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

摘要

The substitution reactions of [Cr(SALM)(OH2)2]~+ (SALM =N, N- ethylene-bis-salicylamide) and Cr(H2O)_6~(3+) with ranitidine hydrochloride, an antacid have been studied spectrophotometrically over the range 0.5 x 10~(-4) ≤ [Cr(III)complex]_T ≤ 3 x10~(-4), 3.6 ≤ pH ≤ 4.2, 25°C ≤ t ≤ 45°C and I = 0.5 mol dm~(-3) [Cr(III)complex] = ([Cr (III)(SALM)(OH2)2]~+or [Cr(H2O)6]~(3+)]) . This reaction follows a mechanism which takes place via an outer sphere association between [Cr (III)(SALM)(OH2)2]~+, [Cr(H2O)6]~(3+) and ranitidine hydrochloride followed by transformation of outer into inner sphere complex by slow interchange. The anation rate constant at 25°C and I = 0.5 mol dm~(-3) (NaClO4) is found to be 4.43 x 10~(-4) s~(-1) for [Cr(III)(SALM) (OH2)2]~+and 3.05x10~(-4) s~(-1) for Cr(H2O)_6~(3+) . The ΔH~# for k_(an) path are found to be 48.2 ± 0.6, 41.2 ±0.2 kJmpl~(-1) and ΔS~# -147.6 ± 2.0, -174.2 ± 0.6 JK~(-1)mol~(-1) for Cr(III)SALM(OH2)_2~+ and Cr(H2O)_6~(3+) ion respectively.