The kinetics and mechanism of the electrophilic substitution of heteroaromatic compounds. Part XXXV. The nitration of phenylpyrazolones

Abstract

Nitration at the 4-position of 3-methyl-1-p-nitrophenyl-5-pyrazolone and its N- and O-methyl derivatives and at the para-position of 3-methyl-4-nitro-1-phenyl-5-pyrazolone and its N- and O-methyl derivatives has been studied. All the compounds react as the conjugate acid at high acidities, but some undergo a mechanistic changeover to nitration via the free base at low acidity. The nitration rates are compared within the series studied and with those of other heteroaromatic compounds.