Pulse radiolysis studies on the oxidation of organic radicals in aqueous solution

TLDR

Pulse radiolysis has been used to measure absolute rates of ferricyanide oxidation of radicals produced by OH attack on organic solutes, while oxygen competes with ferricyanide for radical oxidation. The study aimed to quantify the percentage of OH attack at the α position in straight and branched‑chain alcohols. The method measured oxidation of diverse hydroxylated compounds and serine, used a radical‑competition model for oxygen‑containing solutions to determine peroxy‑radical rates, and quantified α‑OH attack in alcohols. Radicals from α‑hydrogen abstraction in alcohols oxidize at diffusion‑controlled rates, whereas radicals from other OH attacks are slower, and peroxy‑radical formation approaches diffusion limits.

Abstract

Pulse radiolysis has been used to measure directly the absolute rates of oxidation by ferricyanide ion of various radicals produced by OH attack on organic solutes. These include mono, di- and polyhydroxylic compounds, hydroxy acids, polyethylene oxides of molecular weight 200, 6000 and 20 000 and the amino acid serine. Radicals produced by hydrogen abstraction from α carbon atoms in alcohols are oxidized at, or near, diffusion-controlled rates, whereas the reactions are much slower for radicals formed by OH-attack elsewhere. The technique has been used to measure the percentage OH-attack at the α position for a series of straight and branched-chain alcohols. Oxygen competes with ferricyanide for radical oxidation. The data for oxygen-containing solutions fit a simple radical-competition scheme which has been used to measure rates of peroxy-radical formation. These approach diffusion-controlled limits.