Patent ID: 8729275

Claim:
A process for preparing the compound of formula (I) in which R 1 and R 2 are identical or different and are hydrogen, or are C 1 -C 8 -alkyl which is optionally substituted one or more times by halogen, —OR 3 or —COR 4 , or are C 3 -C 7 -cycloalkyl which is optionally substituted one or more times by halogen, C 1 -C 4 -alkyl or C 1 -C 4 -haloalkyl, or are aryl or aryl-(C 1 -C 4 -alkyl) each of which is optionally substituted one or more times by halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, —COR 4 or sulphonylamino, R 3 is hydrogen, C 1 -C 4 -alkyl or C 1 -C 4 -alkylcarbonyl or is aryl which is optionally substituted one or more times by halogen, C 1 -C 4 -alkyl or C 1 -C 4 -haloalkyl, and R 4 is hydroxyl, C 1 -C 4 -alkyl or C 1 -C 4 -alkoxy, said process comprises reacting (A) a compound of formula (VI) in which R is R 1 or R 2 are defined above with an inorganic sulphide or hydrogen sulphide in a solvent or solvent mixture in a molar ratio between 0.2 and 0.95 mol of sulphide or hydrogen sulphide per mole of the compound of formula (VI) to form a reaction product, and (B) heating the reaction product, which is composed of a mixture of at least on compound of formula (I) and at least one compound of formula (VII) in which R independently at each occurrence is R 1 or R 2 as defined above, and n is an integer between 1 and 50, in a diluent.