Nucleophilic Substitution Reactions of Ethers

Ethers are cleaved by the strong hydrohalic acids HBr or HI (HI is the more reactive of the two): methoxyethane + HI (heat) gives iodomethane + ethanol; methoxybenzene (anisole) + HI gives phenol + iodomethane (the alkyl-oxygen bond cleaves preferentially over the harder-to-break aryl-oxygen bond). Mechanistically, an ether with a primary alkyl group reacts by SN2 (protonation of the ether oxygen, then halide attack at the LESS sterically hindered of the two attached carbons, e.g. attacking the methyl carbon of methoxyethane rather than the ethyl carbon), while a tertiary alkyl ether reacts by SN1. If excess HBr or HI is used, the alcohol product formed in this first cleavage reacts …