Methane condensation reaction

Scheme 55) (235. 236). -The product obtained (77) is probably formed via the protonated form of the thiazole, whose reactivity is treated in Section IV, 1. The light-yellow leucobase (77) is reported to be oxidized by PbOj to the red-black carbinol (78) (236). This condensation reaction is also successful when benzaidehyde is replaced by formaldehyde, bis(2-amino-4-phenylthiazolyl-5)methane (79 i beine obtained (Scheme 56) (237). 

Carbonaceous compounds can also form in the absence of a catalyst by free-radical, gas-phase condensation reactions. The formation of this pyrolytic carbon is known in steam-reforming reactors where it can be controlled to some extent by minimizing the free volume within the reactor chamber. This type of carbon does not form readily with methane but can be severe with larger hydrocarbons. The compounds formed by free-radical reactions tend to be quite different from the graphitic carbon formed by metal catalysts. For example, Lee et al. showed that the compounds formed by passing pure, undi-... 

Natural gas instead of pure methane can also be used in condensation reactions.91 When natural gas is dehydrogenated, the C2-C4 alkanes it contain are converted into olefins. The resulting methane-olefin mixture can then without separation be passed through a superacid catalyst, resulting in exothermic alkylative condensation ... 

What effect do shocks have on the gas phase synthesis of complex interstellar molecules This question has been investigated at least for hydrocarbons through six carbon atoms in complexity by Mitchell (1983, 1984). He has found that if a shock passes through a dense cloud where much of the carbon is already in the form of carbon monoxide, complex hydrocarbons are not formed in high abundance. However, if a shock passes through a diffuse cloud, of density approximately 103 cm-3, where much of the cosmic abundance of carbon is in the form of C+ and to a lesser extent C, a different scenario is present. As the shock cools, the C+ and C, which remain in appreciable abundance for up to 10s yrs after the shock passage, react via many of the reactions discussed above as well as others to produce a rich hydrocarbon chemistry. The net effect is that large abundances of hydrocarbons build up as the cloud cools and eventually reaches a gas density of 3 x 104 cm-3. Do these results bear any relation to the results obtained from ambient gas phase models In both types of calculations, hydrocarbon chemistry appears to require the presence of C+ and/or C both to synthesize one-carbon hydrocarbons such as methane and then, via insertion reactions, to produce more complex hydrocarbon species. Condensation reactions do not appear to be sufficient. 

A familiar example of a condensation reaction is one that occurs between phenol (hydroxybenzene, C6H5OH) and formaldehyde (methanal, HCHO). In this reaction, shown on page 155, the oxygen... 

An important side reaction is a-hydrogen transfer, which leads to the production of methane. Condensation of the metallocene and MAO takes... 

This parallelism is reflected in the proposed mechanism for the ionization of methane which shows that (a) the second step of the scheme invoives attack of an ethyl cation on methane, but the reaction cannot stop there, and goes on to (b), the third step, which involves attack of a secondary-isopropyl cation on methane. The primary and secondary alkyl cations are very strongly acidic species and are unstable under the reaction conditions. The condensation reaction essentially terminates with the much more weakly acidic tertiary-butyl ion. Alkane polycondensation and olefin polymerization side reactions producing stable, less acidic, tertiary ions obscured the simple alkylation reactions of the primary and secondary alkyl cations. Implicit in this mechanism, however, is that it is possible to react an acidic energetic primary cation (such as the ethyl cation) with molecules as weakly basic as methane and thus, the door was opened to new chemistry through activation of the heretofore passive, weakly basic, "paraffins" (20-24). 

Olah (33) has shown that alkyl fluorides undergo a self-condensation reaction (eq. 10) similar to that previously described for the ionization and condensation of methane so that this additional pathway is not an unexpected one. 

Miscellaneous polymerization and condensation reactions have been reported in some patents as generating hydrocarbons from methane, fvir example, methane when heated at I. OO C on AljOs MgAljO (impregnated wjth Mg. Cr and Ft) givesethene and benzene [281. 

The crude trimethylolnitromethane from the condensation commonly contains a small amount. of mono- and dimethylolnitro methane from reactions involving one and two molecules of formaldehyde respectively. It is recrystalHzed from water to a melting point of 150, and is then nitrated. Stettbacher reports that the pure substance after many recrystallizations melts at 164-165 .,.The nitratiop is carried out either with the same mix acid as is used for the nitration of glycerin nitric acid,... 

Recently a movable glow discharge of methane has been investigated mass spec-trometrically over the whole column length19. The mass spectra showed primary fragment ion of methane and ions from condensation reactions up to m/e =113. 

Methane condenses at lower temperatures as methane clathrate hydrate (CH4 ALUO) at 78 K and CH4 ice. A clathrate hydrate is a cage compound in which a gas molecule is trapped inside the water ice crystal lattice. One gas atom is trapped for every seven water molecules. Clathrate hydrates form via reactions exemplified by... 

The carbonium ions can undergo complex reactions. Thus methane can give carbonium ions with C—C bonds by condensation reactions of the type CH44Jf.+.fc H2 + CHJ -.SSf C2Ht T-I H2 + C2HJ, etc. 

The anodic oxidation of alkanes in anhydrous hydrogen fluoride has been studied at various acidity levels from basic medium (KF) to acidic medium (SbFs) to establish optimum conditions for the formation of carbenium ions . The oxidation potential depends on the structure of the hydrocarbon methane is oxidized at 2.0 V, isopentane at 1.25 V vs Ag/Ag. Three cases of oxidation can be distinguished. In basic medium, direct oxidation of the alkane to its radical cation occurs. In a slightly acidic medium, the first-formed radical cation disproportionates to cation, proton and alkane. The oxidation is, however, complicated by simultaneous isomerization and condensation reactions of the alkane. In strongly acidic medium, protonation of the alkane and its dissociation into a carbenium ion and molecular hydrogen occurs. In acidic medium n-pentane behaves like a tertiary alkane, which is attributed to its isomerization to isopentane. The controlled potential electrolysis in basic medium yields polymeric species. 

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