Acyl peroxides

Acyl peroxides Acyl thiophenes Adalat Adamantane Adamantane [281-23-2]... 

In nonaqueous copolymerization, fluorinated acyl peroxides are used as initiators that are soluble in the medium (12) a chain-transfer agent may be added for molecular weight control. 

The acyl peroxide class is chaiacteiized by the following structures ... 

Acyl peroxides of structure (20) are known as diacyl peroxides. In this structure and are the same or different and can be alkyl, aryl, heterocychc, imino, amino, or fiuoro. Acyl peroxides of stmctures (21), (22), (23), and (24) are known as dialkyl peroxydicarbonates, 00-acyl O-alkyl monoperoxycarbonates, acyl organosulfonyl peroxides, and di(organosulfonyl) peroxides, respectively. and R2 ia these stmctures are the same or different and generally are alkyl and aryl (4—6,44,166,187,188). Many diacyl peroxides (20) and dialkyl peroxydicarbonates (21) ate produced commercially and used ia large volumes. 

Physical Properties. Almost all Hquid diacyl peroxides (20) and concentrated solutions of the soHd compounds are unstable to normal ambient temperature storage many must be stored well below 0°C. Most of the soHd compounds are stable at ca 20°C but many are shock-sensitive (187). Other physical constants and properties have been reviewed (187,188). The melting poiats and refractive iadexes of some acyl peroxides are Hsted ia Tables 10-12. 

Reaction of acyl peroxides with copper azide... 

Addition of carboxylic acids or acyl peroxides to alkenes... 

Reaction between acyl peroxides and copper thiocyanate... 

These reactions all involve one-electron transfers in generating the radical, and it is therefore no surprise to find metal ions such as Fe2 /Fe3 and Cu /Cu2 involved. Thus Cu ions are found to accelerate greatly the decomposition of acyl peroxides, e.g. (28) ... 

Attack of molecular oxygen on this carbanion should yield acyl radicals which could react with loss of carbon monoxide, yielding the respective radicals, or with the formation of acyl peroxide radicals ... 

The first published examples of hydrosilation, which appeared about 30 years ago, noted that they were observed to proceed by free-radical mechanisms initiated thermally (about 300°C) (J), by acyl peroxides (4), by azonitriles (5), by ultraviolet light (6), or by y radiation (7). The first hint that catalysts known to be effective for hydrogenation might also be effective for hydrosilation was found in a French patent (8) (1949) which stated that catalysts may be chosen from compounds and salts of the elements of Groups IIA, IVA, IB, and IIB of the periodic table and metals of Group VIII and certain of their salts. No example to demonstrate this was included in the patent. 

VI Galibey. Study of Acyl Peroxides as Initiators of Radical Polymerisation. Ph.D. thesis Dissertation, OGU, Odessa, 1965 [in Russian]. 

The experimental data on the reactions of ketyl radicals with hydrogen and benzoyl peroxides were analyzed within the framework of IPM [68]. The elementary step was treated as a reaction with the dissociation of the O—H bond of the ketyl radical and formation of the same bond in acid (from acyl peroxide), alcohol (from alkyl peroxide), and water (from hydrogen peroxide). The hydroperoxyl radical also possesses the reducing activity and reacts with hydrogen peroxide by the reaction... 

Initiator decomposition studies of AIBN in supercritical C02 carried out by DeSimone et al. showed that there is kinetic deviation from the traditionally studied solvent systems.16 These studies indicated a measurable decrease in the thermal decomposition of AIBN in supercritical C02 over decomposition rates measured in benzene. Kirkwood correlation plots indicate that the slower rates in supercritical C02 emanate from the overall lower dielectric constant (e) of C02 relative to that ofbenzene. Similar studies have shown an analogous trend in the decomposition kinetics ofperfluoroalkyl acyl peroxides in liquid and supercritical C02.17 Rate decreases of as much as 30% have been seen compared to decomposition measured in 1,1,2-trichlorotrifluoroethane. These studies also served to show that while initiator decomposition is in general slower in supercritical C02, overall initiation is more efficient. Uv-visual studies incorporating radical scavengers concluded that primary geminate radicals formed during thermal decomposition in supercritical C02 are not hindered to the same extent by cage effects as are those in traditional solvents such as benzene. This effect noted in AIBN decomposition in C02 is ascribed to the substantially lower viscosity of supercritical C02 compared to that ofbenzene.18... 

J. P. DeYoung, J. Kalda, and J. M. DeSimone, Decomposition kinetics of perfluoroalkyl acyl peroxides in liquid and supercritical carbon dioxide, in preparation. 

Hydrogen peroxide can also be acylated by the Schotten-Baumann process. In this way acyl peroxides are obtained. 

In general, the importance of the acceptor properties of all types of compounds containing an 0—0 bond should be emphasized. A likely function of a peroxidic compound (hydrogen peroxide, alkyl peroxides, acyl peroxides, peroxydisulfate, to mention a few commonly used ones) under photochemical conditions (UV light) should be that of an electron acceptor from an excited state. Moreover, the electron acceptor efficiency is high in view of the dissociative nature of the ET step. 

Reactions of O2 with esters R C(0)0R also pass nucleophilic substitution as an initial step (Sawyer and Gibian 1979). Final products are acyl peroxides or carboxylic acids. The following set of equations explains the product formation ... 

With radical sources other than acyl peroxides, the rearomatization of the a-complex can take place by various, not always well characterized, reactions, such as oxidation by metal salts, hydrogen abstraction by intermediate radicals, disproportionation, and induced decomposition. 

The differences in the rates of decomposition of the various initiators are related to differences in the structures of the initiators and of the radicals produced. The effects of structure on initiator reactivity have been discussed elsewhere [Bamford, 1988 Eastmond, 1976a,b,c Sheppard, 1985, 1988]. For example, k,i is larger for acyl peroxides than for alkyl peroxides since the RCOO- radical is more stable than the RO radical and for R—N=N—R, kd increases in the order R = allyl, benzyl > tertiary > secondary > primary [Koenig, 1973]. 

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