Acyloxy Radicals Research Articles

Activation and transfer of oxygen—XVI: Spontaneous electron transfer in flavinium salt solutions. A new principle for the development of oxygen activation models

Blue coloured 10, 1O a-ring opened intermediates 5 a, 5 b arising in the autoxidation of a dihydroflavin model (Scheme 1) are also formed on proper treatment of some N 1-alkylflavinium salts 7 (Scheme 2). The conditions giving optimal 10,10 a-ring opening have been determined (Figs. 1–2). The flavinium salts (RFl + ox, A −) show spontaneous electron transfer in the dark, producing a flavosemiquinone (RFl·) and a counter-radical, probably a radical cation (RFl-A +·) derived from a flavin adduct (pathway b, Scheme 3). The formation of a neutral, unstable 1-RFl· appeared from the spontaneous N 10-dealkylation (pathway d 2) competing with the O 2-activation (pathway c 1). A generation of CO 2 may occur which indicates the formation of an unstable acyloxy radical (A·) by a decomposition of RFl-A +· (pathway d 3). Cl 3CCOO − can even be catalytically decomposed by RFI + ox. This proves that RFI + ox is recycled from the RFI· -state also (pathway d 1) for which O 2 is not a prerequisite. On the other hand, Cl 3CCOO − is “repaired” under conditions giving a 10,10 a-ring opening (Fig. 3). The preservation of the acid anion and the results of the O 2-balance are consistent with the conclusion that the lO,lO a-ring opening is coupled with or followed by an electron transfer from a peroxy radical to RFl-A +· giving a generation of O 2 (Scheme 4). A 10,10 a-ring opened hydroperoxide 5 a (XHOOH; Scheme 1) is proposed to be the result of a similar one-electron transfer reaction (AOOH; Scheme 4).

The reaction of acyl peroxides with 2,2,6,6-tetramethylpiperidinyl-1-oxy

Benzoyl ana lauroyl peroxides undergo induced decomposition by 2,2,6,6-tetramethylpiperidinyl-1-oxy to form acyloxy radicals and carboxylic acid in equimolar amounts. Formation of the carboxylic acid does not involve free acyloxy radicals.

ChemInform Abstract: A NEW RADICAL DECARBOXYLATION REACTION FOR THE CONVERSION OF CARBOXYLIC ACIDS INTO HYDROCARBONS

AbstractDie Carbonsäure (IIa) wird mit dem Alkohol (I) in die Ester übergeführt, die sich mit Tri‐n‐butyl‐stannan unter neutralen Bedingungen zum Steroid (IIb) reduktiv spalten lassen.

A new radical decarboxylation reaction for the conversion of carboxylic acids into hydrocarbons

The esters of trans-9-hydroxy-10-phenylthio-or -10-chloro-9,10-dihydrophenanthrene are smoothly reduced under neutral conditions by tri-n-butylstannane to furnish, by radical elimination, phenanthrene and the nor-hydrocarbon formed from decomposition of the corresponding acyloxy radical.

An ESR and spin-trap study of the interaction of acyl peroxides with tetrahalomethanes in the presence of iron compounds

1. ESR and spin-trap methods have been used to show that the interaction of Fe(CO)5 or Fe(C5H5)2 with peroxides leads to the formation of acyloxy radicals. Carried out in CCl4, these reactions lead to the formation of both acyloxy and.CC13 radicals. Initiated by the Fe(CO)5 or Fe(C5H5)2+benzoyl peroxide systems, the reaction of BrCCl3 with α-olefins lead to the formation of.CCl3 radicals and adducts of these radicals with the olefin: CCl3CH2.CHR1, where R1=C4H9, C6H13. Initiated by the iron compound + acyl peroxide system, tetrahalomethane addition to olefins proceeds through a radical chain mechanism, chain propagation being through the.CCl3 radicals. 2. Spin adducts of α-phenyl-N-tert-butylnitron with acyloxy and.CCl3 radicals, and 2-methyl-2-nitrosopropane with.CCl3 and CCl3CH2CHR (R is an alkyl) radicals, have been identified.

Primary reactions in crystalline Rochelle salt studied by pulse radiolysis and EPR spectroscopy. The decarboxylation of the acyloxy radical ion

The acyloxy radical ion −O2CCHODCHODCȮ2 (I) was identified in irradiated Rochelle salt by combining the techniques of pulse radiolysis and EPR spectroscopy. This primary radical gives hyperfine couplings due to 13C, 1H, and 23Na and has a broad optical absorption band with the peak at 405 nm. It decomposes by decarboxylation in a first order decay. The half life at 22 °C is 55 ns and the activation energy for decarboxylation is 7.5 kcal mol−1. The G value for the CO2 formation is 2.7 and the extinction coefficient of I is 900M−1 cm−1. No effects of the ferroelectricity of the salt on εmaxG were found.

Organomercurials. II. Substitution processes in the homolytic cleavage of dialkylmercury the formation of alkylmercury(II) derivatives

Alkylmercuric benzoate and chloride formed in the benzoyl peroxide-initiated reaction of dialkylmercury in carbon tetrachloride solutions arise by homolytic displacements. Kinetic isotope effects demonstrate that any alkylmercuri radicals formed in the concurrent reductive elimination to metallic mercury cannot be intermediates leading to alkylmercuric chloride. Benzoyl peroxide and butyryl peroxide show widely divergent behavior as initiators owing to differences in the stabilities of the acyloxy radicals formed on homolysis, the relatively long-lived benzoyloxy radical being effective in S H2 displacements on dialkylmercury in contrast to propyl radicals derived from the highly unstable butyryloxy radicals. The reactivity of oxygen-centered, chlorine and alkyl radicals are compared in homolytic displacements. A unified mechanism is presented for reductive elimination and the various substitution processes observed concurrently in dialkylmercury compounds, in which the radical intermediates are shared in common.

Decomposition of diacyl peroxide—VII : Oxygen scrambling in 1-apocamphoryl peroxide and related diacyl peroxides-general remarks on the relationship between the stability of acyloxy radical and amounts of cage recombinations and ester formation in the decomposition of diacyl peroxide

Thermal decomposition of 1-apocamphoryl peroxide has been investigated in CCl 4 using the 18O-labelled peroxide. 1-Apocamphoryl peroxide is the first example which undergoes radical decomposition, carboxy-inversion and oxygen scrambling reaction between carbonyl and peroxidic O atoms in the peroxide in comparable rates. The major product of the decomposition was the inversion product, 1-apocamphoryl 1-apocamphyl carbonate (52·5%), and only a minute amount of 1-apocamphyl 1-apocamphorate (2·2%) was formed. The rates of oxygen scrambling were found to be 2·70±0·21 × 10 −6 (55°), 1·85±0·12 × 10 −1 sec −1 (70°) and 9·33±0·18 × 10 −5 sec −1 (84·3°) (E a, 27·5 Kcal/mol, ΔS‡, −2·3 e.u.). The cage recombination mechanism was suggested for the oxygen scrambling and the amounts of cage recombination of 1-apocamphoryloxy radical pair were calculated as 65% (55°), 60% (70°) and 52% (84·3°). The yield of the ester and the amount of cage recombination of geminate acyloxy radical pair were rationalized in terms of the stability of acyloxy radicals formed in the cage.

Thermal decomposition of cyclic peroxydiacids

1. New cyclic peroxydiacids were synthesized: peroxydi-cis-hexahydrophthalic, peroxydi-cis-Δ4-tetrahydrophthalic, and peroxydi-cis-endomethylene-Δ4-tetrahydrophthalic. 2. The thermal decomposition of peroxydiacids in acetic acid obeys a first-order equation with respect to the peroxide. As a result of the decomposition of the peroxydiacids, anhydrides are formed. A mechanism was proposed for their formation by cyclization of acyloxy radicals.

The Mechanism of Catalytic Co-oxidation of Cyclohexane with Aldehyde

Co-oxidation of cyclohexane with acetaldehyde in the presence of cobaltous acetylacetonate catalyst has been investigated in benzene at 40∼70°C. In the absence of the aldehyde, cyclohexane is not oxidized, but in its presence in high selectivity (95 %), forming cyclohexanol, cyclohexanone and e-caprolactone. The mechanism of this reaction is different from the reported mechanism of the oxidation of the neat cyclohexane. In co-oxidation, cyclohexane is oxidized consecutively (cyclohexane → cyclohexanol → cyclohexanone → e-caprolactone). In the absence of the catalyst, (I) and (II) proceeded by the reactions of cyclohexane and cyclohexanol with acylperoxy radical which is formed in the autoxidation of aldehyde. The step (III) is the reaction of cyclohexanone with peracetic acid (Baeyer Villiger reaction). With cobalt catalyst, (I) and (II) seem to proceed also by the reaction with acyloxy radical or acylperoxy radical which is produced by the decomposition of peracetic acid.

The Decomposition of Benzoyl Hypochlorite in the Presence of Metal Ions

The decomposition of benzoyl hypochlorite, the intermediate in the Hunsdiecker reaction between chlorine and silver benzoate, is accelerated by light and by azobisisobutyronitrile (AIBN), but not by transition metal ions. The molar yield of the chlorobenzene produced in the decomposition increases as the temperature of the reaction mixture is raised, but is independent of whether or not the reaction is promoted by light or AIBN. It is suggested that this variation in the yield is a result of the readier decarboxylation at higher temperatures of the benzoyloxy radicals which are believed to be intermediates in the decomposition process. No such pronounced effect of temperature on the yield of halides from aliphatic silver carboxylates has been observed, presumably because aliphatic acyloxy radicals decarboxylate readily even at low temperatures.

Reactions of peroxides: II. Reaction of carboxylic acids with iodine and peroxides

AbstractAroyl peroxides andt‐butylperoxy isopropyl carbonate decarboxylate aliphatic carboxylic acids in the presence of iodine to form iodides in high yields. The aroyl peroxides also abstract carboxylic acid hydrogen from aromatic and perfluorocarbon acids. A proposed scheme is presented for the reaction of aroyl peroxides with carboxylic acids illustrating homolytic decarboxylation as taking place in an equilibrium between a pair of acyloxy radicals. These radicals are derived from the peroxide and acid and maintained in association by hydrogen bonding and iodine complexation.

Tert‐butyl peresters as initiators in vinyl polymerization. Part III

AbstractPeresters can decompose thermally by several modes. There can be simple scission of the OO bond or a simultaneous scission of both the OO and the CC bond to split out carbon dioxide. The decompositions of tert‐butyl peracetate, tert‐butyl per(phenyl acetate) and tert‐butyl per(diphenyl acetate), have been studied and it has been shown that whereas tert‐butyl peracetate decomposes primarily into alkoxy and acyloxy radicals, the other two dissociate into the products with simultaneous splitting of carbon dioxide in a single stage reaction. This suggests that peresters with groups that would form relatively stable radicals undergo a synchronous scission of the two bonds to split out a molecule of CO2.

Tert‐Butyl peresters as initiators in vinyl polymerization part II.

AbstractPeresters dissociate thermally to acyloxy and alkoxy radicals. Further, the acyloxy radicals may dissociate into a carbon radical and carbon dioxide. Alternatively the peresters may break into these products in a single stage reaction. The decompositions of tert‐butyl‐α.α‐diphenyl perpropionate and tert‐butyl percinnamate have been studied and it has been shown that whereas the former dissociates into the products in a single stage reaction, only 72–73% of tert‐butyl percinnamate dissociates by a single stage decomposition reaction and the rest isomerises to yield cinnamic acid.The polymerization rate of styrene, using tert‐butyl‐α.α‐diphenyl perpropionate as initiator at 60±1°C is proportional to the square root of the initiator concentration and the first power of the monomer concentration.

Tert‐Butyl peresters as initiators in vinyl polymerizations. I.

AbstractPeresters dissociate thermally to alkoxy and acyloxy radicals. The acyloxy radical may dissociate further into an aryl radical and carbon dioxide. Alternatively they may break into these products in a single stage reaction. The decomposition of tert‐butyl perbenzoate has been studied and it has been shown that the primary products of the dissociation of this ester are alkoxy and acyloxy radicals.The polymerization of styrene, using tert‐butyl perbenzoate, tert‐butyl percinnamate and tert‐butyl percrotonate has been studied at 120 ± 1°C. It has been shown that the rate of polymerization is proportional to the square root of the initiator concentration and the 3/2 power of the monomer concentration.

Studies of Isocyanide. II. The Reaction of Isocyanide with Some Radical Sources

Abstract The reactions of cyclohexyl isocyanide with some radical sources, such as perbenzoic acid, benzoyl peroxide, t-butyl perbenzoate, N-nitrosoacetanilide, potassium phenylazoformate and di-t-butyl peroxide, have been studied. The isocyanide does not contribute kinetically to the mechanism of the decomposition of benzoyl peroxide, but the lone pair electrons existing on the carbon atom of isocyanide react very easily with free radicals, especially with acyloxy radicals. In the reaction with benzoyl peroxide, t-butyl perbenzoate or the N-nitrosoacetanilide acyloxy radical chiefly contributes to the reaction. With potassium phenylazoformate, the phenyl radical is the main reacting species. However, in the case of perbenzoic acid, the reaction is heterolytic, and the main product is cyclohexyl isocyanate.

The electrolysis of some 3‐arylpropionic acids isomerization of free radicals

AbstractThe electrolysis of some substituted 3‐arylpropionic acids has been investigated with a view to a possible rearrangement of free radicals formed through discharge of anions.With 3‐phenylisovaleric acid in methanol containing an excess of sodium acetate the main product isolated was t‐amylbenzene, no rearrangement having occurred.3,3,3‐Triphenylpropionic acid in methanol containing sodium ions gave mainly the phenyl ester of 3,3‐diphenyl‐3‐methoxypropionic acid. The analogous tri‐p‐t‐butylphenylpropionic acid yielded the p‐t‐butylphenyl ester of 3,3‐di‐p‐t‐butylphenyl‐3‐methoxypropionic acid. The latter results are interpreted as involving a novel type of rearrangement of acyloxy radicals, an oxygen atom attacking an aromatic ring at its point of attachment to the C‐3 atom:magnified imageIn a discussion on the mechanism of isomerizations occurring in electrolysis, it is suggested that acyloxy radicals may also play a part rather than alkyl radicals only.