Alcohols and Carbonyls

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Alcohols and Carbonyls
Ethanol. Alkanol family, Aldehydes and Ketones.
Methanol and Methanal
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Index
Ethanol
Homologous series CnH2n1OH
Alcohol structures
Oxidation of alcohols
Aldehydes and Ketones
Methanol
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Ethanol C2H5OH
Functional group -OH
H
H
Hydrogen bonding allows ethanol to dissolve in
water, pH 7. b.p. 78 oC. This effect decreases in
alcohols as the length of the hydrocarbon chain
increases.
C
C
H
H
H
OH
Hydroxyl group
Ethanol is a good solvent, it behaves both like
water and other hydrocarbon solvents.
Combustion of ethanol
CH3CH2OH 3 O2 ? 2 CO 2 3 H2O ?H
- 1367 kJ mol -1
Ethanol can be used as a fuel in cars.
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Ethanol C2H5OH
Manufacture of Ethanol
1. Fermentation
Fermentation is used to make all alcohol based
drinks. Any vegetable matter containing
carbohydrates can be used.
yeast
C6H12O6 ? 2CH3CH2OH 2CO 2
2. Hydration of Ethene (Industrial manufacture of
Ethanol)
C2H4 H2O ? CH3CH2OH
Cracking fractions from crude oil is a cheaper
way to produce ethanol. (more expensive than
making petrol)
Reaction Conditions 300oC , High Pressure 60
Atm. , phosphoric acid catalyst.
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Uses of Ethanol
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Dehydration of ethanol
Catalyst
CH3CH2OH ? C2H4 H2O
Ethanol
Ethene
When hot ethanol is passed over aluminium
oxide ethene gas is produced.
Ethene is very a very important chemical, it is
the basis for many plastics. E.g. Polythene
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Homologous Series CnH2n1OH
Functional molecular structure
Methanol, CH3OH Ethanol C2H5OH Propanol C3H7OH
Straight chain isomers of Alkanols
Propanol C3H7OH, has 2 isomers, propan-1-ol and
propan-2-ol.
propan-1-ol
propan-2-ol
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Naming alcohols
1. Decide on the type of compound (ie. consider
functional group)
alcohol (alkanol)
2. Select the longest chain
4 Cs ? butanol
3. Name the compound with the branched chains in
ascending order.
2-methylbutan-1-ol
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Different types of alcohol
Secondary alcohol, 2 Cs joined to the C bonded
to the OH group
Tertiary alcohol, 3 Cs joined to the C bonded
to the OH group
Primary alcohol, 1 C joined to the C bonded to
the OH group
2-methylpropan-2-ol
propan-2-ol
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Other Alcohols
1. Cycloalkanol
Cyclohexanol is a secondary alcohol
2. Diols (dihydric)
Ethane-1,2-diol Anti freeze
3. Triols (Trihydric) e.g. propane 1,2,3,triol
or Glycerol is used in cosmetics, paints
and nitroglycerine explosives.
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Oxidation of Alcohols
CO carbonyl group
Primary alcohols can be oxidised in two stages,
1st Stage - Hydrogen is lost 2nd Stage - oxygen
is gained.
1st
2nd
Secondary alcohols can be oxidised to form
ketones, Tertiary alcohols do not undergo
oxidation.
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Aldehydes and Ketones
CHO alkanal functional group
CO ketone functional group
Propanone, nail varnish remover and is used in
the making of perspex
Methanal, 40 in water is formalin, and is used
to make polymers
Ethanal, Its trimer (CH3CHO)3 is used as a
sleep inducing drug. It also causes a hangover
Butanone, is a solvent used to make VHS tapes.
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Aldehydes and Ketones
RSC video on silver mirror
(Using mild oxidising agents.)
Distinguishing tests
Aldehydes are oxidised to carboxylic acids
1. Fehlings solution contains Cu2 ions (blue)
which form Cu ion (orange-red) in the
presence of aldehydes.
2. Tollens reagent contains Ag ions, which form
Ag in the presence of aldehydes (silver mirror
test)
3. Acidified Potassium Dichromate orange
Cr2O72-(aq) to green Cr3(aq)
Ketones do not react with oxidising agents.
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Methanol, Steam reforming
The steam used must be pure.
Methanol is oxidised into methanal, either
by 1. Zinc/Chromium oxide catalysts 350-450oC
and 200-300 Atm. 2. Cu/Zn/Al oxide catalysts
175-300oC and 40-100 Atm.
CH3OH O2 ? HCHO H20
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Uses for Methanol and Methanal
Methanol
Methanal
Fuel Added to ethanol to make meths, cleaner flame than hydrocarbons. Added to petrol octane number 114. MTBE (Methyl Tertiary Butyl Ester) Can be converted into petrol using Zeolite. Drugs and Fabrics Formalin, preserve biological specimens Polymers Polymethanal, machine parts Melamine, Electrical insulators Phenol methanal, heat resistant are all thermosettings plastics