Peroxy radicals butylperoxy

A recent report by Bartlett and Guaraldi (5) provides convincing evidence for the existence of the tetroxide as an intermediate in the selfreactions of ferf-butylperoxy radicals. They estimate AH for the formation of tetroxide by dimerization of peroxy radicals to be —6 kcal. per mole and AEact for decomposition of the tetroxide to alkoxy radicals and oxygen to be 11 kcal. per mole. 

In Table III the rate constants, k p, for reaction of several substrates with tert-butylperoxy radicals are compared with the rate constants, kp, for reaction with their own peroxy radicals. 

Rate Constants per Labile Hydrogen for Reaction of Substrates with Their Own Peroxy Radicals, (kp) and with tert-Butylperoxy Radicals (k p) at 30°Ca... 

Examination of Table III reveals that reactivities of peroxy radicals are strongly dependent on their structure. Reactivities are influenced by both steric and polar effects,26,30-32 and, in general, increase as the electron-withdrawing capacity of the a substituent increases. Acylperoxy radicals, which possess a strong electron-withdrawing substituent, are considerably more reactive than other alkylperoxy radicals. For example, the benzoylperoxy radical is 4 X 104 times more reactive than the ferf-butylperoxy radical. 

The e.s.r. spectrum of the peroxy-radical is very different from that of the parent radical, so that the extent of reaction can be determined directly from the composite e.s.r. spectrum of the deposit. For example the spectra of t-butyl and t-butylperoxy radicals and of a deposit containing a mixture of the two radicals are shown in Fig. 14. 

Percent product distribution acetone 24.5 5.1, 2-methyl-2-propanol 18.8 4.0, 2-methyl-2-hydroperoxypropane 36.7 7.5, 2-methyl-propanal 14.0 3.9, 2-methyl-propanol 4.4 1.3, tertiary butylperoxide < 1.7. The peroxy radicals involved are primary 2-methyl-1-propylperoxy, primary methylperoxy and tertiary 2-methyl-2-propylperoxy. The relatively large yield of tertiary butanol is due to the interaction between CH3OO and tertiary butylperoxy radicals. Computer simulations based on the known rate coefficients for the self-reactions of these radicals [2] gave = 3 x 10" cm molecule s for the cross combination reaction. To simulate the observed ratio of primary alcohol and aldehyde requires a rate coefficient p 3 x 10" cm molecule s for the interaction between 2-methyl-1-propylperoxy and tertiary 2-methyl-2-propyl-peroxy radicals. The oxidation mechanism is quantitatively well understood. 

The substrate scope and mechanism of Rh2(cap)4-catalysed TBHP oxidation of phenol and aniline was discussed. The rate of oxidation of para-substituted phenols to 4-(f-butyldioxy)cyclohexadien ones increased significantly in aromatic hydrocarbon solvents. Comparative results with RuCl2(PPh3) and Cul were provided. The results were consistent with hydrogen atom abstraction by the f-butyl peroxy radical followed by combination of the phenoxy and the f-butylperoxy radicals. Under similar reaction conditions,para-substituted anilines were oxidized to the corresponding nitroarenes, and primary amines were oxidized to carbonyl compounds in moderate to good yields. ... 

Production of singlet oxygen (both Eg and Ag) by selfreaction of s-butylperoxy radicals and the peroxy radicals derived from linoleic acid has very recently been confirmed by analysis of the emission spectra observed during ceric ammonium nitrate oxidation of the. appropriate hydroperoxide ( 8). 

The relative importance of the various pathways depends on the alkyl groups (R). The rate constants for scission of groups (R ) from /-aikoxy radicals (RR C-O) increase in the order isopropylalkyl radical is less important when R is methyl than when R is a higher alkyl group, if the pathway to alkylperoxy radicals is dominant, the resultant polymer is likely to have a proportion of peroxy end groups.200 211... 

Negative reaction constants p1 for the oxidation of sulfides by [10-1-3]—(r-butylperoxy)iodanes are consistent with a mechanism involving rate-limiting formation of a sulfonium species by nucleophilic attack of sulfide on the iodine(III) atom followed by attack of water to give sulfoxide.151 However, in dichloromethane, inhibition by galvinoxyl implicates a free radical mechanism perhaps by homolytic cleavage of the weak iodine(III)-peroxy bond. 

---