Dedicated to Professor Jaromír Kaválek on the occasion of his 75th birthday.
Influence of Cu(II) Ions on the Mechanism of the Ring Transformation of S-(2-Oxotetrahydrofuran-3-yl)-N-(4-methoxyphenyl)isothiouronium Bromide
Article first published online: 21 FEB 2013
© 2013 Wiley Periodicals, Inc.
International Journal of Chemical Kinetics
Volume 45, Issue 4, pages 248–255, April 2013
How to Cite
Váňa, J., Sedlák, M. and Hanusek, J. (2013), Influence of Cu(II) Ions on the Mechanism of the Ring Transformation of S-(2-Oxotetrahydrofuran-3-yl)-N-(4-methoxyphenyl)isothiouronium Bromide. Int. J. Chem. Kinet., 45: 248–255. doi: 10.1002/kin.20761
Contract grant sponsor: Ministry of Education, Youth and Sports of the Czech Republic
Contract grant sponsor: European Social Fund for “Enhancement of R&D Pools of Excellence at the University of Pardubice.”
Contract grant number: CZ.1.07./2.3.00/30.0021.
- Issue published online: 21 FEB 2013
- Article first published online: 21 FEB 2013
- Manuscript Accepted: 4 OCT 2012
- Manuscript Revised: 3 OCT 2012
- Manuscript Received: 9 MAY 2012
- Ministry of Education, Youth and Sports of the Czech Republic
The effect of additional Cu(II) ions on the rate of transformation of S-(2-oxotetrahydrofuran-3-yl)-N-(4-methoxyphenyl)isothiouronium bromide (1) into 5-(2-hydroxyethyl)-2-[(4-methoxyphenyl)imino]-1,3-thiazolidin-4-one (2) has been studied in aqueous buffer solutions. The reaction acceleration in acetate buffers is caused by the formation of a relatively weakly bonded complex (Kc = 600 L·mol−1) of substrate with copper(II) acetate in which the Cu(II) ion acts as a Lewis acid coordinating the carbonyl oxygen and facilitating the intramolecular attack, leading to the formation of intermediate T±. The formation of the complex of copper(II) acetate with free isothiourea in the fast preequilibrium (Kc) is followed by the rate-limiting transformation (kCu) of this complex. At the high concentrations of the acetate anions, the reaction is retarded by the competitive reaction of these ions with copper(II) acetate to give an unreactive complex [Cu(OAc)4]2−. The influence of Cu(II) ions on the stability of reaction intermediates and the leaving group ability of the alkoxide-leaving group compared to the Cu(II)-uncatalyzed reaction is also discussed.