Halogenation of Acetone. A Method for Determining pKas of Ketones in Aqueous Solution, with an Examination of the Thermodynamics and Kinetics of Alkaline Halogenation and a Discussion of the Best Value for the Rate Constant for a "Diffusion-Controlled Reaction". Energetic ...

Article abstract of DOI:10.1021/ja00317a030

The pK_a of a simple ketone can be determined by analysis of the kinetics of halogenation in alkaline solution (J.Am.Chem.Soc. 1982, 104, 895).Details of the determination of the pK_a of acetone are reported.The stoichiometry of chlorination of acetone is 2.15 hypohalites per acetone; bromination consumes 2.83 hypobromites.The major product from chlorination is lactate and not acetate; lactate is a minor product from bromination of acetone.The kinetic significance of the possible side reactions is discussed.The determination of the pK_a requires knowledge of the rate constant for a diffusion-controlled reactionof nonspherically symmetrical molecules in water; the state of our knowledge of this rate constant is reviewed critically.It is shown that for reactions involving diffusion together of reactants which then undergo direct heavy-atom bond making it is very unusual for the diffusion limit to be reached, although the observed rate constant may become insensitive to the thermodynamic rectivity of the reactants.