Preparation of esters of cyclopropane-1,1-dicarboxylic acid

The method of preparing a di-lower alkyl cyclopropane-1,1-dicarboxylate of the formula:

• ##STR2## wherein R is alkyl of 1 to 4 carbon atoms, and R' and R", which may be identical to or different from each other, are each hydrogen, methyl, ethyl or chlorine, provided that at least one of R' and R" is hydrogen,
• in the presence of dimethylformamide or dimethylacetamide, which comprises reacting a di-lower alkyl malonate of the formula
• ROOC--CH.sub.2 --COOR (II)
• wherein
• R has the same meanings as in formula I, with comminuted potassium carbonate having a particle size distribution of 85% or more smaller than 0.1 mm and 70% or more smaller than 0.05 mm, and with a 1,2-dichloroalkane of the formula ##STR3## wherein R' and R" have the same meanings as in formula I, at a temperature of 90.degree. to 160.degree. C.,
• while continuously azeotropically distilling off the water released by the reaction, the molar ratio of dialkyl malonate:
• 1,2-dichloroalkane:
• potassium carbonate being 1:
• (2.5 to 3.5) :
• (1.0 to 1.4).