To a dried reflux apparatus, 8.57 g of anhydrous oxalic acid and 50 mL of carbon tetrachloride are added, the mixture is then heated up to a reflux and turned off afterward. A slow addition of 40 g of phosphorus pentachloride is started, a lot of HCl fumes escape from the mixture. After the addition, the mixture is refluxed for 30 minutes in an RBF apparatus equipped with a calcium chloride drying tube, after which let to stand for 2 hours under agitation. The mixture is fraction distilled to remove oxalyl chloride, phosphoryl chloride, and carbon tetrachloride fractions.
(COOH)2 + 2 PCl5 = 2 POCl3 + (COCl)2 + 2 HCl
Combining the reactants