Chemical behaviour especially oxidation depends on the structural type
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Making ethanol
Can be made by the hydration of steam
Hydration of ethene C2H4 using steam in the presence of a phosphoric catalyst H3P04.
Carried out at a high temperature and moderate pressure.
This reaction is reversible and so reaction of ethene is incomplete
overall a 90% conversion is achieved
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Fermentation
Another method of manufacturing alcohol
Carried out at low temperatures between 25 and 35. An enzyme called zymase is used.
Fermentation of carbohydrates to ethanol is anaerobic. If air was present,ethanol would be oxidiesed to ethanal or ethanoic acid which would affect its flavour.
Carbohydrates are converted into ethanol and carbon dioxide
ethanol can be used in perfumes and is a solvent in methylated spirits and is being developed as an alternative fuel for cars.
Spirits have a higher alcohol content as the fermented drink is distilled by slowly heating the alcohol-water mixture.
The alcohol boils off faster than the water and is then allowed to condense
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Methanol and Methylated spirits
Methylated spirits is undrinkable and tax exempt because it consists of ethanol mixed with small amounts of methanol and coloured die
methanol can be used as a clean burning fuel
used as an additive in high performance rating cars
extremely toxic and can lead to death
it is an important feedstock for the chemical industry and can be converted into methanal and ethanoic acid
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properties of alcohols
Hydrogen bonds formed between O-H affect properties
Melting and boiling points
High melting and boiling points due to H bonds
Have lower volatility than alkanes of a similar mass
Solubility
Can dissolve in water as hydrogen bonds form between the polar O-H groups of the alcohol and water molecules
as chain length increases, solubility decreases
A large part of the alcohol molecule is the non-polar hydrocarbon chain
This does not form hydrogen bonds with water molecules
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Combustion and oxidation of alcohols
Combustion
in lots of oxygen alcohols burn completely to form carbon dioxode and water
Oxidation of Alcohols
primary and secondary alcohols can be oxidised using an oxidising agent eg (acidified) potassium dichromate ions
during the reaction the potassium dichromate changes colour from orange to green
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primary alcohols
Primary alcohols
gently heated with pot. dichrom. oxidised to an aldehyde
propan-1-ol is oxidised to propanal
On stronger heating with excess acidified dichromate the alcohol will be completely oxidised going straight to a carboxylic acid
In a lab the aldehyde needs to be distilled off as it is formed, to prevent it being oxidised to a carboxylic acid to make carboxylic acid,the reaction mixture is heated under reflux before distilling off the product.
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Secondary alcohols
Secondary alcohols
Secondary alcohols are oxidised further by acidified dichromate ions to produce ketones.
Ketomes cannot be oxidised further
Tertiary alcohols cannot be oxidised, stays orange.
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Esterification
Esterification
The reaction of an alcohol with a carboxylic acid to produce an ester and water,sulfuric acid is often used as the catalyst
O-H bond in alcohol is broken and water is formed.
Esters-adhesives and solvents. Can produce different fruity smells
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preparing an ester
in a boiling tube add 1cm of carboxylic acid to 1cm of the alcohol. Add a few drops of sulfuric acid.
place boiling tube in hot water bath (80) for about 5 mins
pour the product into a beaker of cold water
see an oil floating on the surface of the water. This is the ester
Dehydration of an alcohol
alcohol is dehydrated to form an alkene (acid catalyst). Elimination reaction
alcohol heated under reflux, in the presence of phosphoric acid for 40 mins
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