Radicals a-carboxymethyl

In termination reactions, all mesomeric structures may contribute. Cases in point, where one would not immediately expect this to play a significant role are the a-carboxymethyl radicals (Wang et al. 2001). For some of the nucleobase radicals also more than one mesomeric structure maybe written (Chap. 10), and it is not unlikely that also here this aspect has to be taken into account. 

Wang W-F, Schuchmann MN, Bachler V, Schuchmann H-P, von Sonntag C (1996) The termination of CH2OH/CH2O radicals in aqueous solutions. J Phys Chem 100 15843-15847 Wang W-F, Schuchmann MN, Schuchmann H-P, von Sonntag C (2001) The importance of mesomery in the termination of a-carboxymethyl radicals from aqueous malonic and acetic acids. Chem Eur J 7 791-795... 

Exposure of longifolene to manganic acetate in refluxing acetic acid-acetic anhydride furnished in poor yield (9%) the product (66), the stereochemistry of which remains unresolved. Under the same conditions, camphene gave in 30% yield y-lactone mixture (67), in which one isomer predominated 49). A carboxymethyl radical arising from the thermolysis of Mn (III) acetate is considered to be the reactive species in such reactions (50). 

Although they suggested the formation of methyl radicals, they did not actually detect the methyl radicals in aqueous acetic acid. On the other hand, Kaise et al. have observed carboxymethyl radicals CH2COOH and methyl radicals CH3 by using a flow cell by ESR spectroscopy.29) We examined the dependence of radical concentrations on the flow rate and found that the amounts of these two intermediate radicals changed, reflecting the different reaction paths.39 31)... 

Kooyman et a/.232-234 showed that no direct reaction between the arene and Mn(IIl) occurred in the manganic acetate oxidation of benzene, chlorobenzene, and toluene in acetic acid. Products were satisfactorily explained by the participation of carboxymethyl radicals as intermediates analogous to those formed in the manganic acetate oxidation of olefins [see Section II.B.3.a]. Substituted... 

Manganese(m) acetate oxidation (cf. Vol. 3, p. 34) of camphene gives (186) as a 95 5 mixture by carboxymethyl radical insertion no rearranged products were obtained, in contrast to /3-pinene which gave Wagner-Meerwein products only, and no free-radical insertion.279 The E- and Z-isomers of (187) probably result from a non-concerted biradical intermediate formed by benzyne addition to camphene.280 Benzyl-lithium adds to the aminocamphor (188) exclusively from the exo-side whereas only the competing enolization reaction occurs with more sterically hindered organometallics.281... 

The oxidation of substituted aromatic hydrocarbons by Mn(OAc)3 in refluxing acetic acid proceeds by two competing mechanisms (a) a free radical addition of carboxymethyl radical to the nuclear ring, forming 2-arylacetic acids and (b) a benzylic hydrogen abstraction by Mn resulting in the formation of benzyl acetates. " In the presence of strong acids such as sulfuric, trichloro- or trifluoro-acetic acids, only benzylic oxidation products are readily formed at room temperature (equation 207). ... 

For the reaction of Mn " acetate with substituted toluenes in acetic acid (130 °C) under anaerobic conditions, an analogous correlation between log( iy i ) and ff exists (Heiba et al. [Ha] Figure 2). Here, however, the reaction is not the direct interaction of Mn" with the arene but the reaction of carboxymethyl radicals, generated from Mn " acetate, with the a-hydrogen atoms of the alkyl group on the arene (eqs. (22) and (23)). 

The mechanism accounting for the production of these three compounds is a nonchain free-radical process involving carboxymethyl radicals ... 

Alkyl radicals can be obtained by abstraction of a hydrogen atom from an alkyl group by another radical. This method was utilized for the generation of benzyl radicals from toluene with tert-butoxy radical obtained on heating di-ier -butyl peroxide. Benzoyl and carboxymethyl radicals have also been obtained by this method. The reaction gives rise to a complex mixture of products and therefore is of rather limited use. 

The chemistry of Mn(OAc)3 has developed widely since the first description of the reagent. It was the subject of two extensive (9) reviews. Most of the Mn(OAc)3 chemistry involves the generation of a carboxymethyl or acyl radical, which reacts with a variety of substrates. 

Synthetically especially valuable is the oxidation of carbonyl compounds and nitroalkanes by manganese(III) salts to form carboxymethyl and nitromethyl radicals, respectively. These radicals can be trapped by olefins like 1,3-butadiene or aromatic compounds to yield synthetically interesting products. In this case it is very advantageous to generate and regenerate the oxidizing species in situ by indirect electrolysis. This was the basis for the development of a process for the synthesis of sorbic acid viay-vinyl-y-butyrolactone Equations (31)—(35) summarize the im-... 

However, through quartz at 95% conversion, a mixture of I (62%) and l-carboxymethyl-2-phenylcyclooctatetraene (IT) (38%) was obtained. Compound n could be obtained exclusively (92%) from triplet-sensitized irradiation of I with high-energy sensitizers or from the sensitized reaction of methyl phenylpropiolate with benzene. From their experiments with sensitizers, the authors concluded that the primary adduct is formed from triplet alkyne (ET < 69 kcal/mol 1) and ground-state benzene and that the formation of I also proceeds via a triplet state in a two-step radical reaction. Hanzawa and Paquette [64] have also used the photochemical addition of an alkyne to benzene to produce a derivative of tetra-cyclo[3.3.0.02,4.03 6]oct-7-ene. 

A seven-line like signal was detected from carboxymethyl cellulose irradiated with ultraviolet light of 254 nm (Figure 7). When this sample was warmed to ambient temperature for 60 seconds, this multiplet spectrum was transformed rapidly into a prominent doublet signal with a hyperfine splitting constant of 20 gauss. This indicated that the primary free radicals... 

CasteUani RJ, Harris PL, Sayre LM, Fujii J, Taniguchi N, Vitek MP, Founds H, Atwood CS, Perry G, Smith MA (2001) Active glycation in neurofibrillary pathology of Alzheimer disease N(epsilon)-(carboxymethyl) lysine and hexitol-lysine. Free Radic Biol Med 31 175-180 CasteUani RJ, Honda K, Zhu X, Cash AD, Nunomura A, Perry G, Smith MA (2004) Contribution of redox-active iron and copper to oxidative damage in Alzheimer disease. Ageing Res Rev 3 319-326... 

Figure 5 shows time profile of absorabance at 472 nm by pulse radiolysis (0 or 30mM carboxymethyl chitosan solution with 2 mM KSCN under N20 saturation). As seen in Figure 5, the absorbance without polymer is obviously lower than a polymer solution. So, it was confirmed that OH radical reacts with polymer chains. Figure 6 shows the relation between the change of the... 

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