Kinetic study of the Ce(iii)‐ or Mn(ii)‐catalyzed Belousov–Zhabotinsky reactions with mixed organic acid/ketone substrates

Abstract

In a stirred batch reactor, the Ce(III)- or Mn(II)-catalyzed Belousov–Zhabotinsky reaction with mixed organic acid/ketone substrates exhibits oscillatory behavior. The organic acids studied here are: dl-mandelic acid (MDA), dl-4-bromomandelic acid (BMDA), and dl-4-hydroxymandelic acid (HMDA), and the ketones are: acetone (Me2CO), methyl ethyl ketone (MeCOEt), diethyl ketone (Et2CO), acetophenone (MeCOPh), and cyclohexanone ((CH2)5CO). The effects of bromate ion, organic acid, ketone, metal-ion catalyst, and sulfuric acid concentrations on the oscillatory patterns are investigated. Both conventional and stopped-flow methods are applied to study the kinetics of the oxidation reactions of the above organic acids by Ce(IV) or Mn(III) ion. The order of relative reactivities of the oxidation reactions of organic acids in 1 M H2SO4 is Mn(III)(SINGLEBOND)HMDA reaction>Ce(IV)(SINGLEBOND)HMDA reaction>Mn(III)(SINGLEBOND)BMDA, reaction>Mn(III)(SINGLEBOND)MDA reaction>Ce(IV)(SINGLEBOND)BMDA reaction>Ce(IV)(SINGLEBOND)MDA reaction. Spectrophotometric study of the bromination reactions of the above ketones shows that these reactions are zero-order with respect to bromine and first-order with respect to ketone and that ketone enolization is the rate-determining step. The order of relative rates of bromination or enolization reactions of ketones in 1 M H2SO4 is (CH2)5CO≫(MeCOEt, Et2CO, Me2CO)>MeCOPh. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet:30: 595–604, 1998