Question

Account for the following.

Ethylamine is soluble in water whereas aniline is not.

State reasons for the following:

Ethylamine is soluble in water whereas aniline is insoluble in water.

Answer 1

Ethylamine, when added to water, forms intermolecular H-bonds with water and therefore it is soluble in water. But aniline does not form an H-bond with water to a very large extent due to the presence of a large hydrophobic –C₆H₅ group. Hence, aniline is insoluble in water.

Answer 2

Ethylamine (C₂H₅NH₂) exhibits solubility in water because the –NH group effectively forms hydrogen bonds with water molecules, due to the increased electron density on the nitrogen atom resulting from the +I inductive effect of the –C₂H₅ group. Also, the hydrocarbon part, –C₂H₅, is small and contributes much to hydrophobicity.

In Aniline (C₆H₅NH₂), the –NH₂ group is involved in resonance with the directly attached benzene ring, hence limiting its ability to form effective hydrogen bonds with water. Secondly, the benzene ring is substantial and generally hydrophobic. Hence, the net result is the insolubility of aniline in water.