3.11 Amines Flashcards
What are amines?
Organic compounds containing a nitrogen atom.
What are primary amines?
When one hydrogen on the nitrogen has been replaced by an alkyl or aryl group
What are secondary amines?
When two hydrogens on the nitrogen have been replaced by an alkyl or aryl group
What are tertiary amines?
When all three hydrogens on the nitrogen have been replaced
Describe how you name a secondary amine
N-branch main chain amine
Eg N-methylethanamine
How are tertiary amines named?
Named in a similar way to secondary amines using an N- to show that each smaller chain is attached via the nitrogen. Smaller chains named in alphabetical order.
Eg. N-ethyl-N-methylpropan-1-amine
Are amines weak or strong bases?
Amines are weak bases, the lone pair on the nitrogen can accept a proton.
What affects the base strength of an amine?
Base strength depends on how well N lone pair can accept H+. The higher the electron density of the N lone pair, the stronger the base.
As you move from aromatic amines, to primary, then secondary, then tertiary amines, does the base strength increase or decrease?
Increase in base strength
Why are tertiary amines the strongest amine base?
Tertiary amines are the strongest base as the 3 alkyl groups push electron density towards Nitrogen, meaning the highest electron density is on the lone pair, making it more available.
Why are aromatic amines the weakest amine base?
The lone pair of electrons on nitrogen is partially delocalised into the benzene ring, making it less available.
How are amines formed?
Through nucleophilic substitution of ammonia with a haloalkane
How are secondary and tertiary amines formed, as well as quaternary ammonium salts?
Through the nucleophilic substitution of haloalkanes with either a primary amine, secondary amine, or tertiary amine.
How can you make primary amines without the issue of further substitution?
You can instead make primary amines from halo alkanes by reduction of a nitrile in a two step synthesis. Eg reacting bromomethane with KCN to form ethanenitrile, then reducing this to ethanamine
What can be used to reduce nitriles to form amines?
LiAlH4 eg RCN + 4[H] with this forms RCH2NH2
Or
H2 and a nickel catalyst
