Kinetics and mechanism of the reaction of ranitidine hydrochloride with trans-(diaqua)(N,N

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 × 10 ≤ [Cr(III)complex]T ≤ 3 ×10, 3.6 ≤ pH ≤ 4.2, 25C ≤ t ≤ 45C and I = 0.5 mol dm [Cr(III)complex] = ([Cr (III)(SALM)(OH2)2] or [Cr(H2O)6] ]) . 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 25C and I = 0.5 mol dm (NaClO4) is found to be 4.43 × 10 s for [Cr(III)(SALM) (OH2)2] and 3.05×10 s for Cr(H2O)6 3+ . The ∆H for kan path are found to be 48.2 ± 0.6, 41.2 ±0.2 kJmol and ∆S –147.6 ± 2.0, -174.2 ± 0.6 JKmol for Cr(III)SALM(OH2)2 + and Cr(H2O)6 3+ ion respectively.