TY - JOUR

T1 - Characteristic Features of the Gas Chromatographic Separation of Tautomers of Ethyl Acetoacetate

AU - Zenkevich, I. G.

AU - Lukina, V. M.

N1 - Zenkevich I.G., Lukina V.M. // Rus. J. Phys. Chem. A. 2020. V. 94. № 6. P. 1214-1223.

PY - 2020/6/1

Y1 - 2020/6/1

N2 - Abstract: Characteristic features of the gas chromatographic separation of the keto and enol tautomeric forms of ethyl acetoacetate on a capillary column with a BPX-1 standard nonpolar polydimethylsiloxane stationary phase are considered. It is confirmed that the chromatograms of a mixture of tautomers have a specific profile, i.e., a plateau between the peaks of the tautomers, which corresponds to the reversible keto (Formula presented.) enol transformation during separation. It is shown that the enol and keto forms of ethyl acetoacetate have different coefficients of the temperature dependence of the gas chromatographic retention indices (0.19 ± 0.03 and 0.02 ± 0.02, respectively). It is found there is no dependence of the relative peak areas of the tautomers on the nature of the solvent (polar ethyl alcohol and nonpolar hexane) at different temperatures; i.e., such ratios predominantly reflect the position of the keto (Formula presented.) enol equilibrium in the vapor phase of the injector of the chromatograph. It is concluded that this results in similar values of the thermodynamic parameters (standard enthalpy and entropy) of the tautomeric equilibrium determined upon the dosing of samples in different solvents. Possible distortions of the results due to the effects of discriminating between the compositions of the samples injected into capillary columns with gas flow splitting are discussed. An impurity in a sample of ethyl acetoacetate after long-term storage is identified as ethyl 2-hydroxy-3-oxobutanoate, the product of oxidation by dissolved atmospheric oxygen.

AB - Abstract: Characteristic features of the gas chromatographic separation of the keto and enol tautomeric forms of ethyl acetoacetate on a capillary column with a BPX-1 standard nonpolar polydimethylsiloxane stationary phase are considered. It is confirmed that the chromatograms of a mixture of tautomers have a specific profile, i.e., a plateau between the peaks of the tautomers, which corresponds to the reversible keto (Formula presented.) enol transformation during separation. It is shown that the enol and keto forms of ethyl acetoacetate have different coefficients of the temperature dependence of the gas chromatographic retention indices (0.19 ± 0.03 and 0.02 ± 0.02, respectively). It is found there is no dependence of the relative peak areas of the tautomers on the nature of the solvent (polar ethyl alcohol and nonpolar hexane) at different temperatures; i.e., such ratios predominantly reflect the position of the keto (Formula presented.) enol equilibrium in the vapor phase of the injector of the chromatograph. It is concluded that this results in similar values of the thermodynamic parameters (standard enthalpy and entropy) of the tautomeric equilibrium determined upon the dosing of samples in different solvents. Possible distortions of the results due to the effects of discriminating between the compositions of the samples injected into capillary columns with gas flow splitting are discussed. An impurity in a sample of ethyl acetoacetate after long-term storage is identified as ethyl 2-hydroxy-3-oxobutanoate, the product of oxidation by dissolved atmospheric oxygen.

KW - ethyl acetoacetate

KW - gas chromatography

KW - identification of an impurity

KW - influence of temperature

KW - separation of keto and enol tautomers

KW - thermodynamic parameters

UR - http://www.scopus.com/inward/record.url?scp=85085867209&partnerID=8YFLogxK

U2 - 10.1134/S0036024420060357

DO - 10.1134/S0036024420060357

M3 - Article

VL - 94

SP - 1214

EP - 1223

JO - Russian Journal of Physical Chemistry A

JF - Russian Journal of Physical Chemistry A

SN - 0036-0244

IS - 6

ER -