Pyrazole, 3- -, crystal

These are taken up in 250 cc of 2 N caustic soda solution and heated for 1 hour on a boiling water bath. With hydrochloric acid, the pH is then adjusted to 6 to 7 and the precipitate is filtered with suction and crystallized from 75% ethyl alcohol. The resulting 3-(p-aminobenzenesulfonamido)-2-phenyl-pyrazole crystallizes in white crystals and has a melting point of 177° to 178°C. 

AMI semiempirical calculations have shown that, as far as tautomerism is concerned, there is a structural relationship between jS-dicarbonyl compounds and NH-pyrazoles, and in a wide variety of NH-pyrazoles studied " the most stable tautomer was found to be that having the largest single-bond character between the C(3)—C(4) bond. The problem of proton transfer in NH-pyrazole crystals has been subjected to a detailed theoretical study, while a study of the tautomerism of 2-aryl and 2-heteroaryl derivatives of benzimidazole has indicated that tautomerism takes place by the intermolecular relay of protons between stacked molecules. The first report of the stable co-existence of two different histidine tautomers in one peptide crystal structure has appeared. Ab initio calculations have been used to study the tautomerism of both histamine and pyrazolo[3,4-i/]pyridazine in the gas phase and in aqueous solution, and a theoretical study of the NH tautomerism in free-base porphyrin has been undertaken. ... 

In the solid state the CH tautomer (78a) is always readily identified, but the OH and NH tautomers (that, in some cases, coexist in the crystal (73CSC469)) are difficult to differentiate due to the strong hydrogen bonds that shift the u(CO) band to the region of pyrazole vibrations. This source of complications is not present in the fixed forms that can always be identified by their IR spectra, both in solution and in the solid state. 

X-Ray crystal structure determinations of l-(aminocarbonyl)-3-methyl-4-methoxy-l//-pyrazol-5(2H)-one 107 (R = H) and l-(phenylaminocar-bonyl)-3-methyl-4-methoxy-l//-pyrazol-5(2H)-one 107 (R = Ph) demonstrated that both molecules exist in the crystal exclusively as NH-CO tautomers (97T5617). The tautomeric form similar to 104b is realized in the crystal of 4,4-dichloro-substituted pyrazolone 108 (93BSB735). 

The X-ray crystal analysis of 5-trimethylsilanyl-4-trimethylsilanylethynyl-l//-pyrazole-3-carboxylic acid ethyl ester was obtained only with / = 0.17 because the crystals of the molecule diffracted extremely weakly and only a very limited data set was available. This means that although the gross stereochemistry of the molecule has been determined, individual bond lengths are not reliable (88JOM247). 

The crude product obtained above is dried in high vacuum and then dissolved in 4 cc of pyridine. About 3 cc of acetic anhydride is added. The mixture is then heated on the steam bath for about 15 minutes and then evaporated to dryness in vacuo. About 20 cc of water is added. The product is then extracted into 150 cc of ethyl acetate, washed with saturated sodium bicarbonate solution and water, and dried over sodium sulfate. The solvent is removed in vacuo to give a residue which is crystallized from ethyl acetate-benzene to yield about 250 mg of 11/3,17a,21-trihydroxy-6,16a-dimethyl-20-oxo-2 -phenyl-4,6-pregnadieno-[3,2-c] pyrazole 21-aCetate, as described in U.S. Patent 3,300,483. 

Byers, P.K, Carr, N. and Stone, F.G.A. (1990) Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 106. Synthesis and reactions of the alkylidyne complexes [M ( CR)(CO)2 (C6F5)AuC(pz)3 j (M = W or Mo, R — alkyl or aryl, pz — pyrazol-l-yl) crystal structure of pjC PtAu(C6F5)( l3-CMe)(CO)2(PMe2Ph)2 (C6F5)AuC(pz)3 ]. Journal of the Chemical Society, Dalton Transactions, (12), 3701—3708. 

Chelated species are less common. The substituted thiourea 7V-ethoxycarbonyl-/V-[3-(/>-anisyl) pyrazol-5-yl]thiourea (eatu) acts as a monoanionic 0,S-chelate to cobalt(II), forming Co(eatu)2.506 Whereas ethylenethiourea (etu) has been observed to act as a S-donor monodentate in Co (etu)2X2(H20)2 (X = C1, Br), it binds as an S,N-chelate in Co(etu)2(OOCCH3)2.507 Both violet octahedral and blue tetrahedral cobalt(II) compounds Co(pptu)2Cl2 and Cp(pptu)Cl2 respectively were prepared with bidentate A -2-(5-pico 1 y 1)- A"-pheny 11hiourea (pptu) chelated.508 Refluxing Co powder with thiourea in 4-methylpyridine provides a route to isothiocyanates, which form by decomposition of thiourea to ammonium thiocyanate509 with one product, Co(pic)4(NCS)2, characterized by a crystal structure. 

Single crystal X-ray analysis definitively assigned different structures to products of oxidative cyclization of 58 as pyrazolo 1,2-/z][ l,2]diazepin-5(3//)-onc 59 <1984ZNB187> and pyrazolo[l,2-tf]pyrazol-l(5//)-onc 60 <1997ZNB994>, depending on the character of the R2 substituent. 

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