Hydrocarbons linear, activation

The reported results for the adsorption of linear hydrocarbons on activated carbons indicate a general relationship between the amount adsorbed, measured by the specific retention volumes, Vj, and a molecular parameter of the adsorbate related with its molecular weight (boiling point, polarizability or number of carbon atoms) [7-12]. In the case of linear polar molecules, Vg is related to the orientation polarization [13]. 

The kinetics of this C-H activation process have been studied in a series of hydrocarbons, " establishing that (i) linear hydrocarbons are activated faster than their cyclic congeners, a fact attributed to preferential activation of primary, over secondary C H functions, and (ii) aryl C H activation is significantly slower, due to the intermediate being a strongly bound re-arene complex. 

Work in this laboratory has shown also that the Ru(poip)(0)2 complexes (porp = TMP, TDCPP, and TDCPP-Clg) are practically inactive for thermal 02-oxygenation of saturated hydrocarbons . Some activity data for 0.2 mM Ru solutions in benzene under air at 25°C for optimum substrates such as adamantane and triphenylmethane at 6 mM did show selective formation of 1-adamantol and trityl alcohol, respectively, but with turnover numbers of only -0.2 per day the maximum turnover realized was -15 after 40 days for the TDCPP system Nevertheless, this was a non-radical catalytic processes there was < 10% decomposition of the Ru(TDCPP)(0)2, and a genuine O-atom transfer process was envisaged . Quite remarkably (and as mentioned briefly in Section 3.3), at the much lower concentration of 0.05 mM, Ru(TDCPP-Clg)(0)2 in neat cyclooctene gave effective oxidation. For example, at 90°C under 1 atm O2, an essentially linear oxidation rate over 55 h gave about -70% conversion of the olefin with - 80% selectivity to the epoxide however, the system was completely bleached after - 20 h and, as the activity was completely inhibited by addition of the radical inhibitor BHT, the catalysis is operating by a radical process, but in any case the conversion corresponds to a turnover of 110,000 As in related Fe(porp) systems (Section 3.3, ref. 121), the Ru(porp) species are considered to be very effective catalysts for the decomposition of hydroperoxides (eqs. 

FIG. 5 The linear dependences [Eq. (54)] for the adsorption of binary mixtures of hydrocarbons on active carbon (Nuxit-AL) at 293 K ethylene-methane (right semiclosed circles), ethylene-propylene (top semiclosed circles), ethane-methane (bottom semiclosed circles), ethane-ethylene (open circles), and ethane-propane (closed circles). The symbol i(12) denotes the partial adsorbed amount of the ith component. [Reprinted fiom M. Jaroniec, Adsorption from multicomponent gas mixtures on sohd surfaces. Thin Solid Films, 77 273-304 (1980), with permission from Elsevier Science.]... 

In most cases, this is precisely the reaction that limits chain propagation and determines the oxidation rate. Since the strength of the O—bond in hydroperoxide is independent of the structure of the alkyl substituent R and even of the replaconent of R by H, then reaction (2) is exothermic for hydrocarbons with Z)r h < roo— 365 kJ/mol (olefins, alkylaromatic hydrocarbons) and endothermic for hydrocarbons with )r h > 365 kJ/mol (paraffinic and naphthenic hydrocarbons). The activation energy of this reaction is related by a linear correlation to At-n... 

The finding that highly deactivated aromatics do not react with N02 salts is in accord with the finding that their greatly diminished TT-donor ability no longer snffices to polarize NOi. Similarly, (j-donor hydrocarbons such as methane (CH4) are not able to affect such polarization. Instead, the linear nitronium ion is activated by the superacid. Despite the fact that is a small, triatomic cation, the 11011-... 

Since the interaction of linear hydrocarbons is dominated by the van der Waals interaction with the zeohte, the apparent activation energies for cracking decrease hnearly with chain length. In some cases, differences in the overall rate are not dominated by differences in the heat of adsorption but instead are dominated by differences in the enthrones of adsorbed molecules. 

Linear relations between the activation energies and heats of adsorption or heats of reaction have long been assumed to be valid. Such relations are called Bronsted-Evans-Polanyi relations [N. Bronsted, Chem. Rev. 5 (1928) 231 M.G. Evans and M. Polanyi, Trans. Faraday Soc. 34 (1938) 11]. In catalysis such relations have recently been found to hold for the dissociation reactions summarized in Pig. 6.42, and also for a number of reactions involving small hydrocarbon fragments such as the hydro-... 

The lack of steric effects in oxidations of hydrocarbons by Cr(VI) renders D and E unacceptable. The activated complex of scheme C is non-linear and hence does not comply with the magnitude of the observed isotope effect. Two pieces of evidence are quoted which indicate A to be the more probable of the remaining two. Firstly, the p constant of —1.17 is more in agreement with that obtained for bromine atom abstraction from toluenes (—1.369 to —1.806) than those found for solvolyses involving electron-deficient carbon ( — 2.57 to —4.67) . Secondly, the correlation between the relative rates of oxidation of the series... 

Ceresine is the white end-product of the purification of the fossil wax ozokerite, which is found in Miocene lignite deposits at considerable depths, by the separation of foreign and resinous matter and decolorisation by active agents. It is harder than paraffin wax, and has linear and cyclic hydrocarbons with high molecular weight [2]. It is used for waterproofing and oil absorption. 

The enthalpy of the R02 + RH reaction is determined by the strengths of disrupted and newly formed bonds AH= Z>R H—Droo—h- For the values of O—H BDEs in hydroperoxides, see the earlier discussion on page 41. The dissociation energies of the C—H bonds of hydrocarbons depend on their structure and vary in the range 300 - 440 kJ mol-1 (see Chapter 7). The approximate linear dependence (Polany-Semenov relationship) between activation energy E and enthalpy of reaction AH was observed with different E0 values for hydrogen atom abstraction from aliphatic (R1 ), olefinic (R2H), and alkylaromatic (R3H) hydrocarbons [119] ... 

The linear dependence between the activation energy of decomposition of the azocompounds RN2R and the BDE of the R—H bond (D(R—H)) was established [3], The rate constants of the decomposition of azo-compounds in the gas phase and hydrocarbon solvents have close values. The mean value of the rate constant of AIBN decomposition in hydrocarbon and aromatic solutions was recommended to bekd= 1015 x exp(— 127.5/RT) s-1 [2], The values of the activation energies and the rate constants of the decomposition of azo-compounds in the gas and liquid phases can be found in the Handbook of Radical Initiators [4],... 

IT -cyclopentad ienyldicar bony 1 cobalt, CpCo(C0)2 This material is active in the hydrogenation of CO to saturated linear hydrocarbons and appears to retain its "homogeneous", mononuclear character during the course of its catalysis. 

A variety of solid acids besides zeolites have been tested as alkylation catalysts. Sulfated zirconia and related materials have drawn considerable attention because of what was initially thought to be their superacidic nature and their well-demonstrated ability to isomerize short linear alkanes at temperatures below 423 K. Corma et al. (188) compared sulfated zirconia and zeolite BEA at reaction temperatures of 273 and 323 K in isobutane/2-butene alkylation. While BEA catalyzed mainly dimerization at 273 K, the sulfated zirconia exhibited a high selectivity to TMPs. At 323 K, on the other hand, zeolite BEA produced more TMPs than sulfated zirconia, which under these conditions produced mainly cracked products with 65 wt% selectivity. The TMP/DMH ratio was always higher for the sulfated zirconia sample. These distinctive differences in the product distribution were attributed to the much stronger acid sites in sulfated zirconia than in zeolite BEA, but today one would question this suggestion because of evidence that the sulfated zirconia catalyst is not strongly acidic, being active for alkane isomerization because of a combination of acidic character and redox properties that help initiate hydrocarbon conversions (189). The time-on-stream behavior was more favorable for BEA, which deactivated at a lower rate than sulfated zirconia. Whether differences in the adsorption of the feed and product molecules influenced the performance was not discussed. 

Ru" (0)(N40)]"+ oxidizes a variety of organic substrates such as alcohols, alkenes, THE, and saturated hydrocarbons. " In all cases [Ru (0)(N40)] " is reduced to [Ru (N40)(0H2)] ". The C— H deuterium isotope effects for the oxidation of cyclohexane, tetrahydrofuran, 2-propanol, and benzyl alcohol are 5.3, 6.0, 5.3, and 5.9 respectively, indicating the importance of C— H cleavage in the transitions state. For the oxidation of alcohols, a linear correlation is observed between log(rate constant) and the ionization potential of the alcohols. [Ru (0)(N40)] is also able to function as an electrocatalyst for the oxidation of alcohols. Using rotating disk voltammetry, the rate constant for the oxidation of benzyl alcohol by [Ru (0)(N40)] is found to be The Ru electrocatalyst remains active when immobilized inside Nafion films. 

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