Amines contain Hydrogen bonds brought on by the lone pair and the electronegativity of the nitrogen atom, there are also Van der Waals bonds present. Both occur in alcohols too however in alcohols the hydrogen bonding is brought on by the lone pairs of electrons on the oxygen atoms. In amines hydrogen bonding occurs in both primary and secondary but not tertiary as there aren't any hydrogen atoms attached directly to the nitrogen. In alcohol hydrogen bonding occurs in all three structures.
The small amines (short chain) of all 3 structural forms are very soluble in water. All of the amines can form hydrogen bonds with water - even the tertiary ones. Although the tertiary amines don't have a hydrogen atom attached to the nitrogen and so can't form hydrogen bonds with themselves, they can form hydrogen bonds with water molecules just using the lone pair on the nitrogen. Solubility decreases as the hydrocarbon chains get longer. The hydrocarbon chains have to force their way between water molecules, breaking hydrogen bonds between these molecules. However, they don't replace them by anything as strong, and so the process of forming a solution becomes less and less possible as chain length grows. The solubility of the alcohols is the same however the nitrogen is replaced by oxygen which has the same effect.
The intermolecular bonding in alcohols is strong as more energy is required to break the two types of bonding. They therefore have high melting and boiling points.
In the amines the boiling and melting points are relatively low and the boiling point decreases when looking at primary, secondary and tertiary amines respectively. Due to the weakening of the hydrogen bonding as the structure becomes more complex.
Alcohols can show properties of either acids or bases with the O-H group. The oxygen atom has of electrons that allow it to be a weak base in the presence of strong acids.
Amines also act as and are reasonably strong. The basicity of amines depends on the availability of the lone pair of electrons on the nitrogen atom. The nitrogen atom has a that can bind with H+ to form an NH+.
Amines main reaction are;
Nucleophilic acyl substitution - acyl chlorides react with secondary and tertiary amines to produce amides (no heat needed).
Neutralising carboxylic acids - this forms ammonium carboxylate salts. When heated to 200 °C, the primary and secondary amine salts dehydrate to form the corresponding .
Forming ammonium salts - tertiary amines react with strong acids to form ammonium salts.
The main reactions of the alcohols are;
Reduction/deprotonation - because they can behave as weak acids they lose a hydrogen atom.
Nucleophilic substitution - all 3 structures can undergo these reactions however primary and secondary alcohols need a catalyst to initiate them.
Dehydration - they react with ROH to produce ethers and water, there is also an elimination reaction of alcohols to produce alkenes.
Esterification - alcohols are added to carboxylic acids usually under reflux with a catalyst.
Oxidation - primary alcohols are oxidised to form aldehydes and then carboxylic acids, secondary alcohols are oxidised to form ketones, however tertiary alcohols cannot be oxidised.
Another physical property of the amines that the alcohol do not have is such a distinct odour, the amines smell of decay and rotten fish which helps them to be easily recognised.
The alcohols are much stronger bases than amines. Amines can act as bases and nucleophiles in reactions whereas alcohols can act only as bases under standard conditions.
They also have very different uses the alcohols being used for:
- industrial feedstock - to help make other substance
- as a fuel - when they burn they produce carbon dioxide and water
- as a solvent - in perfumes and cosmetics
- as methylated spirits
Whereas the amines are used for:
- Dyes - azo dyes are used widely in the industry
- Drugs - tranquilizers and antihistamines
- Gas treatment - removal of CO2
Both the alcohols and amines are toxic to a certain degree when ingested. Different volumes and concentrations of each effect the human body.
