Homologation of alkanes

Zirconium hydride(s) supported on oxide materials catalyze several classical reactions such as hydrogenation, reductive cyclizahon, cyclo-trimerization and olefin polymerization [43-47]. Notably, it also catalyzes the hydrogenolysis of polyolefins 

Since Zr-H is able both to (i) activate the C-H bonds of alkanes (via cr-bond metathesis) [15, 48] and to carry out their hydrogenolysis (transfer of a least two carbons via a P-alkyl transfer) and (ii) polymerize olefins (via insertion), the ability of such supported Zr-H was tested in the homologation of propane. 

The branched-to-linear ratio of higher homo logs is similar to those observed in a batch reactor (mainly branched alkanes). 

Second, when the flow rate is changed over a wide range (0-8mLmin ), conversion varies linearly with contact time, which indicates that chemical rates are being measured and that the extrapolated selectivities at zero contact time provide information about the reaction mechanism. The primary products are H2 and olefins 

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Alkanesulfonates are the petrochemically derived sulfur analogs of soaps, which are alkane carboxylates based on renewable resources. The main difference between alkanesulfonates and soaps is, however, that alkanesulfonates consist of a rather complex mixture of homologs with different carbon chain lengths and isomers with an almost statistical distribution of the functional group along the hydrophobic carbon chain (Fig. 1), whereas soap is a mixture of homologs of alkane 1-carboxylates with an even number of carbon atoms. 

Paraffin wax is a chemical substance obtained as a residue from the distillation of petroleum and is made up of higher homologs of alkanes with a melting range of 50—90°C. 

Simonetti DA, Ahn JH, Iglesia E. Catalytic co-homologation of alkanes and dimethyl ether and promotion by adamantane as a hydride transfer co-catalyst. ChemCatChem 2011 3 704-18. 

Fig. 17. An homologous series of alkane probes is generally used because good values for their adsorbed molar areas are available [87]. The linearity of the plot (the alkane line ) lends credence to the procedure.

FIG. 20 CT-lg c Isotherms of homologous sodium alkane 1-sulfonates in water at 45 °C. , Decane 1-sulfonate , dodecane 1-sulfonate , tridecane 1-sulfonate a, tetradecane 1-sulfonate x, pentadecane 1-sulfonate. 

In the homologous series of alkane 1-sulfonates, micellization in aqueous solutions begins with the pentanesulfonate at cM = 1 mol/L. The critical micelle concentrations of the technical alkanesulfonates are cM = 0.002 mol/L (sulfo-chlorination route) and cM = 0.44 g/L (sulfoxidation route). 

Figure 8.5 Mass chromatogram for m/z = 71. This is obtained by running the GC-MS with the mass spectrometer set to register only ions with m/z = 71. It shows a homologous series of -alkanes.

The reaction selectivity is better under these conditions at steady state, because an equihbrated ratio is observed between the resulting higher and lower homolog alkanes. In addition, dynamic conditions allow us to vary the contact time to obtain information about primary products and then about the mechanism. It appears that, in the case of propane metathesis in a stationary regime, conversion increases Hnearly with contact time, which shows that the reaction is under dynamic control with no diffusion Hmitation. Under these conditions, decreasing contact time results in an increase of the selectivity for hydrogen and olefin whereas that of alkanes decreases. Similarly, the alkanes/olefins ratio tends to zero as the contact... 

The above mechanism, implying a bis-alkyl species, is the best way to explain (i) the observed selectivities and (ii) the primary and secondary products. It also takes into account important facts (i) the minor ](=SiO)2ZrH2] supported species (20-35% depending on the oxide support) is more electrophilic and activates C-H bonds of alkane faster than its homolog ](=SiO)3ZrH] (65-80%) [48] (ii) the higher selectivity in isobutene compared to that of methyl-branched pentenes is not consistent with a simple insertion of adsorbed propene into Zr-alkyl species because the concentration of Zr-propyl has to be greater than Zr-Me species (Scheme 3.12). 

Ruthenium catalysts prepared from Ru3(CO)i2 and other related carbonyl-derived complexes have been widely used in reactions of hydrogenolysis, homologation and dimerization of alkanes [114—116]. Catalysts derived from carbonyl precursors usually show higher catalytic activities than conventionally prepared supported mthenium catalysts. This correlates well with the smaller crystallite size achieved by using carbonyl precursors. 

One of the major results of SEC-GC-MS studies is the discovery of an orderly pattern, by which various isomers and homologs of similar chemical species exist in coal liquids. For example almost any direct coal liquefaction process produces very similar species, which differ from each other by size and extent of isomerization but with an orderly distribution pattern. Alkanes... 

Reactions of alkane-1,1-dicarboxylic acids, e.g. la, alkane-1,4-dicarboxylic acids, e.g. lb, and their longer-chain homologs with sulfur tetrafluoride afford mixtures of bis(trifluoromethyl)-alkanes, bis(pentafluoroalkyl) ethers and small amounts of polyethers.118 Total yields, generally, decrease with increasing length of the carbon chain and in the presence of C = C bonds. 

A unique example of alkane-alkene reaction is the homologation of olefins with methane in a stepwise manner over transition-metal catalysts.269 First methane is adsorbed dissociatively on rhodium or cobalt at 327-527°C then an alkene... 

Solubility-Molar Volume Relationships The correlation between aqueous solubility at room temperature and the molar volume has been studied by McAuliffe [5] for different hydrocarbon classes. He discusses linear relationships, presented as graphs, describing the decrease in solubility with increasing molar volume for the homologous series of alkanes, alkenes, alkandienes, alkynes, and cycloalkanes. 

Initially, we will be concerned with the physical properties of alkanes and how these properties can be correlated by the important concept of homology. This will be followed by a brief survey of the occurrence and uses of hydrocarbons, with special reference to the petroleum industry. Chemical reactions of alkanes then will be discussed, with special emphasis on combustion and substitution reactions. These reactions are employed to illustrate how we can predict and use energy changes — particularly AH, the heat evolved or absorbed by a reacting system, which often can be estimated from bond energies. Then we consider some of the problems involved in predicting reaction rates in the context of a specific reaction, the chlorination of methane. The example is complex, but it has the virtue that we are able to break the overall reaction into quite simple steps. 

Bond cleavage would be expected to lead to a homologous series of alkanes, alkenes, and esters to Cio if the fatty acid were oleate, but it would give higher homologs if the fatty acid were stearate. The principal products are, in fact, alkanes, alkenes, and a homologous series of methyl esters. The highest member of the alkane series found in irradiated methyl oleate... 

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