Substituent and temperature effects on the reactions of benzylchlorocarbene with alcohol

Abstract

The insertion reaction of the para-substituted benzylchlorocarbenes with methanol shows a second-order dependence in methanol, but only a first-order dependence in ethylene glycol. The results are consistent with a mechanism whereby the carbene inserts into the O–H bond of the alcohol dimer or oligomer by electrophilic attack of the carbene on the oxygen lone pair to produce a reversibly formed ylide intermediate. The effects of the substituents indicate that electron-releasing group favours rearrangement while electron-withdrawing group facilitates insertion. Photolysis of halogenodiazirines in methanol at low temperatures give rise to V-shaped Arrhenius behaviour and the importance of N₂ in influencing the reactivity of the singlet halogenocarbene in the matrix is demonstrated.