Peroxides aryl products

The production of aryl radicals from peroxides normally provides a cleaner method of arylation than the methods based on the decomposition of azo and diazo compounds, and, in the case of benzenoid compounds, better yields of arylated products are obtained. The... 

Aryl alkyl amines gave hydroxylamine 0-arylsulfonates when reacted with arylsul-fonyl peroxide. The products were later decomposed to azomethine and further hydrolysis results in the corresponding amine with one less carbon atom. Thus when p-methoxy-benzylamine was treated with p-nitrophenylsulfonyl peroxide at —78 °C in ethyl acetate, p-methoxybenzaldehyde and p-methoxyaniline were obtained . Cyclic amines with p-nitrophenylsulfonyl peroxide were converted to the Al-(p-nitrophenylsulfonyloxy)amine derivatives, which further rearranged to ring-expanded cyclic imines in good yields (equation 9 f. ... 

Thermolysis of 2-thenoyl peroxide in various solvents indicated that the 2-thenoyloxy radical was sufficiently stable towards decarboxylation, and was trapped as such by the substrates (73IJS295). There was very little indication of the production of 2-thienyl radicals. The kinetics of decomposition of a number of substituted 2-thenoyl peroxides and t-butyl 2-perthenoates have been investigated electron-releasing substituents increase the rate of decomposition, while electron-withdrawing groups decrease the rate. 3-Thenoyl peroxide, on the other hand, seems to provide 3-thienyl radicals on decomposition. Low yields of arylation products like (342) were obtained. 

When a monosubstituted benzene is attacked by aryl radical, a mixture of all three isomeric biphenyls is produced, as well as in the GBH reaction [105-107]. The nature of substituents apparently does not play any important role except those of bulky ort/jo-groups. The ortAo-substituted biaryl is always the main product followed by para- and meto-arylation product. The presence of a bulky ortho-tert-huXy group significantly decreases the amount of ort/io-arylation product, indicating the strong ort/io-steric effect. The typical isomer distribution and the yields of biaryls in the arylation of four mono-substituted benzenes with dibenzoyl peroxide are given in the Table 4. 

Methods to selectively arylate any other positions of quinoline have not been reported, although it has been mentioned in the literature that decomposition of benzoyl peroxide in the presence of quinoline affords a mixture of arylated products at the 4- and 5-positions (eq 23). ... 

A more energy-efficient variation of photohalogenation, which has been used since the 1940s to produce chlorinated solvents, is the Kharasch process (45). Ultraviolet radiation is used to photocleave ben2oyl peroxide (see Peroxides and peroxide compounds). The radical products react with sulfuryl chloride (from SO2 and CI2) to Hberate atomic chlorine and initiate a radical chain process in which hydrocarbons become halogenated. Thus, for Ar = aryl,... 

Materials that promote the decomposition of organic hydroperoxide to form stable products rather than chain-initiating free radicals are known as peroxide decomposers. Amongst the materials that function in this way may be included a number of mercaptans, sulphonic acids, zinc dialkylthiophosphate and zinc dimethyldithiocarbamate. There is also evidence that some of the phenol and aryl amine chain-breaking antioxidants may function in addition by this mechanism. In saturated hydrocarbon polymers diauryl thiodipropionate has achieved a preeminent position as a peroxide decomposer. 

Aryl migrations are promoted by steric crowding in the initial radical site. This trend is illustrated by data from the thermal decomposition of a series of diacyl peroxides. The amount of product derived from rearrangement increases with the size and number of substituents ... 

This last result bears also on the mode of conversion of the adduct to the final substitution product. As written in Eq. (10), a hydrogen atom is eliminated from the adduct, but it is more likely that it is abstracted from the adduct by a second radical. In dilute solutions of the radical-producing species, this second radical may be the adduct itself, as in Eq. (12) but when more concentrated solutions of dibenzoyl peroxide are employed, the hydrogen atom is removed by a benzoyloxy radical, for in the arylation of deuterated aromatic compounds the deuterium lost from the aromatic nucleus appears as deuterated benzoic acid, Eq. (13).The over-all reaction for the phenylation of benzene by dibenzoyl peroxide may therefore be written as in Eq, (14). 

Only a few diacvl peroxides see widespread use as initiators of polymerization. The reactions of the diaroyl peroxides (36, R=aryl) will be discussed in terms of the chemistry of BPO (Scheme 3.25). The rate of p-scission of thermally generated benzoyloxy radicals is slow relative to cage escape, consequently, both benzoyloxy and phenyl radicals are important as initiating species. In solution, the only significant cage process is reformation of BPO (ca 4% at 80 °C in isooctane) II"l only minute amounts of phenyl benzoate or biphenyl are formed within the cage. Therefore, in the presence of a reactive substrate (e.g. monomer), tire production of radicals can be almost quantitative (see 3.3.2.1.3). 

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