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Effect of cetylammonium bromide micelles on decolouration of rosaniline hydrochloride by periodate: Experimental and theoretical approach
Author : R. S. S. Srikanth Vemuri a, P. Shyamala *b and K. Bhargavi b
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ABSTRACT
Rosaniline hydrochloride (RH) is a triaminotriphenyl methane dye, which is widely used as biological stain, mordant, printing, in cotton tannings, and dyeing in textile industry. The reaction obeys first order kinetics with respect to RH and IO4–. The reaction is around hundred times faster in the presence of CTAB compared to aqueous medium under identical conditions. This is due to lower dielectric constant in micellar medium in which the transition state in more stabilized. The rate of the reaction increases with increase in concentration of CTAB up to 0.08 mol dm–3 and thereafter shows a limiting behavior with increase in micellar concentration. The monotonic increase indicates a unimolecular pathway. Using Menger and Portnoy’spre equilibrium kinetic model binding constant was found to be 21.84 mol–1 dm3. This value was found to be in good agreement with the calculated binding constant KM (= pV) = 39.2, where p is partition co-efficient and V is molar volume. In order to account for the catalytic behavior of CTAB, theoretical calculations of single point energy and energy gap were done using GAUSSIAN 09 W program employing density functional theory (DFT) with Becke’s three-parameters hybrid functional in combination of Lee-Yang-Parr functional implemented with LANL2DZ basis sets using conductor like polarizable continuum model (CPCM). (DFT/B3LYP/LANL2DZ/CPCM (solvent = water)). Based on the structures of RH, KIO4 and CTAB, binding energies (BEs) were calculated for the dimer complexes RH-KIO4 and RH-KIO4-CTAB. BEs of the RH-KIO4 and RH-KIO4-CTAB systems have been found to be –60.4 kcal/mol and –70.4 kcal/mol, respectively. The high binding energy (RH-KIO4-CTAB, –70.4 kcal/mol) indicates the catalytic behavior. The HLEG (HOMO-LUMO Energy Gap) measures the stability of the system. A large HLEG implies high stability (less reactive) and slight gap implies low stability (highly reactive). In this work, RH-KIO4-CTAB system, the gap is reduced around 1.28 times than the RH-KIO4 system which clearly indicates that the CTAB surfactant plays a vital role in this reaction. It explains that catalytic behavior of CTAB by theoretical approach.
KEYWORD
Catalysis, CTAB, decoloration, pseudo phase model, surfactants