Higher Alkonium Ions

Higher Alkonium Ions The acid-induced H-D exchange of isobutane (49) in deuterosulfuric acid was studied by Otvos and coworkers. All nine methyl hydrogens were readily exchanged, but not the methine hydrogen. The mechanism for this observation is considered to involve the initial formation of trivalent zerz-butyl cation (50), probably in an oxidative 

The tert-butyl cation (50) reforms isobutene, according to Bartlett et al. Nenitzescu et al., ° and Schmerling, by hydride abstraction from isobutane involving the tertiary C-H bond only, through intermediate structure 52, and thus no methine hydrogens would exchange with the deuterosulfuric acid. 

In contrast, Olah et al showed that in superacidic media, for example, DSOsF-SbFs or DI SbK, and at low temperatures, initially only the methine hydrogen is exchanged (with the acid), indicating that no deprotonation-protonation equilibria involving species such as 50 and 51 are involved in the strong superacidic medium. The reaction proceeds through the intermediary of the 53 protonated isobutane [Eq. (5.11)]  

Subsequent reactions exchange the methyl hydrogens through protonation (deuteriation) of the methyl groups. 

Clear evidence for a C-C protonated C4H1C ion (55) (which would resemble 52) has been obtained by Siskin/ while studying the I II TaFs catalyzed ethylation of excess ethane with ethylene in a flow system [Eq. (5.12)]. n-Butane was obtained as the only product no isobutane was detected. This remarkable result can be explained by C-H bond ethylation of ethane by the ethyl cation, thus producing the hypercoordinate 55 carbocation intermediate, which, subsequently, by proton elimination, yields n-butane (56). The use of a flow system that limits the contact of the product n-butane (56) with the acid catalyst is essential. Prolonged contact causes isomerization of n-butane to isobutane to occur (see Chapter 6). 

---

Proponium Ions and Analogs The higher alkonium ions, such as protonated propane (C3H9+) [and also protonated butane (C4H1T), etc.], have been observed in the gas phase by In solution, the higher hydrocar-... 

Higher alkonium ions. Hiraoka and Kebarle also examined the next two homologues of the alkonium ions, 3119 and C4H11 . As in there is the possibility of either... 

---