Kinetics and mechanism of the oxidation of alcohols by ferrate ion

Abstract

A kinetic study of the reduction of ferrate ion under basic conditions has been completed. The observation that a typical aliphatic ether, tetrahydrofuran, is oxidized at a rate comparable to that of aliphatic alcohols, such as cyclopentanol, indicates that the reaction between ferrate and alcohols is likely initiated by attack of the oxidant at an a-C-H bond, a conclusion that is consistent with the occurrence of primary deuterium kinetic isotope effects (2.8-4.3 at 25°C) when a-hydrogens are replaced by deuterium. Because only acyclic products are obtained from the oxidation of cyclobutanol by ferrate, it may be concluded that free radical intermediates are involved in the reaction. The insensitivity of the reaction rates to substituent effects during the oxidation of substituted mandelic acids indicates that substantial charges are not built up in the transition state. All of these observations are most readily accommodated by a mechanism in which the reaction is initiated by a 2 + 2 addition of an Fe=O bond to the a-C-H of an alcohol to give an organometallic intermediate that subsequently decomposes by homolytic cleavage of the resulting C-Fe bond. Comparisons are made with the reactions between alcohols and other high-valent transition metal oxides. On a rkalisk une ktude cinktique de la reduction de l'ion ferrate dans des conditions basiques. Le fait qu'un ether typique, le tktrahydrofurane, est oxyde a une vitesse comparable B celle des alcools, comme le cyclopentanol, indique que la rkaction entre le ferrate et les alcools est probablement initike par une attaque de l'oxydant sur la liaison a-C-H; cette hypothese est en accord avec le fait que l'on observe un effet isotopique primaire du deuterium (2,8-4,3, a 25°C) lorsqu'on remplace les hydrogenes-a par du deutkrium. En se basant sur le fait que l'on n'obtient que des produits aliphatiques lors de l'oxydation du cyclobutanol par le ferrate suggkre que des interrnkdiaires radicalaires sont impliques dans la reaction. Le fait que les vitesses de reaction d'oxydation d'acides mandkliques substituks ne soient pas sensibles B la nature des substituants indique qu'il n'y aurait pas d'accumulation de charge dans l'ktat de transition. Le meilleur mkcanisme permettant d'expliquer tous ces rksultats implique une reaction initiee par une addition 2+2 d'une liaison Fe=O sur la liaison a-C-H d'un alcool qui conduit a un intermediaire organomktallique que se decompose par la suite par un clivage homolytique de la liaison C-Fe qui en resulte. On a fait des comparaisons avec les rkactions des alcools avec d'autres oxydes de mktaux de transition de valence ClevCe.[Traduit par la rkdaction]

Ferrate(VI) in the Treatment of Wastewaters: A New Generation Green Chemical

“…Figure 8 clearly indicated that HFeO 4 -and FeO 4 2-species are predominant species in neutral and alkaline solutions, at which the Fe(VI) was known to be relatively stable towards its spontaneous dissociation [37]. The ferrate salts when dissolved in water, oxygen is evolved and ferric hydroxide is precipitated (equation (14)).…”

“…The lowest rate of decomposition was occurred at pH higher than ~9-10, while it increased significantly at lower pH values [35,38]. The reaction kinetics followed second-order below pH 9.0, while first order above pH 10.0 [37]. The decomposition of ferrate(VI) hence, described by the following equilibrium and kinetic models [36]: (20) Reactions clearly showed that the forward reactions (15) to (20) (except reaction (16)) are relatively slow steps hence, could be the rate determining steps.…”

Heterogeneous photocatalytic reduction of ferrate(VI) in UV‐irradiated titania suspensions: Role in enhancing destruction of nitrogen‐containing pollutants

“…The experiments were conducted in the pH range 8.5-10.0. The rate of spontaneous decomposition of Fe(VI) in water at pH ≥ 8.5 does not contribute significantly in studying the photocatalytic reduction of Fe(VI) in an alkaline medium [12,13].…”

A novel procedure for acid-catalysed K2FeO4 oxidation of benzyl alcohol in organic phase

“…K 2 FeO 4 has been reported to oxidize a variety of organic functional groups such as amines and particularly alcohols, for which a number of publications can be found in the literature (Audette et al 1971(Audette et al , 1972Kim et al 1984Kim et al , 1986Lee and Gai 1993;Delaude et al 1995;Delaude and Laszlo 1996;Caddick et al 2000;Takehiro et al 2001;Song and Wang 2003;Song et al 2006a). Studies involving K 2 FeO 4 generally employ alkaline aqueous conditions (Audette et al 1971(Audette et al , 1972Takehiro et al 2001;Song et al 2004) in which K 2 FeO 4 is very soluble but unstable.…”