Propane ions, decomposition

The lifetimes of ions studied by ion cyclotron resonance (ICR) are commonly of the order of milliseconds [254], In terms of eqn. (9), the limits tx and t2 of the observation window are zero and of the order of milliseconds, respectively. Reactive ions of longer lifetimes are not distinguished from those with the more usually encountered lifetimes (< /is). Using ICR, it has been found that decomposition of the molecular ion of 1, 5-hexadiyne (c.f. Sect. 5.7) to lose H occurs predominantly at times greater than microseconds [344], An ICR mass spectrometer constituting the second half of a tandem mass spectrometer has been used to study decomposition of propane ions up to times of milliseconds [775], The observation window in this case extended from tx — /is to... 

On the other hand, the formation of ethylene was ascribed mainly to the unimolecular decomposition of a neutral excited propane molecule. These interpretations were later confirmed (4) by examining the effect of an applied electrical field on the neutral products in the radiolysis of propane. The yields of those products which were originally ascribed to ion-molecule reactions remained unchanged when the field strength was increased in the saturation current region while the yields of hydrocarbon products, which were ascribed to the decomposition of neutral excited propane molecules, increased several fold because of increased excitation by electron impact. In various recent radiolysis 14,17,18,34) and photoionization studies 26) of hydrocarbons, the origins of products from ion-molecule reactions or neutral excited molecule decompositions have been determined using the applied field technique. However, because of recent advances in vacuum ultraviolet photolysis and ion-molecule reaction kinetics, the technique used in the above studies has become somewhat superfluous. 

Alkaline earth oxides (AEO = MgO, CaO, and SrO) doped with 5 mol% Nd203 have been synthesised either by evaporation of nitrate solutions and decomposition, or by sol-gel method. The samples have been characterised by chemical analysis, specific surface area measurement, XRD, CO2-TPD, and FTIR spectroscopy. Their catalytic properties in propane oxidative dehydrogenation have been studied. According to detailed XRD analyses, solid solution formation took place, leading to structural defects which were agglomerated or dispersed, their relative amounts depending on the preparation procedure and on the alkaline-earth ion size match with Nd3+. Relationships between catalyst synthesis conditions, lattice defects, basicity of the solids and catalytic performance are discussed. 

Combining thianthrene radical ion(l+) with free radicals to produce thianthrenium salts has also been achieved. Decomposition of various cumene hydroperoxides (83MI6) and of azobis(2-phenoxy-2-propane) (85MI1) gave 5-arylthianthrenium ions together with 5-(propen-2-yl)thianthrenium perchlorate in the latter case. 

Under ordinary mass spcctrometric conditions only unimolecular reactions of excited ions occur, but at higher ionization chamber pressures bimolecular ion molecule reactions are observed in which both the parent ions and their unimolecular dissociation product ions are reactants. Since it requires a time of 10 5 sec. to analyze and collect the ions after their formation all of the ions in the complete mass spectrum of the parent molecule are possible reactants. However, in radiation chemistry we are concerned with the ion distribution at the time between molecular collisions which is much shorter than 10 5 sec. For example, in the gas phase at 1 atm. the time between collisions is 10 10 sec. and in considering the ion molecule reactions that can occur one must know the amount of unimolecular decomposition within that time. By utilizing the quasi-equilibrium theory of mass spectra6 it is possible to calculate the ion distribution at any time. This has been done for propane at a time of 10 10 sec.,24 and although the parent ion is increased by a factor of 2 the relative ratios of the other ions are about the same as in the mass spectrum observed in 10 r> sec. Thus for gas phase radiolysis the observed mass spectrum is a fair first approximation to the ion distribution. In... 

Primary alcohols in particular give an M — 18 peak due to loss of water from the molecular ion although this peak may partly arise from thermal decomposition of the alcohol in the ion source. Initial migration of a hydrogen on the alkyl chain is followed by cleavage of the carbon-oxygen bond, see, for example, the spectrum of propan-l-ol, Fig. 3.81, which shows strong peaks at m/z 59, 42, 31... 

The effect of electrical fields on the radiolysis of ethane has been examined by Ausloos et and this study has shown that excited molecules contribute a great deal to the products. The experiments were conducted in the presence of nitric oxide, and free-radical reactions were therefore suppressed. The importance of reactions (12)-(14) was clearly demonstrated by the use of various isotopic mixtures. Propane is formed exclusively by the insertion of CH2 into C2H6 and the yield is nearly equal to the yield of molecular methane from reaction (14). Acetylene is formed from a neutral excited ethane, probably via a hot ethylidene radical. Butene and a fraction of the propene arise from ion precursors while n-butane appears to be formed both by ionic reactions and by the combination of ethyl radicals. The decomposition of excited ethane to give methyl radicals, reaction (15), has been shown by Yang and Gant °° to be relatively unimportant. The importance of molecular hydrogen elimination has been shown in several studies ° °. ... 

The rare-gas sensitized radiolysis of propane has been studied in the gas phase and in the liquid phase". Charge transfer from the rare-gas ion to propane is followed by ionic reactions. In particular, the decomposition of C3H8 to give CH4 by reaction (4) is important, as is the ion-molecule reaction of C2H5 with propane to give ethane by reaction (7). 

The volume of activation of AnI (and iil)-like reactions is around -10 to -20mLmoN as the separation of charges polarises solvent molecules and pulls them in to solvate the new ions, a process known as electrostriction. Therefore, increasing pressure disfavours homolytic and favours heterolytic pathways. The plots of rate of decomposition of cyclohexanol nitrate or propane-1,2-diol dinitrate versus applied pressure at 170 °C are U-shaped, with a minimum between 0.4 and 0.8 GPa, in accord with a change in mechanism... 

Preliminary results with a manganese-substituted Keggin ion catalyst that has an extremely stable PWi 1039 - backbone (Figure 1), shows some promise with small hydrocarbons(l). This catalyst can be heated to 65 °C for long periods without decomposition. An initial experiment with ethane and t-butyl hydroperoxide in benzene gave 2 turnovers of ethane to ethanol in three hr at 65 °C, while with propane the turnover number was 24 and provided isopropanol and n-propanol in a 5 1 ratio (Table m). 

Zinc polar plane [0001] where zinc ions are more outwardly positioned than oxygen ions oxygen polar plane [0001], where ions are more outwardly positioned than zinc ions, and the non polar prismatic plane [1010], where both zinc and oxygen ions are on the same plane. They have reported that catalytic decomposition of propan-2-ol was highest on [0001] polar surface of zinc oxide. It is further reported that catalyst morphology and activity is influenced by zinc oxide precursors [8]. 

Bowker et al.[12] have concluded that adsorption occurs only on [0001] face of zinc oxide and hence represents the active face. Also surface defects are reported to be present on the two polar surfaces[13,14], Akhter et al.[7] have shown that alcohols interact most strongly with zinc polar surface wherein the surface dipoles are pointing outwards. Berlowitz and Kung[6] have further shown that the decomposition rates of propan-2-ol were 3-5 times higher on zinc polar surface than 0-polar surface. Watos et al.[15] have concluded that charge of a surface zinc ion decreases as [0001] > [1010] > [0001] plane, making the latter plane most metallic. 

DFP is stable and in the absence of moisture can be stored for considerable periods without decomposition. Hydrolysis in neutral aqueous solution occurs slowly. The reaction is catalyzed by both acid and base. At pH>7, hydrolysis is proportional to the hydroxide ion concentration and at high pH is extremely rapid. The product is always diisopropyl phosphoric acid (equation 38), except under more forcing conditions which eventually produce phosphate (and propan-2-ol). The hydrolysis is strongly catalyzed by the addition of a-effect nucleophiles such as hypochlorite, peroxide, hydroxylamine, hydroxamic acid and their substituted derivatives . Under basic conditions, such nucleophiles (HOX) are present as the anion and are responsible for the rapid initial displacement of fluoride ion from DFP to give intermediate 36 shown in equation 39. Displacement of OX by hydroxide ion regenerates the catalytic OX anion. The reaction with hydrogen... 

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