Preparation of oxazolidine-2,4-diones

A process for the preparation of an oxazolidine-2,4-dione of the formula ##STR3## where R.sup.1 is aryl of 6 to 12 carbon atoms which is unsubstituted or substituted by one or more halogen atoms, methyl or methoxy, R.sup.2 is hydrogen, methoxymethyl, alkyl of 1 to 4 carbon atoms or vinyl and R.sup.3 has the same meanings as R.sup.2 and in any particular compound R.sup.2 and R.sup.3 may be identical or different, wherein a urea derivative of the formula

• R.sup.1 --NH--CO--NH--R.sup.4
• where R.sup.1 has the above meanings and R.sup.4 has the same meanings as R.sup.1 or is hydrogen, and in any particular compound R.sup.1 and R.sup.4 may be identical or different, is reacted with a 2-hydroxy-carboxylic acid ester of the formula ##STR4## where R.sup.5 is alkyl of 1 to 10 carbon atoms or cyclohexyl, at from 100.degree. to 250.degree. C.