[Cl:1][C:2]([Cl:19])=[CH:3][CH:4]1[C:6]([CH3:8])([CH3:7])[C:5]1(C(OCC)=O)[C:9]([O:11]CC)=[O:10].[OH-].[K+].C(O)C.Cl>O>[CH3:7][C:6]1([CH3:8])[CH:4]([CH:3]=[C:2]([Cl:19])[Cl:1])[CH:5]1[C:9]([OH:11])=[O:10]The mixture of ethyl 2-(2,2-dichlorovinyl)-3,3-dimethyl-1-ethoxycarbonylcyclopropanecarboxylate (1.5 g.) potassium hydroxide (2.0 g.) and ethanol (150 ml.) is refluxed for 2 hours, after which it is poured into water (500 ml.) and carefully acidified with concentrated hydrochloric acid. The white oily precipitate which is formed is collected by extraction with carbon tetrachloride, the extracts dried with anhydrous sodium sulphate, and the solvent evaporated under reduced pressure. The residual oil is heated under nitrogen to about 150°-160° C. for about 1.5 hours, and then cooled to form a crystalline mass. Recrystallisation from n-hexane yielded 2,2-dimethyl-3-(2,2-dichlorovinyl)cyclopropane carboxylic acid, m.p. 87°-90° C., believed to be principally the trans-isomer.
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