Abstract
The reactivity of Zn
2+
and VO
2+
ions towards pyridinyl Schiff bases, in the absence or presence of a
p
-sodium sulfonate group (HPSNa and HPS, respectively), provided polar and less polar catalyst complexes, which were characterized by various measurements. Stability constants of Zn-complexes [Zn(PS)
2
and Zn(PSNa)
2
], and VO-complexes [VO(PS)
2
and VO(PSNa)
2
] were measured spectrophotometrically. A typical (ep)oxidation processes of 1,2-cyclohexene or cyclohexane using 30% aqueous H
2
O
2
catalyzed by our synthesized catalyst system, were tested. VO-complexes were found to be more effective catalysts than Zn-chelates. The polarity of Zn- and VO-complexes, i.e. the presence of
p
-SO
3
Na, displayed an observable influence on their catalytic performance chemoselectively. The polar catalyst system, Zn(PSNa)
2
and VO(PSNa)
2
, in polar solvents such as H
2
O, MeOH, acetonitrile and acetone exhibited higher catalytic activity towards the (ep)oxidation processes than the less polar catalysts, Zn(PS)
2
and VO(PS)
2
. In a less polar solvent such as CHCl
3
, polar catalysts showed higher conversion, but low chemoselectively, whereas the less polar catalysts showed relatively higher conversion and chemoselectivity. Under solvent-free conditions, less polar complexes were found to be more efficient catalysts than the polar chelates.