyl phosphites and triaryl phosphites with methanol preferably in the presence of a basic transesterification catalyst.  In carrying out the latter process the reaction mixture is distilled in the presence of sufficient methanol to prevent back-transesterification of the trimethyl phosphite and to permit co-distillation of methanol and all the trimethyl phosphite from the reaction mixture while maintaining some methanol in the distillation residue.  Trimethyl phosphite may be separated from the gaseous distillation mixture by adding a methanol azeotrope former to the mixture either before or after condensing the mixture and stripping a mixture of methanol and the azeotrope former from the trimethyl phosphite.  Suitable azeotrope formers are cyclohexane, benzene, toluene, acetonitrile, ethyl nitrate, acetone, methyl acetate, methyl borate, thiophene, methyl cyclohexane, methyl cyclopentane, cyclopentene, cyclopentane, n-pentane, hexanes, heptenes, n-octene, 2,2,4-trimethyl pentane and other octanes and dipropyl ether.  The basic transesterification catalyst is suitably Na, K, Li, sodium, potassium or lithium hydride, sodium borohydride, lithium aluminium hydride, NaOH, sodium, potassium or lithium sulphide, sodium methylate or ethylate, sodium or potassium phenolate, butyl lithium, phenyl sodium, aluminium isopropoxide, sodium cetylate or octadecylate, diethyl aniline, quinoline, monododecyl monomethylamine, pyridine and monododecyl dimethyl amine.  When an alcoholate is used it may be formed "in situ" by adding the appropriate metal to the methanol.  A wide variety of aryl-substituted phosphites including substituted aryl phosphites may be used in the transesterification reaction and several such phosphites are specified including triphenyl, tricresyl, diphenyl methyl- and phenyl dimethyl-phosphites. The transesterification can be carried out by a batch, recycle or continuous technique.  In the batch technique methanol and the aryl substituted phosphite are added to the reaction vessel in such proportion as to provide an excess of methanol and the basic catalyst then added.  Reaction is generally effected at 80-150 DEG  C. and the mixture distilled while adding to the distillation pot sufficient methanol to prevent back-transesterification of the trimethyl phosphite and the distillate comprising a mixture of methanol and methyl phosphite is either collected for further processing or mixed with an azeotrope former and distilled to yield pure trimethyl phosphite. In the recycle technique the aryl phosphite, methanol and catalyst are added to a reaction vessel provided with a distillation column and heating means and the distillation column is provided with a condenser from which the condensate is conveyed to the product vessel.  The latter is also provided with a distillation column and heating means and the gases from the top of the distillation column are condensed in a condenser and recycled to the reaction vessel. In this form of the process an azeotrope former and additional methanol may be added to the product vessel and the condensate from the distillation column may be separated in a liquid separator to form a methanol rich layer and an azeotrope-former rich layer and the methanol rich layer fed to the reaction vessel while the azeotrope-former rich layer is returned to the product vessel. Suitable apparatus for carrying out the continuous technique comprises a reaction vessel equipped with heating means, means for charging the reactants and catalyst, and piping for the continuous outflow of the transesterified mixture to a co-distillation vessel which is equipped with heating means, piping means for a continuous outflow of non-volatiles, a fractionation column provided with a condenser and a fraction splitter to permit partial flow of the condensate to the top of the column as reflux and the remainder to flow to a collection vessel for the condensed volatiles from the co-distillation vessel.  The reactants and catalyst are suitably maintained in the reaction vessel at 80-150 DEG  C. and after an appropriate residence time the transesterified mixture is fed continuously to the co-distillation vessel maintained at 80-150 DEG C. where a mixture of methanol and trimethyl phosphite is vaporized and passes up the fractionation column to the condenser where it is condensed.  The condensate in the collection vessel is a solution of trimethyl phosphite in methanol which can be reacted continuously with a suitable chemical reagent, e.g. sulphur, while continuously stripping methanol and returning it to the reaction vessel or a methanol azeotrope former may be added to the condensate which is then fed to a continuous fractionation column from which the methanol azeotrope passes overhead and is condensed into a methanol-rich layer and a methanol azeotrope-former-rich layer which are recycled to the appropriate stream.  The concentrated trimethyl phosphite passes down the column and is collected as bottoms product. The trimethyl phosphite product or the various mixtures containing it along with methanol and/or azeotrope former may be further processed to yield derivatives of trimethyl phosphite. Thus reaction may be effected with (a) sulphur to yield trimethyl phosphorothionate, (b) with selenium to yield trimethyl phosphoro-selenonate, (c) with CH3Br or CH3I or sodium or potassium iodide or bromide to yield dimethyl methyl phosphonate and (when methanol is also present) dimethyl hydrogen phosphite, (d) with HCl, HBr and HI to yield dimethyl hydrogen phosphite and the corresponding methyl halide, (e) with phenols and alkyl, alkenyl, and other alcohols including polyhydric alcohols under basic catalysis to yield various triphosphites and mixed phosphites containing methyl groups and other aliphatic or aryl groups, (f) with oxygen and oxygen-containing gas mixtures and catalysts to yield trimethyl phosphate, (g) with alkylene oxides to yield trimethyl phosphate and ethylene, (h) with nitrogen oxides or peroxides to yield trimethyl phosphate, (i) with chloral to yield dimethyl dichlorovinyl phosphate, and (j) with an alkylene dibromide to yield the corresponding tetramethyl alkylene bis-phosphonate. Other phosphite esters produced by transesterification of the trimethyl phosphite with other alcohols and phenols may also be reacted with sulphur and selenium to form the corresponding phosphorothionate or phosphoroselenonate esters, with corresponding alkyl halides to form isomeric phosphonates and with oxygen, oxygen-containing gas, peroxides, hydroperoxides or nitrogen oxides to form the corresponding phosphates. The trimethyl phosphite or the various mixtures containing it may also be hydrolysed with water to form dimethyl hydrogen phosphite. Details are given for carrying out the various further reactions mentioned and several products obtainable by such reactions are specified.  Other reactions referred to are (1) the production of bis- or poly-phosphonates by reaction of organic di- or poly-halides with tri-methyl phosphite and several suitable halides are specified and (2) the reaction of dimethyl hydrogen phosphite with chloral to form O,O-dimethyl - 1 - hydroxy - 2,2,2 - trichloroethyl phosphonate, the reaction being carried out in the presence as solvent of the dimethyl methyl phosphonate also obtained in reaction (3) above.  The trimethyl phosphite and other triphosphite products obtained by transesterification can also be reacted with thiophenols or mercaptans to give thiophosphite products or with unsaturated mono- or dibasic organic acids, or unsaturated aldehydes or glycerides to yield useful commercial products.  Several examples are given for the production of trimethyl phosphite, derivatives thereof, and other tertiary phosphite esters and their derivatives. Reference has been directed by the Comptroller to Specification 933,029.