Purification is achieved by bubbling sulfur dioxide into a solution of 50g of the aldehyde in 250mL of boiled water, under nitrogen, at 0o, until precipitation is complete. The bisulfite addition compound is filtered off rapidly and, after washing with a little water, is refluxed in 17% HCl (200mL) under nitrogen until a clear solution is obtained. Neutralisation with NaHCO3 and extraction with ether separated the aldehyde which is recovered by drying the extract, then distilling twice, under nitrogen. [Kyte et al. J Chem Soc 4454 1960, Beilstein 21 I 287, 21 III/IV 3495, 21/7 V 293.]