Acetyl peroxide decomposition

Goldstein and co-workers have pointed out that this oxygen exchange can take place at least partly through nonradical rearrangements 9.25 or 9.26,82 and isotope effects in acetyl peroxide decomposition are consistent with significant concerted decomposition.63... 

Martin et that attempts to trap the acetoxy radical with iodine, galvinoxyl or diphenylhydrazyl were either unsuccessful or ambiguous. However, isotopic labeling experiments show that cage recombination does occur and the mechanism of acetyl peroxide decomposition may be formulated as... 

Secondary isotope studies are consistent with the suggested mechanism for acetyl peroxide decomposition. It was concluded from the data given in Table 90 that little or no methyl radical character was developed in the rate-determining step . This view has been contested with data from a study of and 0-iso-tope effects in the decomposition of acetyl peroxide. The carbon isotope effect in... 

The thermal decomposition of diacyl peroxides has been the most frequently employed process for the generation of alkyl radicals. The rate and products of the unimolecular decomposition of acetyl peroxide have been the subject of many studies. Acetyl peroxide decomposes at a convenient rate at 70-80°C both in the solution and in the gas... 

The competitive method employed for determining relative rates of substitution in homolytic phenylation cannot be applied for methylation because of the high reactivity of the primary reaction products toward free methyl radicals. Szwarc and his co-workers, however, developed a technique for measuring the relative rates of addition of methyl radicals to aromatic and heteroaromatic systems. - In the decomposition of acetyl peroxide in isooctane the most important reaction is the formation of methane by the abstraction of hydrogen atoms from the solvent by methyl radicals. When an aromatic compound is added to this system it competes with the solvent for methyl radicals, Eqs, (28) and (29). Reaction (28) results in a decrease in the amount... 

The methoxy group of methyl acetate formed during the thermal decomposition of acetyl peroxide appears as an emission, whereas methyl chloride shows enhanced absorption. Consider the reaction sequence in equation (40). 

The kinetic form of the decomposition in various solvents indicates competing unimolecular homolysis of the peroxide link (a) and radical induced decomposition (b). Other diacyl peroxides behave similarly, except that, in the case of acetyl peroxide, induced dceomposition is much less important. More highly branched aliphatic or a-phenyl-substituted diacyl peroxides decompose more readily, partly because induced decomposition is more important again and partly because of the occurrence of decomposition involving cleavage of more than one bond (for a mechanistic discussion of these cases, see Walling et al., 1970). 

The polarization of biphenyl, deserves special comment. If, as indicated in Scheme 2, its immediate precursor is a radical pair consisting of two phenyl radicals, then it should be formed without detectable net polarization since if Ag = 0. Analogous results have been reported in the decomposition of other peroxides for example, ethane formed from acetyl peroxide shows net emission. To account for this, it has been suggested (Kaptein, 1971b, 1972b Kaptein et al., 1972) that nuclear spm selection which occurs in the primary radical pair—in... 

The back recombination of the pair of acetoxyl radicals with the formation of parent diacetyl peroxide was observed in special experiments on the decomposition of acetyl peroxide labelled by the lsO isotope on the carbonyl group [78,79]. The reaction of acetyl peroxide with NaOCH3 produces methyl acetate and all lsO isotopes are contained in the carbonyl... 

The various initiators are used at different temperatures depending on their rates of decomposition. Thus azobisisobutyronitrile (AIBN) is commonly used at 50-70°C, acetyl peroxide at 70-90°C, benzoyl peroxide at 80-95°C, and dicumyl or di-t-butyl peroxide at 120-140°C. The value of the decomposition rate constant kj varies in the range... 

Few examples have been reported (5, 8, 9, 10, 12, 24) of cage recombination of simple alkoxy or acyloxy radicals to form O—O bonds in isolable molecules. This paper explores further the implications of the observed (17, 22, 23) scrambling of label seen in acetyl peroxide carbonyl-18O recovered after partial decomposition. 

Isotope Scrambling During the Decomposition of Acetyl Peroxide-Carbanyl-18O. Determination of Carbonyl Label. Isotope scrambling... 

Table III. Solvent Effects on the Decomposition Rate of Acetyl Peroxide...

Acetyl peroxide (solid) explodes on shock. It should be prepared and used without interruption and should be handled by remote control (Refs 54 71). The commercially available 30% solution in dimethyl phthalate will not give crystalline acetyl peroxide under ordinary-circumstances. The solution has a flash point of 45°C. Heating it above 50°C causes orderly, but fairly rapid decomposition (Ref 62)... 

Calvert and Hanst88 using infrared analysis, have also re-investigated the photooxidation of acetaldehyde at 20°C. using 3130 A. radiation. Acetaldehyde pressures were chiefly about 42.5 nun., but the oxygen pressure was varied from 0 to 745 mm. Analyses were made for carbon monoxide, carbon dioxide, formic acid, methanol, acetic acid, peracetic acid, acetyl peroxide, methyl hydroperoxide, and unreacted acetaldehyde (Table X). Chains were short. Although they do not detect methyl hydroperoxide or diacetyl peroxide, the non-observance of a peroxide does not necessarily mean it is not formed. The decomposition of hydroperoxides on the smallest particle of catalyst is remarkably fast. 

Estimates of the probability of escape of radical pairs in conventional solvents have been made by product analysis of the decomposition of diacyl peroxides. For example, Braun et al. [22] estimated that 60 to 80% of the methyl radicals produced in the thermolysis of acetyl peroxide escape geminate cage recombination. However, Guillet and Gilmer [25] showed that for longer chain and Cjj radicals the probability was much lower, ranging from 5% at 760C to 16% at 262<>C (Table VI). 

In this section, several typical CINPD spectra will be shown. These spectra can be explained by Kaptain s rules. Typical net absorptive and emissive CINDP signals were observed during the thermal decomposition of acetyl peroxide (AP) in hexachloroacetone at 110 °C as shown in Fig. 4-8. Here, enhanced absorptive signals were observed for CH3CI and CH4 and emissive ones for CH3COOCH3 and CH3-CH3. 

Fig. 4-8. 60 MHz H-CIDNP spectrum of the thermal decomposition of acetyl peroxide in hexachloroacetone. (Reproduced from Ref. [8] by permission from Kluwer Academic Publishers)...

Problem 4.1. Prove the enhanced absorptive CIDNP observed for CH3CI and CH4 during the thermal decomposition of acetyl peroxide (AP) in hexachloroacetone. 

In non-aqueous solutions the Kolbe electrosynthesis takes place with high eflSciency at platinized platinum and gold, as well as at smooth platinum, anodes increase of temperature and the presence of catalysts for hydrogen peroxide decomposition, both of which have a harmful effect in aqueous solution, have relatively little influence. The mechanism of the reaction is apparently quite different in non-aqueous solutions and aqueous solutions in the former no hydroxyl ions are present, and so neither hydroxyl radicals nor hydrogen peroxide can be formed. It is probable, therefore, that direct discharge of acetate ions occurs at a potential which is almost independent of the nature of the electrode material in a given solvent. The resulting radicals probably combine in pairs, as in aqueous solution, to form acetyl peroxide, which subsequently decomposes as already described. ... 

The effect of solvent on the rate of decomposition of diacyl peroxides has been studied extensively. Data for the decomposition of acetyl peroxide in various solvents at two different temperatures are given in Tables 84 and 85. It is apparent that the rates differ little with solvent variation. The decomposition of diacetyl peroxide in /-butyl alcohol and in ethyl alcohol do show appreciable rate differences, the rate coefficients are 0.31 x 10 and 10.1 x 10 secat 60 °C, respectively . This difference in rate is most likely associated with induced decomposition. Again only a small variation in rate is observed in the decomposition of pro-pionyl and butyryl peroxide with solvent change as seen in Table 86. 

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