A reexamination of the ozone-triphenyl phosphite system. The origin of triphenyl phosphate at low temperatures

The reaction of ozone with triphenyl phosphite (P) at -78 degrees C affords a labile 1:1 complex (PO3) together with small amounts of triphenyl phosph ate (PO) (Q. E. Thompson, J. Am. Chem. Sec. 1961, 83, 845). In this work we found that the amount of PO present initially after complete ozonation of P in toluene was 12 +/- 2% at -78 degrees C and 11 +/- 2% at -95 degrees C. Partial ozonation of solutions of P in toluene at -78 degrees C gave mixtu res of P, PO, and PO3 whose composition changed with time as a result of th e reaction of P with PO3 to give additional PO. Between -25 and -60 degrees C, the rate constant of the latter reaction is given by the expression log k (M-1 s(-1)) = (8.64 +/- 0.04) - (11.44 +/- 0.74) kcal/RT. This reaction at -78 degrees C is too slow to account for the PO formed during the ozonat ion, which is proposed to arise instead by competitive reactions of an inte rmediate. The solubility of PO in toluene at -78 degrees C was measured as 0.06 M, and that of PO3 about 6 times greater.