Free-radical mechanisms of the

The configurational stability of sulfinamides was investigated by Cram and Booms (257). They found that sulfinamides undergo racemization at room temperature but with a very long induction time. This indicates that the racemization process is a consequence of a homo-lytic scission of the sulfur-nitrogen bond involving the formation of an achiral sulfinyl radical. The free radical mechanism of the racemization of sulfinamides is supported by the fact that they initiate the polymerization of styrene and methyl methacrylate. 

A free-radical mechanism has been suggested for the nitrosation of 1,2-phenylenediamine (22) by peroxynitrite PN/CO2. 1,2,3-Benzotriazole (26) was formed as a result of an intramolecular nucleophilic displacement on the diazo hydroxide (25) by the neighbouring amine group. The authors suggest that the mechanism involves an initial H-atom abstraction or one-electron oxidation from (22) by CO3 , followed by the reaction of the product (23) with NO. The inhibitory effects of azide support a free-radical mechanism of the reaction. 

Free radical mechanisms of the photolytic decomposition of R MCOR (M = Ge, Sn) were considered in a number of earlier fundamental studies30,31. The nature of the resulting reaction products identified in nonpolar (alkanes, benzene, either in the presence or in the absence of a radical trap) or polar (alcohols, pyridine) media has allowed the proposal of a generalized reaction mechanism of the photolysis of R GeCOR compounds (Scheme 2). 

Le Bras, M., Bourbigot, S., Delporte, C., Siat C., and Le Tallec, Y. 1996. New intumescent formulations of fire retardant polypropylene Discussion about the free radicals mechanism of the formation of the carbonaceous protective material during the thermo-oxidative treatment of the additives. Fire Mater. 20 191-203. 

It was proved by a separate experiment that isotope mixing in a mixture of methane and methane-i proceeds very slowly even above 600 °C. Thus, it must be concluded that, in the pyrolysis, the formation of the partially deuterated methanes is a result of free radical reactions and not of the secondary exchange of the methanes. Consequently, these results support the free radical mechanism of the acetaldehyde decomposition. 

Additional support for a free radical mechanism of the copper catalyzed reaction of red phosphorus with CH3CI or benzyl chloride comes from the isolation of methane, ethane, ethylene and propene in the CH3Cl-reaction and of trans stilbene and toluene in the PhCH2Cl-reaction, in addition to phosphonous dichlorides, RPCI2 (R = CH3, CgHjCHj ) 51) ... 

Fig. 23 Kh asch addition reaction of tetrachloromethane or chloroform with 1-alkenes and free-radical mechanism of the chain reaction with CCI4 [22, 26]...

Evans et al. (10) have shown that OH radicals produced by the Fenton reagent can initiate the polymerization of vinyl compounds and that the OH radicals, which in the first instance attack the double bond of the monomer, are built into the polymer chain. Stein and Weiss (45) have used the hydroxylation of benzene and of other simple aromatic compounds (e.g., benzoic acid and nitrobenzene) to detect these radicals. In the action of OH radicals on benzene in aqueous systems the formation of phenol and of diphenyl indicated a free radical mechanism of the following type ... 

The evidence for the free radical mechanisms of the reaction between ferrous and ferric ions and hydrogen peroxide is fully discussed in the article by J. H. Baxendale in this volume, and it is necessary here only to summarize and comment on those features especially relevant to hemoprotein reactions. This evidence is essentially indirect. Experiment shows very reactive intermediates to be present and extensive kinetic studies reveal competition reactions for these intermediates in that the overall order of the reaction is found to depend on the reactant concentrations. A free radical mechanism is adopted because it accounts for the chemical reactivity of the system in the oxidation of substrates (Fenton s reaction) and the initiation of the polymerization of vinyl compounds (Baxendale, Evans, and Park, 84) and it provides a set of reactions which largely account for the observed kinetics. The set of reactions which fit best the most recent experimental data is that proposed by Barb, Baxendale, George, and Hargrave (83) ... 

A free radical mechanism of the reaction was proposed, based upon the kinetic evaluation of the relevant elementary reactions (13), which was essentially the same as that proposed by Bryce and Kebarle (2). This mechanism accounts for the formation of the main products—i.e., methane, propylene, butadiene, ethylene, and the minor products such as ethane and 2-butene isomers. 

The ratio of 2, 3, and 4 isomers formed in the reaction of pyridine (8) with polyfluoroalkyl bromides and iodides ( 5 5 1) is approximately constant in all theses reactions and is consistent with free radical mechanism of the process. Quinoline and... 

When antioxidants such as amines or sterically hindered phenols were added in the PE wax an increased induction period and a lower oxidation rate were noticed. On the contrary, in the presence of free-radical generators, especially organic peroxides such as dibenzoyl peroxide and dicumyl peroxide the oxidation proceeded faster. These results are the consequence of the free-radical mechanism of the PE wax oxidation. 

A free-radical mechanism of the stabilizing action of diallqrlstan-nane derivatives in the process of photodecomposition of polyvinyl chloride has been proposed in an interpretation of the results obtained in an investigation of the activity of dibutyltin diacetate, labelled with carbon in the butyl group. After the irradiation, the butyl group is detected in polyvinyl chloride. Apparently the formation of cross-links and oxidation of the macromolecules during UV irradiation of the polymer is prevented when the butyl group is added to the macroradicals. The possible mechanism of the action of dibutyltin diacetate is described by the scheme [42] ... 

H. Anderson [11] used differential thermal and thermogravimetric analyses to confirm the free radical mechanism of the thermal decomposition of epoxide resins, proposed by M. B. Neiman and associates. It was shown in this work that an important stj e in the pyrolysis of an epoxide resin is isomerization of the epoxide group to a carbonyl, which is accompanied by an exothermic effect and is observed in the temperature interval 350-400°C. The thermogravimetric curves confirmed that the rate of pyrolysis of samples of epoxide resins hardened with maleic anhydride is less than that of samples hardened with amines (metaphenylenediamine). 

Sevilla MD, Becker D, Yan M (1990) The formation and structure of the sulfoxyl radicals RSO , RSOO , RSO2, and RSO2OO from the reaction of cysteine, glutathione and penicillamine thiyl radicals with molecular oxygen. Int J Radiat Biol 57 65-81 Horowitz A, Rajbenbach LA (1975) The free radical mechanism of the decomposition of alkylsulfonyl chlorides in hquid cyclohexane. J Am Chem Soc 97 10-13... 

SCHEME I. Free radical mechanism of the Polonovski reaction of morphine N-oxide (II, R=H) and acetic anhydride yielding 3,6,17-- triace tylnormorphine (I jL, R=Ac), and heroin (I-d, R=Ac). 

While in pure alkanes the lifetime of the ions is very short, this is not necessarily the situation in the presence of solutes. In some cases, solute anions and cations formed by electron capture and charge transfer, respectively, may have considerably long lifetimes. If this occurs, it is possible that ionic reactions take place and therefore the free radical mechanism of the chain reaction has to be established. This can be done by various methods such as the addition of electron, charge and radical scavengers, and the determination of the effect of these additives on the chain reaction. Another method is to show that the same reaction can also be initiated thermally or photochemically. 

The free radical mechanism of the gamma radiation induced decomposition of alkanesulfonyl chlorides (RSO2CI) in cyclohexane was studied C35-37) to obtain kinetic and thermochemical information on the reactions of alkylsulfonyl radicals CRSO2). Previously discussed systems are relatively simple and their kinetic analysis is almost straightforward. The radiolysis of alkanesulfonyl chlorides presents a more complex situation. The problems encountered in the radiolysis of alkanesulfonyl chlorides will be illustrated in the C-C6H12 MeS02Cl system (36,37). 

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