METHOD FOR THE CONTINUOUS PREPARATION OF HYDANTOIN DERIVATIVES, AND APPARATUS FOR THE APPLICATION THEREOF

1. Process for the continuous preparation of 5-substituted hydantoins of the general formula see diagramm : EP0001394,P6,F2 in which R1 denotes hydrogen or alkyl and R2 denotes alkyl or alkenyl, or R1 and R2 conjointly represent an alkylene radical with 4 or 5 C atoms in the main chain, by reaction of aldehyde-cyanohydrins or ketone-cyanohydrins of the general formula see diagramm : EP0001394,P6,F4 in which R1 and R2 are defined as above, with ammonium carbonate in an aqueous medium at an elevated temperature, characterised in that equimolar amounts of the reactants are employed, the reaction is carried out in co-current in two or more separate stages with a rising temperature level within the range from 60 to 100 degrees C, in particular with the first stage at a temperature of 60 to 85 degrees C and the last stage at a temperature of 90 to 100 degrees C, and the ammonia formed during the reaction is taken off continuously from each stage, following which solid hydantoin of the formula I is separated off, in a pure form, from the reaction solution after crystallisation, and the mother liquor is recycled to the reaction after separating off the water of reaction but after introducing the ammonia formed during the reaction and after feeding in carbon dioxide and an additional amount of NH3 so that ammonium carbonate is formed in an amount corresponding to the cyanohydrin of the formula II which is to be reacted.