FLASH-PHOTOLYTIC GENERATION OF ACETOPHENONE ENOL - THE KETO ENOL EQUILIBRIUM-CONSTANT AND PKA OF ACETOPHENONE IN AQUEOUS-SOLUTION
FLASH-PHOTOLYTIC GENERATION OF ACETOPHENONE ENOL - THE KETO ENOL EQUILIBRIUM-CONSTANT AND PKA OF ACETOPHENONE IN AQUEOUS-SOLUTION
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DOI：
10.1021/ja00333a049
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发表时间：
1984-01-01
影响因子：
15
通讯作者：
WIRZ, J
中科院分区：
文献类型：
--
作者：
CHIANG, Y;KRESGE, AJ;WIRZ, J
用Norrish II型光消除法测定了γ-羟基丁苯酮在稀盐酸水溶液中的酮化速率。这些数据与酸催化苯乙酮烯醇化的比速率相结合，给出了酮-烯醇平衡常数的值，这与在NaOH溶液中测得的烯醇化和酮化速率常数的另一个结果很好地一致。这些测定的平均值为pke=7.90+-。0.02。这与已知的苯乙酮烯醇酸离解常数相结合，得到pKaK=18.24。苯乙酮以碳酸形式电离的酸度常数为0.03。目前的结果允许估计质子从H3O+转移到苯乙酮烯醇型离子的β-碳原子的比速率。=(4.2+-。1.2)。1010M~(-1)S~(-1)，这表明该反应是通过酸和底物之间氢键溶剂桥下的质子转移进行的。
Acetophenone enol was generated by Norrish type II photoelimination of .gamma.-hydroxybutyrophenone, and its rate of ketonization has been measured in dilute aqueous HCl solutions. These data, in combination with the specific rate of acid-catalyzed enolization of acetophenone, give a value of the keto-enol equilibrium constant which is in good agreement with another result based upon enolization and ketonization rate constants measured in NaOH solutions. The average of these determinations gives pKE = 7.90 .+-. 0.02. This, when combined with the known acid-dissociation constant of acetophenone enol, leads to pKaK = 18.24 .+-. 0.03 for the acidity constant of acetophenone ionizing as a carbon acid. The present results allow an estimate of the specific rate of proton transfer from H3O+ to the .beta.-carbon atom of acetophenone enolate ion, .kappa. = (4.2 .+-. 1.2) .times. 1010 M-1 s-1, which is so great as to suggest that this reaction occurs through proton transfer down hydrogen-bonded solvent bridges between acid and substrate.