Abstract: | Kinetics and Mechanism of Aryldiazonium Salt Photolysis in Methanol. Determination of Absolute Rate Constants of Some Reaction Steps For benzene diazonium tetrafluoroborate and some p-substituted derivatives, the following values are determined: - velocity constants for the photochemical electron transfer from pyrene and benzanthracene to aryl diazonium salts in acetonitrile solution (determination by quenching the donor fluorescence).
- velocity constants for electron transfer under the condition of pulse radiolysis in tert.-butanol-water solution;
- quantum yields and product composition (ArOMe, ArF and ArH, respectively) for the photolyses in methanol in the presence of varying concentrations of 2-methyl-2-nitroso-propane as a quencher of the thermal chain reaction.
The electron transfer reaction comes out be a diffusion controlled reaction, kE = 2 …︁ 3 × 1010 M−1 s−1. For the total reaction a kinetic model is set up which affords absolute velocity constants from the experimental results for the following steps: Hydrogen transfer within the case radical pair documentclass{article}pagestyle{empty}begin{document}$ overline {{rm Ar} - {rm N} = {rm N}{rm . CH}_{rm 3} {rm OH}{rm .}} {rm }^ oplus $end{document} (formation of ArH) kH ≈ 1011 s−1; Maximal values for the photo-solvolyses (formation of Ar⊕ → ArOMe and ArF, respectively), ks ≲ 10−1; Trapping of aryl radicals outside of the solvent cage by t-BuNO, kq ≈ 2 × 107 M−1 s−1. The results are discussed in the light of the kinetic model and some other facts. |