Stella V J, Gish R
J Pharm Sci. 1979 Aug;68(8):1047-9. doi: 10.1002/jps.2600680833.
The ionization kinetics of 1.3-diketone carbon acids are slow relative to those of classical acids and bases. The ionization kinetics of three 4'-substituted 2-phenyl-1,3-indandiones, 4'-chloro-, 4'-methoxy-, and 2-phenyl-1,3-indandione itself, were studied at 25 degrees and ionic strength 0.1 using stopped-flow spectrometry and a pH jump technique. A log k'obs-pH profile for the approach to the ionization equilibrium was consistent with a reaction scheme postulated earlier for the ionization of another carbon acid, phenylbutazone. The percent enol versus diketo form of the acids and the pKaenol and pKadiketo were calculated from the kinetic data. Hammett plots of the various kinetic and equilibrium constants supported a mechanism for acid deprotonation consistent with proton abstraction being the predominant process when very weak bases such as water were the proton acceptors. Desolvation effects and the work required to get the two reacting molecules together in the correct configurations predominated when the proton abstraction was by stronger proton acceptors.
相对于经典酸碱而言，1,3 - 二酮碳酸的电离动力学较为缓慢。采用停流光谱法和pH跃变技术，在25℃和离子强度0.1的条件下，研究了三种4'-取代的2 - 苯基 - 1,3 - 茚满二酮（4'-氯 - 、4'-甲氧基 - 以及2 - 苯基 - 1,3 - 茚满二酮本身）的电离动力学。对于电离平衡的趋近过程，log k'obs - pH曲线与先前为另一种碳酸——保泰松的电离所假设的反应方案相一致。根据动力学数据计算了酸的烯醇式与二酮式的百分比以及pKaenol和pKadiketo。各种动力学常数和平衡常数的哈米特图支持了酸去质子化的一种机制，即当像水这样的非常弱的碱作为质子受体时，质子夺取是主要过程；而当质子夺取是由更强的质子受体进行时，去溶剂化效应以及使两个反应分子以正确构型结合在一起所需的功起主导作用。
