How do aliphatic amines differ from aromatic amines?

Aliphatic and aromatic amines are distinguished primarily by the nature of the organic groups attached to the nitrogen atom and their resulting chemical and physical properties.12

Structural Differences

• Aliphatic amines contain only aliphatic groups attached to the nitrogen atom.2
• Aromatic amines feature one or more aryl groups (such as a phenyl ring) directly attached to the nitrogen atom.2

Key Differences in Properties

• Basicity: Aliphatic amines are stronger bases than ammonia, whereas aromatic amines are substantially weaker.1
• Density: Aliphatic amines are generally less dense than water, while aromatic amines are typically slightly heavier than water.1
• Optical Properties: Aliphatic amines are transparent to ultraviolet light, whereas aromatic amines exhibit strong absorption of certain wavelengths.1
• Toxicity and Handling: While many aliphatic amines are relatively harmless, aromatic amines can be dangerous poisons; for example, aniline can destroy blood hemoglobin and is linked to cancer. Both types can act as irritants, but aromatic amines are notably capable of being absorbed directly through the skin.1