2-Propyl cation, direct alkylation with

The direct protonation of isobutane, via a pentacoordinated carbonium ion, is not likely under typical alkylation conditions. This reaction would give either a tertiary butyl cation (trimethylcarbenium ion) and hydrogen, or a secondary propyl cation (dimethylcarbenium ion) and methane (37-39). With zeolites, this reaction starts to be significant only at temperatures higher than 473 K. At lower temperatures, the reaction has to be initiated by an alkene (40). In general, all hydrocarbon transformations at low temperatures start with the adsorption of the much more reactive alkenes, and alkanes enter the reaction cycles exclusively through hydride transfer (see Section II.D). 

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. 

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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