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Tautomerization of hydrazone

Ring-chain tautomerism of hydrazones of 1,3-dicarbonyl compounds 99MI21. [Pg.205]

The mechanism of the Wharton reaction is analogous to that of the Wolff-Kishner reduction. Addition of hydrazine to a, 3-epoxy ketone 1 gives rise to hydroxyl-hydrazine 6, which dehydrates to afford the intermediate, hydrazone 7. Tautomerization of hydrazone 7 then leads to diazene 8, a common intermediate as the Wolff-Kishner reduction. But different... [Pg.152]

The possible amino-imino tautomerism of sulfonamides 98 [76AHC(S1), p. 438] and hydrazones 99 [76AHC(S1), p. 438] has been previously discussed. [Pg.215]

Ring-chain tautomerism was observed in a series of l,2,3,6-tetrahydro-l,2, 4-triazine 4-oxides 5 in nonpolar solvents (e.g., CCI4) by NMR spectroscopy. Depending on the nature of substituents R and R, the ratios of the cyclic form of 1,2,4-triazine 5a to the open-chain form of hydrazone 5b were found to be up to 45 55 (77ZOR2617). [Pg.266]

Evidently, analogously to the mentioned cyclization of similar oximes to ben-zisoxazole derivatives (See Section II.A), reaction can take place only in compounds with suitable configuration. However, in case of hydrazones, due to the tautomeric equilibrium of both possible configurations, the reaction usually achieves complete conversion. The usual setup involves heating with the respective hydroxide if an ester group is present, it is partially or completely hydrolyzed to the corresponding acids, which, in addition, can also undergo decarboxylation. [Pg.200]

Oxidative processes (route B) represent another common route to triazolopyridines (compounds described in Schemes 54 and 55). These preparations all start from aldehyde hydrazones and use different oxidative reagents for the cyclization (Table 2). Generally, those conditions are milder than condensation methods. Moreover, the oxidizing reagents are compatible with other moieties, even the sugar-derived polyol 209. In the case of compound 208, the hydrazone (major diastereomer) was obtained by tautomerization of the corresponding enhydrazine, the... [Pg.615]

The problem of the tautomerism between hydrazones and azo compounds has been the subject of considerable controversy. The details of the problem have been reviewed recently [104]. Among the causes of the dispute are the fact that phenylhydrazones are readily oxidized in air to give phenylazohydro-peroxides which resemble azo compounds in their spectra (both visible and ultraviolet) and the fact that the hydroperoxides may decompose to azo compounds [105]. [Pg.421]

In theory, azo dyes can undergo tautomerism azo/hydrazone for hydroxyazo dyes azo/imino for aminoazo dyes, and azonium/ammonium for protonated azo dyes. A more detailed account of azo dye tautomerism can he found elsewhere. [Pg.513]

Azo-hydrazone tautomerism Azo-hydrazone tautomerism (83) (Section 58.2.3.2) is a well-established phenomenon in o,o -dihydroxydiarylazo compounds, the various species existing in solution as an equilibrium mixture the composition of which is determined by a number of factors including substituents in the azo compound, the nature of the solvent, etc. It has been invoked to account for the formation of isomeric 2 1 cobalt(III) complexes by symmetrical o,o -dihydroxydi-... [Pg.63]

The A-acylimine-enamide tautomerism of methyl 2-acetamidoacrylate has been studied641 by means of ab initio calculations. A 13C NMR investigation has been undertaken to study the tautomerism between the hydrazone imine and diazenylen-amine forms of 3-(arylhydrazono)methyl-2-oxo-l,2-dihydroquinoxalines,642 and the effects of temperature and side-chain on the imine-enamine tautomerism in quinoxalinone and pyridopyrazinone systems have been studied.643 A detailed... [Pg.589]

The ring-chain tautomerism of the hydrazone derivatives has been discussed in a monograph (79MI1) and more thoroughly in a review (88KGS3). [Pg.16]

Table 22. Thermodynamic data for the azo hydrazo tautomerism of 35 (R = H) in CDCI3 solution and in the solid state calculated from -AG/RT= In K= AH/RT+ AS/R (K = [hydrazone form]/[azo form])... Table 22. Thermodynamic data for the azo hydrazo tautomerism of 35 (R = H) in CDCI3 solution and in the solid state calculated from -AG/RT= In K= AH/RT+ AS/R (K = [hydrazone form]/[azo form])...
Kurasawa et a/.112,113 published two papers on H and 13C NMR of 3-(arylhydrazono)methyl-2-oxo-l,2-dihydroquinoxalines (51), describing the existence of hydrazone imine-diazenylenamine tautomerism. [Pg.40]

Because azo dyes are of commercial importance as colouring materials, the azo/ hydrazone tautomerism of hydroxy-substituted azo compounds has been intensively studied [71, 228]. In the case of 4-phenylazo-l-naphthol (16a), an increase in the solvent polarity displaces the tautomeric equilibrium towards the more dipolar quinone hydra-zone form (16b) [72-74, 74a, 74b, 150-154]. In addition, the NH and OH groups of both tautomers are capable of forming hydrogen bonds with suitable solvents. Due to... [Pg.117]

Mechanism The reaction involves converting a ketone to the corresponding hydrazone A, which undergoes a base-catalyzed double bond migration (tautomerization) of the initially formed hydrazone to an azo-isomer B, and the loss of N2 then follows to give carbanion C. Finally, an alkane derivative is formed by protonation of carbanion C (Scheme 6.30). [Pg.255]

Ring-chain tautomerism of functionally substituted hydrazones 88KGS3. [Pg.47]

The electrochemistry of hydrazones, azines, and other derivatives of hydrazine is complicated by the possibility of tautomerization. The following forms must be considered [54,55] ... [Pg.441]

The structure of sugar phenylosazones, derivatives first prepared by Fischer in 1884, has remained undefined. Besides Fischer s open-chain structure, a tautomeric azo-hydrazone structure and ring structures have been proposed. Although work in the last two decades involving ultraviolet spectra studies - and examination of the acetylated - and... [Pg.129]

Cp) 138.3 (C-OH) and those of =NNHC6H5 in 86 were 142.6 (Q) 115.5 (CJ 129.6 (Cm) 124.5 (Cp) 186.1 (C=0). A similar approach was used9 for azo dyes with intramolecular hydrogen bonds. 2-Hydroxy-5-tcr/-butylazobenzene 87 (model azo compound) and 3-methyl-l-phenylpyrazole-4,5-dione 4-phenyl-hydrazone 78 (hydrazone model) and compound 48, as a representative of classical tautomeric system, werestudied. The 13Cchemicalshiftsofthephenylgroupsenable an estimation of hydrazone content from chemical shifts of Q, Cc and Cp to be 66%, 61% and 66%, respectively. [Pg.268]


See other pages where Tautomerization of hydrazone is mentioned: [Pg.801]    [Pg.594]    [Pg.521]    [Pg.801]    [Pg.594]    [Pg.521]    [Pg.421]    [Pg.156]    [Pg.304]    [Pg.38]    [Pg.41]    [Pg.530]    [Pg.195]    [Pg.888]    [Pg.100]    [Pg.576]    [Pg.888]    [Pg.172]    [Pg.249]    [Pg.41]    [Pg.60]    [Pg.103]   
See also in sourсe #XX -- [ Pg.334 ]




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