Laser flash photolysis study of the decay kinetics of carbocations of 1,2,2,4-tetramethyl-1,2-dihydroquinoline in the porous glass in the presence of methanol

Abstract

The efficiency of formation and the decay kinetics of carbocations formed under the photolysis of 1,2,2,4 tetramethyl 1,2 dihydroquinoline in methanol and in a porous glass filled with methanol or dried in air or in vacuo were studied by the laser flash photolysis techniques. In MeOH, the carbocations recombine via the second order law in the reaction with the MeOanion formed in an equimolar amount and decay via the first order law in the reaction with the solvent with rate constants of 3•10 8 L mol -1 s -1 and 1.4•10 3 s -1 , respectively. When the solution is placed into the porous glass, no recombination of the carbocations with MeO -is observed, and the reaction with the solvent is somewhat inhibited (rate constant 8•10 2 s -1 ). More than tenfold inhibition of the reaction of the carbocations with methanol is observed on going to a monolayer of MeOH on the surface. The main route of carbocation decay in the porous glass dried in vacuo is the geminate recombination with the SiO groups. The corre sponding kinetics is described in terms of the model of freely diffusing reactants.

Laser Flash Photolysis of Benzophenone in Polymer Films

“…It is expected that γ is a relatively low value of, e.g., 1–10. , We recall that γ is a width of a distribution of a logarithm of a rate constant. High γ (more than ∼10) means a huge span of rate constants and does not have physical meaning that way.…”