Mechanism of the Non-Aryne Hydroxydehalogenation of Unactivated Aryl Halides

Article abstract of DOI:10.1021/jo01298a006

The hydroxydehalogenation of aryl halides upon reaction with aqueous alkali at temperatures up to 333 deg C was examined to determine the nature of an ipso hydroxydehalogenation process reported in 1957 to compete with the aryne mechanism.The reactions of p-iodo-, p-bromo-, and p-chlorotoluene with aqueous solutions of sodium or potassium hydroxide or carbonate, carried out in Pyrex glass tubes with exclusion of traces of transition metals, led in all cases to the same product distribution. m-Cresol and p-cresol, the two main products, formed with a para/meta ratio of0.82+/-0.03, consistent with the occurence of the aryne mechanism only.Addition of traces of copper salts or conducting the reaction in a Monel bomb, as done by other investigators, caused the occurence of a non-aryne ipso hydroxydehalogenation.This effect was not produced by nickel, iron, manganese, or cadmium.The ipso hydroxydehalogenation observed in previous studies is identified as a copper-catalyzed process.