PHYSICAL PROPERTIES OF AMINES: CLASS 12
Physical State and Odour:
- Lower aliphatic amines (small chain) are gases with a fishy odor.
- Primary amines with three or more carbon atoms are liquid.
- Higher molecular weight amines are solid.
- Aniline and other arylamines are usually colorless but may turn colored upon storage due to atmospheric oxidation.
Solubility in Water:
- Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules.
- Solubility decreases with an increase in molar mass of amines due to the growing hydrophobic alkyl part.
- Higher amines are essentially insoluble in water.
Comparative Solubility with Alcohols:
- Amines are less soluble in water than alcohols due to the difference in electronegativity (Nitrogen: 3.0, Oxygen: 3.5).
- Alcohols are more polar than amines and form stronger hydrogen bonds, making them more soluble in water.
- Between butan-1-ol and butan-1-amine, butan-1-ol will be more soluble in water due to stronger hydrogen bonding capabilities.
Solubility in Organic Solvents:
- Amines are soluble in organic solvents such as alcohol, ether, and benzene.
Intermolecular Association and Boiling Points:
- Primary and secondary amines form intermolecular hydrogen bonds:
- Primary amines show more hydrogen bonding due to two available hydrogen atoms, resulting in stronger intermolecular association.
- Secondary amines have one hydrogen available, leading to weaker hydrogen bonding than primary amines.
- Tertiary amines lack hydrogen atoms for hydrogen bonding, so they do not form intermolecular associations.
- Order of boiling points among isomeric amines is as follows:
- Primary amines > Secondary amines > Tertiary amines (due to decreasing hydrogen bonding).
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