Question

write Alkylation of amines : Hofmann’s

exhaustive alkylation ​

Answer 1

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When a primary amine is heated with excess of primary alkyl halide it gives a mixture of secondary amine, tertiary amine along with tetraalkylammonium halide

If excess of alkyl halide is used tetraalkyl ammonium halide is obtained as major product. The reaction is known as exhaustive alkylation of amines.

The tetraalkylammonium halides are called quaternary ammonium salts which are crystalline solids. They are the derivatives of ammoium salts in which all the four hydrogen atoms attached to nitrogen in N⊕H4 are replaced by four alkyl groups (same or different). Primary, secondary and tertiary amines consume three, two and one moles of alkyl halide respectively to get converted into quaternary ammonium salt. The reaction is carried out in presence of mild base NaHCO3, to neutralize the large quantity of HX formed. If the alkyl halide is methyl iodide, the reaction is called exhaustive methylation of amines.

For example : When methylamine is heated with excess methyl iodide, it gives tetramethyl ammonium iodide.