Patent GB-998310-A (GB)
Title: Purification of triaryl phosphates
IPC: C07F9/12
Filed: 1962-02-21
Abstract: A triaryl phosphate is purified by continuously distilling the impure phosphate so as to remove high boiling impurities continuously as a base product and to take off both low boiling impurities and the triaryl phosphate in vapour form.  The distillation is preferably a fractional distillation carried out in a column from which the low boiling impurities are taken off overhead while purified triaryl phosphate is taken off from an intermediate point in the column.  The impure triaryl phosphate may be subjected to a preliminary distillation to reduce the amount of high boiling impurities, e.g. a flash distillation, a preliminary continuous fractionation which may be carried out in the same manner as the above defined continuous distillation. The impure triaryl phosphate may be obtained by reacting a phenol with phosphorus oxychloride in the presence of a catalyst, e.g. magnesium chloride, stannic chloride, titanium tetrachloride or a titanium ester.  The phenol may be phenol itself, o-, m-, or p-cresol, cresylic acid, a xylenol, a trimethyl, tetramethyl or pentamethyl phenol, an analogous ethyl, isopropyl, n-propyl, n-butyl, sec.-butyl, tert.-butyl or amyl substituted phenol, a halo-phenol or a nitro-phenol.  The distillation including any preliminary fractional distillation is preferably carried out at sub-atmospheric pressure and is preferably conducted with base pressures of from 15 to 50 mm. Hg and with overhead pressures of from 5 to 35 mm Hg and suitable residence times are from 6 to 30 minutes in the column (for the triaryl phosphate and low-boiling impurities) and 1 to 7 hours for the base residue.  Suitable overhead and base temperatures are 260 DEG  to 285 C. and 300 to 320 DEG  C. respectively for tertiary phosphates of xylenol while for triphenyl phosphate and tricresyl phosphate the temperatures are preferably 30 DEG  to 40 DEG  C. and 15 DEG  to 20 DEG  C. lower respectively. Suitable types of distillation apparatus are described with reference to drawings (not shown) and an example is given for the purification of tricresyl phosphate.ALSO:A triaryl phosphate is purified by continuously distilling the impure phosphate so as to remove high boiling impurities continuously as a base product and to take off both low boiling impurities and the triaryl phosphate in vapour form. The distillation is preferably a fractional distillation carried out in a column from which the low boiling impurities are taken off overhead while purified triaryl phosphate is taken off from an intermediate point in the column.  The impure triaryl phosphate may be subjected to a preliminary distillation to reduce the amount of high boiling impurities, e.g. a flash distillation, or a continuous fractionation which may be carried out in the same way as the above defined continuous distillation.  The impure triaryl phosphate may be obtained by reacting a phenol with phosphorus oxychloride in the presence of a catalyst, e.g. magnesium chloride, stannic chloride, titanium tetrachloride or a titanium ester.  The phenol may be phenol itself, o-, m- or p-cresol, cresylic acid, a xylenol, a trimethyl, tetramethyl or pentamethyl phenol, an analagous ethyl, isopropyl, n-propyl, n-butyl, sec.-butyl, tert.-butyl or amyl substituted phenol, a halo-phenol or nitro-phenol.  The distillation including any preliminary fractional distillation is preferably carried out at subatmospheric pressure and is preferably conducted with base pressures of from 15-50 mm. Hg. and with overhead pressures of from 5-35 mm. and suitable residence times are from 6-30 minutes (for the triaryl phosphate and low-boiling impurities) and 1-7 hours for the base residue.  Suitable overhead and base temperatures are 260-285 DEG C. and 300-320  DEG C. respectively for tertiary phosphates or xylenol while for triphenyl phosphate and tricresyl phosphate the temperatures are preferably 30-40  DEG C. and 15-20  DEG C. lower respectively.  Suitable types of distillation apparatus are described with reference to drawings (not shown) and an example is given for the purification of tricresyl phosphate.