Ethyl cation direct alkylation with

Propane as a degradation product of polyethylene (a byproduct in the reaction) was ruled out because ethylene alone under the same conditions does not give any propane. Under similar conditions but under hydrogen pressure, polyethylene reacts quantitatively to form C3 to C6 alkanes, 85% of which are isobutane and isopentane. These results further substantiate the direct alkane alkylation reaction and the intermediacy of the pentacoordinate carbonium ion. Siskin also found that when ethylene was allowed to react with ethane in a flow system, n-butane was obtained as the sole product, indicating that the ethyl cation is alkylating the primary C—H bond through a five-coordinate carbonium ion [Eq. (5.66)]. 

Lewis superacid-catalyzed direct alkylation of alkanes is also possible with alkyl cations prepared from alkyl halides and SbFs in sulfuryl chloride fluoride solution. " Typical alkylation reactions are those of propane and butanes by 2-butyl and ZerZ-butyl cations. The ClfU-Sbfs and C2H5F-SbF5 complexes acting as incipient methyl and ethyl cations besides alkylation preferentially cause hydride transfer. Since intermolecular hydride transfer between different carbocations and alkanes are faster than alkylation, a complex mixture of alkylated products is usually formed. A significant amount of 2,3-dimethylbutane was, however, detected when propane was propylated with the 2-propyl cation at low temperature [Eq. (6.36)]. No 2,2-dimethylbutane, the main product of conventional acid-catalyzed alkylation, was detected, which is a clear indication of predominantly nonisomerizing reaction conditions. 

When usiag HF TaF ia a flow system for alkylation of excess ethane with ethylene (ia a 9 1 molar ratio), only / -butane was obtained isobutane was not detectable even by gas chromatography (72). Only direct O -alkylation can account for these results. If the ethyl cation alkylated ethylene, the reaction would proceed through butyl cations, inevitably lea ding also to the formation of isobutane (through /-butyl cation). 

The yield of the alkane-alkene alkylation in homogeneous HF-TaF5 depending on the alkene-alkane ratio has been investigated by Sommer et al.149 in a batch system with short reaction times. The results support direct alkylation of methane, ethane, and propane by the ethyl cation and the product distribution depends on the alkene-alkane ratio (Figure 5.14). 

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. 

Similarly, Siskin " found that when ethylene was allowed to react with ethane in a flow system, only n-butane was obtained. This was explained by the direct alkylation of ethane by ethyl cation through a pentacoordinated carbonium ion (equation 127). The absence of a reaction between ethyl cation and ethylene was explained by the fact that no rearranged alkylated product (isobutane) was observed. 

Direct, acid catalyzed esterification of acryhc acid is the main route for the manufacture of higher alkyl esters. The most important higher alkyl acrylate is 2-ethyIhexyi acrylate prepared from the available 0x0 alcohol 2-ethyl-1-hexanol (see Alcohols, higher aliphatic). The most common catalysts are sulfuric or toluenesulfonic acid and sulfonic acid functional cation-exchange resins. Solvents are used as entraining agents for the removal of water of reaction. The product is washed with base to remove unreacted acryhc acid and catalyst and then purified by distillation. The esters are obtained in 80—90% yield and in exceUent purity. 

A cation homologous series is evident for l-allq l-5-amino-l,2,4-triazolium, allq l = methyl [355], ethyl [169], propyl [169], 1-methylethyl [169], cydo-propylmethyl [169], hexyl [169] and heptyl [169], though a direct comparison is only possible with the bromide salts [169] when alkyl (R) is Et, Pr, Me2CH, Hex or Kept, where the consequences of successive introduction of methylene groups can be seen. 

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