Pyrolysis of beta-hydroxyketones and alpha-ketoesters: Gas-phase elimination kinetics of 3-hydroxy-3-methyl-2-butanone and methyl benzoylformate

The rates of gas-phase elimination reactions of methyl benzoylformate (I) and 3-hydroxy-3-methyl-2-butanone (2) were obtained at T = 600 K. The two substrates undergo unimolecular first-order elimination for which the Arrhenius equations are, respectively, log k = 13.2 - 53270/(4.574 x 600) for (I) and log k = 12.4 - 53060/(4.574 x 600) for (2). The products of pyrolysis of (I) are benzaldehyde, formaldehyde and CO, while those of (2) are acetaldehyde and acetone. The kinetics of the elimination reactions show benzoylformic acid to be 10(6)-fold more reactive than (1), and pyruvic acid ca. 10(5)-fold more reactive relative to (2); an indication of the rate-controlling part played by the acidity of the hydrogen atom involved in the elimination process of the present compounds in this particular type of reaction. (C) 1997 John Wiley & Sons, Inc.