malonic acids a reaction temperature of from 30 u00b0 100 u00b0 c at a reduced pressure of from 40 1000 mbar should be set the reaction is preferably carried out at a temperature from 50 u00b0 70 u00b0 c and from 100 1000 mbar isolation of the malonic acid and alkylmalonic acids dissolved in water and the removal of the water with the aid of organic solvents are carried out using two different preferred variants 1st variant from 50 95 of the water used originally is removed by distillation the distillation preferably takes place under reduced pressure at a temperature from 40 u00b0 60 u00b0 c then an organic solvent is added in which the malonic acid or the alkylmalonic acid is insoluble and the remaining water is removed azeotropically suitable solvents for this purpose are those which as the azeotrope contain relatively large amounts of water but separate into two phases upon condensation the aqueous phase is eliminated suitable solvents include hydrocarbons and relatively long chain ethers such as toluene cyclohexane and dibutyl ether the water removed by distillation can be reused in subsequent batches the malonic acid and alkylmalonic acids which crystallize from the organic solvent are removed by filtration washed and dried in vacuo the filtrate including the wash liquid of the organic solvent can be reused for subsequent batches either directly or after distillation from time to time it is especially the recycling of all the solvents that increases the yield if as yet unhydrolyzed or only monohydrolyzed alkyl.