AQA Chemistry A-Level 3.3.5: Alcohols Detailed Notes PDF
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These detailed notes cover the production, oxidation, and elimination reactions of alcohols. The notes cover different methods for producing alcohols such as hydration and fermentation, and describe the oxidation reactions of primary and secondary alcohols to form aldehydes and ketones. The notes also explain the dehydration of alcohols to form alkenes.
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AQA Chemistry A-level 3.3.5: Alcohols Detailed Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...
AQA Chemistry A-level 3.3.5: Alcohols Detailed Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 3.3.5.1 - Production of Alcohols Alcohols contain an -OH group and follow the general formula CnH2n+1OH. They can be produced via two main methods. Hydration This method produces alcohols from alkenes in the presence of an acid catalyst. Phosphoric acid is commonly used as the catalyst under aqueous conditions at 300oC and high pressures. Example: This process has a very high percentage yield as ethanol is the only product. Therefore the hydration method is favoured as an industrial process. Fermentation In this process, enzymes break down starch from crops into sugars which can then be fermented to form alcohol. This method is cheaper than hydration as it can be carried out at a lower temperature. However it has to be fermented in batches, meaning it is a much slower process with a lower percentage yield. Ethanol is a common biofuel produced in this way. It is said to be carbon neutral as the carbon given out when it is burned is equal to the carbon taken in by the crops during the growing process. Example: https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 3.3.5.2 - Oxidation of Alcohols Alcohols can be primary (1o), secondary (2o) or tertiary (3o). 1o and 2o alcohols can be oxidised to produce various products but 3o alcohols are not easily oxidised. Example: 1o alcohols can be heated in the presence of acidified potassium dichromate and distilled to produce aldehydes. Example: When heated further under reflux conditions, 1o alcohols oxidise further to produce carboxylic acids. Example: https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 2o alcohols can be oxidised when heated in the presence of acidified potassium dichromate to produce ketones. Example: Potassium Dichromate (K2Cr2O7) This is used in the oxidation of alcohols as the oxidising agent. It is reduced as the alcohol is oxidised. This can be observed as a colour change from orange to green when the alcohol is oxidised. Example: https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 3.3.5.3 - Elimination Reactions Alkenes can be formed from the dehydration of alcohols, where a molecule of water is removed from the molecule. In order to do this excess of hot sulfuric acid is added and aluminium oxide is used as a catalyst. Mechanism The H+ acidic ions are reformed in the reaction showing how they act as a catalyst. This reaction means that addition polymers can be produced from fermentation without the need for crude oil, a nonrenewable resource. Fermentation produces the primary alcohol which is then dehydrated to produce an alkene used in the production of addition polymers. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc
