Kinetics and mechanism of the reaction of sulphur(IV) with N,N?-ethylene-bis(sali-cylidiniminato)manganese-(III) in aqueous solution

Abstract

The reaction of (diaqua)(N,NЈ-ethylene-bis(salicylidiniminato)manganese(III) with aqueous sulphite buffer results in the formation of the corresponding mono sulphito complex, [Mn(Salen) respectively are: 2.97 Ϯ 0.27, 42.4 Ϯ 0.2, Ϫ55.3 Ϯ 0.6 (i ϭ 1); 11.0 Ϯ 0.8, 33 Ϯ 3, Ϫ75 Ϯ 10 (i ϭ 2); 20.6 Ϯ 1.9, 32.4 Ϯ 0.2, Ϫ72.9 Ϯ 0.6 (i ϭ 3). The trend in reactivity (k 2 Ͼ k 1 ), a small labilizing effect of the coordinated hydroxo group (k 3 /k 2 Ͻ 2), and substantially low values of ⌬S # suggest that the mechanism of aqua ligand substitution of the diaqua, and aqua-hydroxo complexes is most likely associative interchange (I a ). No evidence for the formation of the O-bonded sulphito complex and the ligand isomerization in the sulphito complex, (Mn III -OSO 2 : Mn III -SO 3 ), ensures the selectivity of the Mn III centre toward the S-end of the S IV species. The monosulphito complex further undergoes slow redox reaction in the presence of excess sulphite to produce Mn II , S 2 O 6 2Ϫ and SO 4 2Ϫ . The formation of dithionate is a consequence of the fast dimerization of the SO 3Ϫ . generated in the rate determining step and also SO 4 2Ϫ formation is attributed to the fast scavenging of the SO 3Ϫ . by the Mn III species via a redox path. The internal reduction of the Mn III centre in the monosulphito complex is insignificant. The redox reaction of the monosulphitomanganese(III) complex operates via two major paths, one involving HSO 3Ϫ and the other SO 3 2Ϫ . The electron transfer is believed to be outersphere type. The substantially negative values of activation entropies (⌬S # ϭ Ϫ(1.3 Ϯ 0.2) ϫ 10 2 and Ϫ(1.6 Ϯ 0.2) ϫ 10 2 J K Ϫ1 mol Ϫ1 for the paths involving HSO 3Ϫ and SO 3 2Ϫ respectively) reflect a considerable degree of ordering of the reactants in the act of electron transfer.

Ligand substitution and electron transfer reactions of trans-(diaqua)(salen)manganese(iii) with oxalate: an experimental and computational study

“…17 This complex undergoes fast aquation to Mn III (salen)(OH 2 ) 2 + when dissolved in water. 16,17 The optical spectrum of the diaqua complex in aqueous medium (pH 3) displays l max , nm (3 max , dm 3 mol À1 cm À1 ): 235 (40 240), 279 (18 120) which agreed well with the previously reported values. 17 The GR grade (E. Merck) oxalic acid (H 2 OX), potassium oxalate, perchloric acid, sodium hydroxide and glacial acetic acid were used as received.…”

“…However, the studies devoted to understand the mechanisms of ligand substitution and redox reactions of Mn III are limited. In view of the importance of oxalate in biology and Mn III (salen) as a suitable oxidant for oxalate oxidation, we, in continuation of our other investigations 16,17 of the mechanism of ligand substitution and electron transfer at the Mn III centre, present here a thorough study on trans-Mn III (salen)(OH 2 ) 2 + + oxalate system over extended pH and temperature ranges. To the best of our knowledge there is no earlier literature report on such a study, although oxidation of oxalate by higher valent manganese has been the topic of several investigations in the past.…”

Synthesis and characterization of xanthene-bridged Schiff-base dimanganese(iii) complexes: bimetallic catalysts for asymmetric oxidation of sulfides

“…The results for the asymmetric sulfoxidation suggest that the effective additives for the dimanganese catalysts act as deprotonating agents. The pK a value of the coordinated water molecule in the salen mangasese(III) complex [Mn(salen)(H 2 O) 2 ] + was reported to be 7.40 (5) at 25 • C. 40 The added bases can abstract a proton from the coordinated water in the dimanganese complex [Mn 2 (L)(solv) 2 (H 2 O) 2 ] 2+ (L = L 2 or L 3 , solv = coordinated solvent) to form the complex monocation [Mn 2 (L)(solv) 2 (OH)(H 2 O)] + . In the monocation, the coordinated hydroxide ligand would regulate the structure of the two Mn-salen units through intramolecular hydrogen bonds or a hydroxo bridge, which imply that the oxygen transfer occurs at the outside of the cofacial cavity.…”

Study of Kinetics of Bromophenol Blue Fading in Alcohol-Water Binary Mixtures by SESMORTAC Model

“…where k is the second-order rate constant in pure S 1 . Finally the equation of rate constant in mixture solutions is (18) where k obs is the observed first-order rate constant in binary mixture solution. The dimension of k 1 is in (dm 3 mol −1 ) n+1 (time) −1 and the dimensions of k −1 and k 2 are in (dm 3 mol −1 ) n (time) −1 and (time) −1 .…”

“…(because the interaction of added solvent mixture after each mc point with the species already presented in solution is not the same as before that point and it causes a change in the values of n and fundamental rate constants of reaction), respectively and we have: 10), ( 13) and (18) follow Arrhenius law. So, we may write: (24) Where in equation ( 10) we have and in equations ( 13) and ( 18) we have .…”