The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Formazyls. III. A new method of synthesis of pyrazoles. Application to the synthesis of 3-arylazopyrazoles and 3-aminopyrazoles》. Authors are Fusco, Raffaello; Romani, Roberto.The article about the compound:1,5-Diphenyl-1H-pyrazole-3-carboxylic acidcas:13599-22-9,SMILESS:OC(=O)C1=NN(C(=C1)C1=CC=CC=C1)C1=CC=CC=C1).Synthetic Route of C16H12N2O2. Through the article, more information about this compound (cas:13599-22-9) is conveyed.
cf. C.A. 42, 1232d. Compounds of the ArN:NC(Hal):NNHAr type studied in the previous work show the properties of both formazyls and hydrazonic halides because of the C(Hal):NNH group common to the 2 classes. In the present work their behavior as hydrazonic halides was examined by an investigation of their cyclization to pyrazolic and other heterocyclic systems according to methods of synthesis alrady developed by F. and collaborators. This offered the possibility of preparing pyrazoles with arylazo groups in the 3-position, which have not been described, and which should be reducible to NH2 derivatives PhN:NCCl:NNHPh (I) was used as a starting compound In general I was found to be more reactive than the hydrazonic halides previously studied, probably because of the great mobility of the Cl atom in such a central position. However, this reactivity does not result in high yields, but in darkening, evolution of gas, isonitrile odor, formation of resins, and general difficulty in isolating the desired products. Of the various methylenic agents studied, β-ketonic acid nitriles and β-diketones gave the best results. A suspension of 2.58 g. (0.01 mol) I in 20 cc. anhydrous MeOH, poured into 0.01 mol AHcCNaCN in 20 cc. anhydrous MeOH at 0° (spontaneous heating, evolution of gas, darkening, and precipitation of NaCl), allowed to stand ice-cold 20 h., and the precipitate washed with MeOH and water and purified by MeOH, yields 0.2-0.3 g. of 1-phenyl-3-phenylazo-4-cyano-5-methylpyrazole, PhN.N:C(N:NPh).C(CN):CMe, yellow, m. 130°, not hydrolyzed by prolonged heating in alc. KOH at 100°. Under the same conditions from I and BzCHNaCN, with final purification by glacial AcOH, is obtained 0.5 g. 1,5-diphenyl-3-phenylazo-4-cyanopyrazole, lustrous orange-yellow, m. 204-5°. A suspension of 2.58 g. I in anhydrous MeOH, poured into an equimol. weight of AcCHNaCOCH2OPh in anhydrous MeOH at 0° (energetic reaction), allowed to stand cold, and the precipitate purified by EtOH, yields 0.2 g. 1-phenyl-3-phenylazo-4-acetyl-5-(phenoxymethyl)pyrazole, peach, m. 168°. When heated with p-O2NC6H4NHNH2 (II) in 50% AcOH, it forms the p-nitrophenylhydrazone, C30H25O3N7, orange-red, m. 218-19°. In the same way, 2.58 g. I and Ac2CH2 yield, after purification by MeOH, 0.3-0.5 g. of 1-phenyl-3-phenylazo-4-acetyl-5-methylpyrazole (III), orange-yellow, m. 179°. With II in 50% AcOH, III gives a p-nitrophenylhydrazone, C24H21O2N7, orange-red, m. 222°; with semicarbazide, a semicarbazone, C19H19ON7, yellow, m. 193-4°. III (0.5 g.) and 50 cc. 40% HNO3, refluxed 30 min. (the mixture turns yellow, nitrous vapors are evolved, and a little resin is formed), cooled to 0°, the product washed with water, macerated with aqueous Na2CO3, the yellow solution decolorized, filtered, acidified with HCl, and the precipitate purified by dilute MeOH, yield 1-(p-nitrophenyl)-3-phenylazo-5-methyl-4-pyrazolecarboxylic acid, light brown-yellow, m. 205°. Hot III (0.5 g.) in 20 cc. 80% AcOH, treated with excess powd. Zn, the solution, when decolorized, dried in vacuo, the residue taken up in MeOH, filtered hot, cooled, and the precipitate purified rapidly by MeOH (the product tends to oxidize rapidly), yields 1-phenyl-3-phenylhydrazino-4-acetyl-5-methylpyrazole, m. approx. 170° (difficult to purify because of its great tendency to oxidize to III). III (2 g.) in 200 cc. MeOH, 1 g. Raney Ni, and several drops aqueous NaOH, treated with H under 3 atm. pressure until hydrogenation is complete (about 4 h.), filtered, acidified (Congo red) with concentrated HCl, concentrated to a small volume, distilled to dryness in vacuo, the residue taken up in 20 cc. water, water added successively until all the solid dissolves and then seps., filtered, and the residue purified by MeOH, yield 0.6 g. of 1-phenyl-3-amino-4-acetyl-5-methylpyrazole (IV), m. 195-6°. The aqueous solution, treated with NaOAc, increases the yield to a total of 0.7-0.8 g. Treatment of the aqueous solution with NaOH and steam distillation yield approx. 0.6 g. of PhNH2. IV is the 1st 3-aminopyrazole reported. It gives a p-nitrophenylhydrazone, C18H18O2N6, orange-red (from AcOH), m. 256° (decomposition). IV (0.05 g.) in 4 cc. 10% HCl and a small excess of solid NaNO2, kept ice-cold until clear and poured into excess alk. 2-naphthol, precipitates a dark red compound IV (0.1 g.) in 5 cc. 10% HCl, diazotized with NaNO2, the excess HNO2 eliminated with urea, 5 cc. concentrated HCl and a trace of CuCl added (N is evolved), boiled to complete the reaction, allowed to stand, and the precipitate purified by MeOH, yields 1-phenyl-3-chloro-4-acetyl-5-methylpyrazole, m. 67°. All these experiments show the well-defined aromaticity of 3-amino derivatives (V) of pyrazole and point to the existence of the IV form in the possible tautomeric equilibrium: IV ⇋ PhN.NH.C(:NH).CAc:CMe. Another method of preparing V more easily was studied, viz., by the action of diazo compounds on substituted malonic acids to form the corresponding formazyl ketones or aldehydes, according to the general reaction: RCOCH2CH-(CO2H)2 + 2ArN2X → RCOCH2C(:NNHAr)N:NAr (VI) + HX + CO2, and cyclization by mineral acids to the pyrazoles having the arylazo chain in the 3-position: VI H2O → ArN.N:C(N:NAr).CH:CR. However, all attempts to couple diazo compounds with (formylmethyl)- and acetonylmalonic acids gave only intractable pitches. But an aqueous suspension of 2.7 g. BzCH2CH(CO2H)2 in 18 cc., neutralized with NaHCO3, 12 g. NaOAc added, heated until dissolved, cooled to 0°, PhN2Cl (from 1.1 g. PhNH2, 4.8 cc. concentrated HCl, 20 cc. water, and 0.85 g. NaNO2) added, kept several hrs. at 0°, and the precipitate purified by dilute AcOH and EtOH, yields N,N’-diphenyl-C-phenacylformazan, BzCH2C(:NNHPh)N:NPh (VII), red, m. 110°. HCl, added to the mother liquor from the precipitation of VII, filtered, and the residue purified by EtOH and dried at 150°, yields PhN.CPh:CH.C(CO2H):N, m. 185° [cf. Ber. 20, 2185(1887)]. All attempts to cyclize VII under various conditions led to uncrystallizable pitches. Hence the method based on the use of formazyl halides remains the only one for the preparation of V.
In addition to the literature in the link below, there is a lot of literature about this compound(1,5-Diphenyl-1H-pyrazole-3-carboxylic acid)Synthetic Route of C16H12N2O2, illustrating the importance and wide applicability of this compound(13599-22-9).
Reference:
Isoquinoline – Wikipedia,
Isoquinoline | C9H7N – PubChem