pKa constant determination of two triazole herbicides : Tebuconazole and Penconazole

Eva Čadková (1) , Michael Komárek (2) , Jean Debord (3, 4, 5) , Della Puppa Loïc (6) , François Bordas (6) , Jean-Claude Bollinger (6)

1 Department of Agro-Environmental Chemistry and Plant Nutrition
2 Department of Environmental Geosciences [Prague]
3 PIST - Pharmacologie des Immunosuppresseurs et de la Transplantation
4 Service de Pharmacologie, toxicologie et pharmacovigilance [CHU Limoges]
5 UNILIM - Université de Limoges
6 GRESE - Groupement de Recherche Eau, Sol, Environnement

We determined the acidity constants of tebuconazole and penconazole, two fungicides from the group of 1,2,4-triazoles. Potentiometric titrations were performed in a 20 % (v/v) acetonitrile/water mixture at 25 °C and at a fixed ionic strength (KNO3, 0.1 mol*dm−3). The pKa values (representing thermodynamic constants) were determined to be 5.0 ± 0.1 and 5.2 ± 0.1 for tebuconazole and penconazole, respectively. These values could be used in pure water solutions to consider the protonated or deprotonated forms when studying the field behavior of these fungicides. Molecular modeling calculations allowed identifying the N4 atom as the protonation site.

Mots clés: Triazole pesticides; Potentiometric titrations; Protonation constant; Protonation site; Molecular modeling

Domaines: Sciences de l'environnement; Chimie analytique

Eva Čadková, Michael Komárek, Jean Debord, Della Puppa Loïc, François Bordas, et al.. pKa constant determination of two triazole herbicides : Tebuconazole and Penconazole. Journal of Solution Chemistry, 2013, 42, pp.1075-1082. ⟨10.1007/s10953-013-0012-z⟩. ⟨hal-00929974⟩