Abstract: The invention relates to a process for preparing 1-substituted 5- and/or 3-hydroxypyrazoles of the formulae I and II in which R1 is C1-C6-alkyl, C2-C6-alkenyl, C2-C6-alkynyl, C3-C6-cycloalkyl or C1-C4-alkoxy, where these groups may be substituted by halogen, C1-C4-alkoxy, phenoxy, C1-C6-alkoxycarbonyl, C1-C6-alkylthiocarbonyl or by a cyclic ring system having 3-14 ring atoms, which comprises reacting an alkyl 3-alkoxyacrylate of the formula III in which R2, R3 independently of one another are C1-C6-alkyl or C3-C6-cycloalkyl with a hydrazine of the formula IV in which R1 is as defined above a) at a pH of 6-11 to give 5-hydroxypyrazoles of the formula I or b) at a pH of 11-14 to give 3-hydroxypyrazoles of the formula II.

Abstract: The invention relates to a method for the production of 1-substituted 5-hydroxypyrazoles of formula (I) wherein R1 is C1-C6-alkyl, C2-C6-alkenyl, C2-C6-alkinyl, C3-C6-cycloalkyl or C1-C4-alkoxy, whereby these groups can be substituted by halogen, C1-C4-alkoxy, phenoxy, C1-C6-alkoxycarbonyl, C1-C6-alkylthiocarbonyl or a cyclic ring system with 3-14 ring atoms, by reacting a) an alkylvinylether of general formula (III) wherein R2 is C1-C6-alkyl or C3-C6-cycloalkyl, with phosgene (IVa), “diphosgene” (IVb) or “triphosgene” (IVc) to form acid chlorides of formula (V), b) transforming said acid chlorides by eliminating hydrogen chloride into the corresponding 3-alkoxyacrylic acid chloride of formula (VI) and c) reacting said acid chloride with hydrazines of formula (VII) wherein R1 has the above cited meaning, to form 5-hydroxypyrazoles of formula (I).