4.8 - Organic synthesis and analysis Flashcards
What are the different separating techniques
- Separating miscible liquids
- Separating immiscible liquids
- Separating insoluble liquids
- Soluble solids from solutions (purification by recrystallising)
What are the different ways of separating miscible liquids
- distillation
Used if products do not decompose at or close to boiling point and if the boiling point is low. If boiling point different by around 20 degrees simple distillation is used - fractional distillation
Used if boiling points are closer together as fractionating column enables more efficient separation - vacuum distillation
Used if boiling point is high, as reducing pressure reduces the boiling point
What are the different ways of separating immiscible liquids
- steam distillation
Used when substances decompose close to their boiling points, steam is passed into the mixture and volatile compounds pass into the condenser with the steam forming a mixture of water and molecule - separating funnel
Enables aqueous layer and an organic layer to be separated - solvent extraction
Used when a compound has different solubility in two immiscible solvents, the compound dissolves in one solvent and is separated using a funnel
How are insoluble solids separated
- filtration
Uses filter paper and a funnel, fluted filter paper is quicker as larger surface area and one layer but Büchner funnel preferable
How are soluble solids separated from a solution
- if the solid is a solute in the solution crystallisation is used, the mixture is boiled and then cooled, it is concentrated enough crystals form if not heat and cool again to increase concentration
Purification of a solid product by recrystallisation
1. Dissolve the solid in the minimum volume of hot solvent
2. Filter to remove insoluble impurities
3. Allow the solution to cool forming crystals
4. Filter
5. Wash the solid with a small amount of solvent
6. Dry at temperature below the melting point
What is polymerisation and the difference between the two types of polymerisation
- addition polymerisation
The joining of small monomers to form longer polymer chains
Monomers contain C=C bonds forming only a polymer
eg. Ethene > polyethene
- condensation polymerisation
The joining of many monomers forming a polymer and a small molecule (H2O/HCl)
What are the different types of condensation polymerisation
Polyamides (COOH and NH2)
a. Nylon- 6,6
monomers: 1,6-diaminohexane and hexandioic acid
- Can break Nylon-6,6 with hydrolysis OH-/H2O and heat or H+/H2O and heat
b. Nylon-6 (captolactan - ring is broken)
monomer: 6-aminohexanoic acid
c. Kevlar (bullet proof vets)
monomers: benzene-1,4-dioic acid and 1,4-diaminobenzene
Polyesters (COOH and OH)
PET: polyethyleneterephthalate
- durable and waterproof (plastic)
monomers: benezenedioic acid and ethane-1,2-diol
What are the three different forms of chromatography
- Paper/thin layer chromatography
- Gas chromatography (GC-MS)
- High performance liquid chromatography (HPLC)
What is paper/thin layer chromatography
Paper: stationary phase - cellulose fibre of paper
Thin layer: stationary phase - silica or alumina on plastic/glass
- the mobile phase is a suitable liquid solvent or mixture
- a pure substance is one spot a mixture is multiple spots
- the movement of a substance depends on its relative attraction to the stationary/mobile phase
- substances with greater attraction to the solvent travel quicker and further up the paper
- substance with less attraction to the solvent travel slower and less distance up the paper
It there is more than one spot
- rotate the chromatogram 90 degrees and repeat with a different solvent to separate all compounds
Colourless spots can be sprayed with UV or ninhydrin to become visible
What is gas chromatography (GC-MS)
A gas mixture (mobile phase) is passed through a liquid on an inert solid (stationary phase), a carrier gas sweeps the mixture onto the column (hydrogen/helium/argon) the temperature of the column can be varied and is sometimes raised
The retention time is recorded and components with the highest boiling time (more polar) have the longest retention time,e as they spend most of the time condensed as a liquid at the bottom of the column
What is high performance liquid chromatography (HPLC)
Used to separate compounds that vaporise at high temperatures where they start to decompose, the column is packed with solid particles of a uniform size and the mixture is dissolved in a suitable solvent, the mixture is forced through at high pressure
Normal: non-polar compounds pass through more quickly
Reversed: polar compounds pass through more quickly (most common)
What is retention factor (Rf) and how is it calculated
Rf value is the ratio of the distance the substance moves to the solvent
Rf = distance travelled by compound / distance travelled by solvent
What is NMR
High resolution NMR causes splitting patterns within peaks, splitting is identified as the number of adjacent hydrogens (n+1)
We can then look at chemical shift data to identify structures
(OH is always a singlet)
Singlet - one line on the graph
Doublet - two lines on the graph
Triplet - three lines on the graph
Quartet - four lines on the graph
NMR is used alongside IR and mass spec
eg. propan-1-ol
CH3CH2CH2-O-H
3:2:2:1 no. hydrogens
CH3 - triplet splitting CH2
CH2 - sextet 5 hydrogens
HC-O - triplet CH2
R-OH - singlet
Organic synthesis
- only given up to a four step synthesis
lengthen a carbon chain by
- acidified KCN + halogenoalkane > nitrile
Nitrile can be hydrolysed to a carboxylic acid or reduced to an amine
- acidified KCN + Carbonyl > hydroxynitrile
- friedel-crafts alkylation of an aromatic compound
Increases the carbon chain on a benzene ring
shorten a carbon chain by
- heat a carboxylic acid with soda lime > alkene, has one less carbon
- methyl ketone + iodine in alkaline conditions produces triiodomethane and an aldehyde with one less carbons
