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Alcohols
15.1 Alcohols-introduction: Crude oil(non-renewable) Carbohydrates (renewable)
Cracking + hydration Fermentation + distillation
Alcohols have a hydrocarbon chain with an OH group, Fast rate of reaction slow rate of reaction
R-OH Continuous process batch process
• the OH group increase reactivity Pure product aq. Product
• The OH group creates a v-shape at 105° from the lone
pair repulsion
• Can be classified as primary, secondary and Biofuel: a fuel derived or produced from renewable
tertiary depending how many R groups are on the C biological sources
atom.
Primary Secondary Tertiary
15.3 Reactions of Alcohols:
OH OH OH
R - C -H R-C-R R-C-R Alcohols burn completely in oxygen, therefore used a lot
H H R as a fuel eg. Methylated spirits
Elimination reactions-results in dehydration of the
• Has H bonding due to the OH group compound, the leaving group is always water.
• High melting point, requires a lot of energy to
overcome the electrostatic attraction in hydrogen
bonding (between lone pairs and slightly positive H
atoms)
• Become less soluble the longer the hydrocarbon
chain becomes as the chain is insoluble but the OH
group is soluble
Naming-you take the root of the longest hydrocarbon
chain and add the suffix -ol if other functional groups 1. The lone pair of electrons on the O atom is attracted to
are present then you use the prefix hydroxy-. When the H+ ion released by the acid catalyst.
there’s more than one OH group you use di-, tri-, tetra- 2. O donates the lone pair of electrons in a dative bond,
forming a positive charge across the compound
3. A C-H bond adjacent to the C atom with the OH group
15.2 Ethanol production: breaks, the electrons move between the carbon atoms to
form a double bond.
Ethanol is one of the most used alcohols, for social 4. The C atom has too many bonds so breaks the weakest
drinking, aftershaves, cosmetics and as chemical C-O bond.
feedstock. 5. Produces alkene, water and reforms acid catalyst
Ethanol from crude oil- Conditions: Aluminium oxide, pressure of 600K,
1. Ethene is produced when concentrated acid catalyst
crude oil undergoes
thermal cracking Oxidation-combustion is complete oxidation but alcohols
2. Ethene is hydrated can also be oxidised in stages, primary and secondary
(water added across the alcohols have different products.
double bond via
electrophilic addition)
3. Requires phosphoric acid as a catalyst
fermentation-occurs in plants as carbohydrates are
broken down in the presence of yeast enzymes, in Primary alcohol + [O] -> aldehyde + [O] -> carboxylic
limited oxygen. Via anaerobic respiration. acid
C6H12O6 ——-—————> 2C2H5OH + 2CO2
Anaerobic respiration is effected by: temperature, you
need an optimum temperature for the enzymes; the
amount of air exposed, too much air will mean there’s a Secondary alcohol + [O] ——> ketone + water
plentiful supply of oxygen and so it’s no longer
anaerobic; if the conditions become too alcoholic as Tertiary alcohols cannot be oxidised as it requires
ethanol is produced the enzymes stop working. breaking a C-C bond
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