Adequate purification of (CAS NO.) can usually be obtained by fractional distn through an efficient column. can be removed by prior refluxing with CaC₂ or with coarse Mg filings at 80-90 °C for Sdays, or by distn from a large excess of quinoline (1 % AcOH in quinoline) at 75mm pressure. Acetic anhydride can also be dried by standing with Na wire for up to a week, removing the Na and distilling from it under vacuum. (Na reacts vigorously with acetic anhydride at 65-70°C). Dippy and Evans let the anhydride (500g) stand over P₂O₅ (50g) for 3h, then decanted it and stood it with ignited K₂CO₃ for a further 3h. The supernatant liquid was distd and the fraction b 136-138°C, was further dried with P₂O₅ for 12h, followed by shaking with ignited K₂CO₃, before two further distns through a five-section Young and Thomas fractionating column. The final material distd at 137.8-138.0°C. Can also be purified by azeotropic distn with toluene: the azeotrope boils at 100.6°C. After removal of the remaining toluene, the anhydride is distd [sample had a specific conductivity of 5×10^-9 ohm^-1cm^-1].

RapM procedure: Shake with P₂O₅, separate, shake with dry K₂CO₃ and fractionally distil.