The main impurities are usually EtOH and water, with both of which it forms azeotropes. and unsaturated compounds can be removed by washing with conc H₂SO₄ until no further coloration is produced. The Ethyl bromide (CAS NO. ) is then washed with water, aq Na₂CO₃, and water again, then dried with CaCl₂, MgSO₄ or CaH₂, and distd. from P₂O₅. Olefinic impurities can also be removed by storing the ethyl bromide in daylight with elementary bromine, later removing the free bromine by extraction with dil aq Na₂SO₃, drying the ethyl bromide with CaCl₂ and fractionally distilling. Alternatively, unsaturated compounds can be removed by bubbling oxygen containing ca 5% ozone through the liquid for an hour, then washing with aqueous Na₂SO₃ to hydrolyse ozonides and remove hydrolysis products, followed by drying and distn.