Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media

Abstract

The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en) 2 (H 2 O) 2 ] 3+ in CF 3 SO 3 H solution ([Co III ] = (2-6) Â 10 )3 M, [ptz] = 2.5 Â 10 )4 M, [H + ] = 0.02 ) 0.05 M, I = 0.1 M (H + , K + , CF 3 SO 3 ) ), T = 288-308 K) and [Co(edta)] ) in aqueous HCl ([Co III ] = (1 ) 4) Â 10 )3 M, [ptz] = 1 Â 10 )4 M, [H + ] = 0.1 ) 0.5 M, I = 1.0 M (H + , Na + , Cl ) ), T = 313 ) 333 K)were studied under the condition of excess Co III using u.v.-vis. spectroscopy. The reactions produce a Co II species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k obs ) on [Co III ] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en) 2 (H 2 O) 2 ] 3+ ion was found to be independent of [H + ]. In the case of the [Co(edta)] ) ion, the k obs dependence on [H + ] was linear and the increasing [H + ] accelerates the rate of the outer-sphere electrontransfer reaction. The activation parameters were calculated as follows: DH " = 105 ± 4 kJ mol )1 , DS " = 93 ± 11 J K )1 mol )1 for [Co(en) 2 (H 2 O) 2 ] 3+ ; DH " = 67 ± 9 kJ mol )1 , DS " = ) 54 ± 28 J K )1 mol )1 for [Co(edta)] ) .

Formation of a promazine radical and promazine 5‐oxide in the reaction of promazine with hydrogen peroxide: Mechanistic insight from kinetic and EPR measurements

“…The spectra of promazine 5‐oxide revealed two low‐field electronic transition bands at 335 and 297 nm (Fig. 1) in the ultra‐violet spectral range (λ max , nm (ε max , dm 3 mol −1 cm −1 ): 228(24,300), 269(10,300), 297(6500), 335(4700)) 20. The reaction was monitored in the acidic chloride media, in which promazine exists in its protolytic form with a protonated nitrogen atom in the alkyloamine group in a substituent.…”