Blanc chloromethylation

These conditions protonate the formaldehyde carbonyl making the carbon much more electrophilic.

The benzyl alcohol thus formed is quickly converted to the chloride under the reaction conditions.

[4] These species may account for the fact that moderately and strongly deactivated substrates that are inert to Friedel-Crafts reactions like acetophenone, nitrobenzene and p-chloronitrobenzene[5] do show marginal reactivity of limited synthetic utility under chloromethylation conditions.

[4] Highly activated arenes like phenols and anilines are not suitable substrates, since they undergo further electrophilic attack by Friedel-Crafts alkylation with the formed benzylic alcohol/chloride in an uncontrolled manner.

In general, the formation of diarylmethane side product is a common outcome.