Pyrazoles, methyl phenyl, nitration

In the nitration of methylphenylpyrazoles, Parrini [57AC(R)929] showed that a mixture of nitric and sulfuric acids leads to nitration first in the para position of the phenyl ring and second in the 4-position of the pyrazole ring. 4-Nitro-(4-nitrophenyl) derivatives were obtained from 3,5-dimethyl-1-phenylpyrazole and 3-methyl-5-phenylpyrazole. 

The nitration (fuming nitric acid) of 5-chloro-3-methyl-l-phenylpyrazole is reported to give a mononitro product (presumably the 4-nitrophenyl derivative) and a dinitro product 5-chloro-3-methyI-4-nitro-l-(4-nitro-phenyl)-pyrazole (1900CB2595 11LA329). 

A comprehensive report has described the nitration of 3-hydroxy-1-phenyl pyrazoles [75JCS(P2)1609]. These hydroxy compounds are tautomeric with pyrazolones but at equilibrium the hydroxy form is favored. 3-Hydroxy-5-methyl-l-phenylpyrazole is nitrated in acetone using pentyl... 

In some cases l-methyl-5-nitro- and l-methyl-3,5-dinitropyrazole can form as a result of deoxygenation [76], Nevetheless, the nitration of 2-benzylpyrazole 1-oxide by sulfuric-nitric acid mixture leads to 2-benzyl-3-nitropyrazole 1-oxide in quantitative yield. Further nitration takes place in the phenyl 4-position forming 3-nitro-2-(4-nitrobenzyl)pyrazole 1-oxide and then in the pyrazole 5-position to give 3,5-dinitro-2-(4-nitrobenzyl)pyrazole 1-oxide as the final product [77],... 

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