Chlorine Dioxide as an Electron‐Transfer Oxidant of Olefins. Preliminary Communication

The kinetics and product studies of oxidation of eight olefins 1 ‐ 8 by ClO 2 in H 2 O in the pH range 3‐7 are described. The reaction is faster as the pH decreases. At pH < 4, ClO 2 reacts equimolarly with olefins to yield isomeric mixtures of chlorohydrines and 1,2‐dioxygenated products, following the equation:The order of reactivity is: ( E )‐stilbene > indene > β‐methylstyrene > acenaphthylene > α‐methylstyrene > styrene > cyclohexene > allylbenzene. A multi‐stage radical‐cation mechanism is proposed, in which an initial reversible protonation:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm ClO}_{{\rm 2}} + {\rm H}^{\rm +} \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} \left[{{\rm HClO}_{\rm 2}} \right]^ + $$\end{document}is followed by an electron‐transfer stage (rate‐determining):The cation‐radical thus produced, adds rapidly an additional ClO 2 to form dioxygenated products. The chlorohydrines most likely arise from HClO additions to the olefinic double bonds, which, in turn, generate from dismutation of 2 HClO 2 into HClO + H + + ClO   3 − .