Kinetics and mechanism of the reaction of ranitidine hydrochloride with trans-(diaqua)(N,N^’-ethylene-bis-salicylamide) chromium(III) and hexa-aquachromium(III) ion – a comparative study

Abstract

The substitution reactions of [Cr(SALM)(OH₂)₂]⁺ (SALM =N, N^’– ethylene–bis-salicylamide) and Cr(H₂O)₆^3<b>+</b> with ranitidine hydrochloride, an antacid have been studied spectrophotometrically over the range 0.5 ´ 10^-4 £ [Cr(III)complex]_T £ 3 ´10^-4, 3.6 £ pH £ 4.2, 25^oC £ <i style="">t</i> £ 45^oC and <i style="">I</i> = 0.5 mol dm^-3 [Cr(III)complex] = ([Cr (III)(SALM)(OH₂)₂]⁺or [Cr(H₂O)₆]^3<b>+</b>]<b>)</b> . This reaction follows a mechanism which takes place via an outer sphere association between [Cr (III)(SALM)(OH₂)₂]⁺, [Cr(H₂O)₆]^3<b>+</b> and ranitidine hydrochloride followed by transformation of outer into inner sphere complex by slow interchange. The anation rate constant at 25^oC and <i style="">I</i> = 0.5 mol dm^-3 (NaClO₄) is found to be 4.43 ´ 10^-4 s^-1 for [Cr(III)(SALM) (OH₂)₂]⁺and 3.05´10^-4 s^-1 for Cr(H₂O)₆^3<b>+</b> . The D<i style="">H</i>^# for <i style="">k</i>_an path are found to be 48.2 ± 0.6, 41.2 ±0.2 kJmol^-1and <img src='/image/spc_char/delta.gif' border=0><i style="">S</i>^# –147.6 ± 2.0, -174.2 ± 0.6 JK^-1mol^-1 for Cr(III)SALM(OH₂)₂⁺ and Cr(H₂O)₆^3<b>+</b> ion respectively.