Aim

To prepare a sample of 1-Bromobutane for use in a laboratory

Background Chemistry

One way of preparing 1-Bromobutane is to start with Butan-1-ol and replace the -OH group on it with a -Br group by means of a substitution reaction. The reaction requires a supply of HBr which has to be produced ‘on-site’ as bottled HBr is unavailable as a reagent. The reaction can be represented by the equation:

This is a nucleophilic substitution reaction, and the products are impure, and various stages of purification is required before a sample of reasonable purity can be obtained.

theory

(1) Sodium Bromide reacts with Sulphuric Acid to form Hydrogen Bromide and Sodium Hydrogen Sulphate.

(2) Hydrogen Bromide is oxidised to Bromine molecules as concentrated Sulphuric Acid is a very good oxidising agent. The Sulphuric Acid reacts to form Sulphur Dioxide gas.

(3) Hydrogen Bromide dissociates and the Bromide ion from it attacks the Carbon atom with the -OH function group in Butan-1-ol and displaces the -OH function group forming a Bromo function group and a hydroxide ion, which then associates itself with another H+ ion to form water.

(4) A molecule of Sulphuric Acid attacks the lone pair on an -OH function group, releasing a molecule of water, and a mixture of Butoxybutane and But-1-ene is formed, along with the regenerated Sulphuric Acid.