Alcohols

• A biofuel is a fuel derived or produced from renewable biological sources.
• Carbon neutral activity: an activity that there is no net carbon emission of carbon to the atmosphere.
• Carbon neutral fuel: one that releases carbon dioxide to the atmosphere when burnt is balanced by the carbon dioxide absorbed by plant from which it was originally obtained, during photosynthesis.
• Fermentation: the reaction is catalysed by the zymase present in yeast. The reaction is carried out in anaerobic conditions in about 37 degrees celsius. This is a batch process and are used to produce ethanol. But this method doesn't produce pure ethanol, but rather a dilute solution of ethanol at 5% by volume.
• Other components involved: planting/ harvesting, transport, extracting sugar, distilling ethanol, fertiliser production- all burn and release carbon dioxide.
• Direct hydration of ethene: 2 ethene + 2H2O ---> ethanol + water. Temperature of 300 degrees Celsius, pressure of 70 atm, conc. H3PO4/ H2SO4. This is a continuous process.
• Fermentation: starting material is plant sugar and it is renewable, slow rate or reaction, batch process, low energy use, low yield, impure product.

  Hydration of ethene: stating material is crude oil and it is non-renewable, waste rate of reaction, continuous process, high energy use, high yield, pure product.
• Aldehyde: functional group is -CHO. General formula is CnH2nO. -al.
• Ketone: function group is -CO. General formula is CnH2nO. -one.
• Carboxylic acid: functional group is -COOH. CnH2nO2. -oic acid.
• Primary and secondary alcohols can be oxidised gently and in stages using mild oxidising agents such as acidified potassium dichromate- K2Cr2O2/ H2SO4.
• To prepare aldehydes, the primary alcohols are warmed with a solution of acidified potassium dichromate. The aldehyde is immediately removed by distillation from the reaction mixture. This stops the aldehydes from further oxidation to carboxylic acids. The alcohols are the reducing agent in the reaction.
• The intermolecular forces in aldehydes is dipole-dipole, which is weaker than hydrogen bonds in alcohols, so they have the lowest boiling points. The colour of the dichromate changes from orange to green because Cr2O7 2- has been reduced to Cr3+.
• Primary alcohols can be oxidised to carboxylic acids by acidified potassium dichromate and the reactants are heated under reflux.
• Primary alcohols oxidised to aldehydes which are oxidised to carboxylic acids.

  Secondary alcohols are oxidised to ketones.
• Presence of carboxylic acids: using sodium hydrogen carbonate or sodium carbonate. The reaction is effervescence because of the carbon dioxide that is formed. The gas turns limewater cloudy.
• Primary alcohol oxidised to aldehyde and a water molecule.

  Aldehyde oxidised to carboxylic acid (no water formed).

  Primary alcohol oxidised twice to carboxylic acid and a water molecule.

  Secondary alcohol oxidised to ketone and a water molecule.
• Aldehydes are reducing agents and ketones are not.
• Tollens' reagent is a solution of silver nitrate dissolved in dilute aqueous ammonia. It acts as a mild oxidising agent. When an aldehyde is mixed with Tollens' reagent in a clean test tube and heated in a water bath, a silver mirror is developed inside the test tube. The reaction is a redox reaction where aldehyde is oxidised to a carboxylic acid and the Ag ions from the Tollens' reagent are reduced to silver metal.

  Ketones have no reaction with Tollens' reagent.
• Fehling's solution is a blue solution containing copper II ions in an alkaline solution. It acts as a mild oxidising agent. When an aldehyde is boiled with Fehling's solution, a brick red predicate of copper I oxide is formed. The reaction is a redox reaction where the aldehyde is oxidised to a carboxylic acid and the coper II ions are reduced.

  Ketones have no reaction with Fehling's solution.
• Oxidise an alcohol under reflux: 1y alcohol to carboxylic acids, 2y alcohol to ketones. Test is sodium carbonate.

  Oxidise an alcohol under distillation: 1y alcohol to aldehydes, 2y alcohol to ketones. Test is Tollens or Fehlings.
• Alcohols can undergo elimination reaction when heated with concentrated sulphuric acid to give the corresponding alkene. The alcohol loses the -OH and a H atom from the adjacent carbon atom to form H2O. The reaction is also called a dehydration reaction.