cis-3,4-Dichlorocyclobutene

Distil the cyclobutene at 55mm through a 36-in platinum spinning band column, a fore-run b 58-62o/55mm is mainly 1,4-dichlorobutadiene. When the temperature reaches 70o the reflux ratio is reduced to 10:1 and the product is collected quickly. It is usually necessary to apply heat frequently with a sun lamp to prevent any dichlorobutadiene from clogging the exit in the early part of the distillation [Pettit & Henery Org Synth 50 36 1970].