Preparation of bromoethane

In order to produce a halogenoalkane from an alcohol we must replace the OH group with a halogen. However, the OH^- ion is said to be a poor leaving group. The negatively charged ion is attracted by the positive charge left behind on the carbon atom, making it more difficult to remove. We usually get round this problem by adding an acid. This converts the poor leaving group, OH^-, into the much better leaving group, neutral H₂O.

The ethanol used in this experiment is converted into bromoethane which is distilled out. Halogenoalkanes are immiscible with water and the product can be seen as white, oily drops underneath the water. We shall be using the Quickfit apparatus again - you may want to remind yourself about this.

C₂H₅OH(l) + KBr(s) + H₂SO₄(l) ⇒ C₂H₅Br(l) + KHSO₄(aq) + H₂O(l)

Video - the preparation of bromoethane

What was the orange colour that was seen during this reaction and where did it go? Check here.