Amines Flashcards
What is a primary amine
N is attached to 1 carbon atom
What is a secondary amine?
N is attatched to 2 carbon atoms
What is a tertiary amine
N is attached to 3 carbon atoms
What is a quaternary ammonium salt
N is attached to 4 carbon atoms and has a +ve charge
what are properties of primary secondary and tertiary amines
- N has a lone pair
- can accept a proton
- can donate to a delta +C
(acts as a base and nucleophile)
What are properties of a quaternary ammonium salt
no lone pair
N doesn’t react
What shape do amines have
pyramidal due do 3 bonding pairs and one lone pair
What shape do quaternary ammonium salts have
tetrahedral
What are the boiling points of amines
lower compared to alcohols with the same carbon chain
- H bond in amines is weaker as N is less electronegative than O
What is the solubility of amines
short amine chains are soluble in water as they firm H bonds with water
how can you prepare Aliphatic amines
nucleophilic stubstitution
What is a limitation of using nucleophilic substitution to form amines
a mixture of amines is formed due to the product also acting as a nucleophile
- therefore a low yeild of primary amine is produced
- other products: secondary/tertiary amines and quaternary ammonium salt
How can you minimise further substitution when forming an amine using nucleophilic substitution
use a large excess of ammonia to lead to a better yeild of amine
How does the amine product produce haloalkanes?
- the amine product from nucleophilic substitution can also react with the halogenoalkane as the N has a lone pair which can act as a neucleophile
- this leads to a mixture of haloalkanes being made
How do further substitutions occur in amines
- nucleophilic substitution occurs between halogenoalkane and ammonia to produce a primary amine
- primary aline reacts with unused halogenoalkane to produce a secondary amine
- secondary will react with halogenoalkane to produce tertiary
- tertiary reacts to make quaternary ammonium salt
What will occur if a large excess of halogenoalkane is used in nucleophilic substitution with an amine
leads to a high yield of quaternary ammonium salt
How are amines prepared from nitriles
nitrile functional group is reduced with hydrogen gas and nickle
What are quaternary ammonium salts used for
cationic sufactants
What is the equation for reduction of a nitrile
RCN + 2 H2 > RCH2NH2
What is an advantage of preparing amines from nitriles
- high yield of primary amine because product doesn’t react with the nitrile
Outline the 2 step method for forming an amine from a halogenoalkane
- KCN is used as a nucleophile in nucleophilic substitution of the halogenoalkane
- H2 and Ni catalytic hydrogenation
What is the equation for catalytic Hydrogenation
RCN + H2 > RCH2NH2
What is an advantage of using the 2 step method to make an amine
purer product is obtained
What are aromatic amines
contain a benzene ring (arenes)
How are aromatic amines formed
by the reduction of nitrogen benzene using HCl as a reducing agent and tin (Sn) as the catalyst
What is the equation for the formation if amines from nitrobenzene
C6H5NO2 + 6[H] > C6H5NH2 + H2O
What does the strength of amines as a base depend on
the availability of the lone pair
What are properties of aromatic amines
- weaker base
- lone pair on the N is less available because it overlaps with the delocalised ring
What are properties of aliphatic amines
- stronger bade
- lone pair on N is more available
- R group pushes electrons towards N atom (positive push effect)
