Alcohols

• Alcohols have the formula ROH and can be produced through hydration or fermentation.
• In hydration, alcohols are produced from alkenes in the presence of a phosphoric acid catalyst under aqueous conditions at 600K and high pressures.
• Hydration has a very high percentage yield as the alcohol is the only product and so is favoured in industry.
• In fermentation, enzymes break down starch from crops into sugars which are fermented by yeast in anaerobic conditions in normal temperature and pressure to form alcohol.
• Fermentation is cheaper and is said to be carbon neutral, however it has to be fermented in batches with and has a low percentage yield.
• The fermentation equation is starch -> glucose -> ethanol + carbon dioxide or H(C6H10O5)OH -> C6H12O6 -> 2 C2H5OH + 2 CO2.
• Alcohols can be oxidised when heated in the presence of acidified potassium dichromate, which turns orange to green.
• Primary alcohols when oxidised by distillation produce aldehydes and when oxidised under reflux oxidise further to produce carboxylic acids.
• Secondary alcohols can be oxidised to produce ketones.
• Tertiary alcohols are not easily oxidised.
• Alkenes can be formed by the dehydration of alcohols in an elimination reaction where a molecule of water is removed from the alcohol.
• In dehydration, electrons from a lone pair on the alcohols oxygen transfer to a H+ ion. The electrons then move to a now positive oxygen molecule and water is eliminated. The electrons in a hydrogen bond move to create a double bond between the carbon chain and the H+ is reformed as a catalyst.
• Aldehydes have the formula RCHO and can be tested for by Tollen's reagent which forms a silver mirror or by Fehling's solution which turns blue to red.
• Ketones have the formula RCOR.
• Alcohols can be produced by the reduction of aldehydes or ketones in a nucleophilic addition reaction in aqueous conditions.
• In nucleophilic addition, a H- nucleophile attacks the carbon with the oxygen double bond, and the electrons move from the double bond to the oxygen, breaking the bond and giving the oxygen a negative charge. The oxygen then reacts with a H+ to form an alcohol.
• When nucleophilic addition happens with a CN- nucleophile, synthesis occurs as the carbon chain length increases by one and a hydroxy-nitrile is produced.
• KCN is often used as the reagent to form a hydroxy-nitrile as HCN is hard to store and reacts to form harmful byproducts.