Sunday, April 23, 2017 Alcohols L.O: To understand the structure of alcohols and describe some reactions involving alcohols

Do you remember making wine in year 8? Alcoholic drinks contain the alcohol ethanol. The drink is produced by fermenting plant sugars What is the combustion equation for ethanol?

Why does beer / wine smell and taste of vinegar when it is left out? Ethanol is oxidised into ethanoic acid by microbes which live in the air Ethanol can also be oxidised by some oxidising agents like potassium dichromate

Alcohols Alcohols (which are organic compounds as they contain carbon) have an –OH functional group, with the general formula CnH2n+1OH Methanol – CH3OH Ethanol – C2H5OH Propanol – C3H7OH Different alcohols are part of the same homologous series as they have the same general formula

What do you observe when sodium is reacted with water http://www.youtube.com/watch?v=aGaWwnMy KVE

Alcohol As Solvents Alcohols such as methanol and ethanol can dissolve most compounds that water dissolves but they can also dissolve substances that water cannot, such as oils, fats and hydrocarbons Ethanol is the solvent for perfumes and aftershaves (it can mix with the oils (giving the smell) and the water) Methylated spirits (meths) is ethanol with other chemicals added to it – meths are used as paint cleaners and fuels (though they are poisonous to drink so are dyed)

Ethanol Ethanol is also useful as a fuel – for use in cars and other vehicles, it is usually mixed with petrol

Producing Ethanol – Hydration of Ethene Ethanol can be produced in 3 major ways. You need to know the advantages and disadvantages of each method Ethene, which is obtained from crude oil, can be reacted with steam under high temperature and pressure to form pure ethanol. Ethene + Steam  Ethanol C2H4 + H2O  C2H5OH Conditions = 300oc, 60-70atmospheres Advantages 100% atom economy (See 7.1) 95% yield Produces 96% pure ethanol Disadvantages Feedstock is non-renewable. Ethene must be produced by cracking which requires energy. Process requires a lot of energy.

Producing Ethanol – Fermentation of Sugar For thousands of years humans have been producing ethanol by fermentation of sugar. Common feed stocks are maize, corn and sugar cane. Glucose  Ethanol + Carbon Dioxide C6H12O6  2C2H5OH + 2CO2 Conditions = 25-37oc, 1atmosphere However the product is impure as concentrations higher than 15% denature the enzymes killing the yeast. To purify it distillation is used, which uses energy. Advantages Uses renewable feedstock Operates at low temperatures and pressures Carbon neutral fuel source Disadvantages Produces impure ethanol Atom economy is 51% Still requires fossil fuels for purification Feed stock needs to be grown which takes land which could be used to grow food instead.

Exam Questions Method 1 is the least sustainable as it uses ethene which comes from crude oil and is not renewable. Methods 2 and 3 use renewable resources which can be regrown. Atom economy. A process which produces less waste is more sustainable. If waste products can be used elsewhere the process is more sustainable.

Exam Questions Sodium fizzes slowly Sodium fizzes violently on surface of water No reaction Ethanol and water both contain O-H groups so react similarly. However hexane only contains C-H and C-C bonds so is unreactive.

Exam Questions High concentrations of ethanol denature the enzymes in yeast killing it. Fractional Distillation The mixture of ethanol and water is heated. Ethanol has a lower boiling point than water so evaporates and is collected first.

Exam Questions High concentrations of ethanol denature the enzymes in yeast killing it and the reaction does not complete. Also other reactions take place using the glucose.

Exam Questions At high temperatures the enzymes in the yeast denature killing it. However at low temperatures there is little energy for the reaction to take place and the reaction is too slow.

Exam Questions

Kerboodle alcohol ‘on your marks’

Ethene + Steam  Ethanol Ethanol can be manufactured by reacting ethene (from cracking crude oil) with steam –phosphoric acid is used as a catalyst: - Ethene + Steam  Ethanol C2H4+ H2O C2H5OH In the reaction ethanol is the only product – the process is continuous as long as ethene and steam are fed into one end of the reaction vessel, ethanol will be produced These features make it an efficient process, but as ethene is made from crude oil, which is a non-renewable resource, it cannot be replaced once it is used up and it will run out one day

Ethanol & Fermentation Ethanol can also be made via fermentation – sugar from plant material is converted into ethanol and carbon dioxide… Enzymes found in single-celled fungi (yeast) are the natural catalysts that can make this process happen (this is a renewable resource): - C6H12O6  2C2H5OH + 2CO2 More than 90% of the world’s ethanol is made by fermentation