Process for the preparation of cyclopropane derivatives

A process for preparing esters and amides of gem-dihalocyclopropanecarboxylic acids which comprises contacting an aqueous phase containing an alkali metal hydroxide and an organic phase containing both a haloform and an alkenecarboxylic acid derivative of the formula ##STR8## wherein R is hydrogen, alkyl or phenyl and R.sub.1 and R.sub.2 each independently is hydrogen or alkyl, R.sub.3 is alkyloxy or substituted amino with the proviso that when R.sub.2 is hydrogen, R.sub.3 is only tert-alkyloxy or substituted amino, in the presence of as catalyst a quaternary onium compound of the formula ##STR9## in which R.sup.1, R.sup.2 and R.sup.3 each is alkyl or cycloalkyl of up to 40 carbon atoms and Y is an anion selected from hydroxide, iodide, bromide, chloride, fluoride, alkyl sulfate, tetrafluoroborate or tosylate.