A-LEVEL OCR ChEMISTRY NOTES
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Properties of Alcohols
- Alcohols are a homologous series of saturated organic compounds with -OH groups attached
- Alcohols can form hydrogen bonds in polar solvents, e.g. water, making them soluble. As chain length increases, solubility decreases
- Longer alkyl chains have a greater surface area for contact and a greater number of electrons, allowing stronger London forces of attraction. Therefore, as chain length increases, boiling point increases, and volatility decreases
Oxidation of Alcohols
- Primary alcohols can be oxidised to aldehydes. Conditions: gentle heating. Oxidising agent and immediate distillation
- Primary alcohols can be further oxidised to carboxylic acids. Conditions: heat under reflux, no distillation, oxidising agent.
- Secondary alcohols can be oxidised to ketones. Conditions: heat under reflux and oxidising agent.
- Tertiary alcohols cannot be oxidised as they do not have an H atom on the carbon bonded to the -OH group
- Acidified potassium dichromate(VI) is a suitable oxidising agent
Reactions of Alcohols
- Alcohols can be combusted as a fuel source, forming carbon dioxide and water
- e.g. C2H5OH + 3O2 → 2CO2 + 3H2O
- Alcohols can be dehydrated to form an alkene and water, using a concentrated phosphoric acid catalyst and heating under reflux e.g.
- The alkenes produced can be used to form addition polymers without using monomers derived from crude oil
- Alcohols undergo substitution by reacting with hydrogen halides. The hydrogen halides are formed by reacting a sodium halide with sulfuric acid:
NaX (s) + H2SO4 (aq) → NaHSO4 (aq) + HBr (aq)
- The hydroxyl group on an alcohol is replaced with a halogen