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Explain Hoffmann's exhaustive methylation. |
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Answer» Solution :METHYLATION of amines : The reaction in which a hydrogen ATOM attached to nitrogen atom of amines is replaced by methyl group is called methylation of amines. HOFFMANN's exhaustive methylation : The process of convert- ing a primary, secondary or tertiary amine into quaternary ammonium halide by heating them with excess of methyl iodide, is called exhaustive methylation or Hoffmann's exhaustive methylation. Thus when methyl amine is heated with excess of methyl iodide it forms dimethylamine (secondary amine), then trimethylamine (a tertiary amine) and finally of quaternary ammonium iodide. The reaction is carried out in the PRESENCE of mild base `NaHCO_(3)`, to neutralize the large quantity of HI formed. (1) `underset("Propanamide")(CH_(3)-N)H_(2)+ underset("methyl iodide")( CH_(3)-I)overset(triangle)(rarr) underset("dimethylamine")((CH_(3))_(2)N-) H +HI` (2)`underset("dimethylamine")((CH_(3))_(2)N-)H+ underset("methyl iodide")( CH_(3)-I)overset(triangle)(rarr) underset("trimethylamine")((CH_(3))_(4)N+)HI` (3)`underset("dimethylamine")((CH_(3))_(2)N)+ underset("methyl iodide")( CH_(3)-I"")overset(triangle)(rarr) underset(underset(("quaternary ammonium aslt"))("tetramethyl ammonium iodide"))((CH_(3))_(4)overset(+)(N)overset(-)(I)"")` |
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