Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1999-06-14
2000-03-21
Ramsuer, Robert W.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C07D23122
Patent
active
060404582
DESCRIPTION:
BRIEF SUMMARY
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, alkenyl, alkynyl, cycloalkyl, aryl or heteroaryl and substituted alkyl, alkenyl, alkynyl, cycloalkyl, aryl or heteroaryl, ##STR3##
The literature discloses that N-substituted 3-hydroxypyrazoles are obtained by oxidizing corresponding pyrazolidinones [J. Gen. Chem. USSR, Engl. Trans. 31 (1961) 1770; Chem. Heterocycl. Comp. 5 (1969) 527; J. Prakt. Chem. 313 (1971) 115; J. Prakt. Chem. 318 (1976) 253; J. Med. Chem. 34 (1991) 1560; J. Prakt. Chem. 313 (1971) 1118; DE-A 34 15 385; PCT/EP 96/02,891].
As oxidizing agents in these processes, use is made of 318 (1976) 253; J. Prakt. Chem. 313 (1971) 1118], (1971) 1118; PCT/EP 96/02,891].
With regard to industrial preparation of 3-hydroxypyrazoles, oxidation with elemental sulfur has the disadvantage that considerable amounts of sulfur reduction products are formed, which require complex work-up and disposal.
The use of elemental halogens is likewise unsuitable for an industrial synthesis of 3-hydroxypyrazoles, since the yields leave something to be desired and separating off the byproducts formed to a considerable extent is complex. Furthermore, the use of large amounts of elemental halogen as oxidizing agent is a disadvantage both for environmental reasons and also with regard to cost.
The known oxidation processes using peroxides require, on the one hand, complex purifications and only offer, on the other hand, an unsatisfactory yield with the use of expensive reagents, so that they are not suitable with regard to an industrial synthesis. The use of atmospheric oxygen as oxidizing agent [J. Prakt. Chem. 313 (1971) 115 and J. Prakt. Chem. 313 (1971) 1118] has the disadvantage that the reaction must be carried out in a strongly acidic medium. This gives rise to a considerable consumption of bases during work-up, resulting in a considerable production of salt, which is undesirable from the ecological aspect.
PCT/EP 96/02,891 describes oxidation using atmospheric oxygen in organic solution in the presence of iron salts and copper salts. However, in this process the oxidizing agent air forms explosive air/solvent vapor mixtures which are of concern for safety reasons and make stringent requirements of safety methods.
It is an object of the present invention to provide an economic and technically 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, alkenyl, alkynyl, cycloalkyl, aryl or heteroaryl and substituted alkyl, alkenyl, alkynyl, cycloalkyl, aryl or heteroaryl, ##STR5## which comprises carrying out the reaction in water in the presence of a base using oxygen as oxidizing agent.
In the oxidation of the pyrazolidinones II, a procedure is generally followed in such a manner that an aqueous basic solution of II is treated with air or pure oxygen gas.
Suitable bases are inorganic or organic bases whose pK.sub.a is above 7.
The process according to the invention does not require complete deprotonation of the compound II. In the event of incomplete deprotonation of compound II, the pH of the reaction medium is below 7. Particularly advantageously, the process is carried out at pH>7. In this process the base is added to compound II at least in an equimolar amount.
Adding base increases the solubility of the pyrazolidinones to the extent that they are accessible for a reaction in water. To keep the carbon content of the reaction waste water very low, inorganic bases are preferred, such as hydroxides or carbonates of the alkali or alkaline earth metals, such as sodium hydroxide, potassium hydroxide, magnesium hydroxide, potassium carbonate or sodium carbonate. To avoid the solution becoming depleted in base when being treated with oxygen gas, nonvolatile bases are preferred.
Organic bases are equally suitable in princip
REFERENCES:
patent: 5922886 (1999-07-01), Konig et al.
J. Gen. Chem. 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. 1991, 34, 1560-1570.
J. Prakt. Chem. 313, 1118 (1971).
Gotz Roland
Keil Michael
Klintz Ralf
Konig Hartmann
Rack Michael
BASF - Aktiengesellschaft
Ramsuer Robert W.
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