Commercially important alcohols

The essentials

Methanol and ethanol are the two most important alcohols in industry. Both are used as solvents and starting materials for many chemicals, but they differ greatly in toxicity.

Key points

• Methanol (CH₃OH), called "wood spirit", was once made by destructive distillation of wood. Today it is made by catalytic hydrogenation of carbon monoxide: CO + 2H₂ → CH₃OH, at high pressure and temperature with a ZnO–Cr₂O₃ catalyst.
• Methanol is a colourless liquid used as a solvent in paints and varnishes and for making formaldehyde. It is highly poisonous: drinking small amounts can cause blindness and larger amounts can cause death.
• Ethanol (C₂H₅OH) is obtained commercially by fermentation of sugars, e.g. from molasses, sugarcane or fruits. The enzyme invertase converts sucrose into glucose and fructose, and zymase (from yeast) converts these into ethanol and carbon dioxide. Fermentation takes place in the absence of air.
• If air gets in, oxygen converts ethanol to ethanoic acid, which spoils the taste of alcoholic drinks.
• Ethanol is a colourless liquid used as a solvent in paints and in making many carbon compounds.
• Denatured alcohol: commercial ethanol is made unfit for drinking by mixing in copper sulphate (to give colour) and pyridine (a foul-smelling liquid).
• Ethanol is also obtained by hydration of ethene.

Common mistakes

• Thinking zymase converts sucrose directly; invertase acts first.