Selective carbonylation of propane in HF–SBF₅: control of the activation step via the hydrocarbon/carbon monoxide ratio

Abstract

The selectivity of propane carbonylation in HF-SbF5 is found to depend on the propane/CO ratio, and is rationalized in terms of two competing activation processes for the alkane.

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].…”

Formation of Carboxylic Acids from Small Alkanes in Zeolite H-ZSM-5

“…573 K), no conversion of propane was reported at 473 K and below. [13] However, in analogy with the superacid-catalyzed protolytic activation of propane, [5,6] the Haag and Dessau mechanism (Scheme 1) would rationalize the formation of the same products.…”

Superacid‐Catalyzed Reactions

“…Tertiary carbenium ions, which are produced by protolysis of CÀH bonds of branched alkanes in HF-SbF 5 , undergo skeletal isomerization and disproportionation before reacting with CO. 412 Two acylium (acyloxonium) ions, propanoyl cation (ethylcarboxonium ion, 112) and isobutyryl cation (isopropylcarboxonium ion, 113), were detected which, upon quenching (ethanol or NaHCO 3 /H 2 O), give the corresponding acids or esters [Eq. 408 It was also found that alkyl methyl ketones react with CO in the HF-SbF 5 superacid system to form oxocarboxylic acids after hydrolysis (Scheme 5.41).…”