11. Amines
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What are amines?
Nitrogen-containing organic compounds
What are amines derived from?
Ammonia
What is a primary amine?
An ammonia molecule with one of the hydrogen atoms replaced by an alkyl or aryl group
What is a secondary amine?
An ammonia molecule with two of the hydrogen atoms replaced by an alkyl or aryl group
What is a tertiary amine?
An ammonia molecule with all three of the hydrogen atoms replaced with an alkyl or aryl group
What is an alkyl group?
A saturated hydrocarbon side group derived from an alkane
What is an aryl group?
An unsaturated hydrocarbon side group derived from an arene
What happens when the lone pair in a tertiary amine is used for bonding?
A quaternary ammonium salt is formed
What does it mean, if a molecule is aliphatic?
It is not aromatic i.e. it doesn’t have a benzene ring
How can amines be prepared?
• nucleophilic substitution of a halogenoalkane * reduction from nitriles
How many ways can amines be prepared?
2
What products does the preparation of amines from halogenoalkanes result in?
A mixture of primary, secondary and tertiary amines and their salts
What products does the preparation of amines from a nitrile result in?
Primary amines only
How would amines be prepared, if you wanted to produce primary amines only?
Reduction from a nitrile
What are the reactants for production of amines through nucleophilic substitution?
A halogenoalkane and excess ammonia
Conditions for the production of amines through nucleophilic substitution?
Excess ammonia (dissolved in ethanol) - warmed in a sealed vessel
Why is ethanol used to dissolve the ammonia when producing amines through nucleophilic substitution?
As water would protonate the NH3
What does ammonia act as in the nucleophilic substitution to form amines?
A nucleophile
How can it be ensured that a primary amine is the main product from nucleophilic substitution?
Using excess ammonia
Why is nucleophilic substitution not the most efficient method of producing primary amines?
As a mixture of 1°, 2°, 3° amines and 4° salts are formed
Why is a mixture of 1°, 2° and 3° amines, as well as 4° salts, formed in nucleophilic substitution?
The primary amine produced can act as a nucleophile to form a secondary amine and so on
How are nitriles reduced to form amines?
Using a strong reducing agent e.g. LiAlH₄ in dry ether followed by addition of dilute acid, at room temperature
What reducing agents can be used to form amines?
LiAlH₄ OR Nickel catalyst and hydrogen gas
How many times can you reduce a nitrile?
Once