Oxygen ions with hydrocarbons

Table II. Stoichiometric Reactions of Oxygen Ions with Hydrocarbons on MgO ...

The paramagnetic oxygen ions 0 , 01> and 0J have been formed on magnesium oxide and studied by EPR spectroscopy. The reactivity of these ions with hydrocarbons follows the sequence 0 >>03> >02. Both with alkanes and alkenes the initial reaction is thought to be hydrogen atom abstraction. 

Two reviews address the reactions of bare transition metal atoms and ions with hydrocarbons in the gas phase and the reactions of monosubstituted alkanes with bare transition metal ions. 2 A study of the reactivity of ground-state, neutral transition metal atoms from the left hand side of the 4d series (Y through Mo) shows that they are unreactive towards linear alkanes but that they will react with cyclopropane and alkenes.3 Atomic metal cations form a 1 1 adduct with tribenzocyclotriyne in a Fourier-transform ion cyclotron resonance spectrometer. Reaction of molecular oxygen with M(C2H4) results in ligand exchange to M02 for the early first row transition metals. Activation of the O—O bond and product formation is observed for ccnnplexes of Sc+,Ti+andV+.5... 

The metal-ion complexmg properties of crown ethers are clearly evident m their effects on the solubility and reactivity of ionic compounds m nonpolar media Potassium fluoride (KF) is ionic and practically insoluble m benzene alone but dissolves m it when 18 crown 6 is present This happens because of the electron distribution of 18 crown 6 as shown m Figure 16 2a The electrostatic potential surface consists of essentially two regions an electron rich interior associated with the oxygens and a hydrocarbon like exterior associated with the CH2 groups When KF is added to a solution of 18 crown 6 m benzene potassium ion (K ) interacts with the oxygens of the crown ether to form a Lewis acid Lewis base complex As can be seen m the space filling model of this... 

Inclusion of additional alkyl groups on the aromatic ring leads to decongestants with longer duration of action. Thus, reaction of the arylacetonitrile, 109, obtainable from hydrocarbon, 107, by chloromethylation (108), followed by displacement of the halogen by means of cyanide ion with ethylenediamine, leads to xylometazoline (111). The analogous reaction of the oxygenated derivative, 110, affords oxymetazoline (112). ... 

Comparison of Reactions Involving Oxygen Ions on MgO. One of the most significant observations in this series of studies was the large difference in the reactivities of the three forms of oxygen ions on MgO. Taking ethylene as an example, 0 ions reacted readily at -60°C and 07 ions reacted at 25°C with a half-life of 5 min., whereas about two-thirds of the 07 ions remained unreacted after contact with CaHi at 175°C for 2 h. These results, which are qualitatively the same for other simple hydrocarbons, indicate that the order of reactivity is 0 07 07. 

A solid oxide fuel cell (SOFC) consists of two electrodes anode and cathode, with a ceramic electrolyte between that transfers oxygen ions. A SOFC typically operates at a temperature between 700 and 1000 °C. at which temperature the ceramic electrolyte begins to exhibit sufficient ionic conductivity. This high operating temperature also accelerates electrochemical reactions therefore, a SOFC does not require precious metal catalysts to promote the reactions. More abundant materials such as nickel have sufficient catalytic activity to be used as SOFC electrodes. In addition, the SOFC is more fuel-flexible than other types of fuel cells, and reforming of hydrocarbon fuels can be performed inside the cell. This allows use of conventional hydrocarbon fuels in a SOFC without an external reformer. 

Oxygen ions thus created migrate selectively through the membrane to the anode, where they undergo a similar half-cell reaction with a gaseous fuel (either H2, syngas, or a hydrocarbon) to produce H2O and CO2. The flow of electrons liberated and consumed at the anode and cathode, respectively, deliver some portion of the reversible work of the reaction to the... 

Hope et al. (116) presented a combined volumetric sorption and theoretical study of the sorption of Kr in silicalite. The theoretical calculation was based on a potential model related to that of Sanders et al. (117), which includes electrostatic terms and a simple bond-bending formalism for the portion of the framework (120 atoms) that is allowed to relax during the simulations. In contrast to the potential developed by Sanders et al., these calculations employed hard, unpolarizable oxygen ions. Polarizability was, however, included in the description of the Kr atoms. Intermolecular potential terms accounting for the interaction of Kr atoms with the zeolite oxygen atoms were derived from fitting experimental results characterizing the interatomic potentials of rare gas mixtures. In contrast to the situation for hydrocarbons, there are few direct empirical data to aid parameterization, but the use of Ne-Kr potentials is reasonable, because Ne is isoelectronic with O2-. 

This concludes the discussion of the stabilities of carbocations with hydrocarbon-based structures and also of different methods for deriving equilibrium constants to express these stabilities. The remainder of the chapter will be concerned mainly with measurements of stabilities for oxygen-substituted and metal ion-coordinated carbocations. Consideration of carbocations as conjugate acids of carbenes and derivations of stabilities based on equilibria for the ionization of alkyl halides and azides will conclude the major part of the chapter and introduce a discussion of recent studies of reactivities. 

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