Seizi Kozuka

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

Abstract 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 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 reaction of phosphites with sulphoxides

Abstract In reactions between phosphites and sulphoxides, the basicity of the phosphorus atom in phosphites appears to play an important role in determining the reaction process. Triphenyl phosphite and diphenyl methyl phosphite were oxidized quantitatively to the corresponding phosphates by treating with phenyl methyl sulphoxide, while trimethyl phosphite was found to rearrange to dimethyl methylphosphonate by the catalytic action of sulphoxides. Similarly, triethyl phosphite was found to rearrange to diethyl ethylphosphonate. Dimethyl phenyl phosphite gave a mixture of dimethyl phenyl phosphate and a phenyl methyl methylphosphonate in the reaction with phenyl methyl sulphoxide.

The mechanism of the reactions of 2- and 4-alkylpyridine N-oxides with acetic anhydride

Abstract The reaction of 2-benzylpyridine, 2- and 4-picoline N-oxides with acetic anhydride has been investigated by means of kinetic and 18O-tracer experiments. The large kinetic isotope effects found for all these reactions suggest the proton-removal step to be rate-determining. The uneven distribution of 18O between the alcohol and carbonyl O- atoms of the esters formed appears to result from the confonnational preference of the “anhydrobase” intermediates. The slight effect of salts and substituents on the rate are also discussed.

The reactions of trimethyl(methylthio)- and trialkyl(arylthio)stannanes with alkyl halides

Abstract The reaction of trimethyl(methylthio)stannane with methyl iodide was reinvestigated. Trimethylsulfonium iodide and iodotrimethylstannane were the products which were isolated. Trialkylhalostannanes and alkyl aryl sulfides were obtained in nearly quantitative yield by the reaction of trialkyl(arylthio)stannanes with alkyl halides. The rate of the reaction of the trialkyl(arylthio)stannanes with an alkyl iodide was much slower than that of trimethyl(methylthio)stannane under the same reaction conditions. Nucleophilic attack of the stannyl sulfur atom on the alkyl halide is suggested as the first step of the reaction.

Rearrangements of tertiary amine oxides—XXIII : Reaction of α, N-diphenylnitrone with acetic anhydride

Abstract The reaction of the α, N-diphenylnitrone with acetic anhydride has been investigated using homogeneously 18O-labelled acetic anhydride. The amount of 18O incorporated into the carbonyl group of the resulting benzamide suggests an intramolecular reaction. The rates of the reaction were measured by changing the solvent and the substituents. The large reactivity of the nitrones having electron-releasing substituents and others suggests that the NO bond cleavage is the rate-determining step of the reaction.

The decomposition of daiacl peroxide—IV : Baeyer-Villiger reaction of optically active 3-methyl-4-phenyl-2-butanone

Abstract The stereospecificity of the Baeyer-Villiger reaction of optically active 3-methyl-4-phenyl-2-butanone was investigated. 1-Phenyl-2-propyl acetate was the only oxidation product while the configuration of the original ketone was completely retained in the product.

Rearrangement of tertiary amine N-oxides—XXVII : Mechanism of the reaction of isoquinoline N-oxide with substituted benzenesulfonyl chlorides☆

Abstract Kinetic experiments have been carried out on the reactions of isoquinoline N-oxide with p-toluenesulfonyl and other substituted benzenesulfonyl chlorides, varying solvent and salt compositions. The rate was correlated by the second-order equation, i.e., v = [N → O] × [ArSO2Cl], and was found to be accelerated in polar media. The addition of chloride ion was found to increase the rate considerably, while the rates of the over-all reaction became greater with arenesulfonyl chlorides bearing stronger electron-withdrawing substituents (ϱ = +2·0). By the use of 1-deuterated isoquinoline N-oxide a small kinetic isotope effect (kH/kD = 1·2) was observed for this reaction. Based on these kinetic observations the rate-determining step of this reaction is considered to be the cleavage of NO bond. Meanwhile, from the 18O-tracer experiments in several solvents using uniformly 18O-labelled p-toluenesulfonyl or p-bromobenzenesulfonyl chloride the migration of arenesulfonate was found to proceed mainly via oxygen-bridged ion pair pathway.

A kinetic study for the reaction of aryloxytrimethylsilane with methanesulfinyl chloride giving aryl methanesulfinate

Abstract A nucleophilic attack of phenoxy-oxygen has been suggested as the mechanism of the reaction of aryloxytrimethylsilane with methanesulfinyl chloride.

Photoxidation of di-t-butyl thioketone

Abstract The photo-oxygenation of the title compound leads to the corresponding ketone and sulfine. A mechanism for the reaction is elucidated.

Reaction of lepidine, quinaldine and 1-methylisoquinoline N-oxides with acetic anhydride

Abstract The mechanism of the reactions of lepidine, quinaldine and 1-methylisoquinoline N-oxides with acetic anhydride has been studied by means of both kinetic and 18 O tracer experiments. In all cases, the over-all rate of the reaction is markedly affected both by the change of solvent and by the addition of salts. In the case of lepidine N-oxide, a large kinetic isotope effect, k H /k D = 7·7 in acetonitrile, suggests that the proton-removal is the rate-determining step. This is also the case for 6-methylquinaldine N-oxide which gives the kinetic isotope effect, k H / k D = 7·4 (at 30·). In the case of quinaldine N-oxide, however, the kinetic isotope effect is small, k H / k D (at 30°), while quinaldine N-oxide originally trideuterated loses deuterium during the reaction, depicting that the proton-removal is a reversible step and the succeeding NO bond cleavage is the rate-determining step. In the case of 1-methylisoquinoline N-oxide, in which k H / k D is 3·5 in dioxan at 30· both proton-removal and NO bond cleavage are equally important in the energy profile of the reaction.