The amines which are soluble in water

(A) Methanamine
(B) Ethanamine
(C) Propanamine
(D) Benzylamine

Choose the correct answer from the options given below:

(A), (B) and (C) only

The correct answer is Option (4) → (A), (B) and (C) only

The solubility of amines in water is determined by their ability to form intermolecular hydrogen bonds with water molecules.

$\text{Solubility} \propto \text{Hydrogen Bonding Capability} \propto \frac{1}{\text{Size of Hydrophobic Alkyl Group}}$

• Small Amines (A, B, C):
• Methanamine ($\text{CH}_3\text{NH}_2$), Ethanamine ($\text{CH}_3\text{CH}_2\text{NH}_2$), and Propanamine ($\text{CH}_3\text{CH}_2\text{CH}_2\text{NH}_2$) all have small, short alkyl groups.
• The strong hydrogen bonding between the amine group and water molecules easily overcomes the weak hydrophobic nature of the small alkyl chains.
• Therefore, these are highly soluble in water.
• Large Amines (D):
• Benzylamine ($\text{C}_6\text{H}_5\text{CH}_2\text{NH}_2$) contains a large, bulky, and highly hydrophobic phenyl ring ($\text{C}_6\text{H}_5$).
• The large hydrophobic part of the molecule dominates the intermolecular interactions, hindering the formation of hydrogen bonds with water molecules.
• Therefore, Benzylamine is only sparingly soluble or insoluble in water.

The highly soluble amines are (A), (B), and (C).