Hydroxyl radical carboxylic acid reactions

With the great development of living radical polymerization (LRP), one can now easily prepare linear polymers with different monomers and functional chain ends. The past decade has seen a boost in new synthetic strategies for cyclic polymers. Lepoittevin et al. [78] pioneered a new synthetic method for cyclization of PSTY by combining NMRP and esterification. 4-Hydroxyl-2,2,6,6-tetramethyl-pyperidine-l-oxy (HTEMPO) and 4,4 -azobis(4-cyanovaleric acid) were used in a combination, yielding linear PSTY with both hydroxyl and carboxylic acid chain ends. Subsequently, the cyclization reaction was catalyzed by l-methyl-2-chloropyridinium iodide and triethylamine (Scheme 27). Because the esterification reaction is not highly efficient, especially when used in polymer systems, this method was only successful with low molecular weight PSTY (<4 kDa). 

Changes in aliphatic side chains are mainly initiated by the abstraction of a hydrogen atom from a C-H bond. This produces a free radical which in the absence of O2 can combine with similar free radicals to give dimerization products or with CO2 [probably the CO2 ion. (40)] to give monoamino-dicarboxylic acids. In oxygen these are replaced by oxidative reactions which produce carbonyl, hydroxyl, and carboxyl groups through hydro-peroxy intermediates ... 

Reaction pathway for carboxylic acids reacting with hydroxyl radical. 

Manevich Y, Held KD, Biaglow JE (1997) Coumarin-3-carboxylic acid as a detector for hydroxyl radicals generated chemically and by gamma radiation. Radiat Res 148 580-591 Maples KR, Johnson NF (1992) Fiber-induced hydroxyl radical formation correlation with mesothelioma induction on rats and humans. Carcinogenesis 13 2035-2039 MarkG, Korth H-G, Schuchmann H-P, von Sonntag C (1996) The photochemistry of aqueous nitrate revisited. J Photochem Photobiol A Chem 101 89-103 Maskos Z, Rush JD, Koppenol WH (1990) The hydroxylation of the salicylate anion by a Fenton reaction and v-radiolysis a consideration of the respective mechanisms. Free Rad Biol Med 8 153-162... 

The atmospheric chemical kinetics of linear perfluorinated aldehyde hydrates, Cx-F2x+iCH(OH)2, have been measured for x = 1,3, and 4, focusing on formation (from aldehyde, by hydration), dehydration, and chlorine atom- and hydroxyl radical-initiated oxidation.211 The latter reaction is implicated as a significant source of perfluorinated carboxylic acids in the environment. 

Undecylenic acid has also been shown to react with the surface preferentially at the alkene end, leaving the terminal carboxylic acid group free for further reaction [53], This result was somewhat unexpected as the Si-H sites are considered to be somewhat acidic and the oxophilic nature of silicon should thermodynamically favor reaction with the hydroxyl group of the acid. The preferential reactivity with the alkenyl end is consistent with a free radical, rather than a nucleophilic mechanism. The acid function can be activated with N-hydroxy succinimide (NHS) to facilitate coupling with amine tagged molecules. Schematically,... 

It has been reported that formic acid is the most abundant carboxylic acid in the troposphere [127], In wet deposition, along with acetic acid, it accounts for up to 18% of the total acidity in rain in some areas [128]. The main chemical sink for atmospheric carboxylic acids is their reaction with the hydroxyl radical. 

Dagaut, P, Wallington, T.J., Liu, R., Kurylo, M.J. (1988) The gas-phase reactions of hydroxyl radicals with a series of carboxylic acids over the temperature range 240-440 K. Int J. Chem. Kinetics 20, 331-338. 

The introduction of a hydroxyl group at the -carbon atom both increases the reactivity of the molecule and results in the appearance of radicals formed by abstraction from the a-position (e.g. CHg.C(OH). CO2H from lactic acid). These observations, and those described earlier for the reactions of alcohols, ethers, and ketones, are correlated by the assumption that the hydroxyl radical is markedly electrophilic the carbonyl and carboxylic groups deactivate the C—H bonds in their vicinity, reaction tending to occur predominantly at more distant sites, whereas the hydroxyl and alkoxyl groups, having available p electrons, activate the C—H bonds to which they are attached, as represented by the contribution of such structures as (38) and (39) to the transition state for the reaction ... 

The ionic character of alcohols suggests that, especially in a solvent containing hydroxyl groups (e. g., alcohols and/or carboxylic acids), the following reaction (eq. (15)) could produce HOO radicals directly ... 

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