Amines — Part 2: Reactions, tests and aniline: visual lesson, ISC Class 12 Chemistry

Lesson

Reactions of amines

Part 2 — the lone pair at work: nucleophilic reactions, tests and the chemistry of aniline.

In this lesson you will

Write alkylation and acylation reactions with mechanisms
Use nitrous acid, the carbylamine reaction and Hinsberg’s test to distinguish 1°, 2° and 3° amines
Write the preparation and reactions of aniline, including electrophilic substitution, and explain why it is acetylated before nitration

Concept

Alkylation with mechanism

The N lone pair attacks the carbon of an alkyl halide (SN2), displacing X⁻; loss of H⁺ gives the next amine. Repeated alkylation leads to 2°, 3° amines and finally a quaternary ammonium salt.

\ce{CH3CH2NH2 + CH3I -> CH3CH2NHCH3 + HI}

\ce{(CH3)3N + CH3I -> (CH3)4N+I-}

Concept

Acylation with mechanism

1° and 2° amines react with acid chlorides, anhydrides or esters to give amides (nucleophilic acyl substitution): the N lone pair adds to the C=O carbon, then Cl⁻ is lost and H⁺ removed (pyridine takes up HCl). 3° amines (no N–H) are not acylated. Benzoylation with C₆H₅COCl (Schotten–Baumann, in NaOH) gives benzamides.

\ce{CH3CH2NH2 + CH3COCl -> CH3CH2NHCOCH3 + HCl}

\ce{C6H5NH2 + C6H5COCl -> C6H5NHCOC6H5 + HCl}

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