Process for producing N-substituted 3-hydroxypyrazoles

Details Process for producing N-substituted 3-hydroxypyrazoles Process for producing N-substituted 3-hydroxypyrazoles

1998-01-08

1999-07-13

Lambkin, Deborah C.

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C07D23110

Patent

active

059228865

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP96/02891 filed on Jul. 2, 1996 The present invention relates to a process for preparing N-substituted 3-hydroxypyrazoles of the formula I ##STR2## where R.sup.1 is unsubstituted or substituted alkyl, aryl or heteroaryl and substituted alkyl, aryl or heteroaryl, ##STR3##
It is known from the literature that N-substituted 3-hydroxypyrazoles are USSR, Engl. Trans. 31, 1770 (1961); Chem. Heterocycl. Comp. 5, 527 (1969); J. Prakt. Chem. 313, 115 (1971); J. Prakt. Chem. 318, 253 (1976); J. Med. Chem. 34, 1560 (1991); J. Prakt. Chem. 313, 1118 (1971); DE-A 34 15 385!.
Oxidants used here are 318, 253 (1976); J. Prakt. Chem. 313, 1118 (1971)!, 1118 (1971)!.
For the purposes of an industrial preparation of the 3-hydroxypyrazoles, the oxidation using elemental sulfur has the disadvantage that considerable amounts of reduction products of sulfur are formed and these require complicated work-up and disposal.
The use of elemental halogens is likewise not suitable for an industrial synthesis of the 3-hydroxypyrazoles, since the yields leave something to be desired. Furthermore, the use of large amounts of elemental halogen as oxidant is a drawback both for environmental reasons and also in view of the costs.
The known oxidation processes using peroxides require, on the one hand, complicated purifications and, on the other hand, use expensive reagents and give only unsatisfactory yields, so that they are not suitable for an industrial synthesis.
Only the use of atmospheric oxygen as oxidant offers a sensible alternative. However, the processes of this type which are known have the disadvantage that the reaction has to be carried out in a strongly acid medium. In the work-up, this gives rise to a considerable consumption of bases resulting in significant salt formation which is undesired from an ecological point of view. According to the literature, the oxidation by means of atmospheric oxygen is carried out in the presence of double molar amounts of iron salts or catalytic amounts of copper salts, with it being stated in the latter case that iron salts are inferior under catalytic conditions to the copper salts.
It is an object of the present invention to provide an economically and industrially safe and simple process for preparing 3-hydroxypyrazoles.
We have found that this object is achieved by a process for preparing N-substituted 3-hydroxypyrazoles of the formula I ##STR4## where R.sup.1 is unsubstituted or substituted alkyl, aryl or heteroaryl and substituted alkyl, aryl or heteroaryl, ##STR5## wherein the oxidation is carried out in the presence of metal salts using atmospheric oxygen as oxidant.
In the oxidation of the pyrazolidinones II, the procedure is generally to first admix an essentially neutral solution of II with catalytic amounts of a metal salt and subsequently to pass air into this mixture.
Suitable metal salts are, in particular, salts of iron in the oxidation state II or III (e.g. iron(II) chloride, iron(III) chloride, iron(II) sulfate and iron(III) sulfate), salts of copper in the oxidation state I or II (e.g. copper(I) chloride, copper(II) chloride, copper(I) sulfate and copper(II) sulfate) and also corresponding salts of main group or transition metals.
The metal salts are generally used in amounts of from 0.01 mol % to 20 mol %, preferably from 0.5 mol % to 10 mol %, in particular from 1 mol % to 5
This oxidation is usually carried out at from 0.degree. C. to the boiling point of the solvent used, preferably from 20.degree. C. to 100.degree. C.
Suitable solvents are water and aliphatic hydrocarbons such as pentane, hexane, cyclohexane and petroleum ether, aromatic hydrocarbons such as toluene, o-, m- and p-xylene, halogenated hydrocarbons such as methylene chloride, chloroform and chlorobenzene, alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol and tert-butanol, carboxylic esters such as ethyl acetate and also N-methylpyrrolidone and dimethylformamide, particularly preferably dimethylformamide and N-methylpyrrolidone.
Mixtures of said solve

REFERENCES:
J. of Chem. Soc. Perkin Trans. II, 1982, 1599-1603.
Acta Chem. Scand. 27 (1973) 2051-2074.
J. Fur Prakitische Chem., Band 313, Heft 1, 1971, S. 115-128.
J. Fur Praktische Chem., vol. 313(1), 1971, pp. 115-128.
J. Fur Praktische Chem. Band 313, Heft 2, 1971, S. 236-246.

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