Blanc Reaction

This Reaction, Which Is Comparable To A Friedel-Crafts Alkylation, Is Useful For The Preparation Of Chloromethylated Arenes (for Example, The Merrifield Resin Based On Polystyrene) From The Parent Arene With Formaldehyde, HCl, And ZnCl₂.

Mechanism Of The Blanc Reaction

The Lewis Acid ZnCl₂ effects Formation Of An Oxonium Ion Which Is Reactive In Electrophilic Aromatic Substitution. The Intermediate Zinc Alkoxide Reacts With The Arene To Form The Chloromethylated Product And Zinc Oxides:

When The Concentration (or, Effective Concentration In The Case Of Polymer Residues) Is High, The Formation Of Side Products Due To A Second Addition Are Observed:

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