Amines
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Why can primary amines act as a base? What else can it act as?
The N has a lone pair which can accept a proton A nucleophile as this lone pair can donate to a delta positive C
Why can secondary amines act as a base? What else can it act as?
The lone pair on N can accept a proton A nucleophile as the lone pair can donate to a delta positive C
Why can tertiary amines act as a base? What else can it act as?
The N has a lone pair which can accept a proton A nucleophile as this lone pair can donate to a delta positive C
Can quaternary ammonium salts act as a base?
Nope There is no lone pair on the N so it does not react
2 ways to prepare an amine?
Nucleophilic substitution Catalytic hydrogenation
What is the equation for the reaction of bromoethane and an excess of NH3? Why is an excess used? What is the mechanism?
CH3CH2Br + 2 NH3 —-> CH3CH2NH2 + NH4Br To avoid further substitution Nucleophilic substitution
What is the disadvantage of forming amines via nucleophilic substitution?
A low yield of primary amine is produced
Why is a low yield of primary amine formed for nucleophilic substitution?
A mixture of amine products formed due to product also acting as a nucleophile
What is another name for preparing an amine using catalytic hydrogenation?
Reduction of a nitrile
What are the two steps for the reduction of a nitrile?
RBr + CN- —-> RCN + Br- RCN + 2H2 ——> RCH2NH2
Overall equation for reduction of a nitrile
RCN + 2H2 ——> RCH2NH2 Nickel catalyst!
What is the advantage of reducing a nitrile Why
High yield of product formed Product does not react with nitrile
How to form an aromatic amine
Reduction of nitrobenzene using Sn/ HCl
What is the equation for the reduction of nitrobenzene
Nitrobenzene + 6[H] —-> amino benzene + 2H2O
What salt is produced from the reduction of nitrobenzene Why is this formed?
C6H5NH3+Cl- Reaction is carried out using HCl so amino benzene reacts with HCl
What is used to liberate the free amine after the reduction of nitrobenzene What is the equation?
NaOH RNH3+Cl- + NaOH —-> amino benzene + H2O + NaCl
Are amines strong bases? Why?
No they’re weak bases They partially dissociate in water
What happens when ammonia acts as a base?
The lone pair on N is donated to accept a proton
What is the equation for ammonia and H+
NH3 + H+ —-> NH4+
What does the strength of amines as. bases depend on?
The availability of the lone pair
Aromatic amines are stronger bases than aliphatic amines. true or false?
False
Why Are aromatic amines weaker bases?
The lone pair on N overlaps with the delocalised ring (negative inductive effect) Making lone pair less available
Why are aliphatic amines strong bases?
R group pushes e- towards lone pair on N (positive inductive effect) Making lone pair on N more available
How does chain length affect the positive inductive effect?
Effect increases/ is stronger with increasing chain length