Amines Flashcards
Amine
Organic molecule derived from ammonia: alkyl groups replace the hydrogen on NH3
Primary amine
When 1 alkyl group replaces the 1 hydrogen in NH3
How to name primary amines?
Alkyl group name (eg butyl)
Amine
2-propylamine
Secondary amine
When 2 alkyl groups replace 2 hydrogen on the NH in the molecule
Naming secondary amines
N-
(Number of carbon the NH is bonded to on short chain if necessary)-
Shorter chain alkyl group-
(Number of carbon the NH is bonded to on long chain if necessary)-
Longer chain alkyl group
Amine
Tertiary amines
Where 3 of the hydrogen are replaced by 3 alkyl groups on the NH3
Naming tertiary amines
N-
Shortest chain alkyl groups in alphabetical order (separated by -N-)
-number of carbon in the longest chain carbon is bonded to-
Longest chain alkyl
Amine
What bonds can primary and secondary amines form between each other?
(London forces and permanent dipole dipole forces)
HYDROGEN BONDS
Why can secondary and primary amines form H bonds to each other?
Because they contain hydrogen bonded to nitrogen
Nitrogen is electronegative to attract the pair of electrons in N-H to its nucleus enough so hydrogen is polarised to form H bonds to a line pair of electrons
What forces can tertiary amines form?
London forces and permanent dipole dipole forces
Why can tertiary amines not form hydrogen bonds to other tertiary amines?
Because it has no N-H bonds (all Hydrogen in the amine group is replaced with alkyl groups)
Why do primary and secondary amines have higher boiling points than tertiary amines?
Secondary and primary amines can form London forces, permanent dipole forces AND HYDROGEN BONDS
Tertiary amines can only form London forces and permanent dipole-dipole forces
So the former require more energy to overcome the hydrogen bonds between molecules
Amines vs corresponding alcohol: boiling point
O-H bond in alcohol is more polar than N-H bond in amine
So the hydrogen bond is stronger in alcohol than in the amine SO H bonds requires more energy to overcome in the alcohol so the amine has a lower boiling point
(If factor of carbon chain length is consistent across both molecules)
Can short chain amines (of all classifications) dissolve in water?
Yes
Why can all amines with short carbon chain dissolve in water?
Because hydrogen can form H bonds to lone pair of electrons on the nitrogen in ALL amines
Thus if the energy released is stronger making these h bonds than energy required to break hydrogen bonds/bonds bwteeen amines the amine can dissolve
Are secondary and primary amines more soluble in water?
Yes because they can form more hydrogen bonds to the water than a tertiary one
Why can long chain alkyl groups in an amine prevent dissolving in water?
Because the long chain alkyl groups will interfere with the hydrogen bonds between the water
Do primary amines dissolve most in water?
Yes because they can form most hydrogen bonds than any other
2 ways of synthesising a linear (aliphatic amine)
Halogenoalkane + ammonia
Reduction of a nitrile/amide
Halogenoalkane + ammonia conditions
Excess concentrated ammonia in ethanol
Heated in a sealed tube
Mechanism for ammonia + halogenoalkane
Nucleophilic substitution
Halogen is substituted for ammonia
Hydrogen is lost from ammonia (attracted to 2nd ammonia molecule)
Products of ammonia + halogenoalkane
Ammonium salt (ammonium ion+halide ion-)
And a primary amine of the same length
Reduction of a nitrile/amide conditions
Warm nitrile/amide and 4 LiAlH4 in dry ether
Hydrolysis with dilute acid
Product of reduction of nitrile
Just the PRIMARY amine
Can reduction of a nitrile ever produce a secondary/tertiary amine?
No because of the way nitriles have a C triple bond N then the carbon the nitrogen is on will always only be bonded to 1 alkyl group
Therefore only primary amines are possible
Products for reduction of an amide
The amine of the same classification
And water
How does reduction of an amide work?
The C=O bond breaks and 2 hydrogen bond to the carbon
We used 4[H] so the other 2 H form water with the lost oxygen
No change is made to the nitrogen hydrogen part = form amine of same classification as amide
Synthesis of aromatic amines uses what molecule?
Nitro aromatic compounds eg nitrobenzene
First step of synthesis of aromatic amine conditions
Reflux
With tin and concentrated HCl
First step of synthesis of aromatic amines is a…
Redox reaction
First step of synthesis of aromatic compounds reaction
Nitrobenzene + 6[H] + H+ ——> carbon chainNH3 +2H2O
Second step of synthesis of aromatic amines
Steam distillation under NaOH (aq)
RNH3+ +OH- ——> RNH2 + H2O
How many reducing agents is needed for synthesis of aromatic amine from nitrobenzene?
6
