Alcohols and carboxylic acids

Alcohols and carboxylic acids are two more organic families. Ethanol is the alcohol you'll meet most — made by fermentation or from ethene — and oxidising an alcohol gives a carboxylic acid, which behaves like a typical weak acid and forms esters.

Making ethanol

Ethanol can be made two ways. Fermentation uses yeast to convert sugars into ethanol and carbon dioxide at warm temperatures — a renewable, slower, batch process. Hydration of ethene (adding steam across the double bond with a catalyst) is fast and continuous but uses a finite fossil feedstock. Comparing the two is a common exam question.

Reactions of alcohols

Alcohols (containing the –OH group) burn cleanly in air, which is why ethanol is used as a fuel. They can be oxidised — by warming with an oxidising agent, or by the air with bacteria — to form a carboxylic acid. This is the link between the two families.

Carboxylic acids

Carboxylic acids (containing –COOH) are typical weak acids: they turn litmus red, react with carbonates to give carbon dioxide, and neutralise alkalis. Ethanoic acid is the one in vinegar. Remember to write a full structural formula showing every atom and bond — the condensed –CO₂H is not accepted as a full structure.

Esters

Warming a carboxylic acid with an alcohol (and an acid catalyst) makes an ester plus water. Esters are the sweet-smelling compounds used in flavourings and perfumes — a neat, frequently examined reaction that ties the alcohol and acid families together.