Hydrogen Atom Abstraction by Permanganate:  Oxidations of Arylalkanes in Organic Solvents

Abstract

Oxidations of arylalkanes by (n)()Bu(4)NMnO(4) have been studied in toluene solvent: toluene, ethylbenzene, diphenylmethane, triphenylmethane, 9,10-dihydroanthracene, xanthene, and fluorene. Toluene is oxidized to benzoic acid and a small amount of benzaldehyde; other substrates give oxygenated and/or dehydrogenated products. The manganese product of all of the reactions is colloidal MnO(2). The kinetics of the reactions, monitored by UV/vis spectrometry, show that the initial reactions are first order in the concentrations of both (n)()Bu(4)NMnO(4) and substrate. No induction periods are observed. The same rate constants for toluene oxidation are observed in neat toluene and in o-dichlorobenzene solvent, within experimental errors. The presence of O(2) increases the rate of (n)()Bu(4)NMnO(4) disappearance. The reactions of toluene and dihydroanthracene exhibit primary isotope effects: k(C)()7(H)()8/k(C)()7(D)()8 = 6 (+/-1) at 45 degrees C and k(C)()14(H)()12/k(C)()14(D)()12 = 3.0 (+/-0.6) at 25 degrees C. The rates of oxidation of substituted toluenes show only small substituent effects. In the reactions of dihydroanthracene and fluorene, the MnO(2) product is consumed in a subsequent reaction that appears to form a charge-transfer complex. The rate-limiting step in all of the reactions is hydrogen atom transfer from the substrate to a permanganate oxo group. The enthalpies of activation for the different substrates are directly proportional to the DeltaH degrees for the hydrogen atom transfer step, as is typical of organic radical reactions. The ability of permanganate to abstract a hydrogen atom is explained on the basis of its ability to form an 80 +/- 3 kcal/mol bond to H(*), as calculated from a thermochemical cycle. (This bond strength is slightly lower than given in earlier calculations.) Rates of H(*) abstraction by (n)()Bu(4)NMnO(4) correlate with rates of abstraction by oxygen radicals.

Axial ligand tuning of a nonheme iron(IV)–oxo unit for hydrogen atom abstraction

“…KIE values of 10-20 (average 17) were obtained in all of the reactions, consistent with COH bond cleavage being the rate-determining step (Table 1 and SI Table 3) (33)(34)(35)(36)(37). These large KIE values exceed the semiclassical limit (i.e., KIE Ͻ 7) and suggest a tunneling behavior in the reaction mechanism or another phenomenon that creates these high values (see below).…”

Metal Ion Catalyzed Oxidation of L-Lysine by Alkaline Permanganate Ion-A Kinetic and Mechanistic Approach

“…L-lysine is a basic amino acid and carries a +ve charge. In view of this, we undertook a study of the oxidation of L-lysine by KMnO 4 in alkaline medium and also we compared uncatalysed and catalyzed reactions.…”

“…All kinetic measurements were performed under pseudo-first order conditions with L-lysine (4x10 -4 mol dm -3 to 1.2x10 -3 mol dm -3 ) having constant KMnO 4 (2x10 -4 mol dm -3 ), ionic strength (0.50 mol dm -3 ). The reaction was initiated by previously mixed thermally equilibrated solution of of MnO 4 -, Cu(II)/ Ni(II)/ Zn(II) and L-lysine and required quantities of sodium hydroxide and sodium perchlorate at difference temperature ranges (273K -308K).…”

“…Among the six oxidation states of manganese (+2 to +7) permanganate Mn(VII) is the most potent oxidation state in acid as well as in alkaline medium [1][2][3] . The mechanism by which the multivalent oxidant oxidizes substrate depends not only on the substrate but also on the medium 4 used for the study. In strongly alkaline medium, the stable reduction products 5,6 of the permanganate ion (MnO 4 -) is manganate ion (MnO 4…”

Study of Nickel (II) Catalysed Oxidation of Glycylglycine by Heptavalent Manganese: A Kinetic Study

“…Among the six oxidation states of manganese (+2 to +7), permanganate, Mn(VII) is the most potent oxidation state in acid as well as in alkaline medium [1][2][3][4][5][6][7][8][9][10]. The mechanism by which the multivalent oxidant oxidizes a substrate depends not only on the substrate but also on the medium [11] used for the study. In strongly alkaline medium, the stable reduction product [12][13][14][15] of the permanganate ion is manganate ion, MnO 4 2-.…”