Hydroxyl radical amine reactions

Salomon J, Elad D (1973) Photochemical reactions of nucleic acid constituents. Peroxide-initiated reactions of purines with alcohols. J Org Chem 38 3420-3421 Salomon J, Elad D (1974) Ultraviolet and y-ray-induced reactions of nucleic acid constituents. Reactions of purines with amines. Photochem Photobiol 19 21-27 Samuni A, Neta P (1973) Hydroxyl radical reaction with phosphate esters and the mechanism of phosphate cleavage. J Phys Chem 77 2425-2429... 

Nitrations are highly exothermic, ie, ca 126 kj/mol (30 kcal/mol). However, the heat of reaction varies with the hydrocarbon that is nitrated. The mechanism of a nitration depends on the reactants and the operating conditions. The reactions usually are either ionic or free-radical. Ionic nitrations are commonly used for aromatics many heterocycHcs hydroxyl compounds, eg, simple alcohols, glycols, glycerol, and cellulose and amines. Nitration of paraffins, cycloparaffins, and olefins frequentiy involves a free-radical reaction. Aromatic compounds and other hydrocarbons sometimes can be nitrated by free-radical reactions, but generally such reactions are less successful. 

Another function of ascorbic add is to generate Fe(II) from Fe (III), which is part of the Haber-Weiss-Fenton Reaction (77). In that reaction, peroxide is reduced to the hydroxyl radical, HO, an extremely powerful oxidizing agent. It should also be noted that ascorbic acid can chelate metals 18 and will promote the carbohydrate-amine browning reaction (79-20). 

On the other hand, the indirect type of ozonation is due to the reactions of free radical species, especially the hydroxyl radical, with the organic matter present in water. These free radicals come from reaction mechanisms of ozone decomposition in water that can be initiated by the hydroxyl ion or, to be more precise, by the hydroperoxide ion as shown in reactions (4) and (5). Ozone reacts very selectively through direct reactions with compounds with specific functional groups in their molecules. Examples are unsaturated and aromatic hydrocarbons with substituents such as hydroxyl, methyl, amine groups, etc. [45,46],... 

Samuni A, Goldstein S, Russo A, Mitchell JB, Krishna MC, Neta P. (2002) Kinetics and mechanism of OH-radical and OH-adduct radical reactions of nitroxides with their hydroxyl amines. J Am Chem Soc 124 8719-8724. 

The rate constants for deprotonation of the trimethylamine radical cation by the parent amine and by hydroxyl radicals were estimated as 1 x 10 and 1 x 10 M s , respectively [84]. The rate constants for the different steps involved in the reaction of oxygen with a-aminoalkyl radical 31 (Scheme 7) were determined by pulse radiolysis with conductivity detection [85]. 

On the basis of studies using nanosecond time resolution, Holcman and Sehested suggested that the reaction of hydroxyl radicals with dimethylaniline occurs via the intermediate formation of a hydroxyl radical-amine adduct [100], as described in Scheme 8. 

The mechanism of hydroxyl-radical-mediated oxidation of aromatie amines has recently been reinvestigated by Tripathi and Sun, who used time-resolved Raman spectroscopy as a diagnostic tool. Their studies suggest that the initial transient formed in the reaction of hydroxyl radicals with the neutral / -phenylene diamine is the amine radical cation and not the OH-adduet of the amine as originally believed. 

Methylation of amines in nucleotides and proteins plays important roles in biological function. Methyl transferases accept a wide range of nucleophiles such as halides, amines, hydroxyls, and enolates [reactions (a) and (b), Scheme 8.6] [42-44], For example, in the biosynthesis of novobiocin, methylation takes place at only one phenolic carbon and not the remaining three hydroxyl groups [45, 46]. On the other hand, methyl transfer to electron-deficient substrates often occurs under radical mechanisms requiring methylcobalamin as the cofactor, as shown in the biosynthesis of fosfomycin, where only one of the two enantiotopic hydrogen was replaced by the methyl group [reaction (c), Scheme 8.6] [47]. 

A number of procedures for the hydroxylation and amination of radicals are reported. They offer attractive alternatives to the classical ionic processes. Extremely mild reaction conditions characterize most of these radical procedures. They offer promising perspectives for the synthesis of natural products and other complex polyfunctionalized molecules. 

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