Organic chemistry lesson 13

reaction of amines with acidsreaction of amines with alkanoyl halidesreaction of primary amines with carbonyl compoundsmeans of distinguishing between classes of amines



1. Reaction of Amines with Acids:
When amines react with acids, they undergo acid-base reactions to form salts. The amine acts as a base and accepts a proton (H+) from the acid. The resulting salt is formed by the ammonium cation (RNH3+) and the anion of the acid.

Example: RNH2 + HCl → RNH3+Cl-

2. Reaction of Amines with Alkanoyl Halides:
Amines can also react with alkanoyl halides (acyl halides) to form amides. The halogen atom attached to the alkanoyl halide is replaced by the amine group, resulting in the formation of an amide bond.

Example: RNH2 + RCOX → RCONHR + HX (where X = halogen atom)

3. Reaction of Primary Amines with Carbonyl Compounds:
Primary amines can react with carbonyl compounds, such as aldehydes or ketones, to form imines or Schiff bases. In this reaction, the nitrogen of the primary amine forms a double bond with the carbon of the carbonyl group.

Example: RCH=O + RNH2 → RCH=NHR + H2O

Means of distinguishing between classes of amines:
There are several methods to distinguish between different classes of amines, including:

1. Solubility: Primary amines are generally more soluble in water compared to secondary and tertiary amines due to the presence of a hydrogen atom on the nitrogen, which can form hydrogen bonds with water molecules.

2. N-Methylation: Primary amines can be methylated by treatment with methyl iodide and a base to form a tertiary amine. Secondary amines can also be methylated to form quaternary ammonium salts.

3. Reaction with Nitrous Acid: Primary amines react with nitrous acid (HNO2) to form a diazonium salt, which is an unstable compound. Secondary and tertiary amines do not react with nitrous acid. This reaction can be used as a distinguishing test.

4. Boiling Point: Tertiary amines generally have higher boiling points compared to primary and secondary amines due to the presence of more alkyl groups attached to the nitrogen atom, which increase intermolecular forces.

5. Chromatographic Methods: Techniques such as thin-layer chromatography (TLC) or gas chromatography (GC) can be used to separate and analyze different classes of amines based on their different retention times or chromatographic behavior.