Homologation of methane

PerD32 Perry, D. The number of structural isomers of certain homologs of methane and methanol. J. Amer. Chem. Soc. 54 (1932) 2918-2920. 

Alkyl, adj. Aliphatic pertaining to a straight- or branched-chain grouping of carbon atoms derived from methane or a homolog of methane. Examples methyl, ethyl, propyl, butyl, amyl. 

The literature contains very few references, with the exception of those already noted in the pressnre oxidation of methane, to the oxidation of homologs of methane higher than ethane, such as propane, butane, and isobutane, indicative of a lack of interest in these hydrocarbons. This is probably due to the fact that much smaller quantities of the higher gaseous homologs are available at sufficiently low cost to warrant investigation, and to the extreme complexity of the resulting mixtures obtained. 

Perry D (1932) The Number of Structural Isomers of Certain Homologs of Methane and Methanol. J Am Chem Soc 54 2918... 

It should be noted at this point that primary and secondary reaction products can be distinguished not only by kinetic data (13) but also by suppression of the secondary reactions. E.g substitution of 2,2,2-trifluoroethanol for p-dioxane as solvent for HCoCCO) suppresses homologation and methane formation addition of a phosphine to give the less acidic catalyst HCo(CO)3PR3 has the same effect, as has the substitution of the less acidic catalyst HMn(CO)5. 

Reduction of C02 past formic acid generates formaldehyde, methanol or methane (Eqs. (16-18)), and ethanol can be produced by homologation of the methanol. The liberation of water makes these reactions thermodynamically favorable but economically less favorable. The reductions typically require much higher temperatures than does the reduction to formic acid, and consequently few homogeneous catalysts are both kinetically capable and able to withstand the operating conditions. 

Within the reaction parameters used, the nickel catalyst is highly selective towards carbonylation. With the exception of trace a-mounts of methane formed, no other hydrogenation product is found. This is in contrast with cobalt whose carbonylation catalytic activity is enhanced by hydrogen but generally associated with aldehyde formation and homologation. 

These species show different promoting effects on the activity and selectivity of the homologation of methyl acetate with CO + H2 (carbonylation to acetic acid, homologation to ethyl acetate and hydrogenation to methane) (5). 

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... 

Most of the investigations into disproportionation reactions have mainly concentrated on chlorofiuoro derivatives of methane and ethane. When trichlorofluoromethane is refluxed with aluminum trichloride or aluminum tribromide, dichlorodifluoromethane and carbon tetrachloride are obtained. Dichlorofluoromethane yields chlorodifiuoromethane and chloroform chlorofiuoro derivatives of ethane and longer chain homologs exhibit a tendency towards isomerization as well as disproportionation, i.e. intramolecular halogen atom exchange. In this case, both types of reaction take place simultaneously. In other words, disproportionation of l,l,2-triehloro-1.2,2-trifiuoroethane (1) forms l,l,1.2-tetrachloro-2,2-difluoroethane (2) and... 

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. 

Such an example has been demonstrated by Johnson and Sames, who chose a platinum-mediated dehydrogenation as a key step in the synthesis of the antimitotic rhazinilam 33 (Scheme 6) [20], The key intermediate 27 was converted into the imine 28, which was allowed to react with Me Pt(//-SMe2)]2 to afford the platinum complex 29. Subsequent treatment with triflic acid resulted in elimination of methane and furnished the cationic complex 30. Upon thermolysis in trifluoroethanol, the complex lost a second methane molecule, which resulted in the activation of the ethyl group. A subsequent /1-hydride elimination gave the hydrido-Pt(n) complex 31. Treatment with aqueous KCN followed by hydrox-ylamine removed the platinum and yielded the liberated amine 32. Johnson and Sames added a homologization and a macrolactamization and completed the total synthesis of rhazinilam (33) by removal of the carboxyl group. 

A variety of solvents have higher boiling points than that of water but do not have polar structures. The most accessible of these are the hydrocarbons, which come in a series from the smallest (methane) to higher homologs (ethane, propane, butane, and so on) and are abundant in the solar system. Methane, ethane, propane, butane, pentane, and hexane have boiling points of about 109, 184, 231, 273, 309, and 349 K, respectively, at standard terran pressure. Thus, at a mean surface temperature of 95 K, methane (which freezes at 90 K) would be liquid, implying that oceans of methane could cover the surface of Titan. 

This is unlikely, however, since in methanol homologation studies, methane is generated preferentially, even when there are comparable amounts of methanol and ethanol present in the reaction media (55). Acetic acid decarboxylation has also been suggested as a pathway for methane formation ... 

The behavior of methane is different from the higher homologs in that the hot insertion product, CH4S undergoes extensive, pressure-independent fragmentation, even at X = 2490 A. The principal reaction... 

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