Mordenite ether formations

The catalytic activity of various zeolites in the Claisen rearrangement was investigated. It was found that H-mordenite and HB catalyse the rearrangement of allyl phenyl ether to 2-allylphenol and the cyclisation of latter compovmd to 2-methyldihydrobenzofuran. The reaction was accompanied by the formation of dimers and oligomers, which could be suppressed by triphenylphosphine treatment of the catalysts. This treatment led in the case of HB to better selectivities to the major reaction products. 

H-mordenite and HB are able to catalyse the Claisen rearrangement of allyl phenyl ether. The reaction is accompanied by the cyclisation of the initial rearrangement product and other acid catalysed side reactions. A drawback is the formation of dimers and oligomers, but improvement with respect to these undesired side reactions can be achieved by deactivation of the outer surface of the zeolite with triphenylphosphine in the case of H13. 

Copper-containing mordenite catalysts have also been reported to be active for carbonylation of vapor-phase methanol [170]. Initially, the predominant reaction products were hydrocarbons resulting from methanol-to-gasoline chemistry, but after about 6 h on stream at 350 °C the selectivity of the catalyst changed to give acetic acid as the main product. A recent investigation was carried out with in situ IR and solid-state NMR spectroscopies to probe the mechanism by detecting surface-bound species. The rate of carbonylation was found to be enhanced by the presence of copper sites (compared to the metal-free system), and formation of methyl acetate was favored by preferential adsorption of CO and dimethyl ether on copper sites [171],... 

The reaction of ethanol with ammonia on zeolite catalysts leads to ethylamine. If, however, the reaction is carried out in the presence of oxygen, then pyridine is formed [53]. MFI type catalysts H-ZSM-5 and B-MFI are particularly suitable for this purpose. Thus, a mixture of ethanol, NH3, H2O and O2 (molar ratio 3 1 6 9) reacts on B-MFI at 330 °C and WHSV 0.17 h 1 to yield pyridine with 48 % selectivity at 24 % conversion. At 360 °C the conversion is 81% but there is increased ethylene formation at the expense of pyridine. Further by-products include diethyl ether, acetaldehyde, ethylamine, picolines, acetonitrile and CO2. When applying H-mordenite, HY or silica-alumina under similar conditions pyridine yields are very low and ethylene is the main product. The one-dimensional zeolite H-Nu-10 (TON) turned out to be another pyridine-forming catalyst 54]. A mechanism starting with partial oxidation of ethanol to acetaldehyde followed by aldolization, reaction with ammonia, cyclization and aromatization can be envisaged. An intriguing question is why pyridine is the main product and not methylpyridines (picolines). It has been suggested in this connection that zeolite radical sites induced Ci-species formation. 

Halogenation and nitration of arenes, substitution reactions ofaliphatics Ether and ester formation, thiols from alcohols and H2S, amines from alcohols and NHj (mordenite, erionite)... 

An a-elimination involving a carbenoid intermediate was proposed by Chang and Silvestri, This mechanism was originally speculated by Schwabb and Gates for the formation of traces of olefins in the dehydration of methanol to dimethyl ether over mordenite. It was considered unlikely, however, that the oleflns were formed by dimerization of two free carbenes in view of the high reactivity of carbenes. Rather, a concerted reaction between methylene donor and acceptor was proposed involving simultaneous cc-elimination and sp insertion into methanol or dimethyl ether. 

A similar shape selectivity was reported in the more reeent study of modified mordenite, faujasite, and ZSM-5 zeolites by Se wa and Tachibana [72]. The mordenite zeolites, treated with SiCH at 973 K in Na form and then exchanged to protonic form, ve 98% selectivity to monomethylamine and DMA, with <1% diemthyl ether (DME) as a side product, at a methanol conversion > 90%. The reaction was performed with a feed of composition NH /CH OH/ N2 = 1 1 31 mol% at atmospheric pressure and in the temperature range 300400°C. The formation of TMA is limited by the eatalyst pore openings, which were smaller than the TMA molecule. Under the conditions of the laboratory experiments, no catalyst deactivation was observed [72]. 

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