Reactions of biphenyl, diphenylmethane, and bibenzyl with acetyl hypoiodite

Abstract

The iodination of biphenyl with acetyl hypoiodite gave only products iodinated in the p-position; reactions with diphenylmethane and bibenzyl gave both o- and p-iodides in ratios of 0·14 : 1 and 0·28 : 1, respectively, probably because of the smaller steric effect for ortho substitutions. Study of competitive reactions gave the following relative reactivities for para iodination: 100 for biphenyl, 57 for diphenylmethane, and 97 for bibenzyl. This reflects the resonance and inductive effects of the phenyl group. Further, α-acetoxy- and/or α-hydroxy-derivatives were formed with diphenylmethane and bibenzyl under the same conditions. A mechanism involving a radical attack on the methylene group is suggested. The effects of sulphuric acid and water on the iodination and/or α-substitution are discussed in terms of the intermediacy of protonated acetyl hypoiodite.