One process is to react the mixed phosphinic acid with triethylamine and trichlorosilane in toluene to produce the mixed phosphine followed by
oxidation to produce the mixed phosphine oxide (see E. P. Horwitz et al., Sol. Ext. and Ion Exch., 4, 449-494, 1986.): ##STR3## However, during the
addition of trichlorosilane a voluminous, thick white precipitate is obtained and it is not possible to stir the reaction mixture unless large amounts
of solvent are used. Difficulties are also encountered with stirring during the hydrolysis. As a result, yields are erratic and poor. Further work
showed that the triethylamine can be eliminated, which reduced the stirring problems. However, if the toluene solution of the acid was below 20° C.
during the addition of trichlorosilane, the reaction mixture would freeze into a sticky solid which made stirring extremely difficult. Yet the
reaction could not be heated above 30° C. during trichlorosilane addition because unreacted trichlorosilane boils at about 31° to 32° C.
It is also possible to produce the mixed phosphine oxide from the mixed phosphinic acid by means of a Grignard reaction. However, the use of a
Grignard reagent requires handling ether, which is highly flammable. Special equipment and facilities are required which are not economical for making
small amounts of materials or for making materials that do not justify the expense. |