Eschweiler–Clarke reaction

The reaction is generally performed in an aqueous solution at close to boiling.

The formic acid acts as a source of hydride and reduces the imine to a secondary amine.

Loss of carbon dioxide gas renders the reaction irreversible.

Despite being more hindered, the formation of the tertiary amine is more favorable, as the intermediate in iminium ion is formed without needing to protonate.

[6] Altered versions of this reaction replace formic acid with sodium cyanoborohydride.