Usual impurities of Diethyl ether (CAS NO. ) are water, EtOH, diethyl peroxide (which is explosive when concentrated), and aldehydes. Peroxides [detected by liberation of iodine from weakly acid (HCl) solutions of KI, or by the blue colour in the ether layer when 1mg of Na₂Cr₂O₇ and 1 drop of dil H₂SO₄ in 1mL of water is shaken with 10mL of ether] can be removed in several different ways. The simplest method is to pass dry ether through a column of activated alumina (80g Al₂O₃/700mL of ether). More commonly, 1L of ether is shaken repeatedly with 5-10mL of a soln comprising 6.0g of ferrous sulfate and 6mL of conc H₂SO₄ in 110mL of water. Aqueous 10% Na₂SO₃ or stannous chloride can also be used. The ether is then washed with water, dried for 24h with CaCl₂, filtered and dried further by adding sodium wire until it remains bright. The ether is stored in a dark cool place, until distd from sodium before use. Peroxides can also be removed by wetting the ether with a little water, then adding excess LiAlH₄ or CaH₂ and leaving to stand for several hours. (This also dried the ether.)

Werner removed peroxides and aldehydes by adding 8g AgNO₃ in 60mL of water to 1L of ether, then 100mL of 4% NaOH and shaking for 6min. Fierz-David shook 1L of ether with 10g of a zinc-copper couple. (This reagent was prepared by suspending zinc dust in 50mL of hot water, adding 5mL of 2M HCl and decanting after 20sec, washing twice with water, covering with 50mL of water and 5mL of 5% cuprous sulfate with swirling. The liquid was decanted and discarded, and the residue was washed three times with 20mL of ethanol and twice with 20mL of diethyl ether).

Aldehydes can be removed from Diethyl ether by distn from hydrazine hydrogen sulfate, phenyl hydrazine or thiosemicarbazide. Peroxides and oxidisable impurities have also been removed by shaking with strongly alkaline satd KMnO₄ (with which the ether was left to stand in contact for 24h), followed by washing with water, conc H₂SO₄, water again, then drying (CaCl₂) and distn from sodium, or sodium containing benzophenone to form the ketyl. Other purification procedures include distn from sodium triphenylmethide or butyl magnesium bromide, and drying with solid NaOH or P₂O₅.