Elimination reactions – dehydrating an alcohol

If we dehydrate an alcohol, we are essentially removing a water molecule and the product will be an alkene. The type of reaction is elimination.

This is a common way to make alkenes, either by passing the alcohol vapour over an aluminium oxide catalyst at 300°C or heating the alcohol in the presence of a concentrated sulphuric acid catalyst.

Practice questions

1. (CH₃)₂C(OH)CH₂CH₃, CH₃(CH₂)₄OH and CH₃CH₂CH(OH)CH₂CH₃ are isomeric alcohols. Which isomer will give a pair of E/Z isomers when it is vaporised and passed over an Al₂O₃ catalyst at 300°C?
2. Pentan-2-ol forms a mixture of three products when it is heated with concentrated sulphuric acid. Draw the formula of each product and name it.
3. 2-methylpropan-2-ol undergoes dehydration in the presence of concentrated sulphuric acid.

(a) Name the type of reaction.

(b) Complete the mechanism for this reaction showing all relevant lone pairs of electrons, partial and full charges, and curly arrows.

Answers

1. CH₃CH₂CH(OH)CH₂CH₃

3. (a) elimination

(b)