International Journal of Pure and Applied Chemistry (IJPAC)

 

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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