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

Mild Nitration of Pyrazolin‐5‐ones by a Combination of Fe(NO3)3 and NaNO2: Discovery of a New Readily Available Class of Fungicides, 4‐Nitropyrazolin‐5‐ones

“…However, in these studies, the nitro derivatives were not fully characterized and the yields of the products were not given. In most cases, the pyrazolin‐5‐ones were nitrated by using nitric acid or a HNO 3 /H 2 SO 4 mixture under heating (Scheme c) . The disadvantages of these procedures are harsh acidic conditions and low selectivity.…”

“…The disadvantages of these procedures are harsh acidic conditions and low selectivity. Thus, in the case of phenyl‐substituted pyrazolin‐5‐ones, nitration of both the phenyl and pyrazolone rings occurred …”

“…However,i n these studies, the nitro derivatives weren ot fully characterized and the yields of the products were not given.I nm ost cases, the pyrazolin-5-ones were nitrated by using nitric acid or a HNO 3 /H 2 SO 4 mixture under heating (Scheme 1c). [36][37][38][39][40] The disadvantages of these procedures are harsh acidic conditions and low selectivity.T hus, in the case of phenyl-substitutedp yrazolin-5-ones, nitrationo fb oth the phenyla nd pyrazolone rings occurred. [38] One of the main problems encountered in the selectiveo xidative functionalization of pyrazolin-5-ones, especially 4-substituted derivatives, is their tendency to undergo hydroxylation [41,42] and oxidative dimerization.…”

“…[36][37][38][39][40] The disadvantages of these procedures are harsh acidic conditions and low selectivity.T hus, in the case of phenyl-substitutedp yrazolin-5-ones, nitrationo fb oth the phenyla nd pyrazolone rings occurred. [38] One of the main problems encountered in the selectiveo xidative functionalization of pyrazolin-5-ones, especially 4-substituted derivatives, is their tendency to undergo hydroxylation [41,42] and oxidative dimerization. [41,[43][44][45] These processes proceede asily even under the action of molecular oxygen at room temperature.…”

Synthesis of 1‐methyl‐, 4‐nitro‐, 4‐amino‐and 4‐iodo‐1,2‐dihydro‐3H‐pyrazol‐3‐ones

“…Two nitrating methods, 50% aqueous nitric acid [17] and acetic anhydride in fuming nitric acid [18], have been employed. The former conditions give much higher yields and therefore pyrazole-3-ones 2b-d were treated with 55% aqueous nitric acid at 0 to 80°to give the corresponding 4-nitro derivatives 3b-d in 80, 78 and 70% yield.…”