7.5 Role of Penta-Coordinated Carbonium Ion Intermediates …
175
(13)
C
CH 3
CH 3
H
H 3 C
+
+
C
CH 3
CH 3
H 3 C
H
(14)
C
CH 3
CH 3
H
C
CH 3
CH 3
H 3 C
C
CH 3
H
CH 3 + H +
(15)
+ H +
CH 3 CH CH 2
CH 3 CH 2 CH 3
+
(13)
CH 3 CH CH 3
+
(14)
(7.22)
Therefore, 2,2,3,3-tetramethylbutane (12) and 2,2,3-trimethylbutane (15) are formed
as the primary alkylation products via the reaction pathways suggested for superacid
catalysts. Actually, Olah et al. reported the production of these alkanes in ref. [31].
On the other hand, the electrophilic alkylation of alkanes with alkenes
(R’ 2 CH=CH 2 ) is usually considered to involve the alkylation of the alkane by the carbenium ion derived from the iso-alkane (R 3 CH) via intermolecular hydride transfer
[31], as shown in reactions (7.23)–(7.27) below:
+ H +
R’ 2 C CH 3
+
R’ 2 CH CH 2
(7.23)
+ R 3 CH
R’ 2 CHCH 3 + R 3 C +
R’ 2 C CH 3
+
(7.24)
R 3 C +
R’ 2 CH CH 2
+
R’ 2 C CH 2 CR 3
+
(7.25)
(7.26)
(7.27)
R’ 2 C CH 2 CR 3
+
H -
- H +
R’ 2 CHCH 2 CH 3
R’ 2 C CH 2 CR 3