Catalytic effect of CTAB reverse micelles on the reduction of toluidine blue by ascorbic acid

Abstract

<span style="font-size:9.0pt;mso-bidi-font-size: 12.0pt;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">The kinetics of the reduction of toluidine blue by ascorbic acid has been studied in the presence of CTAB/CHCl₃/hexane/water reverse micelles. In the absence of added acid, the reaction obeys simple first order kinetics with respect to both the reactants. The second order rate constant in the presence of reverse micelles, <i style="mso-bidi-font-style:normal">k</i>_w(0.027 <i style="mso-bidi-font-style:normal">M</i>^-1 s^-1) was found to be about sixty times greater than that in aqueous medium, <i style="mso-bidi-font-style:normal">k</i>_o (4.50×10^-4 <i style="mso-bidi-font-style:normal">M</i>^-1 s^-1) under identical experimental conditions. The significant increase is attributed to the concentration effect in the reverse micelles, and, lower micro-polarity due to the reverse micelles, which facilitates the reaction between oppositely charged ions. The effect of variation of <i style="mso-bidi-font-style:normal">W</i> (= [H₂O]/[CTAB]) at constant [CTAB] and variation of [CTAB] at fixed <i style="mso-bidi-font-style: normal">W</i> has been studied. The kinetics at <i style="mso-bidi-font-style: normal">W </i>< 6 is explained on the basis of the special properties of the entrapped water, while the kinetics at <i style="mso-bidi-font-style:normal">W</i> > 10 is explained on the basis of ionic strength.</span>