Collect. Czech. Chem. Commun. 1999, 64, 1654-1672

Effect of Medium on Acid-Catalyzed Decomposition of N-(Phenylazo)-Substituted Nitrogen Heterocycles

Miroslav Ludwig*, Iva Bednářová and Patrik Pařík

Department of Organic Chemistry, Faculty of Chemical Technology, University of Pardubice, Čs. Legií 565, CZ-532 10 Pardubice, Czech Republic


Four N-(phenylazo)-substituted saturated nitrogen heterocyclics were synthesized and their structure was confirmed by 1H and 13C NMR spectroscopy. The kinetics of their acid-catalyzed decomposition were studied at various concentrations of the catalyst (pivalic acid) in 40, 30, and 20% (v/v) aqueous ethanol at 25 °C. The values obtained for the observed rate constants were processed by the non-linear regression method according to the suggested kinetic models and by the method of principal component analysis (PCA). The interpretation of the results has shown that the acid-catalyzed decomposition of the heterocyclics under the conditions used proceeds by the mechanism of general acid catalysis, the proton being the dominant catalyst particle of the rate-limiting step. The decrease in the observed rate constant at higher concentrations of the catalyst was explained by the formation of a non-reactive complex composed of the undissociated acid and the respective N-(phenylazo)heterocycle. The effect of medium and steric effect of the heterocyclic moiety on the values of catalytic rate constant are discussed.

Keywords: Reaction kinetics; Mechanism; Solvent effects; Triazenes; Chemometrics.