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The Synthesis of Oxalyl Chloride

Nov 23，2022

Oxalyl chloride, the most active of the organic acid chlorides, approaches in activity as a chlorinating or dehydrating agent, inorganic chlorides such as thionyl chloride or phosphorus trichloride. It is more versatile as a reagent than alternative organic acid chlorides. As a bifunctional acid chloride, oxalyl chloride reacts with diamines to form polyamides. It even reacts with both of the nitrogens of urea to form oxalyl urea.

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Synthesis

The oxalic acid must be dry or the yield of oxalyl chloride is cut down to a minimum. Drying may be achieved in an oven at 110℃ for 6-8 hours, having the oxalic acid spread out in a thin layer.During the drying, the oxalic acid tends to cake and thus must be broken up in a mortar from time to time.

To round bottom flask which is cooled with ice-water bath 90g anhydrous powdered oxalic acid is mixed with 400g of pulverized phosphorus pentachloride. The mixture is allowed to stand for 2-3 days at room temperature until the mass is fully liquefied. The reaction products are fractionally distilled by collecting fraction between 60 and 100℃. By repeated distillation, oxalyl chloride is obtained entirely free from phosphorus oxychloride. The yield of the final product is about 50% which is a colorless liquid, with boiling 64℃.

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