Process for preparing N-substituted pyrazoles

Details Process for preparing N-substituted pyrazoles Process for preparing N-substituted pyrazoles

1997-08-20

1998-11-24

Higel, Floyd D.

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

5483771, C07D23112

Patent

active

058409130

DESCRIPTION:

BRIEF SUMMARY
This is a 371 of PCT/EP96/00790 filed Feb. 27, 1996.
The present invention relates to a process for the preparation of N-substituted pyrazoles by reacting pyrazoles with alcohols in liquid phase in the presence of catalysts at elevated temperatures.
DE-A-35 06 972 and U.S. Pat. No. 3,910,949 disclose a process for the N-alkylation of 3,5-diphenylpyrazoles, in which N-unsubstituted 3,5-diphenylpyrazoles are reacted with dimethyl sulfate/aqueous sodium hydroxide solution in the presence of a phase-transfer catalyst.
DE-A-24 25 979 describes the alkylation of 3,5-diarylpyrazoles with alkyl halides or dialkyl sulfates.
The disadvantages of these processes are the use of the very toxic and relatively costly dialkyl sulfates, because the major part of this molecule is not utilized, and the large amount of salt produced.
Chemical Letters (1992) 575-578 discloses a process for the N-alkylation of pyrazoles in which N-unsubstituted pyrazoles are reacted with alcohols in the presence of catalytic amounts of ruthenium, rhodium or iridium/trialkyl phosphite complexes.
The disadvantage of this process is the high cost of the catalysts.
DE-A 43 18 960 and DE-A-44 03 815 disclose a process for the N-alkylation of N-unsubstituted pyrazoles in which N-unsubstituted pyrazoles are reacted with alcohols or ethers in the presence of heterogeneous catalysts in the gas phase.
The disadvantage of this process is, especially in the case of very high-boiling N-unsubstituted pyrazoles, the need to vaporize the starting materials.
It is an object of the present invention to develop a more straightforward and less costly process for the preparation of N-substituted pyrazoles.
We have found that this object is achieved by a novel and improved process for the preparation of N-substituted pyrazoles of the general formula I ##STR1## where R.sup.1 is C.sub.1 -C.sub.12 -alkyl or C.sub.7 -C.sub.20 -phenylalkyl and C.sub.1 -C.sub.12 -alkyl, C.sub.7 -C.sub.20 -phenylalkyl or unsubstituted or substituted aryl radicals, ##STR2## where R.sup.2, R.sup.3 and R.sup.4 have the abovementioned meanings, with an alcohol of the general formula III 400.degree. C. in the presence of a catalyst, wherein the reaction of pyrazole II with compound III in the molar ratio of from 0.001:1 to 1:1 is carried out in liquid phase under a pressure which is slightly below atmospheric or up to a pressure of 250 bar, and acids and/or their alkyl esters or their anhydrides are used, in the molar ratio of from 0.0001:1 to 0.5:1 with respect to the pyrazole II, as catalyst.
The N-substituted pyrazoles I have a lower boiling point than the N-unsubstituted pyrazoles II and are continuously discharged in gaseous form with excess alkylating reagent III from the reactor, but discharge of the product during the reaction is not obligatory.
The process according to the invention can be carried out in the following way:
The reaction can be carried out by bringing a pyrazole II into contact with an alcohol III in the presence of a described catalyst at from 50.degree. to 400.degree. C., preferably 100.degree. to 350.degree. C. under a pressure which is slightly below or is above atmospheric, ie. a pressure of from 0.8 to 250 bar, preferably 0.8 to 100 bar, particularly preferably 0.9 to 100 bar.
The molar ratio of pyrazole II to compound III is, as a rule, from 0.001:1 to 1:1, preferably 0.002:1 to 1:1, particularly preferably 0.003:1 to 1:1.
The reaction is particularly preferably carried out at temperatures, under a pressure and with molar ratios at which the pyrazole II and the catalyst are in the liquid phase and the N-substituted pyrazole I and unreacted compound III are discharged in gaseous form together from the reaction vessel.
The pyrazole II and the catalyst can be initially dissolved or suspended in an inert solvent such as technical white oil or vacuum gas oil.
Suitable catalysts are compounds such as sulfuric acid, phosphoric acid, alkyl- or arylsulfonic acids and their alkyl esters or their anhydrides. The molar ratio of catalyst to pyrazole II is, as a rule, from 0.00

REFERENCES:
patent: 3907824 (1975-09-01), Garber
patent: 5468871 (1995-11-01), Ebel et al.
patent: 5705656 (1998-01-01), Ono

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