Linear free energy relationships for peroxy radical-phenol reactions. Influence of the para-substituent, the ortho-di-tert-butyl groups and the peroxy radical
✍ Scribed by Károly Héberger; Antal Lopata; József Müller
- Publisher
- John Wiley and Sons
- Year
- 1989
- Tongue
- English
- Weight
- 616 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0538-8066
No coin nor oath required. For personal study only.
✦ Synopsis
Calculations were carried out on several data sets to study the mechanism of hydrogen abstraction from phenols by peroxy radicals:
(1)
Rate constants, k values, were collected for the reactions of cumyl-, l-phenylethyland tert-butyl-peroxy radicals with ortho-para-substituted phenol inhibitors. The rate constants were recalculated for the same temperature. Solvent effects were neglected because the solvents used were similar in nature. The phenol ortho substituents were characterized by an indicator variable ZB, accounting for the presence or absence of di-tert-butyl groups. The phenol para substituents were characterized by Charton's UI , u R , and u ; substituent constants.
The dependence of log k values on Itbu, u,, uR, c r i was investigated using stepwise linear regression analysis. The combined data set of 32 reactions gives: log k,333K) = -0 . 8 0 1 ~~ -2 . 4 8 3 ~~ + 3.766 (r = 0.851) log k(333K, = -0 . 9 3 2 ~~ -2 . 3 0 2 ~; + 3.802 and ( r = 0.848)
The results suggest that hydrogen abstraction from phenols by peroxy radicals proceeds by an electrophilic mechanism, and that neither the peroxy-radical nor the ortho-di-tert-butyl groups have considerable effect on the rate of reaction (1).