Acetone electron transfer rate

Holm and Crossland reported the product distribution (Scheme 5 and Table 1) in a reaction between f-BuMgCl and benzophenone. While the 1,2-addition affords the normal product, 1,6- and 1,4-additions should involve the fert-butyl radical for ortho- and para-additions, and the mechanism involves a single-electron transfer (SET). The product distribution indicates that the more sterically crowded benzophenones give more of the SET products. Ashby and Smith ° obtained relative rates for reactions of acetone and benzophenone (Table 2). Noteworthy is that those ketones have opposite reactivity orders toward R MgCl for the R variation. 

The radiation chemistry of 2-propanol is analogous to that of methanol, that is, the main reactive species are Cs and (CH3)2 COH. In alkaline solution, (CH3)2 COH deprotonates to (CH3)2CO . In the presence of N2O or acetone, es is converted to (CH3)2 C0H/(CH3)2C0 by the reactions in Eqs. 30 and 18, or the reaction of Eq. 20, respectively. The solvated electron in 2-propanol has been utilized to study electron-transfer reactions between aromatic radical anions (donor) and aromatic molecules (acceptor) [16]. The donor-acceptor pairs studied were pyrene-anthracene, pyrene-9,10-dimethylanthracene and w-terphenyl-/ -terphenyl. In the first two cases an equilibrium was established and the parameters forward and kback were measured this was the first example of the measurement of an equilibrium constant by use of pulse radiolysis. The rate constants for the electron-transfer reactions were examined in terms of the Marcus theory [17]. 

Would the tricarbonyl manganese function in monomer 8 prevent homopolymerization, or undergo electron transfer from manganese to the propagating radical center Homopolymerization kinetic studies in benzene, benzonitrile, and acetone demonstrated that the effect of manganese was different than that of iron in 1. The rate law was three halves order in the concentration of monomer 8 and half-order in initiator concentration.53... 

Radha and Swamy (278) proposed a possible mechanism for the dehydrogenation of 2-propanol over La2MnM06 (M = Co, Ni, Cu). These authors found that admission of H2, together with the alcohol, does not have any influence on the reaction rate however, admission of acetone with 2-propanol decreases the reaction rate at all partial pressures. It can be inferred that H2 acts as a mere diluent whereas acetone has an inhibiting effect that may be due to its slow desorption. They also measured the conductivity changes of the catalyst in the presence of the reactants or products of the dehydrogenation. As a result of these studies it was concluded that the catalyst surface is covered predominantly with acetone under reaction conditions. Because acetone adsorbs by a donor-type mechanism, as shown by the decrease of the conductivity on its adsorption, its desorption involving electron transfer from the p-type semiconductor catalyst to the adsorbed species can be expected to be the slow process. 

When very dilute solutions of benzophcnonc in ether (pseudo first-order concentrations) react with solutions of /-butyl- and isopropylniagnc-sium halide of increasing concentrations, a rate-levelling effect is observed at 0.1-0.2 M 26 The use of benzophenone in excess leads to extremely high reaction rates. These phettomena are of course remini.scent of the complex-type kinetics of acetone 42. As will be described below, /-butyl- and isopropylmagnesium halides react with benzophenone by an ET-radical mechanism (ET is electron transfer) and acetone by a concerted mechanism. It therefore seems strange to have complex effects for both. 

Much of the kinetic work has been concerned with the oxidation of isopropyl alcohol to acetone in aqueous sulphuric or acetic acids. The rate-determining step definitely involves the breaking of a carbon-hydrogen bond, as isopropyl alcohol is oxidised 6-7 times faster than its 2-deutero derivative . At all acidities, the rate of oxidation shows a first-order dependence on both the concentration of HCr04 and the alcohol, but the dejiendence on [H] varies. In dilute acidic solution the rate is proportional to [H] , to [H] in more concentrated solution and to Ho in 20-60% aqueous sulphuric acid . These observations are consistent with two mechanisms (i) a bimolecular electron transfer process (218) ,... 

Hexachlorobenzene was very slowly photolyzed by direct or acetone-sensitized mechanisms (Choudry and Hutzinger, 1984), but it was photodecomposed much more rapidly (10-6(K)x) in the presence of various amine and indole derivatives (Hirsch and Hutzinger, 1989). Pentachlorobenzene was the only product identified in the amine experiments. Although no mechanistic speculations were engaged in by the authors, it appears plausible that electron transfer within ir-bonded complexes in the excited state could account for the observed rate enhancements. 

The electron self-exchange rate constants for several Fe(II)/Fe(III) porphyrin couples have been measured by H NMR line-broadening techniques in 5 1 acetone/water at -20 The relative rate constants for the [Fe(P)(l-MeIm)2] couples, P = octaethylporphyrin chlorin < isobacteriochlorin, have been attributed to differences in outer-sphere reorganization, related to the steric bulk. The rate-determining step in the metallopophyrin-catalyzed reductions of dioxygen by substituted ferrocenes is the electron transfer between the ferrocene and the metalloporphyrin (M = Fe, Co, and The Marcus relationship provides a... 

The addition of anions derived from malonate diester was studied recently (Fig. 7). Diethyl malonate adds to chalcone in the presence of catalytic amounts of potassium hydroxide and the rate is strongly influenced by sonication. The reaction is completed within 5 min at room temperature in toluene. Such a sensitivity suggested a sonication-induced change of mechanism, confirmed by experiments in the presence of catalytic amounts of DPPH. This radical scavenger partially inhibits the addition the existence of competitive chain electron transfer and polar mechanisms is suggested. Direct evidence is, however, missing. The additions of ethyl cyanoacetate, ethyl acetylacetate, and acetyl-acetone anions display similar characteristics, but the differences between the sonochemical and silent processes are less pronounced. 

Although the nature of this intermediate is not directly established, the determination of ki ( 551 moF s ) in acetone favours a radical-cation species rather than an ion pair whose rate of formation would be diffusion controlled. Direct reaction of [Fe(phen)3] + with SCN to form SCN is thermodynamically unfavourable and this initial complex formation probably serves to lower the potential energy for subsequent electron transfer. The overall rate constants kzkijk-T) obey the Marcus free-... 

The authors noticed no C-H/C-D isotope effect for the reaction of 13 with methanol and ferf-butanol, but saw a KIE k Jk = 1.4) for the O-H/O-D bond, suggesting that the stronger O-H bond is activated preferentially over the weaker C-H bonds (Pig. 12). In addition, the authors observed the formation of acetone upon the oxidation of tert-butanol. Upon comparison of rate constants (which have been normalized to account for the amount of hydrogens available for abstraction), tert-butanol reacts 50 times faster than cyclohexane. The authors propose a proton-coupled electron transfer event is responsible for the observed selectivity this complex represents a rare case in which O-H bonds may be homolyzed preferentially to C—H bonds. In further study, 13 was shown to oxidize water to the hydroxyl radical by PCET [95]. Under pseudo-first-order conditions, conversion of 13 to its one-electron reduced state was found to have a second-order dependence on the concentration of water, in stark contrast to the first-order dependence observed for aUphatic hydrocarbons and alcohols. Based on the theimoneutral oxidation of water (2.13 V v. NHE in MeCN under neutral conditions [96]) by 13 (2.14 V V. NHE in MeCN under neutral conditions) and the rate dependence, the authors propose a proton-coupled electron transfer event in which water serves as a base. While the mechanism for O-H bond cleavage of alcohols and water is not well understood in these instances, the capacity to cleave a stronger O-H bond in the presence of much weaker C-H bonds is a tremendous advance in metal-oxo chemistry and represents an exciting avenue for chemoselective substrate activation. 

Much attention has been paid to the chemistry and biological chemistry of singlet dioxygen and superoxide ion. The lifetime of the former species, known to be solvent-dependent, is much increased for deuterated acetone, acetonitrile, benzene and chloroform compared to the undeuterated solvent. This is a remarkable solvent deuterium isotope effect. Electron transfer to 02 from tetramethylphenylenediamine to give superoxide has been confirmed, the rate of reaction being close to the diffusion-controlled limit. Kinetic studies on the photochemical formation of superoxide from jU-superoxodecacyanodicobalt(III) ions and oxygenated ethanol solutions have been reported. 

---