What is an amine?
- Contain nitrogen atom with lone pair where hydrogens are replaced for organic group.
What are the 4 different types of amines?
- Primary (1 organic group directly bonded to N.)
- Secondary: (2 organic groups directly bonded to N.)
- Tertiary (3 organic groups directly bonded to N.)
- Quarternary ion, forms quarternary ammonium salts (4 organic groups directly bonded to N.)
What are non-aromatic amines known as?
- Aliphatic amines.
What are quarternary ammonium salts used to make?
- Quarternary ammonium salts are used to make cleaning products.
- Examples: shampoo, laundry degertants, washing up liquids.
What are quarternary salts that have a long hydrocarbon tail called?
- Cationic surfactants.
What are quarternary ammonium salts composed of?
- Positive charge on quarternary ion, specifically on N
- Attracted to negative ion ie. Cl⁻
What are cationic surfactants used in/ why?
- Non-polar tail (ie. hydrocarbon chain) attracted to oil/ grease.
- Polar head (positive quarternary ion) attracted to water.
- Allows water/ oil to mix –> removes grease.
- Positive quarternary ion, attracted to negatively-charged fibres and hair. Removes static –> used in hair conditioner, fabric softener.
How do amines react with H⁺?
- Lone pair on N will form dative covalent bond with H+
- Both electrons in bond between N and H⁺ come from N.
What is the strength of amines dependent on?
- Dependent on availability of lone pair of electrons on the nitrogen.
- Higher electron density, more readily available the electrons are to the H⁺ ion.
- Electron density on N dependent on group attached to the N.
What two things can amines act as?
- Bases.
- Nucleophiles.
Put these amines in order of base strength from weakest to strongest:
- Ammonia.
- Aromatic Amines.
- Primary aliphatic amines.
1.) Aromatic Amines.
2.) Ammonia.
3.) Primary aliphatic amines
Why are aromatic amines weak bases?
- Lone pair of electrons on N delocalised into benzene’s ring of electrons.
- Electron density at N reduces so lone pair availability is reduced.
Why are primary aliphatic amines strong bases?
- Alkyl groups push electron density towards N –> positive inductive effect.
- Electron density at N increases so lone pair availability is increased.
What are the 2 ways we can make aliphatic amines?
- Reacting halogenoalkane with excess ammonia.
- Reduction of nitriles
What is downside of producing amines by reacting a halogenoalkane with ammonia?
- Multiple substitutions can occur.
- Forming: primary and secondary amines/ quarterny ammonium salts.
- Impure product/ separated by fractional distillation –> time-consuming.
Why do multiple substitutions occur when making aliphatic amines by reacting excess halogenoalkane with ammonia?
- Primary amines still have lone pair on N so acts as a nucleophile.
- Amine reacts with remaining halogenalkane to produce secondary and tertiary amines/ quarternay ammonium salts.
If halogenoalkane reacts with EXCESS ammonia, what will occur?
- Halogenoalkane runs out.
- No further reaction
- Only 1 substistution.
- Only primary amine produced.
If ammonia reacts with EXCESS halogenoalkane, what will occur?
- NH3 runs out.
- Halogenoalkane and primary amine react –> secondary amine –> tertiary amine –> quarternary ammonium salt.
Why does multiple substitutions reaction when ammonia reacts with EXCESS halogenoalkane stop when we form quarternary ammonium salt?
- No lone pair on quarternary ammonium salt.
- So cannot act as a nucleophile.
Write equation for methylamine reacting with chloroethane to form a secondary amine.
2CH₃NH₂ + CH₃CH₂Cl –> CH₃NHCH₂CH₃ + CH₃NH₃⁺Cl⁻
If Q asks you to draw multiple substitions what would you do?
- Replace H on N with group of halogenoalkane, exluding the negative ion.
What is the cheapest way to make primary amines in industry?
- Reduce nitriles using H2 gas/ nickel catalyst.
How is forming amines from reacting with H2 and Ni different from forming amines using haloalkanes?
- Produces primary amines so only pure product is made.
What are the conditions for producing primary amines by reducing nitrile using the cheaper method?
- React with H2 gas.
- Nickel catalyst.
- High temp/ pressure.
