Amines Flashcards
What are amines?
Amines are organic derivatives of ammonia
What is the functional group of amines?
NR2, where R is a hydrogen or an alkyl group
If the nitrogen atom is bonded to 4 alkyl groups, what do you get?
A positively charged quaternary ion
How do you make an aliphatic amine from a halogenoalkane?
Heat a halogenoalkane with an excess of ethanolic ammonia
What is the problem with forming an amine from a halogenoalkane?
You get a mixture of primary, secondary and tertiary amines
Why are a mixture of products formed when you heat a halogenoalkane with excess ethanolic ammonia?
The nitrogen atom in the amine has a lone pair of electrons making it a nucleophile, meaning it can take part in further substitution reactions
What is the first way of reducing a nitrile to a primary amine?
Reduce using lithium aluminium hydride (LiAlH4) followed by some dilute acid
What is the problem with reducing a nitrile to form an amine using lithium aluminium hydride?
LiAlH4 is far too expensive for industrial use
As LiAlH4 is far too expensive for industrial use, what is the second way of reducing a nitrile to an amine?
Reduce using hydrogen gas and a metal catalyst (e.g. nickel) at a high temp and pressure, which is called catalytic hydrogenation
How do you form an aromatic amine from a nitrobenzene?
- Heat nitrobenzene with tin metal and conc HCl under reflux, which creates a salt
- Then add sodium hydroxide to form phenylamine
Why are amines able to act as weak bases?
Because they accept protons, due to the lone pair of electrons on the nitrogen, that can form a dative covalent bond with a H+ ion
What does the strength of the amine base depend on?
How available the nitrogen’s lone pair of electrons are, the more available, the stronger the base
List in order of strength of base: Aromatic amines, primary aliphatic amines, ammonia
Primary aliphatic amine
Ammonia
Primary aromatic amine
Why are primary aromatic amines the weakest type of base?
The benzene ring draws electrons towards itself and the nitrogen lone pair gets partially delocalised onto the ring, so the electron density on the nitrogen decreases, making the lone pair much less available
Why are primary aliphatic amines the strongest base?
Alkyl groups push electrons onto the attached groups, so the electron density on the nitrogen atom increases, making the lone pair more available
Why are amines nucleophilles?
Due to the lone pair of electrons on the nitrogen atom
What happens when amines are neutralised by acids?
They form ammonium salts (e.g. CH3CH2NH3+CL-
Why are small amines soluble in water?
The amine group can form hydrogen bonds with the water molecules
Why are larger amines not soluble in water?
The bigger the amine, the greater the London forces between the amine molecules and the more energy it takes to break them apart. Also larger carbon chains disrupt the hydrogen bonding in water, but can’t form hydrogen bonds themselves, so large amines are less soluble than smaller ones
When amines dissolve in water, what do they form?
They form alkaline solutions
What happens in copper (II) sulfate solution?
The Cu2+ ions form complexes with the water, forming a blue solution
What happens if you add a small amount of butylamine to copper(II) sulfate
You will get a pale blue precipitate, as the amine acts as a base and takes 2 H+ from the complex, forming a pale blue precipitate of copper hydroxide, which is insoluble
What happens when you add butylamine in excess to copper sulfate solution?
The precipitate dissolves to form a deep blue solution as a complex ion is formed
How do you form a secondary amine from a primary amine?
React with halogenoalkane, and react again to form a tertiary amine
