Abstract
The kinetics of oxidation of the chromium(III) complexes, [Cr(Ino)(H
2
O)
5
]
3+
and [Cr(Ino)(Gly)(H
2
O)
3
]
2+
(Ino = Inosine and Gly = Glycine) involving a ligands of biological significance by N-bromosuccinimide (NBS) in aqueous solution to chromium(VI) have been studied spectrophotometrically over the 25-45°C range. The reaction is first order with respect to both [NBS] and [Cr], and increases with pH over the 6.64-7.73 range in both cases. The experimental rate law is consistent with a mechanism in which the hydroxy complexes [Cr(Ino)(H
2
O)
4
(OH)]
2+
and [Cr(Ino)(Gly)(H
2
O)
2
(OH)]
+
are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant, k
1
, for the oxidation of the [Cr(Ino)(H
2
O)
5
]
3+
(6.90 × 10
−4
s
−1
) is lower than the value of k
2
(9.66 × 10
−2
s
−1
) for the oxidation of [Cr(Ino)(Gly)(H
2
O)
2
]
2+
at 35°C and I = 0.2 mol dm
−3
. The activation parameters have been calculated. Electron transfer apparently takes place via an inner-sphere mechanism.
†Abstracted from the MSc thesis of Mohamed A. Nagdy.