Hydroxyl reaction with organic molecules

If the chemistry of polymer molecules were different from that of simple compounds resembling the repeating units (model compounds), the study of the chemical resistance of organic polymers would be difficult. Fortunately, Nobel laureate Paul Flory found that the rate of esterification of molecules with terminal hydroxyl and carboxyl groups is essentially independent of the size of the molecules. Thus it is customary to assume that the rates of most reactions of organic molecules are similar regardless of the size of the molecule. 

In addition, the hydrated electron acts as a nucleophile, especially with organic molecules that contain halogen atoms (Eq. 6-16). This reaction results in rapid elimination of a halide ion from the initially formed negatively charged organic species. The reaction of Eq. 6-16 is of special interest for the degradation of per-halogenated saturated hydrocarbons that are usually not affected by hydroxyl radicals (Sun et al, 2000). 

Since it is unanimously agreed that MTBE is eUminated via OH radicals, many studies have been performed in order to elucidate the mechanistic pathway of the conversion. OH radicals react with organic molecules by the abstraction of hydrogen from C - H or O - H bonds, via hydroxyl group addition to unsaturated carbon bonds or the interaction with N-, P-, and S-containing bonds [32]. Since in the MTBE molecule no unsaturated carbon bonds and no N-, P-, or S-atoms are present the initial reaction has to concentrate on the abstraction of H atoms or the cleavage of the C - 0 bond. 

Air atmospheric t,/2 2.4-24 h for C4H10 and higher paraffins for the reaction with hydroxyl radical, based on the EPA Reactivity Classification of Organics (Darnall et al. 1976) photooxidation reaction rate constant of 1.02 x 10-11 cm3 molecule-1 s-1 with OH radical with an estimated lifetime x = 14 h during summer daylight (Altshuller 1991). 

Enzymatic hydroxylation of biological molecules is often catalyzed by hydroxylases. These types of enzymes are either oxygenases or peroxidases, in which the source of oxygen is O2 or H2O2, respectively. Cytochrome P-450-dependent enzymes represent a common class of enzymes that carry out hydroxylation reactions. L-Carnitine is a metabolite isolated from many organisms and its biosynthesis begins with the enzymatic hydroxylation of trimethyllysine. The intermediate, 3-hydroxyl-e-(A(A(ALtrimethyl)-L-lysine, is further... 

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