Peroxides s. a. Acyl

Peroxides (s. a. Acyl peroxides. Group IV element-carbon peroxides)... 

Sym. acyl peroxides. Ethereal HgOg-soln. added at -15° to a soln. of phenyl-propiolic chloride in abs. ether, then pyridine added dropwise with stirring, which is continued 2 hrs. diphenylpropiolyl peroxide (Caution, explosive). Y 74.5%. C. Bischoff and K.-H. Platz, J. pr. 312, 2 (1970) also mixed acyl peroxides s. Do Linh Khuong, G. S. Bylina, and Y. A. OPdekop, Akad. Navuk Belarus. SSR, Ser. Khim. Navuk 1970 (3), 74 (Russ) C. A. 73, 87570. 

Soedjak, H.S. and A. Butler. 1990. Characterization of vanadium bromoperoxidase from Macrocystis and Fucus Reactivity of vanadium bromoperoxidase toward acyl and alkyl peroxides and bromination of amines. Biochemistry 29 7974—7981. 

Shi and coworkers found that vinyl acetates 68 are viable acceptors in addition reactions of alkylarenes 67 catalyzed by 10 mol% FeCl2 in the presence of di-tert-butyl peroxide (Fig. 15) [124]. (S-Branched ketones 69 were isolated in 13-94% yield. The reaction proceeded with best yields when the vinyl acetate 68 was more electron deficient, but both donor- and acceptor-substituted 1-arylvinyl acetates underwent the addition reaction. These reactivity patterns and the observation of dibenzyls as side products support a radical mechanism, which starts with a Fenton process as described in Fig. 14. Hydrogen abstraction from 67 forms a benzylic radical, which stabilizes by addition to 68. SET oxidation of the resulting electron-rich a-acyloxy radical by the oxidized iron species leads to reduced iron catalyst and a carbocation, which stabilizes to 69 by acyl transfer to ferf-butanol. However, a second SET oxidation of the benzylic radical to a benzylic cation prior to addition followed by a polar addition to 68 cannot be excluded completely for the most electron-rich substrates. 

Peroxyl Radicals Secondary peroxyl radicals, as are found in most lipid acyl chains, recombine rapidly (2k = 10 -10 M s ) (192, 362) to form a variety of products, including alcohols and ketones (Reaction 67) (361, 362, 366), ketones and alkanes (Reaction 68) (60, 292), or acyl peroxides and peroxyl radicals (Reaction 69) (264, 367, 369). The alcohols thus produced are indistinguishable from H abstraction products of an original LO, but the ketones and dialkyl peroxides are unique to recombination reactions. As any R3OO and RO released from Reaction 68 or Reaction 69a react further, peroxyl radical recombinations also have the potential for propagating lipid oxidation (Section 3.1.4). 

Figure 31. Selected stopped-flow data for the disappearance of (HPX)Fe acyl peroxide (X, ) 416 nm and the concomitant appearance of (HP X)Fe =0 (Xmax) 678 nm. Global analysis of the full spectral window (400-700 nm) for the disappearance and appearance traces using a first-order kinetic model gives kohs = (1-9 0.1) x 10 s for 0—0 bond heterolysis.

Acyl radicals can fragment by loss of carbon monoxide. Decarbonylation is slower than decarboxylation, but the rate also depends on the stability of the radical that is formed. For example, rates for decarbonylations giving tertiary benzylic radicals are on the order of 10 s whereas the benzoyl radical decarbonylates to phenyl radical with a rate on the order of 1 s (see also Table 11.3, Entries 45 to 48). When reaction of isobutyraldehyde with carbon tetrachloride is initiated by f-butyl peroxide, both isopropyl chloride and isobutyroyl chloride are formed, indicating that decarbonylation is competitive with the chlorine atom transfer. 

In contrast to the oxidative generation of radicals described above, reductions of alkyl iodides using tris(trimethylsilyl)silane also produces alkyl radicals under conditions suitable for Minisci-type substitution." Carboxylic acids (a-keto acids) are also useful precursors for alkyl (acyl ) radicals via silver-catalysed peroxide oxidation, or from their l-hydroxypyridine-2-thione derivatives using Barton s method,the latter in non-aqueous conditions. 

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