Page 77 - Book of Abstracts

th
8 Biannual Conference on Chemistry - CHEM 08

Kinetics and Mechanism of the Acid Catalyse Aquation and

Periodate Oxidation of Ternary Dipicolinatochromium(III)
Complex Involving Nitrilotriacetate as Co-ligand

Hassan A. Ewais *, Randa O. AI-Orabi
1,2
1
1 Chemistry Department, Faculty of Science, King. Abdulaziz University, P.O.
Box
80203, Jeddah 21589, Saudi Arabia
2 Chemistry Department, Faculty of Science, Beni-Suef University, Beni-Suef
City, Egypt. E-mail: amroun1967@gmail.com; haemohammed@kau.edu.sa
ABSTRACT

Ternary complexes of chromium(III) play an important role in metal enzyme.
Chromium picolinate are often used as dietary supplements to improve insulin
sensitivity and to correct dyslipidemia The Kinetics and mechanism of the acid
hydrolysis of [Cr (DPA)(NTA)(H2O)] complex (DPA =2,6-
III
2-
Pyridinedicarboxylic acid and NTA= Nitrilotriacetic acid) were investigated. The
chromium complex in acid solution undergoes reversible one-end Cr-DPA
chelate ring opening by Cr-N bond breaking. The first order rate of aquation of
chromium complex [Cr (DPA)(NTA)(H2O)] , has been determined
2-
III
spectrophotometrically in the acid solutions 0.1-0.5 M HClO4 range and at 20-
40 C. The determinate pseudo-first order constant depends on [H ] according to
o
+
the equation:
kobs = ko + kH [H+] .
The oxidation of [Cr (DPA)(NTA)(H2O)] by periodate in an acid solution to Cr
VI
III
has been investigated kinetically under pseudo-first order conditions at different
pH, ionic strength, and temperatures. The kinetics of oxidation obeyed the
following rate law:
rate = k1 K2 [Cr ]T [I ]T /1 + [H ]/K1 + K2 [I ]T
VII
III
VII
+
Where k1 is the rate constant for the electron transfer process, K1– the equilibrium
constant for dissociation of [Cr(III)(DPA)(NTA)(H2O)] to
2-
[Cr(III)(DPA)(NTA)(OH)] + H , K2 – the pre-equilibrium formation constant.
3-
+
Values of k1 = 15.97× 10 s , K1 = 4.653 x 10 mol dm and K2 = 1002.33 dm mol –
–3
–5
3
–2
–1
1 have been obtained at 30 C and I = 0.2 mol dm . The rate oxidation increases
–3
o
with increasing of pH, temperatures and independent on ionic strength.
Thermodynamic activation parameters were calculated. It is suggested that
electron transfer progress through an inner-sphere mechanism by coordination
of IO4 to Cr(III).
-

Keywords: Kinetic and mechanism; Aquation; Oxidation; Ternary complex

BOOK OF ABSTRACTS CHEM 08 (2020) Page 76