New, optimized preparation of 1,2-dichlorocyclobuten-3,4-dione (C4O2Cl2) from squaric acid and oxalyl chloride

1,2-Dichlorocyclobuten-3,4-dione, a key intermediate in the chemistry of cyclobutenes and their derivatives is obtained by the dimethylformamide catalyzed reaction of squaric acid and oxalyl chloride. The process was optimized by using guidelines from thermodynamics, transport properties, and experimental observations, and gives nearly quantitatively a product which can be easily brought to very high purity.