Functional Groups

Introduction to alcohol

• "Alcohol" as we normally refer to it is in fact one member of a greater family of substances
• In organic chemistry, alcohols always end in -anol - so an alcohol with three carbons will be propanol, with one carbon will be methanol etc.
• Alcohols contain carbon and hydrogen, but also contain oxygen
• They have the general formula \(C_nH_{2n+1}OH\)

Properties of alcohols

• Methanol, ethanol and propanol:
• ■ dissolve in water to form a neutral solution
• ■ react with sodium to produce hydrogen
• ■ burn in air
• ■Alcohols can be detected by a reaction with a solution of potassium dichromate (VI) mixed with sulfuric acid. This solution has an orange colour, but turns green in the presence of alcohol
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• Pie de imagen: Ethanol burner

Use and abuse of ethanol

• Ethanol is widely used in alcoholic drinks
• Ethanol production is a massive industry but overconsumption of alcohol is one of the greatest health threats faced by our society
• Alcohol causes about 10% of the deaths and diseases in the UK
• Ethanol is also used as an industrial solvent and fuel
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• Pie de imagen: Alcohol is a causal factor in more than 60 medical conditions, including various cancers, high blood pressure, cirrhosis of the liver and depression

Fermentation

• The use of yeast to produce ethanol from a sugar called glucose
• \(C_6H_{12}O_6\rightarrow 2CO_2 + 2C_2H_5OH\)
• Glucose \(\rightarrow\) Carbon dioxide + Ethanol
• The reaction is catalysed by enzymes produced by yeast
• The temperature must be kept around 25-50'C
• Must be under anaerobic conditions - no oxygen
• Container must be sterile to keep microorganisms out
• Carbon dioxide must be allowed to escape to prevent the build up of pressure
• 

Using ethanol as a biofuel

• Advantages
• Renewable resource
• Emits less carbon dioxide than petrol
• Plants used to produce it use up carbon dioxide
• Produces less soot and carbon monoxide than petrol
• Disadvantages
• Less efficient than petrol
• Vehicle engines require modifications to use ethanol as fuel
• Large amounts of farmland required to produce the necessary crops
• Fossil fuels are used in the production of bioethanol, off setting the reduced emissions

Making vinegar

• Carboxylic acids (containing the functional group -COOH) can be produced from ethanol
• Carboyxlic acids are named the same way as alcohols, but the suffix -anol is replaced by -anoic acid
• This is an oxidation reaction, carried out by microorganisms in aerobic conditions (oxygen is present) or by chemical oxidation
• If oxygen gets into a wine fermenter, the ethanol can be oxidised to produce ethanoic acid, which is also known as vinegar
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• Pie de imagen: Carboxylic acid functional group

Properties of Carboxylic Acids

• Carboxylic acids:
• ■ dissolve in water to produce acidic solutions
• ■ react with carbonates to produce carbon dioxide
• ■ react with alcohols in the presence of an acid catalyst to produce esters
• ■ do not ionise completely when dissolved in water and so are weak acids
• ■ aqueous solutions of weak acids have a higher pH value than aqueous solutions of strong acids with the same concentration

Esters

• Esters have the functional group -COO-
• Esters are formed when an alcohol is combined with a carboxylic acid
• Combining ethanol and ethanoic acid gives the ester ethyl ethanoate and water
• This process is known as esterification
• An ester will always have the name -yl-anoate - eg methylethanoate, butylmethanoate etc.
• (Note: You will not be expected to give the names of
• esters other than ethyl ethanoate, but should be able to
• recognise a compound as an ester from its name or its
• structural formula)
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• 
• Pie de imagen: Esterification

Properties and uses of esters

• Esters are volatile - this means they have a low boiling point .
• Esters are sweet smelling.
• They are used in perfumes and flavourings.
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