Kinetics and mechanism of the reactions of chromium(m) and L-ornithine in aqueous solution

Regional Research Laboratory, Bhubaneswar-751 013, India Department of Chemistry, Utkal University, Vanivihar, Bhubaneswar-751 004, India E-mail : prakash72 @rediffmail.com Fax : 91-0674-2581637 Manuscript received 11 February 2003, accepted 16 April 2003 The anation reaction of L-ornithine (H3L,2+) with chromium(III) has been studied over the range 3.0 ≤ pH ≤ 3.5, 40º ≤ t ≤55º and 0.025 ≤ [H3L2+]≤ 0.2, 1 = 1.0 mol dm-3 (KNO3). This reaction follows a mechanism which takes place via an outer sphere association between Cr3+ and (H3L2+) followed by transformation of the outer into an inner-sphere complex (dictate is formed) by slow interchange. The anation rate constant at 25º and I = 1.0 mol dm-3 (KNO3) is found to be 0.64 x 10-4 s-1 ΔH# and ΔS# for kan path are found to be 55.75 ± 6.0 kJ mol-1 and -138.23 ± 17.0 JK-1 mol-1 respectively. The reaction of Cr3+ with L-ornithine follows an associative interchange mechanism