Show how you would use direct alkylation to synthesize the following compounds.

(a) benzyltrimethylammonium iodide

(b) pentan-1-amine

(c) benzylamine

Alkylation of amines can give good yields of alkylated products in two types of reaction which are as shown below.

(i) Exhaustive alkylation to tetraalkylammonium salt.

In this reaction, mixtures of different alkylated products are ignored if enough alklyl halide is added to alkylate the given amine as many times as possible. Tetraalkylammonium salt is formed from exhaustive alkylation. A mild base such as NaHCO₃ or dilute NaOH is added to deprotonate the intermediate alkylated amines and also to neutralize the large quantitities of HX formed.

(ii) With large excess of ammonia (NH₃)

Ammonia (NH₃) can be used in large excess since it is inexpensive and has a low molecular weight. When large excess of ammonia is added to a primary halide, it forms primary amine and the probalility of dialkylation is very small. Excess ammonia left can be simply evaporated.

(a) Phenylmethanamine reacts with methyl iodide in presence of a milld base, sodium bicarbobate to give benzyltrimethylammonium iodide .

phenylmethanamine methyl iodide benzyltrimethylammonium iodide

reaction a

(b) 1-bromopentane reacts with excess ammonia (NH₃ ) to give pentan-1-amine.

1-bromopentane pentan - 1 -amine

reaction b

(c) (Bromomethyl)benzene reacts with excess ammonia (NH₃) to give (benzylamine).

(Bromomethyl)benzene benzylamine

reaction c