Carboxyalkyl radicals

As with other hydroperoxides, hydroxyaLkyl hydroperoxides are decomposed by transition-metal ions in an electron-transfer process. This is tme even for those hydroxyaLkyl hydroperoxides that only exist in equiUbrium. For example, those hydroperoxides from cycHc ketones (R, R = alkylene) form an oxygen-centered radical initially which then undergoes ring-opening -scission forming an intermediate carboxyalkyl radical (124) ... 

Without other alternatives, the carboxyalkyl radicals couple to form dibasic acids HOOC(CH)2 COOH. In addition, the carboxyalkyl radical can be used for other desired radical reactions, eg, hydrogen abstraction, vinyl monomer polymerization, addition of carbon monoxide, etc. The reactions of this radical with chloride and cyanide ions are used to produce amino acids and lactams employed in the manufacture of polyamides, eg, nylon. 

The radicals derived from ethylene glycol and related compounds react with H202 in an alkaline medium (pH > 7.5), to give101 semidione (11) and carboxyalkyl radicals (12). 

The (oxidizing) a-carboxyalkyl radicals do not react readily with thiols (Table 6.4). They are, however, rapidly reduced by thiolate ions [reaction (20)]. The reactions of thiols with DNA radicals play a very important role in the chemical repair of DNA radicals in cells (Chaps 12.10 and 12.11). The reversibility of the H-donation of thiols, that is, H-abstraction by thiyl radicals, is discussed in Chapter 7.4. 

Most substituted alkyl radicals have absorption maxima well below 250 nm so that the peaks have not been observed (see Table 2). The a-carboxyalkyl radicals show a distinct absorption with max in the region of 300-350 nm and e< 1000 m-1 cm-1, in addition to another band with a maximum below 200 nm. Similar situations appear also when the carboxyl group is bound in an ester or amide. Hydroxyl and amino-groups bound at the radical site of a-carboxyalkyl radicals diminish the absorbance in the 300-350 nm region and increase that at lower wavelengths up to e 5000 M -1 cm-1 at 250 nm. 

In acidic media, e.g., in the presence of acetic acid, the toxic Cr(VI) compounds can easily be reduced to poorly soluble Cr ions. The reduction occurs with a multistep mechanism through the reaction of H atoms. The ot-carboxyalkyl radicals formed in OH + acetic acid reaction after forming a complex Cr(VI)-CH2COOH and dissociation also contribute to Cr(VI) reduction... 

The selective ability of higher-valent metal ions to oxidize organic free radicals has been examined and two mechanisms have been proposed for the decomposition of cerium(iv) carboxylates in the presence of olefins and aromatic hydrocarbons (i) involving a non-decarboxylative route with the generation of carboxyalkyl radicals via thermal decomposition, and ( ) the formation of alkyl radicals and COg in the decarboxylation reaction. E.s.r. studies using cerium(iv) have been used to provide evidence for the formation of the sulphite radical anion SO3 in the oxidation of sulphite. ... 

Thermal decomposition of peroxides generates a variety of radical groups which can covalently react with CNTs. This strategy has been employed in particular by Peng and co-workers who functionalized sidewalls with benzoyl, lauroyl and carboxyalkyl derivatives [38]. 

Figure 7.4. Interactions which determine the relative reactivities of carboxyalkyl (left) and acyloxy radicals.

Pogocki D, Schoneich C (2002) Computational characterization of sulfur-oxygen-bonded sulfuranyl radicals derived from alkyl- and (carboxyalkyl)thiopropionic acids evidence for a -type radicals. J Org Chem 67 1526-1535... 

A study of the effect of the structure and size of the amine radical (butylamine, dibutylamine, hexylamine, piperidine, aniline) on its reactivity in the nucleophilic replacement of tosyloxy groups in cellulose tosylate has shown (29) that this reactivity depends primarily on the basicity of the amine. TTiis assumption was confirmed by a study of the interaction of cellulose toxylates of different degrees of substitution (DS from 0.3-1.7) wit iminodiacetic and anthranilic acids 30, 31). TTie degree of substitution of the reaction products with respect to the N-carboxyalkyl(aryl)amino groups was found to be lower than that of the corresponding N-alkyl(aryl)araino derivatives. 

In the radiolysis of aliphatic carboxylic acids, carboxylic add esters and amides preferred formation of a-carboxyalkyl type radicals (e.g., R CH COOR) are observed. 

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