Organic synthesis and analysis
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What is important to remember in organic synthesis
To keep the number of steps as small as possible to maximise the yield of the target molecule.
What is the oxidising agent we use for most reactions (A-level)
Acidified potassium dichromate
List the various reducing agents and which reactions they are used in
1) NaBH4: Will reduce polar unsaturated groups such as C=O but not non-polar unsaturated groups such as C=C. This is because it generates the nucleophile :H- (hybrids ion) which attacks C+ but is repelled by C=C. 2) Hydrogen with a nickel catalyst H2/Ni which reduces the C=C bond but not C=O 3) Tin and hydrochloric acid Sn/H+ which reduces R-NO2 and R-NH2
How can alcohols be dehydrated
Alcohols can be converted to alkenes by passing their vapours over heated aluminium oxide or by acid catalysed elimination reactions.
How do you test for an alkene and what is the result
• shake with bromine water • the original red-brown colour of the bromine water disappears.
How do you test for a halogenoalkane and what is the result
1) add NaOH and warm 2) acidify with HNO3 3) add AgNO3 - a precipitate of the silver halide forms
How do you test for an alcohol and what is the result
• add acidified K2Cr207 • orange colour turns green (primary,secondary alcohols and aldehydes)
How do you test for an acid
• Add NaHCO3 • bubbles observed as CO2 given is
How to go from an Alkane to haogenoalkane?
Br2 or Cl2 UV light Free radical substitution
How to go from a haogenoalkane to an amine
Alcoholic NH3 heat under pressure Nucleophilic substitution
How to go from a halogenoalkane to a nitrile
KCN Ethanolic Aqueous Heat Nucleophilic substitution
How to go from a nitrile to an amine
LiAlH4 in ether OR H2 Ni 200⁰c Reduction
How to go from an amine to an amide
Acyl chloride or acid anhydride Room temp Nucleophilic addition elimination