Solvent effect on reversible self-termination reactions of aromatic free radicals

✍ Scribed by I. V. Khudyakov; V. A. Kuzmin; A. I. Yasmenko; W. Smit; J. Salve; C. R. H. I. De Jonge

• Publisher: John Wiley and Sons
• Year: 1984
• Tongue: English
• Weight: 605 KB
• Volume: 16
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550161203

✦ Synopsis

Rates and thermodynamic data have been obtained for the reversible self-termination reaction: 2k1 R' + R' G=-D Involving aromatic 2-(4'dimethylaminophenyl)indandione-1,3-y1 (I), 244'diphenylaminophenyl)indandione-1,3-y1 (II), and 2,6 di-tert-butyl-4-(p-phthalylvinyl)-phenoxyl (III) radicals in different solvents. The type of solvent does not tangibly affect the 2k1 of Radical(I), obviously due to a compensation effect. The log(2k1) versus solvent parameter E,( 30) curves for the recombination of radicals (II) and (III) have been found to be V shaped, the minimum corresponding to chloroform. The intensive solvation of Radical (11) by chloroform converts the initially diffusion-controlled recombination of the radical into an activated reaction. The log (2k_,) of the dimer of Radical (I) has been found to be a linear function of the Kirkwood parameter ( E -1 ) / ( 2 ~ + l), the dissociation rate increasing with the dielectic constant of the solvent. The investigation revealed an isokinetic relationship for the decay of the dimer of Radical (I), an isokinetic temperature p = 408 K and isoequilibrium relationship for the reversible recombination of Radical (1) with p" = 651 K. For Radical (I) dimer decay ln(2k_,) = const + 0.8

In K , where K is the equilibrium constant of this reversible reaction. The transition state of Radical (I) dimer dissociation reaction looks more like a pair of radicals than the initial dimer. The role of specific solvation in radical self-termination reactions is discussed 2k-1