Towards Halomethylated Benzene-Bearing Monomeric and Polymeric Substrates

Abstract

This paper presents the trends in the halomethylation reaction of aromatic hydrocarbons and polymeric analogues. Much interest is devoted to the chloromethylation vis-à-vis other halomethylations, even though the incorporated chloromethyl group is the least chemically reactive among the common halomethyl groups (CH2Cl, CH2Br, CH2I). While bromomethylation stands second behind chloromethylation in terms of chemists' interest, a few cases of iodomethylation are cited, and only one case of fluoromethylation was reported. Various halomethylating systems have been devised, starting from the early one, paraformaldehyde/hydrogen halide, then those involving the in situ formation of halomethyl methyl ether (HalMME), and ending with those giving rise to other intermediate halomethylating species. Halomethylated aromatic polymers, including even the fluoromethylated ones, can be achieved by other means, such as polymerization of halomethyl-containing monomers, halogenation of pendent methyl groups and halogen exchange reaction (halex reaction) within halomethyl groups. Reaction conditions, i.e., solvents, catalysts and promoters, are surveyed. Exploitation of the concomitant Friedel–Crafts alkylation in the course of halomethylation is illustrated by some examples. In addition, the quaternization of halomethylated aromatic polymers (particularly the chloromethylation) is inevitably linked to halomethylation; thus, it is selectively evoked to valorize further the halomethylation reaction.