Nitrogen Compunds Flashcards
How can you prepare amines from:
a) Nitriles
b) Amides (Hofmann degradation)
c) Ammonia
a) Nitriles: reduction with LiAlH4
b) Amides: reduction with Br2 and NaOH
c) Ammonia: react with halogenoalkane (excess conc NH3 in ethanol)
How do amines act as bases?
Put the following in order of increasing basicity:
Ammonia, Methylamine, phenylamine
The nitrogen atom has a lone pair of electrons, so it can accept a proton.
Phenylamine, ammonia, methylamine
Phenylamine has an arene ring which decreases the electron density and availability of the lone pair.
Methylamine has alkyl groups which have an inductive effect. They increase the electron density of the nitrogen.
How do amines act as ligands in complex ion formation? Use the example of copper (II) ions in solution.
The nitrogen has a lone pair of electrons that allow it to form dative covalent bonds with the metal ion.
Deprotonation with some amine = a blue precipitate. Ligand exchange with excess amine = a deep blue solution.
Overall: [Cu(H2O)6]2+ + 4CH3NH2 -> [Cu(CH3NH2)4(H2O)]2+ 4H2O
Describe and explain the following physical properties of amines:
a) Solubility
b) Boiling points
c) Characteristic smell
a) Amines are water soluble due to hydrogen bonding - increases as chain length and R groups decrease
b) Amines have higher boiling points than alkanes due to hydrogen bonding - increases with chain length
c) Add HCl to get rid of fishy smell; add NaOH to get fishy smell back
What type of reaction do amines undergo with acyl chlorides?
Addition-elimination
CH3CH2NH2 + CH3COCl -> CH3CONHCH2CH3 + HCl
How is paracetamol synthesised from phenol? Give the reagents and conditions for each step.
- Nitration of phenol: NaNO3 + H2SO4
- Reduction: NaBH4 or Tin and HCl
(Distillation is used to separate isomers - Ethanoic anhydride: or CH3COCl
Describe the process of preparing phenylamine from nitrobenzene.
- Add nitrobenzene and tin to a flask. Then add concentrated HCl until all the H2 gas is given off
- Excess NaOH is added to redissolve the Sn(OH)4
- Steam distillation - add water. Emulsion forms
- Salting out - phenylamine is more soluble in water than in a saturated salt solution
- Solvent extraction - run off the phenylamine layer and add ethoxyethane
- Pellets of KOH are added to dry the ethoxyethane and remove unreacted HCl
- Distil ethoxyethane off. Phenylamine comes off at 180C
In the preparation of a diazonium salt:
a) What reagents are required?
b) Why must the temperature be kept at 5 degrees C?
a) Nitrous acid (provides HNO2) and hydrochloric acid
b) If the temp is too low, reaction will be too slow; if temp is too high, diazonium ion decomposes to form phenol
In the preparation of an azo dye:
a) What reagents are required?
b) What is this type of reaction called?
c) Why are azo compounds coloured?
d) What makes the azo compound stable?
e) Why is methyl orange soluble in water?
a) Phenol dissolved in alkali (NaOH) and chilled benzenediazonium chloride
b) Coupling reaction
c) They absorb light of a specific wavelength
d) The N=N bond becomes part of the delocalised system
e) The amine (NH2) group H bonds with water and the SO3-Na+ forms ionic bonds and is hydrated by water
State the properties of amides.
- Are stable and relatively unreactive
- Have high melting and boiling points - form H bonds
- Soluble in water - enough energy is released from hydrogen bond formation
Give two ways of preparing amides from acyl chlorides
- Ammonia - CH3COCl + NH3 -> CH3CONH2 + HCl
- Amine - CH3COCl + CH3NH2 -> CH3CONH2CH3 + HCl
Acyl chlorides are often prepared from carboxylic acids
What is the difference between condensation polymerisation and addition polymerisation?
How are the different types of polymers disposed?
Condensation: two monomers join to form a polar polymer - a small molecule is released. Are biodegradable (hydrolysis) and photodegradable.
Addition: an unsaturated monomer forms a saturated polymer. Non-biodegradable (landfill build up), so require burning (produces toxic fumes) or depolymerisation.
Disposal of polymers requires incineration to reduce bulk waste and recycling to preserve oil resources.
State the properties and uses of the following polymers:
a) Nylon
b) Kevlar
c) Terylene (PET)
d) Poly(ethenol)
e) Poly(propeneamide)
a) High tensile - alternative to wool, silk; used in stockings
b) Hardest material - used in bulletproof vests; aircraft;
c) Flexible - used in plastic; clothing
d) Soluble - used in liquitabs; laundry bags
e) Used in water treatment; contact lenses
What are amino acids?
The building blocks of proteins. They consist of an amino (NH2) group and a carboxyl (COOH) group.
State and explain the properties of amino acids:
a) Natural state
b) Melting temperature
c) Solubility
d) Amphoteric
e) Chirality
a) Solids at room temp - zwitterions
b) High melting temps - they crystallise in giant lattice with strong ionic forces (electrostatic) between zwitterions
c) Soluble in water, not organic solvent
d) Act as buffers - in acidic solution they are bases, in alkali they are acids
e) All except glycine are optically active
