Successive Displacements of Phenoxy by Methoxy Groups in Triphenyl Phosphite Ozonide: Mechanism of the Accelerated Singlet Oxygen Formation with Pyridine and Methanol

Article abstract of DOI:10.1021/ja00345a054

The ozonides from triphenyl phosphite, methyl diphenyl phosphite, and phenyl dimethyl phosphite form a series (1-3) which liberate singlet thermally at rates incresing by an order of magnitude for each substitution of methoxy for phenoxy.Trimethyl phosphite ozonide (4) fits in this series, although the very low temperature limit of its stability has not been determined.When triphenyl phosphite ozonide (1) is treated with methanol and pyridine in methylene chloride and yields singlet oxygen at an accelerated rate, the phenyl methyl phosphates 6 and 7 and trimethyl phosphate (8) are produced in a total amount corresponding to the singlet oxygen evolved.The lower the temperature, the greater the predominance of trimethyl phosphate (8) in the product.Each of the mixed phosphite ozonides 2 and 3 is in turn subject to accelerated singlet oxygen formation by the action of methanol and pyridine; in each case the phosphates formed contain at least one more methoxy group than the starting ozonide.These facts establish the mechanism of the accelerated singlet oxygen liberation as a successive displacement of phenoxy by methoxy groups on the initial phosphite ozonide, each newly formed aliphatic-aromatic phosphite ozonide decomposing thermally at its own increased rate.