Kinetics and mechanism of O–O bond cleavage in the reaction of [RuIII(edta)(H2O)]− with hydroperoxides in aqueous solution

Abstract

The reactions of [Ru(III)(edta)(H(2)O)](-) (1) (edta = ethylenediaminetetraacetate) with tert-butylhydroperoxide ((t)BuOOH) and potassium hydrogenpersulfate (KHSO(5)) were studied kinetically as a function of oxidant concentration and temperature (10-30 degrees C) at a fixed pH of 6.1 using stopped-flow techniques. Kinetic results were analyzed by using global kinetic analysis techniques. The reaction was found to consist of two steps involving the rapid formation of a [Ru(III)(edta)(OOR)](2-) intermediate, which subsequently undergoes heterolytic cleavage to form [(edta)Ru(V)=O](-). Since [(edta)Ru(V)=O](-) was produced almost quantitatively in the reaction of 1 with the hydroperoxides (t)BuOOH and KHSO(5), the common mechanism is one of heterolytic scission of the O-O bond. The water soluble and easy to oxidize substrate 2,2'-azobis(3-ethylbenzithiazoline-6-sulfonate (ABTS), was employed to substantiate the mechanistic proposal. Reactions were carried out under pseudo-first order conditions for [ABTS] >> [hydroperoxide] >> [1], and were monitored as a function of time for the formation of the one-electron oxidation product ABTS (*+). The detailed suggested mechanism is consistent with the reported rate and activation parameters, and discussed in reference to the results reported for the reaction of [Ru(II)(edta)(H(2)O)](-) with H(2)O(2).

Kinetics and mechanism for oxidation of [RuIII(edta)(H2O)]− with peroxydisulfate in aqueous medium

“…The findings of this work, together with those for the reaction of [Ru III (edta)(H 2 O)] À with ROOH (R ¼ H, t Bu, and SO À 4 ), strongly suggests that the formation of [(edta)Ru V (¼O)] À species in the reaction of 1 with S 2 O 2À 8 takes place through an alkali-cation-assisted outer-sphere electron-transfer process not via oxo-transfer as observed for ROOH [10,11].…”

“…Although [(edta)Ru V ¼O] À is the common major product in the reaction of 1 with S 2 O 2À 8 and other precursor oxidants, H 2 O 2 , t BuOOH, and KHSO 5 , above results rule out the possibility of a common mechanism. The reaction of 1 with ROOH (R ¼ H, t Bu, and SO À 3 ) proceeds via aquo-substitution leading to the formation of [(edta)Ru III (OOR)] 2À/3À , which subsequently undergo heterolytic cleavage of the O-O bond resulting in the formation of Ru(V)-oxo species [10,11]. The formation of Table 1.…”

“…Anal. Calcd (%) for C 11 [4,16]. All chemicals used were of reagent grade obtained from Aldrich Chemical Company and were appropriately degassed before use.…”

“…Our longstanding collaboration has resulted in some significant publications on kinetic and mechanistic studies of Ru-edta complexes [7][8][9][10][11][12], exploring their potential in various biochemical processes. The present work stems from our continued interest in kinetic and mechanistic studies of the interaction of Ru-edta complexes with various oxidants, namely NaOBr [9], H 2 O 2 [10], t BuOOH, KHSO 5 [11], with the objective of acquiring mechanistic knowledge regarding the formation of the high-valent [(edta)Ru V ¼O] À species which had been proposed earlier [13] [14], we for the first time report the peroxydisulfate oxidation of Ru(III)-edta complex to Ru(V)-oxo complex. The mechanism of the overall oxidation process is discussed in reference to the previously reported data for the reaction between [Ru III (edta)(H 2 O)] À and ROOH (R ¼ H, t Bu, and SO À 4 ) [10, 11].…”

Oxidation of Ru(III)-Bound Thiocyanate with Peroxomonosulfate: Kinetic and Mechanistic Studies

“…We have reported earlier that the reaction of [Ru III (edta)(H 2 O)] − with HSO 5 − results in the formation of the [Ru V (edta)O] − complex. However, [Ru III (edta)(H 2 O)] − reacts with HSO 5 − to produce [Ru V (edta)O] − at a considerably slower rate (7.0 M −1 s −1 at 25°C) than it reacts with SCN − (270 M −1 s −1 at 25°C ) to produce [Ru III (edta)(SCN)] 2− . The free [Ru III (edta)(H 2 O)] − generated at the end of the reaction (Eq.…”