The kinetics and mechanism of the electrophilic substitution of hetero-aromatic compounds. Part XLI. Nitration of 3-hydroxy-1-phenyl-pyrazoles

Abstract

The kinetics have been studied for the nitration of 3-hydroxy-5-methyl-4-nitro-1-phenylpyrazole and its N-and O-methyl derivatives at the para-position and of 3-hydroxy-5-methyl-1-p-nitrophenylpyrazole and its N-and O-methyl derivatives at the 4-position. All the compounds undergo a mechanistic changeover from nitration of the free base at low acidity to nitration of the conjugate acid at high acidity. Rates are compared within the series studied and with those of other heteroaromatic compounds.