Structure and Nomenclature

The prefix "N-" is crucial in the nomenclature. It indicates that the methyl group (-CH₃) is directly attached to the nitrogen atom, not to a carbon atom on the benzene ring. If the methyl group were attached to a carbon on the benzene ring (e.g., at the ortho, meta, or para positions), it would form isomers of methylaniline (such as o-toluidine), which are different compounds. N-Methylaniline is a secondary amine.

Physical Properties

1.Appearance: Colorless to pale yellow oily liquid, darkens gradually upon exposure to light.

2.Odor: Characteristic amine-like, faint fishy or ammoniacal odor.

3.Boiling Point: Approximately 194–196°C

4.Density: Approximately 0.989 g/mL

5.Solubility: Slightly soluble in water; readily soluble in organic solvents such as ethanol, diethyl ether, and chloroform.

Chemical Properties

1.Weak Basicity: As an amine, it is weakly basic and can react with acids to form salts. For example, it reacts with hydrochloric acid to form N-methylaniline hydrochloride.

2.Alkylation Reaction: It can undergo further alkylation to produce N,N-dimethylaniline (a tertiary amine).

3.Acylation Reaction: Reacts with acyl chlorides or acid anhydrides to form N-methyl-N-phenylamides.

4.Reaction with Nitrous Acid:

Unlike most aliphatic secondary amines, when N-methylaniline reacts with nitrous acid (HNO₂), the influence of the benzene ring leads primarily to the formation of an N-nitrosoamine (a yellow oily substance or solid), rather than the rearrangement seen in other cases.

This is an important distinguishing reaction (different from primary and tertiary amines).

5.Oxidation: Can be oxidized, yielding complex products.

6.Electrophilic Substitution Reactions: The benzene ring can undergo electrophilic substitution (e.g., halogenation, nitration, sulfonation). Since the -NHCH₃ group is a strong ortho-para director, reactions occur predominantly at the ortho and para positions.

Preparation Methods

Industrial Method: Prepared by the reaction of aniline with methanol in the presence of an acidic catalyst (such as sulfuric acid) under high temperature and pressure. This is a reversible alkylation reaction, typically yielding a mixture of N-methylaniline and N,N-dimethylaniline, which requires separation by fractional distillation.

Laboratory Method: It can be obtained in relatively high purity by reacting aniline with methylating agents such as iodomethane or dimethyl sulfate.