PHOTOINITIATED AUTOCATALYTIC CHAIN DECOMPOSITION OF PHENYL AZIDE.

Article abstract of DOI:10.1021/ja00315a042

Quantum yields of disappearance of phenyl azide ( phi -PhN//3) were determined for 10** minus **5-10** minus **1 M acetonitrile solutions at room temperature by monitoring changes in its electronic absorption spectra. For dilute solutions, phi -PhN//3 equals 0. 5; however, at higher concentrations phi -PhN//3 values greatly exceed unit efficiency and indicate a chain decomposition mechanism. At ca. 2 multiplied by 10** minus **1 M, phi -PhN//3 approximately equals 3000! A plot of left bracket phi -PhN//3 right bracket vs. log left bracket PhN//3 right bracket appears exponential and since a plot of the chain length, n, vs. left bracket PhN//3 right bracket is linear (r**2 equals 0. 972), when n is calculated from an exponential function, the experimental results provide evidence for a branching chain reaction also known as an autocatalytic (spontaneously explosive) reaction. The branching chain mechanism is thought to result from reaction of a phenyl nitrene intermediate with a ground-state phenyl azide molecule to form two phenyl nitrenes. A 1,4-tetraazadiene or triaza species may also participate in the chain reaction.