To a reflux apparatus add 74 g of anhydrous oxalic acid and 200 mL of dry ethanol, reflux for 4 h. Cool down and set up for a distillation, discard ethanol which comes off at 80°C, discard water which comes off at 100°C, collect the diethyl oxalate which comes off at 160-170°C. Prepare 40 mL of conc. a solution of sodium chloride add it to separatory funnel then add the distillate too to the separatory funnel. Discard the bottom layer, dry the diethyl oxalate with anhydrous calcium chloride.
The solution after 4h of reflux
The crude diethyl oxalate after distillation
Washing with conc. sodium chloride solution and collect the upper layer.