Blanc chloromethylation

The blanching reaction is a reaction names of organic chemistry and named after Gustave Louis Blanc ( 1872-1927 ). Through them, a chloromethyl group (- CH2Cl ) can be introduced into aromatics.

Reaction

Educts of Blanc reaction besides the aromatic formaldehyde hydrochloric, and Lewis acids such as zinc chloride or aluminum chloride. The reaction proceeds in the sense of SEAr reaction ( electrophilic aromatic substitution).

Reaction mechanism

In the presence of acid catalysts can be implemented with little formaldehyde reactive aromatics.

In the presence of acid catalysts, but the reaction usually does not stop at the stage of the benzyl alcohol, but reacts in a Friedel -Crafts alkylation to Diarylmethane next 1 In contrast, if the reaction in the presence of high concentration of HCl on through, we obtain from the as an intermediate product resulting benzyl alcohol, the corresponding benzyl chlorides 2

Shortcoming

Although the chloromethylation to Blanc is a very efficient method, it has a serious drawback: the reaction of formaldehyde with hydrogen chloride is formed to a small extent highly carcinogenic bis (chloromethyl ) ether. Hence their need should be reviewed critically in the synthesis planning.