Methane alkylation, ethylene

In on attempt to generate primary (trivalent) cations and to simulate the ethylene-methane alkylation, ethyl chloride was reacted with methane (eq. 3) under alkylation reaction conditions (28). When no propane or propylene product was observed, the energetically more favorable reaction of methyl chloride with ethane was carried out (eq. 3a). These two reactions proceeded without any involvement of the alkane and provide evidence that the ethylene-methane alkylation proceeds through a more stabilized species such as a pentacoordinoted carbonium ion. The behavior of these alkyl chlorides will be discussed separately after the alkylation chemistry. 

These stages result in the formation of the active form of the catalyst. The next is the key stage of ethylene insertion at the methane-alkyl bond, whose multiple repetition results in the polymeric chain growth. The reaction ceases when the metal in the catalytic complex is reduced to the trivalent state. 

Me3CCH2CMe2C H40H. M.p. 8l-83"C, b.p. 286-288°C. Made by alkylation of phenol. Forms oil-soluble resins with methanal (salts used as oil additives) and surfactants (with ethylene oxide). 

The elimination of alcohol from P-alkoxypropionates can also be carried out by passing the alkyl P-alkoxypropionate at 200—400°C over metal phosphates, sihcates, metal oxide catalysts (99), or base-treated zeoHtes (98). In addition to the route via oxidative carbonylation of ethylene, alkyl P-alkoxypropionates can be prepared by reaction of dialkoxy methane and ketene (100). 

ALKYLATION OF ALIPHATIC COMPOUNDS The first reported alkylation of branched-chain alkanes by ethylene, over aluminum chloride (69), made it possible to alkylate alkanes (except methane and ethane) with straight chain or branched alkenes. 

Abbreviations acac, acetylacetonate Aik, alkyl AN, acetonitrile bpy, 2,2 -bipyridine Bu, butyl cod, 1,5- or 1,4-cyclooctadiene coe, cyclooctene cot, cyclooctatetraene Cp, cyclopentadienyl Cp, pentamethylcyclopenladienyl Cy, cyclohexyl dme, 1,2-dimethoxyethane dpe, bis(diphenyl-phosphino)ethane dppen, cis-l,2-bis(di[Atenylphosphino)ethylene dppm, bis(diphenylphosphino) methane dppp, l,3-bis(diphenylphosphino)propane eda,ethylenediamine Et,ethyl Hal,halide Hpz, pyrazole HPz, variously substituted pyrazoles Hpz, 3,5-dimethylpyrazole Me, methyl Mes, mesityl nbd, notboma-2,5-diene OBor, (lS)-endo-(-)-bomoxy Ph, phenyl phen, LlO-phenanthroline Pr, f opyl py, pyridine pz, pyrazolate Pz, variously substituted pyrazolates pz, 3,5-dimethylpyrazolate solv, solvent tfb, tetrafluorobenzo(5,6]bicyclo(2.2.2]octa-2,5,7-triene (tetrafluorobenzobanelene) THE, tetrahydrofuran tht, tetrahydrothicphene Tol, tolyl. 

Several extensions of these reactions are possible with respect to the electrophilic reagent as well as to the structure of the adduct. Thus functionalized alkyl groups, such as 2-hydroxyethyl and 2-hydroxy-2-phenylethyl, can be introduced into the pyridine ring at the position by treating l-lithio-2-phenyI-l,2-dihydropyridine with ethylene epoxide and styrene epoxide, respectively.144 When polyhalides such as CF3I are used, bis-(substituted-pyridyl)methanes and the dimeric substituted dipyridyls are obtained along with other products.144... 

In alkane-alkene alkylation systems it is always the Jt-donor alkene that is alkylated by carbocations formed in the system. In the absence of excess alkenes (i.e., under superacidic conditions), however, the cr-donor alkanes themselves are alkylated. Even methane or ethane, when used in excess, are alkylated by ethylene to give propane and n-butane, respectively ... 

Alkylation of methane, ethane, propane, and n-butane by the ethyl cation generated via protonation of ethylene in superacid media has been studied by Siskin,148 Sommer et al.,149 and Olah et al.150 The difficulty lies in generating in a controlled way a very energetic primary carbenium ion in the presence of excess methane and at the same time avoiding oligocondensation of ethylene itself. Siskin carried out the reaction of... 

Figure 5.14. Selectivity dependence of alkylation on the ethylene-alkane ratio for the following reactions ethylene + methane ( ), ethylene + ethane (o), ethylene + propane (A), ethylene + n-hutane ( ).

Mechanistically, two pathways are logical (Scheme 3). The ethyl cation can directly alkylate methane via a pentacoordinated carbonium ion (Olah) (path a), or alternatively, although a less favorable pothway (b), the ethyl cation could abstract a hydride ion from methane. The methyl cation thus formed, which is less stable by 39 kcal/mole (26), could then react directly with ethylene. In the latter case, propylene and/or polymeric material would probably be formed since the hydrogen required for a catalytic reaction has been consumed by the formation of ethane. 

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