- General formula CnH2n+1(OH)
- Structural differences:
Chemical behaviour especially oxidation depends on the structural type
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- 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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- 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
- 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
- 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
- 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 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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- 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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