Mordenite acetal formation

H-Mordenite catalyzes the smooth conversion of simple aldehydes and alcohols to form acetals at 30° in the liquid phase. From the examples in Table XXVII, it is apparent that in these heterogeneous catalytic systems, acetal formation is dependent on the structures of both the aldehyde and the alcohol involved. Thus, for a given aldehyde, yields of acetal decreased in the order primary > secondary > tertiary that is, branching at the a-carbon of the alcohol reduced the equilibrium conversion to acetal. In the isobutyraldehyde reactions, an extremely sharp drop in conversion was observed upon changing from isopropanol to fert-butanol as reactant. This observation suggests that, in addition to the increased steric interactions between organic reactants encountered in the tert alcohol system, molecular sieving-type interactions within the narrow mordenite pore system are operative. 

Acetal and ketal formation from aldehydes, resp. ketones and alcohols occurs over mordenite and other acidic zeolites [91] slightly above ambient temperatures in the liquid phase. The reaction is not confined to simple alcohols, diols can also be converted (e.g., cyclohexanone reacts with ethylglycol to 1,4, dioxaspiro(4,5)decane [2]). Note that it is likely that desorption controls the rate of such reactions as the product molecules are larger than the reactants and have, hence, a higher adsorption constant. 

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],... 

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