any light onto this controversy, so steps B and C have been listed separately.The oberved order of reaction with respect to H+ concentration is empirical in this work, since, according to the mechanism, the order should in fact be unity. However, the evidence of acid-catalyzed aldol condensation of MEK precludes exact first-order acid dependence.Other Results. The findings of Neish et al. (1945) cannot be refuted on the basis of this work. The Neish system contained a very strong acid with no effective water concentration, so a different mechanism is conceivable. Neish also reported the formation of the cyclic ketal, 2ethyl-2,4,5-trimethyl dioxolane, by the condensation of 1 mol each of 2,3-butanediol and MEK. This compound was not detected in our work, presumably because the equilibrium lies in favor of 2,3-butanediol and MEK in aqueous solution (see Fife et al., 1967Fife et al., , 1970Fife et al., , 1971.
ConclusionsAqueous 2,3-butanediol was shown to react in a pseudo-first-order reaction in the presence of sulfuric acid to form methyl ethyl ketone. The reaction could be described by a pinacol rearrangement mechanism and had an activation energy of 36 kcal/mol. An empirical order of reaction with respect to H+ concentration of 1.53 was determined. MEK yields exceeding 90 mol % could be consistently obtained, but evidence of acid-catalyzed aldol condensation was noted.The pseudo-first-order reaction incorporated the temperature, acid concentration, and initial reactant concentration, and predicted, a priori, the reaction time course for both MEK and 2,3-butanediol.Dehydration of 2,3-butanediol to MEK in fermentation broths is feasible, and the current model can be used as the first step in the development of a more complete model which is directly applicable to 2,3-butanediol fermentation broths.