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.