Collect. Czech. Chem. Commun. 2004, 69, 2212-2222

Kinetics and Mechanism of Desulfurization Reaction of 1-Methyl-2-phenylquinazoline-4(1H)-thiones

Jiří Hanusek*, Miloš Sedlák, Roman Keder and Vojeslav Štěrba

Department of Organic Chemistry, Faculty of Chemical Technology, University of Pardubice, nám. Čs. legií 565, 532 10 Pardubice, Czech Republic


Kinetics and mechanism of desulfurization reaction of 1-methyl-2-(substituted phenyl)-quinazoline-4(1H)-thiones in sodium methoxide solutions have been studied, giving the corresponding 1-methyl-2-(substituted phenyl)quinazolin-4(1H)-ones. The reaction proceeds in two steps. The first step involves splitting off of sulfur in the form of SH- and is much faster than the second step, whose rate is almost independent of the concentration of water in methanol. At lowest concentrations of methoxide, the rate of the first step increases linearly, but at higher concentrations a gradual decrease in the rate takes place. The rate of the second step, i.e. the transformation of the intermediate formed In into 1-methyl-2-(substituted phenyl)quinazolin-4(1H)-one (2a-2e), is independent of the methoxide concentration but increases with increasing concentration of water in methanol. On the basis of the kinetic dependences, the mechanism for both steps of desulfurization and the structure of intermediate In were proposed.

Keywords: Kinetics; Mechanism; Desulfurization; Quinazolines; Quinazoline-4(1H)-thiones; Methanolysis; Hydrolysis.

References: 20 live references.