Question

How is ethyl bromide prepared in the laboratory?

Answer 1

Ethyl bromide (bromoethane) is prepared in the laboratory by the following method:

1. From ethanol and hydrobromic acid (HBr): Ethyl bromide is formed by the reaction of ethanol with concentrated HBr.The reaction is usually carried out by mixing ethanol with HBr and heating the mixture under reflux.The bromide ion (Br⁻) replaces the hydroxyl (-OH) group in ethanol.
   Equation: \[\mathrm{C_2H_5OH} + \mathrm{HBr} \rightarrow \mathrm{C_2H_5Br} + \mathrm{H_2O}\]
2. Alternate method [PBr₃ (best for primary alcohol → alkyl bromide)]: Phosphorus tribromide (PBr₃) may be used for a more efficient conversion of ethanol to ethyl bromide. Ethanol reacts with PBr₃ to give ethyl bromide.
   Equation with PBr₃: \[3 \mathrm{C_2H_5OH} + \mathrm{PBr_3} \rightarrow 3 \mathrm{C_2H_5Br} + \mathrm{H_3PO_3}\]