Blanc's Reaction

a method of direct introduction of the methyl chloride group C1CH₂ into aromatic compounds. In chloromethylation, a mixture of formalin and hydrochloric acid is usually used, with ZNC1₂, H₂SO₄, or AlCl₃ and, in some cases, SnCl₄ acting as a catalyst.

C₆H₆ + HCHO + HCl → C₆H₅CH₂Cl + H₂O₂

The rate of the Blanc reaction usually increases markedly with the presence of a substitute such as CH₃, C₂H₅, C₃H₇, OCH₃, or OC₂H₅ in the benzene nucleus. Naphthalene and other condensed aromatic compounds as well as polymers containing aromatic nuclei also enter into the Blanc reaction. The reaction was proposed by the French chemist G. Blanc in 1923.