Butyl radicals, from decomposition

The para-nitro ester 71d generated only 4-nitroaniline (70%) and 4,4 -dinitroazoxybenzene (10%) when it underwent decomposition (Scheme 29). These products could have been derived from either a triplet nitrene or a triplet nitrenium ion precursor. Homolysis of the N—O bond to generate radical intermediates was ruled out because of the nearly quantitative yield of pivalic acid derived from 71d. The pivaloxy radical would have undergone rapid decarboxylation to generate CO2 and the rert-butyl radical under these conditions. Since no rearrangement product was observed, it was tentatively concluded that this ester underwent direct decomposition to 4-nitrophenyl-nitrene without the intermediacy of a nitrenium ion. ... 

Hoare and Wellington (22) produced CH3O radicals from the photochemical (50° and 100°C.) and thermal (135°C.) decompositions of di-terf-butyl peroxide in the presence of 02. The initially formed tert-butoxy radicals decomposed to acetone plus methyl radicals, and the methyl radicals oxidized to methoxy radicals. Formaldehyde and CH3OH were products of the reaction the formation of the former was inhibited, and the latter was enhanced as the reaction proceeded. If the sole fate of CH3O were either... 

Thermal decomposition of butane involves the unimolecular decomposition of sec- and n-butyl radicals as chain carrier steps, but little quantitative information can be obtained from the work. The best estimation of the A factor for the thermal decomposition of butyl radical is based on the high-temperature photolysis of 2-methylbutanal and has the value, log A — 15.32.64 Corresponding values for w-propyl radicals2 were 15.3655 and 13.9.62 In view of the complexity of these experimental systems, these compare reasonably with the value of 14.35 in Table XX. 

Ethylene arises from the ethylidene radical. The decomposition of jec-propyl radical to give a hydrogen atom and propene is taken to be the major source of hydrogen atoms this process is not distinguishable from decomposition of i-butane to a hydrogen atom and a butyl radical followed by decomposition of the latter to a methyl radical and propene. 

The occurrence of chains at temperatures slightly above 100 °C was proved by Volman and Brinton ° . They found that methyl radicals from the pyrolysis of di-/-butyl peroxide induce the chain decomposition of propionaldehyde in the temperature range 122-156 °C. 

Another minor reaction product is methane. It appears to be a secondary product, being negligible at low conversions and of increasing importance as the reaction proceeds - . Sworski and Burton have indentified methyl radicals in the system these may originate either from the chain initiation step or from the decomposition of -butyl radicals. Recent identification of C3H6 among the products strongly supports the validity of the latter assumption. 

The chemical reactivities of ketones follow the order terf-butyl > ethyl > methyl, which is the stability order for the cations or radicals of these groups. This suggests that the mechanisms of ketone decomposition involve a rate-determining migration of an electrophilic alkyl moiety of the ketone, perhaps leading to the production of acyl and alkoxy radicals from some partially oxidized intermediate. 

Copper, Silver, and Gold.—The photoisomerization reaction (80) is catalysed by Cu(OAc)2, Cu(acac)2, or CuCl2.288 Cu(ClC>4)2 promotes the photocyclodimerization of -vinylcarbazole (VCZ).290 The process involves initial electron-transfer from the singlet or triplet state of VCZ to Cu11, giving VCZ+ and Cu1. In contrast to its thermal decomposition, irradiation of Ag(BunXPBuns) causes cleavage of the Ag—C bond and the liberation of butyl radicals.291... 

McMillan (1962) photolyzed r-butyl nitrite at 253.7 and 313.0 nm and found that acetone was the major product, with CH3ONO2 and N2 as minor products. He noticed that the acetone quantum yield decreased with increasing pressure. Therefcne he interpreted the acetone as coming from decomposition of an excited r-butoxyl radical, which could be stabilized by collision. Thus the primary process is... 

Finally, we should also note an experiment by Rabinovitch and his students [71.0] in which the thermal decomposition of the sec-butyl radical (formed in a chemical activation process) showed no variation in rate from 0.01 to 200 atmospheres of added hydrogen. ... 

An example of the synthetic application of this reaction is the introduction of a benzoate substituent into the 7-position of norbornadiene. Decomposition of t-butyl peroxybenzoate is effected by Cu(I). The r-butyl radical then abstracts hydrogen from norbornadiene. The Cu(II) is regenerated by oxidation of the resulting radical. The cation then captures benzoate ion, giving the product. 

Reaction of trichloroacetyl isocyanate (3 equivalents) in p-xylene at reflux for 3 days with norbornenes gave, after base treatment, the 2-cyanonorborn-2-ene derivative, e.g. (407) from norbornene itself. The known [4 -t- 2] cycloadduct is not formed reaction is thought to occur by way of the unsaturated imide (408), itself possibly the result of base-promoted disproportionation of an initial [2 + 2] adduct. Decomposition of t-butylazodiphenylcarbinol in benzene occurs by a radical chain mechanism involving t-butyl radicals olefinic compounds act as radical traps norbornene, for example, is hydro-t-butylated to give exo-2-t-butylnorbomane. Stable cyclic... 

However, this is likely not to be the only process. A photolytic decomposition of di(r-butyl)disulfide in low temperature glasses is quite efficient and produces substantial amounts of 2-methyl-2-propanethiol as product which cannot be explained assuming the reaction shown above 187]. The only way to explain the production of this product is to admit the possibility of hydrogen abstraction by the r-butylthiyl radical from the matrix which is considered next. The other option is to admit the existence of hot thiyl radicals generated by photolysis. 

Free radical copolymerization of methyl methacrylate and styrene as well as butyl methacrylate with styrene or isoprene in toluene under microwave irradiation (monomode microwave reactor) has also been carried out (Fellows, 2005). However, no changes in reactivity ratios were observed although more detailed studies were required for the copolymerization of butyl methacrylate and isoprene. The microwave-assisted polymerization procedure accelerated the polymerizations by a factor of 1.7, may be due to an increase in radical flux. It was proposed that the increased radical flux under microwave irradiation is due to rapid orientation of the radicals that are formed from decomposition of the azoisobutyronitrile. This orientation would reduce the number of direct terminations by recombination of the two radical fragments under microwave irradiation and thus, cause a higher radical flux. 

The radical is generated by photolytic decomposition of di-/-butyl peroxide in methylcy-clopropane, a process that leads to selective abstraction of a methyl hydrogen from methylcyclopropane ... 

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