Alcohols, carboxylic acids and esters · Year 13
Alcohols, carboxylic acids and esters are three homologous series that contain oxygen. Alcohols have the –OH group, carboxylic acids the –COOH group and esters the –COO– group. Ethanol is made by fermenting sugar or from ethene, and can be oxidised to ethanoic acid (vinegar). An alcohol and a carboxylic acid react to make a sweet-smelling ester and water.
Key facts
- Alcohols contain –OH: methanol CH3OH, ethanol C2H5OH, propanol C3H7OH, butanol C4H9OH.
- Alcohols burn to give carbon dioxide and water, react with sodium to give hydrogen, and are oxidised to carboxylic acids.
- Fermentation: yeast turns sugar into ethanol and carbon dioxide, warm (about 30 °C) and without air: C6H12O6 → 2C2H5OH + 2CO2.
- Carboxylic acids contain –COOH: methanoic, ethanoic, propanoic and butanoic acid. They are weak acids and react with carbonates to give carbon dioxide.
- Alcohol + carboxylic acid ⇌ ester + water, with concentrated sulfuric acid as a catalyst. Ethanol + ethanoic acid → ethyl ethanoate.
- Esters are volatile with fruity smells: they are used in perfumes and flavourings.