The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Some aldehydes of the pyrazole and 1,2,3-triazole series》. Authors are Huttel, Rudolf.The article about the compound:1H-Pyrazole-5-carbaldehydecas:948552-36-1,SMILESS:O=CC1=CC=NN1).SDS of cas: 948552-36-1. Through the article, more information about this compound (cas:948552-36-1) is conveyed.
In the formation of pyrazoles and isoxazoles from CHCCH(OEt)2 with hydrazines and hydroxylamines (Claisen, Ber. 36, 3664(1903)) it can probably be safely assumed that the aldehyde group reacts first and addition at the triple bond then takes place; in the reaction between PhCCCHO and NH2OH the oxime was isolated as an intermediate product which was isomerized to 3-phenylisoxazole only on addition of a drop of alkali. The reaction of CHCCHO (I) with substances which attack only the triple bond therefore seemed of interest. It was thought that by suitable choice of the reactants it might be possible to obtain heterocyclic aldehydes of types hitherto for the most part unknown. As a matter of fact, aliphatic diazo compounds, NH3 and aryl azides react normally at the triple bond of I and give the desired products. CH2N2 in ether dropped into I, also in ether, is immediately decolorized without evolution of N; the resulting product, C4H4ON2 (II), shows aldehyde properties and on oxidation with AgOH gives exclusively 3-pyrazolecarboxylic acid, m. 210-11°. II is therefore 3-pyrazolecarboxaldehyde. N2CHCO2Et similarly gives 5-carbethoxy-3-pyrazolecarboxaldehyde (III). These results show that the v. Auwers and Ungemach (C. A. 27, 5327) rule for the addition of aliphatic diazo compounds to RCCCO2Et also holds for the aldehydes when R = H. Addition of HN3 to I smoothly yields 2,1,3-triazole-4-carboxaldehyde (IV). PhN3 gives 1-phenyl-1,2,3-triazole-4-carboxaldehyde (V), identified by oxidation with AgNO3-NaOH to the acid (VI), m. 150°. The new aldehydes are solid, odorless and colorless substances, subliming in vacuo below their m. ps. and showing no tendency to autoxidize. They are soluble in 2 N NaOH, some even in 2 N Na2CO3, and can be recovered unchanged. This is the most interesting property of the compounds, which otherwise do not behave in any unusual manner. It is naturally observable only in the difficultly soluble II, III and V, but that the water-soluble IV also dissolves in alkali with salt formation is shown by the fact that it cannot be extracted from the NaOH or even Na2CO3 solution with ether. Since V has no H on a N atom, it must be the aldehyde group of these compounds which is responsible for the salt formation. The question of their structure in alk. solution is reserved for a later investigation. II and III are stable toward 2 N NaOH for a long time and can be recovered quantitatively. III is also stable for a short time but on longer standing in the alk. solution the ester group is saponified and the free acid is obtained. V is also an exception; it can be recovered unchanged only if the alk. solution is immediately neutralized; otherwise, in 10-20 min. the apparently greatly “”strained”” alkali salt stabilizes itself by disproportionation to VI and 1-phenyl-4-hydroxymethyl-1,2,3-pyrazole (VII), insoluble in alkali. Acrolein also immediately decolorizes CH2N2 without evolution of N and in ice there seps. a colorless, flocculent (often partly crystalline) precipitate which on warming to room temperature or treatment with acids or alkalies is immediately altered (probably isomerized), turning yellow or red. It has not as yet been possible to verify the assumption that it is a pyrazolinecarboxaldehyde; oxidation gave neg. results; addition of carbonyl reagents prevented the appearance of color on warming to room temperature but no crystalline product could be isolated. I b720 53.5-5°; it dissolves in water and is clear in all organic solvents except the aromatic hydrocarbons. It is not advisable to carry out reactions with it in benzene; thus, with PhN3 it gave only 33% V as against 90% in ether. The freshly prepared, distilled, colorless I turns yellow quite rapidly at room temperature and on long standing partly polymerizes and becomes dark brown. It also partly polymerizes in water, with deposition of an insoluble brown powder. When refluxed in water it forms a brown flocculent deposit in 10 min. and in 2 hrs. its odor is hardly perceptible. Acids and weak alkalies (NH3, Na2CO3) materially accelerate the polymerization. Whereas NaOH in water gives C2H2 and HCO2Na, in acetone or cyclohexane it forms a crystalline di-Na salt of a trimer of I, leaflets easily soluble in water, reprecipitated by alc., gives a red-violet FeCl3 reaction, reduces AgNO3-NH3, gives on decomposition with H2SO4 and exhaustive extraction with ether the free trimer, C9H8O4 (= 3 I + H2O), prismatic needles from acetone, turns brown 135°, m. 141°, reduces Tollens reagent and gives a violet-red FeCl3 reaction but no yellow color with C(NO2)4. II (84% yield), m. 149-50° from water, reddens fuchsin-SO2, reduces NH3-AgNO3, gives a neg. FeCl3 reaction, takes up Br in AcOH only slowly, reacts neutral to litmus in hot water. III (86%), m. 135° after crystallization from alc. or sublimation in vacuo (at 130°); free acid, m. 245° (decomposition), oxidized by boiling HNO3 (1:1) to 3,5-pyrazoledicarboxylic acid, m. 289° (decomposition). IV (90% crude and 78% pure, sublimed product), m. 141-2° from water or alc. V (75% from I and 1 mol. PhN3 refluxed 6 hrs. in CHCl3), m. 99-100° from benzene-petr. ether or water. VII (250 mg. from 500 mg. V allowed to stand 4 hrs. in 10 cc. of 2 N NaOH), m. 110-11° from water.
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