A Quantitative Study of the Photostimulated Reaction of Iodobenzene with Diethyl Phosphite Ion

The photostimulated reaction of iodobenzene with potassium diethyl phosphite (KDEP) in Me2SO solution to form diethyl phenylphosphonate occurs with raw quantum yields at 313 nm considerably in excess of unity, frequently 20-50. Reaction rate is proportional approximately to the 0.84 power of light intensity. The dependence of quantum yield on KDEP concentration may be interpreted either on the basis that the photons absorbed by iodobenzene or the photons absorbed by a charge-transfer complex of iodobenzene with diethyl phosphite ion are responsible for initiation. Each of these alternatives is compatible with a different initiation mechanism. The quantum yield under conditions such that all the light is absorbed is independent of iodobenzene concentration. These facts are consistent with a radical chain mechanism with initiation as in steps 8 and 9, 8 and 10, or according to Scheme II, propagation according to Scheme I, and termination mainly via step 16 or 17 with a minor contribution from step 18.