Ethyl Bromide Prepared from Ethyl Alcohol

Ethyl bromide (bromoethane) can be prepared from ethyl alcohol (ethanol) through a substitution reaction using phosphorus tribromide (PBr₃) or hydrobromic acid (HBr) in the presence of sulfuric acid. The most common laboratory method involves treating ethanol with red phosphorus and bromine, where the red phosphorus combines with bromine to generate phosphorus tribromide in situ, which then reacts with ethanol to produce ethyl bromide, phosphorous acid, and water. The reaction can be represented as: 3C₂H₅OH + PBr₃ → 3C₂H₅Br + H₃PO₃. This method is preferred because it proceeds with relatively high yields and controlled conditions.

Alternatively, ethyl bromide can be prepared by heating ethanol with hydrobromic acid (HBr) in the presence of concentrated sulfuric acid, which acts as a catalyst and dehydrating agent, driving the reaction forward by removing water formed during the process. This method follows the general mechanism of nucleophilic substitution where the hydroxyl group (-OH) of ethanol is replaced by a bromine atom. The reaction requires heating, and the product ethyl bromide, being more volatile than ethanol (boiling point around 38°C), can be separated through distillation. This preparation demonstrates important organic chemistry principles of functional group transformation, specifically converting an alcohol to an alkyl halide, which is useful because alkyl halides are more reactive and serve as intermediates in synthesizing various organic compounds including ethers, amines, nitriles, and other complex molecules.