Why are amines insoluble in water?

Lower aliphatic amines are insoluble in water because they can form hydrogen bonds with water molecules. When the size of the hydrophobic alkyl part increases, then the molar mass of amines also increases. This decreases its solubility in water. Thus, higher amines are insoluble in water.

Amines exhibit insolubility in water due to the presence of a bulky aromatic ring in their structure, which hinders the formation of hydrogen bonds with water molecules. Since hydrogen bonding plays a crucial role in the solubility of organic compounds in water, the decreased ability to form these bonds leads to lower solubility. So, the larger the hydrophobic aromatic group in the amine molecule, the less soluble it tends to be in water.