Selective carbonylation of propane in superacid media via hydride abstraction by the chlorocarbocations: CCl3 + and CHCl2 +

Abstract

Carbonylation of propane in HF-SbF5 (5 : 1 molar ratio) superacid in the presence of carbon tetrachloride (or chloroform) at -30 "C yields exclusively the isobutyryl ion (isopropyloxocarbenium ion), analysis of the gaseous fluorocarbons generated as side products showing both hydride abstraction by CCI3+ (or CHC12+) and CI/F exchange on the tri-and di-chloromethane formed; in the absence of CCI4 (or CHC13) no reaction takes place under the same experimental conditions.

Superelectrophilic Solvation

“…The trihalomethyl cations CX 3 + (X = Cl, Br, I) were shown to have enhanced reactivities in superacid solution, while polyhalomethanes in the presence of excess AlBr 3 or AlCl 3 exhibit the properties of aprotic superacids . The trihalomethyl cations are capable of hydride abstraction from alkanes and alkyl groups when the reactions are done in the presence of Bronsted or Lewis superacids (eqs 19 and 20), while complex systems such as CBr 4 ·2AlBr 3 , CCl 4 ·2AlCl 3 , and others have been shown to efficiently catalyze the cracking, isomerization, and oligomerization of alkanes and cycloalkanes . Electrophilic solvation ( 68a,b , Scheme ) can be envisaged for these systems.…”

TfOH mediated intermolecular electrocyclization for the synthesis of pyrazolines and its application in alkaloid synthesis

“…It is presumed that TfOH alone is capable of forming an intermediate carbocation I-1 via hydride abstraction from hydrazone by the superacid species TfOH 2 + ( Scheme 1 ). 36,37 The use of other solvents such as H 2 O, DMF, DMSO and ethanol did not result in product formation, as TfOH might be deactivated by these solvents (see ESI, Table S1 † ).…”

Superacid Systems

“…65 The generation of these cations was also used by various teams 66,67 to initiate selective low temperature alkane activation. When these cations are generated in superacidic media, a protosolvation induces a superelectrophilic character, which was supported by Olah on the basis of high-level ab initio calculations.…”