Decomposition Of Diacyl Peroxides Research Articles

Decomposition of diacyl peroxide—V : A new mode of oxygen scrambling in benzoyl 1-apocamphyl carbonate

Specifically 18O-labeled benzoyl 1-apocamphyl carbonate which corresponds to the carboxy-inversion product of 1-apocamphoryl benzoyl peroxide was synthesized and heated in CCl 4. The two carbonyl oxygen atoms and an etheral oxygen atom sandwiched between two carbonyl carbon atoms in benzoyl 1-apocamphyl carbonate were completely scrambled. Heating of 18O-labeled benzoyl 1-apocamphyl carbonate with an equimolar amount of benzoic acid in CCl 4 gave quantitatively 1-apocamphanol, CO 2 and benzoic anhydride. Based on 18O-analysis of these products and other data, an intramolecular mechanism was suggested for the oxygen scrambling in benzoyl 1-apocamphyl carbonate.

Polar and radical paths in the decomposition of diacyl peroxides

Polar and radical paths in the decomposition of diacyl peroxides

The decomposition of diacyl peroxides—I : The thermal decomposition of primary and secondary diacyl peroxide

The mechanism of ester formation in the thermal decomposition of a few primary and secondary diacyl peroxides has been investigated by the analysis of both the 18O-distributions and the stereochemical configurations of the resulting esters, using 18O-labelled and/or optically active diacyl peroxides. The decomposition of primary diacyl peroxides is mainly homolytic. Acetyl peroxide, the lowest member of the primary diacyl peroxide series, was found to decompose only homolytically. The decomposition of δ-phenylvaleryl peroxide, a higher primary homologue, was mainly by homolytic cleavage of the OO bond, however 30% of the ester formed was a product of heterolysis involving carboxy inversion. Ester formation from secondary diacyl peroxides, such as β-phenylisobutyryl and α-methylbutyryl peroxides, was found to proceed mainly through the heterolytic carboxy-inversion process. Carboxy-inversion is discussed in the light of other similar rearrangements.

The decomposition of diacyl peroxide—III : The photochemical decomposition of β-phenylisobutyryl peroxide

The direct photodecomposition of the title peroxide was performed by irradiation in isooctane solution with a low pressure mercury lamp at room temperature. The rate constant of the decomposition was 8·5 × 10 −6 sec −1 (at 0·0162 M/1 of initial concentration, at 25°). Main products were carbon dioxide, 1-phenyl-2-propyl β-phenylisobutyrate, 1,4-diphenyl-2,3-dimethylbutane, n-propylbenzene, β-phenylisobutyric acid, 1-phenyl-2-propyl alcohol and 3-phenyl-2-propanone. All these products are apparently formed by the homolytic decomposition of the peroxide in contrast to the thermal decomposition of the peroxide which was found to proceed mainly through heterolysis. The alkyl dimer, a main product in the decomposition of the optically active peroxide, is optically inactive and an equimolar mixture of meso and (±)-compounds. The alcohol moiety of the resulting ester retained the original configuration by 68% while the carbonyl oxygen kept the original 18O-label by 85%. These observations are interpreted in terms of two competing reactions i.e., a 4-membered cyclic process and a radical recombination in solvent cage. The acetophenone-photosensitized decomposition proceeded more smoothly. Since the products are similar to those in the direct photolysis of the peroxide, the mechanism may be similar to that of direct photolysis. In this case, however, the acid was the main product.

The decomposition of diacyl peroxides—II : Lewis acid-catalysed decomposition of β-phenylisobutryl peroxide

Optically active (+)- and carbonyl- 18O-labelled β phenylisobutyryl peroxides were decomposed in the presence of antimony pentachloride in light petroleum. Optically active (+)-1-phenyl-2-propyl β-phenylisobutyrate, (+)-β-phenylisobutyric acid, 2-chloro-1-phenylpropane, n-propylbenzene and carbon dioxide were obtained as main products. The carbonyl oxygen of the peroxide was retained as much as 83 ∼ 89% in the carbonyl group of the resulting ester while the alcohol portion of the ester showed 91% retention of configuration. It was possible to observe through an infrared spectroscopic analysis the intermediate, 1-phenyl-2-propyl β-phenylisobutyryl carbonate, which resulted from the decomposition of the peroxide. These data were interpreted in terms of an ionic mechanism. The mechanism of the ester formation is discussed in a detailed comparison with that of the thermal decomposition of β phenylisobutyryl peroxide. Here too, the rearrangement process via carboxy-inversion is considered as the main path for ester formation.

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The radiolytic decomposition of diacyl peroxides, azocompounds and bisulphides in aromatic solvents (benzene, toluene) had been examined by us in a number of papers. It has been shown that the decomposition of these solutes is sensitized, i.e. caused by solvent-solute energy transfer. Stern-Volmer constants of the energy transfer for all the aromatic-substituted compounds examined are approximately equal and are found to be ≈ 5 × 10 2 l/mol. Maximum G-values, attained when the energy transfer is total, increase in the order: azo-compounds—bisulphides—peroxides. A comparison has been made of the radiolysis, photolysis, γ- and photoluminescence of three-component solutions with two energy acceptors, one chemically decomposing (benzoyl peroxide), the other a scintillator (PPO or p-terphenyl). The decrease of the quantum yield of sensitized benzoyl peroxide decomposition in the presence of a scintillator, and the quenching of the sensitized scintillator luminescence by peroxide, were explained in terms of a competition between the two energy acceptors as the energy transferred from the solvent. Comparison of the kinetic behaviour of the solutions on γ- and photo-irradiation indicates that energy transfer occurs from the excited molecules of the solvent in the first singlet (fluorescent) state. It has been shown that benzene photosensitized trans-cis-isomerization of stilbene is a result of triplet-triplet energy transfer from the solvent (the Stern-Volmer constant is about 10 4 l/mol). On γ-irradiation of benzene solutions this process is interfered with by the isomerization caused by free radicals produced by the irradiation of the solvent. The benzene-photosensitized o-nitrobenzaldehyde rearrangement into o-nitrozobenzoic acid is caused by triplet-triplet energy transfer at concentrations < 2 × 10 −4 mol/l and by singlet-singlet energy transfer at higher concentrations. This was demonstrated by comparing the concentration dependence of the photosensitized aldehyde rearrangement with that of the benzene fluorescence-quenching by aldehyde. A similar concentration dependence was found for radiolytic rearrangement of the aldehyde in solution. The sensitized reactions described above were used to estimate the G-values of the solvent molecules in fluorescent and triplet excited states. For benzene these G-values were found to be ≈ 4–6 and ≈ 0·4 molecules respectively per 100 eV of energy absorbed.

Thermal decomposition of optically active unsymmetrical azoalkanes. (−)-(S)-1,1′-Diphenyl-1-methylazomethane

The ratio, (Kc/Kr)cage, of the rate of coupling of the 1-phenylethyl radical with the benzyl radical to the rate of its rotation with respect to the benzyl radical in the solvent cage has been determined for several solvents. The optically pure title compound, (−)-(S)-4, has been prepared and its absolute configuration determined. Thermal decomposition of (−)-(S)-4 yields (−)-(R)-1,2-diphenylpropane, (−)-(R)-9, with partial retention of configuration. The maximum rotation of (−)-(R)-9 has been determined. At 100° in benzene, cyclohexane, chlorobenzene, (all containing ca. 1 M butanethiol) and butanethiol, the cage effects for the decomposition of (±)-4 were found to be 28.3, 31.7, 33.4, and 18.2%, respectively. Under these conditions (−)-(R)-9 was formed from (−)-(S)-4 with 10.3, 10.9, 13.0, and 17.3% net retention of configuration, respectively. A simple expression for (Kc/Kr)cage can be derived:[Formula: see text]F is the fraction of radicals consumed within the solvent cage and f is the fraction of radicals consumed within the solvent cage that disproportionate. Under the above conditions values for (Kc/Kr)cage were found to be 0.059, 0.069, 0.090, and 0.070, respectively. The values of the cage effect and (Kc/Kr)cage given were calculated assuming f = 0.1, but change little if f is assumed to be 0. The relevance of these results to the stereochemistry of the Wittig and Meisenheimer rearrangements and of the decomposition of diacyl peroxides is discussed.

Catalytic reactions of peroxides : Direct initiation by cuprous species

Cuprous acetate complexes are stable in acetonitrile-acetic acid solutions, and procedures for simple preparations of these solutions are described. Cuprous compounds are useful for the direct initiation of copper-catalyzed decompositions of peroxides at the low temperatures often required to obviate competing ionic rearrangements. Thus, these cuprous solutions can be effectively employed at 0° and lower temperatures to catalyze the homolytic chain decomposition of diacyl peroxides and alkyl hydroperoxides. The copper-catalyzed reactions of peresters with alkenes and other substrates can also be initiated at room temperature simply by stirring with a mixture of copper powder and cupric acetate in acetonitrile-acetic acid solutions. The stoichiometries, rates and kinetic chain lengths of these reactions are delineated with regard to a common mechanism which generally prevails in copper catalysis of peroxide reactions.

Organic Reactions Under High Pressure. IX. Some Observations on the Decomposition of Diacyl Peroxides1

Organic Reactions Under High Pressure. IX. Some Observations on the Decomposition of Diacyl Peroxides¹

Activities of free radicals formed in the decomposition of diacyl peroxides during polymerization of styrene

Activities of free radicals formed in the decomposition of diacyl peroxides during polymerization of styrene

Mechanisms of Decomposition of Diacyl Peroxides

Mechanisms of Decomposition of Diacyl Peroxides

Decomposition of Diacyl Peroxides from exo- and endo-Norbornane-2-carboxylic Acids and exo- and endo-Norbornene-5-carboxylic Acids

<b>Decomposition of Diacyl Peroxides from <b><i>exo</i></b>- and <b><i>endo</i></b>-Norbornane-2-carboxylic Acids and <b><i>exo</i></b>- and <b><i>endo</i></b>-Norbornene-5-carboxylic Acids</b>