(O) Topic 28 - Amines
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What are the three types of amines?
Primary, Secondary and Tertiary
What 2 ways can primary amines be formed?
• Nucleophilic substitution of conc ammonia with halogenoalkanes • By reduction of nitrile compounds
Equations for formation of primary amine through reduction of a nitrile
nitrile + 4[H] -> amine (LiAlH4 in ethoxyethane) nitrile +2H2 -> amine (Ni catalyst + heat)
Explain solubility of amines
Amines are soluble in water due to their polar NH2 group, which allows them to hydrogen bond. However the longer their C chain attached, the less soluble they become, as the chain in non-polar
Explain Boiling point of amines
Boiling point of amines is higher than expected due to their hydrogen bonding between molecules, resulting in more energy being required to break molecules apart.
How are aromatic amines formed
Electrophilic susbtitution of benzene -> nitrobenzene nitrobenzene +[6H] -> aminobenzene + water (Sn +HCl followed by NaOH)
General order of amine base strength
tertiary amine> secondary amine> primary amine> ammonia> aromatic amine
Why is a primary amine a stronger base compared to ammonia
There is a greater electron density on the primary amine’s nitrogen due to the positive inductive effect of the alkyl group. Therefore the primary amine’s nitrogen is more electronegative, and its lone pair of electrons has a greater ability to accept protons.
What happens if a large excess of halogenoalkane is used during nucleophilic substitution with ammonia?
Further substitutions occur and seconds and tertiary salts may be formed, along with quaternery ammonium salts.
What happens if a large excess of ammonia is used in nucleophilic substitutions with halogenoalkanes?
Primary amines are the main product
What is a use of quaternary ammonium salts?
Soap and detergent molecules (surfactants): - Ionic ‘head’ dissolves in water as is polar and hydrophilic - Long alkyl chain ‘tail’ is non-polar and hydrophobic so dissolves grease * Micelles are formed as soap/detergent molecules surround the dirt/grease with hydrophobic tails in the centre, and hydrophillic heads outside, dissolving in the water
Practice
nucleophilic addition-elimination reactions with primary amines and acyl chloride
Uses of aromatic amines?
Used as dyes