Method of preparing 1,2-dimethyl-3,5-diarylpyrazolium methylsulf

Details Method of preparing 1,2-dimethyl-3,5-diarylpyrazolium methylsulf Method of preparing 1,2-dimethyl-3,5-diarylpyrazolium methylsulf

1998-01-13

1998-12-08

Richter, Johann

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

5483751, 5483771, C07D23110

Patent

active

058471545

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP96/03316 filed Jul. 26, 1996.
The present invention relates to a novel process for the preparation of 1,2-dimethyl-3,5-diarylpyrazolium methylsulfates of the formula I ##STR3## where R.sup.1 and R.sup.2 independently of one another are hydrogen, C.sub.1 -C.sub.4 -alkyl, C.sub.3 -C.sub.8 -cycloalkyl, C.sub.1 -C.sub.4 -alkoxy, halogen, nitro, C.sub.1 -C.sub.4 -haloalkyl, aryl or other substituents which are inert under the reaction conditions, in which 1-methyl-3,5-diarylpyrazoles of the general formula II ##STR4## where R.sup.1 and R.sup.2 have the abovementioned meanings are reacted with
1,2-Dimethyl-3,5-diarylpyrazolium methylsulfate compounds have been disclosed, for example 1,2-dimethyl-3,5-diphenylpyrazolium methylsulfate, which is employed as a selective herbicide against wild oats in barley and wheat and as fungicide against powdery mildew in winter wheat and barley. It is known to prepare the abovementioned compound by reacting 1-methyl-3,5-diphenylpyrazole with dimethyl sulfate in xylene (U.S. Pat. No. 3,882,142). A similar procedure is followed for the synthesis starting from 3,5-diphenylpyrazole (U.S. Pat. No. 3,910,949), where 3,5-diphenylpyrazole is first converted with sodium hydroxide to give the sodium pyrazolide, which reacts with dimethyl sulfate to give 1-methyl-3,5-diphenylpyrazole, which, in turn, is subsequently reacted with more dimethyl sulfate to give 1,2-dimethyl-3,5-diphenylpyrazolium methyl sulfate.
The disadvantage of the prior-art processes is the use of dimethyl sulfate, which is highly poisonous and relatively costly.
It was therefore an object of the present invention to provide a synthetic process in which the use of dimethyl sulfate is avoided in a simple and economical manner.
We have found that this object is achieved by the process according to the invention.
The radicals R.sup.1 and R.sup.2 in the compounds of the formulae I and II are preferably hydrogen. Suitable halogen radicals are fluorine, chlorine, bromine and iodine, preferably fluorine, chlorine and bromine. The nature of the substituents R.sup.1 and R.sup.2 is not of essential importance for the process according to the invention as long as they are inert under the reaction conditions.
The process according to the invention is carried out at elevated temperatures, in general at from 60.degree. to 300 .degree. C., preferably 100.degree. to 250.degree. C., in particular 120.degree. to 180.degree. C. It can furthermore be carried out under atmospheric pressure, under reduced pressure or under superatmospheric pressure.
The reactions of the compounds of the formula II ##STR5## with methanol/SO.sub.3, methanol/H.sub.2 SO.sub.4 and methanol/methylsulfuric acid, which yield the compounds of the formula I ##STR6## proceed as shown in the equations below: a) II+2CH.sub.3 OH+SO.sub.3 .fwdarw.I+H.sub.2 O
The compound II is expediently reacted with SO.sub.3 and/or its derivatives H.sub.2 SO.sub.4 and/or CH.sub.3 OSO.sub.3 H in such a ratio that the molar ratio of SO.sub.3, H.sub.2 SO.sub.4 and/or CH.sub.3 OSO.sub.3 H to the compound II is 1.3:1 to 0.8:1, preferably 1.2:1 to 0.9:1, in particular 1.15:1 to 0.95:1. However, SO.sub.3, H.sub.2 SO.sub.4 and. CH.sub.3 OSO3H can also be employed in an excess or in substoichiometric amount to exceed the range indicated above. However, it is particularly advantageous to carry out the reaction in a stoichiometric ratio, ie. in a molar ratio of approximately 1:1.
The third reactant, methanol, is generally employed in the process according to the invention in an excess above the stoichiometric amount, so that the methanol in this case acts as a reactant and simultaneously as the solvent. The molar ratio of the compound II employed to the methanol employed is, as a rule, 0.001:1 to 1:1, preferably 0.01:1 to 0.5:1.
In addition to using an excess of methanol as solvent, it is also possible to use other solvents which are inert under the reaction conditions, such as aliphatic or aromatic solvents. However, the use of an excess of methanol as the solvent

REFERENCES:
patent: 3882142 (1975-05-01), Walworth et al.
patent: 3910949 (1975-10-01), Stepek et al.
Organic Chemistry, 403, (1920).
Organic Chemistry, 539, (1920).
Derwent Abst, JP 690037700 (690517).

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