Kinetics of Tautomeric Reaction in 1-(p-Substituted phenyl)-1, 3-butanediones

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Other Title
  • 1-(p-置換フェニル)-1,3-ブタンジオン類の互変異性化反応の速度

Description

The enol concentrations of 1-(p-substituted phenyl)-1, 3-butanediones (p-XC6H4COCH2COCH3; X = Br[1], Cl[2], H[3], NHCOCH3[4], C2H5[5], CH3[6], OCH3[7], OH[8], NH2[9]) in ethanol wered etermined by the use of a modified Meyer's method, and the kinetics and equilibriumo f the keto-enolt automerismin [1]-[9] weree xamined. The rate constants (k1) for the keto-enol tautomerism and those (k2) for the bromination to the enol form of [1]-[9] at 0-30°C were calculated as (3.1-0.5)×10-3s-1 and 0.1-0.3s-1, respectively. Althpugh the values of k1 decreased as the substituents became more electron-donating, the valuesof k2 were nearly constant regardless of the nature of the substituents. The equilibrium constants (KE) for the keto-enolt automerism of [1]-[9] were determined to be 36.0-2.4; they decreased as the substituents became more electron-donating. The keto-enol tautomerism follows the Hammette quation, consequentlye, lectron-donating and -withdrawing substituents stabilize keto and enol isomer, respectively. This substituent effect is explained by the resonancee ffect. The thermodynamic pcarameters of [1]-[9], ΔH (-8.4-27.1kJ⋅mol-1) and ΔS (-9.7- -69.5 J⋅mol-1⋅K-1), were marked by small in the case of [1]-[4].

Journal

  • NIPPON KAGAKU KAISHI

    NIPPON KAGAKU KAISHI 1989 (1), 15-19, 1989-01-10

    The Chemical Society of Japan

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