Aroyl peroxides

Diacyl peroxides are sources of alkyl radicals because the carboxyl radicals that are intitially formed lose CO2 very rapidly. In the case of aroyl peroxides, products may be derived from the carboxyl radical or the radical formed by decarboxylation. The decomposition of peroxides can also be accomplished by photochemical excitation. 

Intense and analytically useful direct chemiluminescence (CL) has been observed from a rather limited group of organic compounds. These include diacylhydraz-ides, indoles, acridines and acridans, polydimethylaminoethylenes, anthracenes, and aroyl peroxides. A substantial number of other kinds of compounds, when... 

The usual sources used for the homolytic aromatic arylation have been utilized also in the heterocyclic series. They are essentially azo- and diazocompounds, aroyl peroxides, and sometimes pyrolysis and photolysis of a variety of aryl derivatives. Most of these radical sources have been described in the previous review concerning this subject, and in other reviews concerning the general aspects of homolytic aromatic arylation. A new source of aryl radicals is the silver-catalyzed decarboxylation of carboxylic acids by peroxydisulfate, which allows to work in aqueous solution of protonated heteroaromatic bases, as for the alkyl radicals. 

A limitation of the ring expansion reaction is seen when a cyclobutanecarbonyl chloride is reacted. While treatment of D-nor-5a-androstane-16a-carbonyl chloride with 3-chloroperoxybenzoic acid gave the normal product D-nor-5a-androstan-16a-ol (9) via the acyl aroyl peroxide, the only isolated product from the epimer D-nor-5a-androstane-16/ -carbonyl chlo-... 

Alkyl and aryl peroxides display C—C—O absorption in the 1198-1176 cm-1 region. Acyl and aroyl peroxides display two carbonyl absorption bands in the 1818-1754 cm-1 region. Two bands are observed be-... 

Fluorinated diaeyl peroxides have acquired an important role in organo-fluorine chemistry and have become the subject of intensive research.202-204 Bis(per)fluoroaIkanoyI or -aroyl peroxides are generally synthesized in excellent to moderate yields in the same manner as for nonfluorinated peroxides, that is by reaction of acid chlorides or anhydrides with sodium peroxide or hydrogen peroxide.205-206 Similarly, perfluoroalkanoyl chlorides and fluorides, many of which are accessible by industrial processes, react with hydrogen peroxide in the presence of hydroxide to give the diacyl peroxides l.206-207... 

Fig. 50 Pd-catalyzed oxidative C-H arylation using aroyl peroxides...

Reactions of phosphites with peresters have not been reported, and the only example of an acyl or aroyl peroxide studied is dibenzoyl peroxide,... 

In radical polymerization (see Scheme 2), radicals are formed in a first stage determining the rate. Examples used industrially for radical sources, apart from electron radiation, are aroyl peroxides such as bis(2,4-dichlorobenzoyl) peroxide or bis(2,4-methylbenzoyl) peroxide and alkyl peroxides such as dicumyl peroxide or 2,5-dimethyl-2,5-di-/er/-butyl peroxyhexane. In the second stage, the actual crosslinking reaction, a radical addition based on the usual pattern for a radical chain reaction, takes place via the double bonds of the vinyl groups in the polymer. Radical polymerization is today used virtually exclusively for crosslinking solid silicones. 

However, these peroxides have not been utilized for the preparation of telechelics. The less reactive aroyl peroxides give styryl telechelics (40). When employing benzoyl peroxides p-substituted with chloromethyl or aldehyde groups, the telechelics require no further modification before being used as prepolymers (Fig. 3). 

PCBs are produced synthetically by chlorinating the biphenyl (Figure 9.1) with anhydrous chlorine in the presence of iron filings or ferric hydroxide as a catalyst. The crude product is distilled with alkali to remove color, traces of HCl, and the catalyst, resulting in a mixture of chlorobiphenyls with a varying number of chlorine atoms per molecule. Chlorobiphenyls could also be synthesized from (i) arylation of aroyl peroxides, diazonium salts, phenyl hydrazines, and other aryl compounds, (ii) aryl condensation reactions, (iii) addition of chlorine to biphenyl systems, (iv) decarboxylation, and (v) dechlorination reactions. 

Because diacyl peroxides decompose to yield at least two types of radicals (equation 27), they have not yet been successfully used to prepare telechelics. However, the less reactive aroyl peroxides have led to PS telechelics. Because these benzoyl peroxides were p-substituted with chloromethyl or formal groups, the resulting telechelic PS required no further modification to be used as prepolymers (36) and (37). 

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