Kinetics and mechanism of base hydrolysis of tris(3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine)iron(II) in aqueous and micellar media

Abstract

The kinetics of base hydrolysis of tris(3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine)iron(II), ${\text{Fe(PDT)}}_{ 3}^{2 + }$ has been studied in aqueous, cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) media at 25, 35 and 45 °C under pseudo-first-order conditions, i.e. $[ {\text{OH}}^{ - } ]\gg [{\text{Fe(PDT)}}_{ 3}^{2 + } ]$. The reactions are first order in both of substrate ${\text{Fe(PDT)}}_{ 3}^{2 + }$ and hydroxide ion. The rates decrease with increasing ionic strength in aqueous and CTAB media, whereas SDS medium shows little ionic strength effect. The rate also increases with CTAB concentration but decreases with SDS. The specific rate constant, k and thermodynamic parameters (E _a, ΔH ^#, ΔS ^# and ΔG ^#) have also been evaluated. The near equal values of ΔG ^# obtained in aqueous and CTAB media suggest that these reactions occur essentially by the same mechanism such that ${\text{Fe(PDT)}}_{ 3}^{2 + }$ reacts with OH⁻ in the rate-determining step. The ionic strength effect in SDS medium suggests that the rate-determining step involves an ion and a neutral species. The results in this study are compared with those obtained for other iron(II)-bipyridine complexes.