7. Mechanistic
Studies of Aquachloroiridium (III) Catalysis in the Oxidation of 1,
2-Propanediol by N-Bromosuccinimide in Acidic Medium: A Kinetic
Modeling
Bharat Singh*, Shipra Tripathi and Sandeep Kumar
Mishra
Department of Chemistry, University of Allahabad, Allahabad-211002,
India, E- mail:
bschem_au@yahoo.com
Abstract:
Kinetics of oxidation of 1,2-propanediol by N-bromosuccinimide
(NBS) have been investigated in the presence of
aquachloroiridium (III) complex as catalyst and mercuric acetate
as bromide ions scavenger in perchloric acid in the temperature
range 25 to 450C.The reaction showed zero order
kinetics with respect to [NBS]. First order kinetics with
respect to both 1, 2-propanediol and Ir(III) in their low
concentration range tends to shift to zero order in their higher
concentration range. Decreasing effect of both [H+]
and [Cl-] was observed while successive addition of
each of mercuric acetate and succinimide showed negligible
effect on the rate of reaction. Variation of ionic strength of
the medium was found to have zero effect on the rate of the
reaction. Formic acid and acetic acid were identified as
oxidation products. Activation parameters for the slow and rate
determining step of the proposed mechanism, which involves the
formation of the most activated complex, [Cl5Ir – O--
CH (CH3) (CH2OH)]3- prior to
the slowest step, have been obtained from the rate measurements
at 25,30,35,40,and 450C.The rate law in agreement with the
observed kinetic results has been deduced as :
Keywords: Kinetics and mechanism, NBS-oxidation, Ir (III)
catalysis, 1,2-propanediol.
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