S(=O)(=O)(O)O.[O:6]=P12OP3(OP(OP(O3)(O1)=O)(=O)O2)=O.[Cl:20][C:21]1([Cl:29])[C:24]([Cl:25])=[C:23]([Cl:26])[C:22]1([Cl:28])[Cl:27]>>[Cl:20][C:21]1([Cl:29])[C:24](=[O:6])[C:23]([Cl:26])=[C:22]1[Cl:27].[Cl:20][C:21]1([Cl:29])[C:24]([Cl:25])=[C:23]([Cl:26])[C:22]1([Cl:28])[Cl:27].[Cl:20][C:21]([Cl:29])=[C:24]([Cl:25])[C:23]([Cl:26])=[C:22]([Cl:28])[Cl:27]In a 1 liter flask, a mixture of 78 g of concentrated sulphuric acid and 78.5 g of phosphorus pentoxide was poured onto 100 g of 96% pure hexachlorocyclobutene [96 g (0.368 mole) of hexachlorocyclobutene; remainder hexachloro-1,3-butadiene], with stirring (molar ratio of hexachlorocyclobutene:sulphuric acid:phosphorus pentoxide=1:2:1). The mixture was heated at 100° C. for 3 hours. After cooling, the reaction mixture was poured onto ice, the organic phase was then separated immediately from the aqueous phase and the latter was extracted three times with petroleum ether. The petroleum ether solution and the organic phase were combined and dried with sodium sulphate, the petroleum ether was distilled under normal pressure and the residue was subjected to fractional distillation under 35 mbars. 43.6 g of tetrachlorocyclobutenone, 14.3 g of hexachlorocyclobutene and 3.6 g of hexachloro-1,3-butadiene were obtained. The selectivity of the reaction was 69.0% of theory with a conversion of 85% of theory.
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