Hydrocarbons atom transfer from

Hydrogen Atom Transfer from Hydrocarbons to Peroxy Radicals. The ready conversion of one chain carrier to another in hydrocarbon oxidations by the addition of a hydroperoxide is illustrated in Table VII. 

Steric effects in oxidation are found primarily in the H-atom donor as, for example, isobutane versus 2,4-dimethylpentane where both co-oxidation and added hydroperoxide measurements indicate isobutane to be 1.4 times as reactive toward either R02 radical [38,39], For a series of branched alkanes, the value of kp was more sensitive to changes in steric bulk on the adjacent carbon than on the same carbon but all values were within a factor three [39], Increasing size in f-R02 radicals has little effect on the value of kp for H-atom transfer from primary, secondary or tertiary sites [69]. However, kp for a given hydrocarbon does increase by a factor of about 5—10 as R02 is changed from a tertiary to secondary or primary ROa [78], Moreover, in the oxidation of aromatic compounds, the ratio of kp s for H-atom transfer to parent R02- and to f-Bu02-correlate with meta substituent constants which suggests that this difference in reactivity is due mainly to polar effects [86]. 

The primary motivation for these studies is the analysis of the reactivity patterns of organic compounds, when Ce(IV) is used as an oxidant. These patterns are determined for the most part by product analysis of selected series of organic compounds. The results obtained in two studies that bear more directly on the chemical behavior of Ce(IV) as an oxidant for hydrocarbons have been interpreted to indicate different mechanistic behavior of Ce(IV). In a product study of the oxidation of isodurene (1,2,3,5-tetramethyl benzene) by ceric ammonium nitrate compared to anodic oxidation, Eberson and Oberrauch (1979) concluded that the oxidation by Ce(IV) occurs via a H atom transfer from the alkylaromatic compound to Ce(IV). Badocchi et al. (1980) measured the variation of second-order rate constants for the oxidation of a series of alkylaromatic compounds with added Ce(III). These results along with those from the determination of kinetic deuterium isotope effect were dted to support a mechanism involving radical cations. The Ce(IV)/Ce(III) functions as an electron acceptor/donor in such a mechanism. 

Khenkin and Neumann discovered that SET from polycyclic arenes to a mixed-addenda heteropoly acid (HPA), Hj[PV2M0jj 0 (j], can be followed by oxygen atom transfer from the HPA to the radical cation (Scheme 14.7) [38], This type of reactivity is well known in the area of heterogeneous gas-phase oxidation as a Mars-van Krevelen mechanism, whereby a metal oxide at high temperature transfers oxygen atom from the lattice to an activated hydrocarbon substrate, but in homogeneous catalysis, it is veiy rare. 

The atom and bond concepts dominate chemistry. Dalton postulated that atoms retained their identities even when in chemical combinations with other atoms. We know that their properties are sometimes transferable from one molecule to another for example, the incremental increase in the standard enthalpy of formation of a normal hydrocarbon per CHj group is —20.6 1.3 kJmol . We also know that more often there are subtle modifications to the electron density. 

Chipot C, Angyan JG, Ferenczy GG, Scheraga HA (1993) Transferable net atomic charges from a distributed multipole analysis for the description of electrostatic properties — a case-study of saturated-hydrocarbons. J Phys Chem 97(25) 6628—6636... 

We propose that the first step in the formation of quinones, as shown in Scheme 3 for BP, involves an electron transfer from the hydrocarbon to the activated cytochrome P-450-iron-oxygen complex. The generate nucleophilic oxygen atom of this complex would react at C-6 of BP in which the positive charge is appreciably localized. The 6-oxy-BP radical formed would then dissociate to leave the iron of cytochrome P-450 in the normal ferric state. Autoxidation of the 6-oxy-BP radical in which the spin density is localized mainly on the oxygen, C-l, C-3 and C-12 (19,20) would produce the three BP diones. 

In addition to the ability to react nonspecifically with hydrocarbons, active nitrogen can readily participate in energy transfer reactions with volatile organometal-lic compounds, leading to atomic emission from the metal atom. By use of appropriate optical filters, selective detection of elements such as aluminum, lead, tin, and mercury has been achieved in the presence of large excesses of organics [58],... 

Radical ion pairs also react by proton, atom, or group transfer. We illustrate proton transfer in reactions of aromatic hydrocarbons with tertiary amines. These reactions cause reduction or reductive coupling. In the reduction of naphthalene, the initial ET is followed by H" transfer from cation to anion, forming 67 paired with an aminoalkyl radical the pair combines to generate... 

All these data are in favor of a homolytic mode of oxygen transfer from Vv alkyl peroxides to hydrocarbons, and the mechanism suggested in Scheme 4, based on that of oxidation by Vv-peroxo complexes (Scheme 2), was tentatively attributed to a biradical V17 — OR—O species which can add to arenes and abstract hydrogen atoms from alkanes. It is probable that the absence of a releasable coordination site adjacent to the triangular alkyl peroxide group in (22) precludes the possibility of the alkene coordination to the metal and therefore prevents its heterolytic epoxi-dation. 

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