Primary amine
Contains one alkyl group attached to the nitrogen atom as only 1 hydrogen atom in ammonia has been replaced
-> so there’s only 1 carbon chain attached to the nitrogen
-> so on for secondary and tertiary
Quaternary ammonium compounds
Produced from tertiary amines when the nitrogen’s lone pair of electrons forms a dative covalent bond to a 4th alkyl group
-> so it has 4 alkyl groups on the nitrogen atom
-> eg ammonium salts
2 prtooerties if amines
- -NH2 is the functional group
- N has a lone pair on it
What does ‘N’ mean
H is substituted for the first thing in the name
Preparation of primary amines techniques
- By the reaction of ammonia with halogenoalkanes
- By the reduction of nitriles
Primary amines from the reaction of ammonia with halogenoalkanes
Halogenoalkane + ammonia -> amine + ammonium halide
Conditions
- heat in sealed flask with excess concentrated ammonia in ethanol
- NH3 has a lone pair and acts as a nucleophile
- mechanism: nucleophilic substitution
- the amine product also acts as a nucelophile due to the lone pair in the N -> causes further substitution
• if excess ammonia is used then a primary amine is the major product
• if the halogenoalkanes is in excess then successive substitution is more likely to occur
Primary amines from reduction of nitriles
Nitrile + hydrogen -> amine
Conditions:
1. Hydrogen in presence of nickel catalyst
-> used in industry
OR
2. Hydrogen (reducing agent) is LiAlH4 in dry ether
-> done in lab + expensive
Why is Primary amines from reduction of nitriles better
Gives better yield and no other products
Preparation of aromatic compounds technique
By reduction of nitro compounds
Aromatic amines from reduction of nitro compounds
Conditions:
- heat under reflux with tin and excess concentrated HCl, followed by adding contrasted NaOH
• since excess acid is used, the protonated form of phenylamine
ie. The phenylammonium ion is formed
• concentrated NaOH is added to remove the hydrogen ion from the NH3+ group -> the addition of concentrated alkali liberates the free amine
Uses of quaternary ammonium salts
• Cationic surfactants
-> surfactants reduce the surface tension of liquids ie. Soaps and detergents
-> the positive nitrogen is attracted to the negatively charged surfaces such as fibres, hair ie fabric conditioner
Base strength of amines
- Amines are weak Bronsted-Lowry bases
-> H+ acceptors, lone pair donor (Lewis bases) - form dative bond
• the more available (to be donated) the lone pair on the nitrogen atom, the stronger the base
Alkyl groups
- they push electron density towards the nitrogen atom
-> this is called the positive inductive effect
-> this makes the lone pair of electrons on the N atom more available therefore a stronger base
Increasing base strength
tertiary > secondary > primary > ammonia
Aromatic amines (benzene)
In benzene, p orbitals overlap and the electrons become delocalised in a ring (can move outside orbital)
Base strength of aromatic amines
In aromatic amines, the N lone pair is partially delocalised into the benzene ring, lowering the base strength as it makes the lone pair less available to be donated
What are aromatic amines
Amiens attached to a benzene
Increasing base strength and why
(Aromatic, ammonia, primary amine)
Lowest
Aromatic amines
• Lone pair on N
• Drawn into ring of delocalised electrons
• Lone pair on N is less available
• Weak base
Ammonia
• Lone pair on N
• Available to be donated/H+ acceptor
• Weak base
Primary amines
• Positive inductive effect of R group
• Push electron density towards N atom
• Makes lone pair of electrons on N atom more available
• Stronger base
Use of quaternary ammonium salts in fabric cleaners
The hydrocarbon rail attaches to grease while the charged head dissolves in water making it easier to wash away dirt
Use of quaternary ammonium salts in hair products
The cationic head sticks to the negatively charged surfaces of hair improving condition
Use of quaternary ammonium salts in fabric softeners
The positive charge can neutralise static electricity by bonding to negatively charged fibres in the fabric
Why are quaternary ammonium salts useful as surfactants if they have long hydrocarbon chains
Becuase they posses both polar and non polar parts
What are amines
Organic compounds that come from ammonia
How do amines come about
When one of more H atoms in an ammonia molecule are replaced with alkyl groups
