P-Nitrophenylhydrazones

Experimental details for the preparation of oximes, phenylhydrazones and p-nitrophenylhydrazones will be found under Aromatic Aldehydes, Section IV,135,4-6. 

Heat 0-25 g. of the compound with 3 ml. of alcohol, add 0-25 g. of p-nitrophenylhydrazine, and heat the suspension until the reaction appears complete. The p-nitrophenylhydrazone soon separates. Filter, preferably after standing overnight, wash with a little cold alcohol, and then recrystallise from alcohol. 

Compounds related to phenylhydrazine react in an analogous way p Nitrophenylhydrazine yields p nitrophenylhydrazones 2 4 dinitro phenylhydrazine yields 2 4 dinitrophenylhydrazones... 

The Frasca method for obtaining 1-arylindazoles also involves a C(3)—C(3a) ring closure (67CJC697). It consists in the cyclization of p-nitrophenylhydrazones of ketones and aldehydes with polyphosphoric acid. The Barone computer-assisted synthetic design program has found several new methods for preparing indazoles (79MI40409). The selected method involves the transformation of jV, jV -diphenylhydrazides (596) into 1-phenylindazoles (597) by means of trifluoromethanesulfonic anhydride. The yields vary from 2% (R = H) to 50% (R = Ph). 

The product of the eoupling of (a) with p-nitrobenzenediazonium chloride is identieal with the p-nitrophenylhydrazone of [h). The oxidation of weostrychnidine to strychnidone by permanganate (1932) and of ncobrueidine to brucidone (1927) are probably analogous, and it is now found that by the aetion of p-nitrobenzenediazonium ehloride, neostrychnine is eonverted into stryehnone p-nitrophenylhydrazone. 

Aldehyde enamines react with aromatic diazonium salts in two ways, depending on the degree of substitution at the enamine earbon (130). Thus the piperidine enamine of butyraldehyde (60) reacted with p-nitrophenyl-diazonium chloride to give the p-nitrophenylhydrazone of the a-keto aldehyde (190). 

The enamine (191) from isobutyraldehyde on treatment with p-nitrophenyl-diazonium chloride, on the other hand, gave the p-nitrophenylhydrazone of acetone (192) and presumably N-formyl piperidine, although the latter was not isolated. 

Regarding the amine-catalyzed rearrangement of the p-nitrophenylhydrazone [81JHC723 83JCS(P2)1203], all the amines catalyze the reaction nevertheless, depending on the nature of the amine, different catalysis laws are observed. Tertiary amines and secondary amines with great... 

Dehydrogenation of lupenone p-nitrophenylhydrazone with iodine and t-butox-ide followed by treatment with aqueous TiClj gave the A -3-ketone glochidone in 50% yield. " The trihydroxylupane (162) is formed on hydroboration of betulin. " ... 

Di nitro-(p-anisaldehyde)-4 -nitrophenyl-kydrazone or 2,6-Dinitro-3-methoxybenz aldehyde-4-nitrophenylhydrazone, It orange plates exploding at ca 260°. Was obtained by treating 2,6-dinitro-3-methoxybenzalde-hyde with p-nitrophenylhydrazone, as described in Ref 2... 

Dinitro-(p-anisaldehyde)-(4i -nitrop eny/-hydrazone), dk brn crysts, mp 275°. Was prepd by treating 3,5-dinitro-4-methoxybenz-aldehyde with p-nitrophenylhydrazone as described in Ref 2... 

Reflux a mixture of 0.5 g of p-nitrophenylhydrazine, 0.5 g of the aldehyde (or ketone), 10-15 ml of ethanol and 2 drops of glacial acetic acid for 10 minutes. Add more ethanol if the boiling solution is not homogeneous. Cool the clear solution, filter off the p-nitrophenylhydrazone and recrystallise it from ethanol or acetic acid. 

Alternatively, dissolve approximately equivalent amounts of the aldehyde (or ketone) and the solid reagent in the minimum volume of cold glacial acetic acid, and reflux for 15 minutes. The p-nitrophenylhydrazone separates on cooling or upon careful dilution with water. 

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