Amines Flashcards
How do you classify amines as primary, secondary and tertiary?
If there is one alkyl group attached to the nitrogen, it is primary
If there are two alkyl groups attached to the nitrogen, it is secondary
If there are three alkyl groups attached to the nitrogen, it is tertiary
What are quaternary amines?
Where the nitrogen has four alkyl groups attached. These will form ammonium cations, which are positively charged
What are the two main ways of making primary aliphatic amines?
Starting from halogenoalkanes or nitriles
What is equations for the formation of a primary amine from a halogenoalkane?
Halogenoalkane + NH3 -> Primary amine + HX
What conditions must be used for the formation of primary amines from halogenoalkanes?
For gaseous ammonia, the mixture must be heated in a sealed container
Alternatively, the halogenoalkane can be mixed with conc aqueous ammonia.
Ammonia should be in excess
Why should ammonia be in excess when forming amines from halogenoalkanes?
The amine formed has a nitrogen containing a lone pair of electrons, which means it could act as a nucleophile, competing with ammonia for the attack on the halogenoalkane, which will form a secondary amine.
To minimise the chance of secondary amines from being formed, ammonia is used in excess, so it outcompetes the primary amine as a nucleophile
What does some of the excess ammonia react with to form?
Some excess ammonia will react with produced HCl to form an ammonium chloride salt.
So a better equation would be:
Halogenoalkane + 2NH3 -> Primary amine + NH4Cl
Through what process can primary amines be produced from nitriles?
Nitriles can be reduced to primary amines
What is the reducing agent for the reduction of nitriles to primary amines?
Lithium tetrahydridoaluminate
What is the equation for the reduction of ethanenitrile to ethyl amine?
CH3CN + 4[H] -> CH3CH2NH2
For the reduction of nitriles to primary amines, what is the solvent and why?
The solvent is dry ether, to ensure that there is no water that could affect the reaction
What is reduced to form aromatic amines?
Nitrobenzene
What is the formula for nitrobenzene?
C6H5NO2
What is the reducing agent and conditions used for the reduction of nitrobenzene to an aromatic nitrile?
The reducing agent is tin mixed with concentrated HCl, and it is heated under reflux
What is product of the the reduction of C6H5NO2?
Phenyl amine (C6H5NH2)
What is the equation for the reduction of nitrobenzene to phenylamine?
C6H5NO2 + 6[H] -> C6H5NH2 + 2H2O
What will phenylamine form due to the acidic conditions, and how is this overcome?
Phenylamine is basic so will react with the acid present to form the phenylammonium ion. However this can easily be converted back to phenylamine with the addition of an alkali (e.g. NaOH)
What is the equation for the conversion of phenylammonium back to phenylamine?
OH- + C6H5NH3+ -> C6H5NH2 + H2O
Why are (some shorter chain) amines soluble in water?
Hydrogen bonds form between the hydrogens attached to the nitrogen in the amine and the oxygen in water
How do amines react with water (use methylamine as the example)?
CH3NH2 + H2O <=> CH3NH3+ + OH-
What are the amines acting as when reacting with water?
As a base (as they are attracting/receiving a proton)
How does the basicity of ammonia compare to methylamine and why?
Methylamine is a stronger base than ammonia, as the methyl group is electron-releasing, and so the nitrogen has an increased electron density (so can more easily receive protons)
How does the basicity of aliphatic amines change as chain length increases?
The basicity increases, but only slightly, as the ethyl and propyl groups are only slightly more electron-releasing than the methyl group
How does the basicity of aromatic amines compare to aliphatic amines and why?
Aromatic amines, like phenylamine, have a much lower basicity than aliphatic amines.
This is because the lone pair of electrons on the nitrogen are displaced towards the pi bond of the electron ring; this makes the nitrogen less electron rich and the lone pairs less available
How do amines react with strong acids?
All amines react with strong acids to form ionic salts.
e.g CH3NH2 + HCl -> CH3NH3+Cl-
What type of mechanism is the reaction between ethanoyl chloride and amines and why?
The reaction is addition-elimination, as one molecule is added to another, and in this joining a small molecule is eliminated (in this case HCl)
What do amines and ethanoyl chloride react to form?
Amides and HCl
What is the functional group of amides?
O=C-NR2
Why do halogenoalkanes and amines react?
The electron-deficient carbon of the halogenoalkane is attacked by the electron-rich nitrogen of the amine
How are secondary amines formed using halogenoalkanes?
Primary amines react with halogenoalkanes to form secondary amines and HX
How are tertiary amines formed using halogenoalkanes?
Secondary amines react with halogenoalkanes to form tertiary amines and HX
How are quaternary amines formed using halogenoalkanes?
Tertiary amines react with halogenoalkanes to form quaternary amines and X-
Why is HX not formed in the formation of quaternary amines used halogenoalkanes?
Because there is no hydrogen to lose from the amine group, as they have all already been replaced by alkyl groups. Instead the product is a quaternary ammonium salt
Why do amines reacting with halogenoalkanes not seem to be a good method of preparation?
As it is likely a mixture of primary, secondary, tertiary and quaternary amines will be produced
What would happen if you had an excess of halogenoalkane?
The full sequence would likely occur for most, producing mostly quaternary ammonium salts
Why are amines able to react with copper(II) ions?
They can act as bases (proton acceptor and electron donator)
What observation will initially be seen from the reaction of amines with copper(II) ions?
A light blue precipitate will be formed
What observation will then be seen with excess amine after the light blue precipitate has been formed?
The light blue precipitate will dissolve and a deep blue solution will emerge
What happens in the reaction between amines and copper(II) ions in the formation of the light blue precipitate?
The 2 amines act as proton acceptors, receiving two hydrogens from the copper complex
What is the equation for the reaction between amines and copper(II) complex in the formation of the light blue precipitate?
[Cu(H2O)6]2+ + 2CH3NH2 -> [Cu(H2O)4(OH)2] + 2CH3NH3+
What happens in the reaction amines and the copper(II) complex in the formation of the deep blue solution?
The complex formed from the first reaction reacts with 4 more amines, which replace 2 H2Os and 2 OHs that were previously around the copper ion
What is the equation for the reaction amines and the copper(II) complex in the formation of the deep blue solution?
[Cu(H2O)4(OH)2] + 4CH3NH2 -> [Cu(CH3NH2)4(H2O)2] + 2H2O + 2OH-
What is used in industry as LiAlH4 is too expensive?
Hydrogen gas with a metal catalyst
