Laser flash photolysis studies of methoxycarbonyl phenyl carbene and its derived carbonyl oxide at room temperature

Abstract

Laser flash photolysis of methyl ..cap alpha..-diazophenylacetate gives triplet methoxycarbonyl phenyl carbene (/sup 3/MPC) exhibiting a transient absorption spectrum (< 270 nm), which shows a pseudo-first-order decay with lifetime of 461 ns in deaerated Freon 113. The triplet carbene readily reacts with an oxygen molecule to afford a corresponding carbonyl oxide in aerated solvents at room temperature. The formation of carbonyl oxide was demonstrated by the buildup of the transient absorption spectrum (lambda/sub max/ approx. 410 nm) at the expense of the absorption band of the carbene. Quenching rate constants of this triplet carbene by 2-methyl-2-butene and methyl alcohol were obtained to be 7.0 x 10/sup 7/ M/sup -1/ s/sup -1/ and 2.7 x 10/sup 8/ M/sup -1/ s/sup -1/, respectively, by means of monitoring the decay of the triplet carbene. The difference of the reactivity between the triplet carbene and the carbonyl oxide toward methyl alcohol has been investigated. The carbonyl oxide is much more stable with methanol than the parent triplet carbene (/sup 3/MPC). Kinetic data reported in this paper demonstrate that the stability of this carbene (/sup 3/MPC) is regarded as an intermediate between reported diphenylcarbene and fluorenylidene.