Halogen promoted selective carbonylation of propane in superacid media

Propane carbonylation on sulfated zirconia catalyst as studied by 13C MAS NMR and FTIR spectroscopy

“…The distribution of the observed reaction products, different from that formed from propane in the presence of solid Brønsted acid catalysts [11] and superacidic media [8,9,37], indicates that the activation of propane by SZ is performed primarily toward the secondary C-H bond of the alkane rather than its C-C bond. This can be realized by either the Lewis acid sites of SZ or by direct formylation by the formyl cation formed as equilibrated species from the formate.…”

“…Activation of propane in the presence of CO on H-ZSM-5 zeolite [11] proceeds in full analogy with the process in superacid media [8,9] via C-C bond cleavage to form methane and an ethyl cation. The ethyl cation abstracts a hydride ion from propane to form an isopropyl carbenium ion.…”

“…Propane carbonylation with CO has been reported to occur in liquid superacids [8,9], in the presence of strong Lewis acids (AlCl 3 ) [10] or acidic zeolite H-ZSM-5 [11], the reactions presuming the generation of intermediate carbenium ions and their trapping by CO. It has been established recently that SZ catalyzes propane conversion at 200-450 • C by a dimerization-isomerization-cracking process, i.e., via a classical carbenium-ion mechanism [12,13].…”

The Chemistry of CO: Carbonylation

“…47 The formation of C6 or C7 acids, along with ketones, can be effected by the reaction of cyclic alkanes with CO in the presence of HF/SbF 5 at ambient temperature and atmospheric pressure. The relative reactivity of the s bonds toward the electrophilic proton was shown to be as follows: primary C-H << secondary C-H < C-C < tertiary C-H. 48 Tertiary carbocations are produced by protolysis of C-H bonds of branched alkanes in HF/SbF 5 . The carbonium ion undergoes skeletal isomerization and disproportionation, followed by reaction with CO to give the product.…”

Carbonylation

“…Selectivity for C -H protolysis in the carboxylation of propane is markedly enhanced by the addition of bromide ion. (232) …”