Tautomerization Rate Research Articles

Keto-enol tautomerization rates of acetylacetone in water-acetonitrile and water-dimethyl sulfoxide mixtures: Rate-partition relationship

The rate of the keto-enol tautomerization of acetylacetone was studied in water-acetonitrile (AN) and water-dimethyl sulfoxide (DMSO) mixtures. The apparent partition coefficients of acetylacetone between n-heptane and these mixed solvents were measured to estimate the free energies of transfer of each tautomer from water to the mixed solvents. The rate constants of enolization and ketonization depended remarkably on the composition of the mixed solvents, and a maximum in the enolization reaction was observed at about 20 mol% DMSO in water-DMSO mixtures. These kinetic solvent effects were analyzed with “rate-partition relationship” (RPR) derived on the basis of the transfer free energy concept, and the unusual kinetic solvent effect observed in water-DMSO mixtures was interpreted in terms of the destabilization of the keto form in the mixed solvents. An applicability of the RPR to other reactions was suggested.

Partition kinetic studies of acetylacetone: Base-catalysis in aqueous phase and solvent dependence

The partition rate of acetylacetone between water and some water-immisible solvents was observed by the “in-liquid ejection” method at 25°C. The effect of base-catalyst, CH 2ClCOO − and CH 3COO −, in the aqueous phase and of several solvents as organic phases on the partition rate constants was examined. All of the results were fairly consistent with the simple relation which was derived based on the assumption that the rate-determining step of the reaction takes place in an aqueous phase, i.e. k p = A . k, where k p is the partition rate constant, A is the equilibrium factor composed of the apparent partition coefficient and the enol fraction of acetylacetone in each phase, and k is the keto-enol tautomerization rate constant in the aqueous phase. The dominant process determining the partition rate of acetylacetone was clarified to be the keto-enol tautomerization in the aqueous phase.

Study of the Fischer cyclization of diarylhydrazones and related secondary hydrazones I. Relative orienting capacity of the p-methyl and p-methoxy groups of diarylhydrazines

A mixture of isomeric N-arylindoles is formed in the Fischer cyclization of N,N-diphenyllydrazones variously substituted in the para position by CH3 or CH3O groups. The intramolecular competition method makes it possible to form a judgment regarding the relative orienting capacity of the substituents in the aromatic ring in the step involving rearrangement of the enamine form of the hydrazone; in this case the effect of the rate of protonation and tautomerization of the hydrazone is excluded. It was established that the rate of rearrangement increases for the para substituents in the order H< CH3< CH3O.

Keto-enol tautomerization rates of acetylacetone in mixed aqueous media

The kinetics of keto-enol tautomerization of acetylacetone was studied in mixed aqueous media by u.v. and NMR spectrometries. As an organic component, aprotic (dioxane and acetonitrile) and protic (methanol, ethanol and t-butanol) solvents were used. The tautomerization reaction was initiated by the vapor injection method. It is found that an aprotic component does not show any specific effect, while alcohol shows a characteristic effect on both of the reactions of ketonization and enolization. From the results of the composition dependency, the participation order of water and the activation parameters for the reaction, the effect of mixed solvent on the rate is interpreted in terms of the preferential solvation and the association of hydroxylic solvent.

Methylidyne-methylidyne-d and water-water-d2 isotope effects on the forward and reverse rates of keto-enol tautomerization of acetone in acidic media

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMethylidyne-methylidyne-d and water-water-d2 isotope effects on the forward and reverse rates of keto-enol tautomerization of acetone in acidic mediaJ. Toullec and J. E. DuboisCite this: J. Am. Chem. Soc. 1974, 96, 11, 3524–3532Publication Date (Print):May 1, 1974Publication History Published online1 May 2002Published inissue 1 May 1974https://doi.org/10.1021/ja00818a027RIGHTS & PERMISSIONSArticle Views507Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (978 KB) Get e-Alerts Get e-Alerts

Zinc(II) catalysed pathways for the enolization of oxalacetate

Keto–enol tautomerization rates are reported for oxalacetate and zinc(II) oxalacetate complexes in acetate buffer solutions at 25°.

Assays of glutamine and its aminotransferase with the enol-borate of phenylpyruvate

A specific spectrophotometric assay for the transamination step of the glutamine aminotransferase reaction (EC2.6.1.15) has been devised with phenylpyruvate as the amino acceptor. The decrease in absorbance of phenylpyruvate enol-borate complex at 300 mμ is dependent upon glutamine, is linear with time, proportional to enzyme concentration, and stoichiometrically equal to the formation of ammonia and phenylalanine. The rate of tautomerization of phenylpyruvate is not limiting. The optical sensitivity of the assay can be controlled by the borate concentration, and rates of 0.001 μmole/min have been measured. The properties of glutamine aminotransferase found are comparable to those reported in previous studies. The affinity for phenylpyruvate ( K m , 1 × 10 −5 m) is higher than for glutamine ( K m , 6 × 10 −3 m). The enzyme is soluble and is found in highest concentration in kidney, where it develops after birth. The enzyme concentration is low in neoplastic tissues. The same reaction can be used for a sensitive and simple measure of the concentration of l-glutamine in plasma and tissues. Its concentrations in a series of rat tissues measured by this method are reported here.

High-reliability computers using duplex redundancy : R. W. Lowrie, Electron. Ind., p. 116 (Aug. 1963)

The low-melting isomers of 2,5-dinitro-1,6-hexanediol (IB) and 2,6-dinitro-l,7-heptanediol (IIB) undergo facile acid-catalyzed epimerization to form the respective high-melting isomers (IA and IIA) in water or in aprotic solvents. The dimethyl ether and bis-phenylurethan derivatives of IB are not epimerized by acid catalysts under the same conditions. The rate of the isomerization, IB → IA, has been determined in n hydrochloric acid at 60° and compared with rates of other acid-catalyzed reactions occurring in this medium. The rates of tautomerization to the nitro form, of the mono and bis-nitronic acids derived from I, have been measured and found to be very rapid relative to the isomerization reaction. Mechanisms for the epimerization and related acid-catalyzed reactions of nitroalkanes are presented and discussed.

Acid-catalyzed aci-nitro tautomerism epimerization of α, ω-bis-hydroxymethyl- α, ω-dinitroalkanes

The low-melting isomers of 2,5-dinitro-1,6-hexanediol (IB) and 2,6-dinitro-l,7-heptanediol (IIB) undergo facile acid-catalyzed epimerization to form the respective high-melting isomers (IA and IIA) in water or in aprotic solvents. The dimethyl ether and bis-phenylurethan derivatives of IB are not epimerized by acid catalysts under the same conditions. The rate of the isomerization, IB → IA, has been determined in n hydrochloric acid at 60° and compared with rates of other acid-catalyzed reactions occurring in this medium. The rates of tautomerization to the nitro form, of the mono and bis-nitronic acids derived from I, have been measured and found to be very rapid relative to the isomerization reaction. Mechanisms for the epimerization and related acid-catalyzed reactions of nitroalkanes are presented and discussed.