Question

Outline the reactions and reagents used to establish the structure of piperidine by exhaustive methylation and Hofmann elimination.​

Answer 1

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.

Piperidine is an organic compound with the molecular formula (CH2)5NH. This heterocyclic amine consists of a six-membered ring containing five methylene bridges (–CH2–) and one amine bridge (–NH–).

industrially, piperidine is produced by the hydrogenation of pyridine, usually over a molybdenum disulfide catalyst:

C5H5N + 3 H2 → C5H10NH

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 NaHCO3, to

neutralize the large quantity of HI formed.

(1) CH3−NPropanamideH2+CH3−Imethyl iodide→△(CH3)2N−dimethylamineH+HI

(2) (CH3)2N−dimethylamineH+CH3−Imethyl iodide→△(CH3)4N+trimethylamineHI

(3) (CH3)2Ndimethylamine+CH3−I methyl iodide→△(CH3)4N+I− tetramethyl ammonium iodide(quaternary ammonium aslt)