Acid-Catalyzed Trimerization of Acetaldehyde:  A Highly Selective and Reversible Transformation at Ambient Temperature in a Zeolitic Solid

Abstract

Acetaldehyde is shown to undergo a reversible Brønsted acid-catalyzed cyclotrimerization reaction, with 100% selectivity, at ambient temperature within the zeolite host material ferrierite. It is shown by in situ solid-state 13 C NMR spectroscopy and other techniques that the cyclic trimer is the only product formed in this reaction. The equilibrium proportions of acetaldehyde and the cyclic trimer at ambient temperature correspond to a conversion greater than 90%. In contrast, in the corresponding acid-catalyzed transformation of acetaldehyde in the liquid state, a broad distribution of products is obtained. The reversibility of the cyclotrimerization reaction in ferrierite is confirmed from the fact that, on adsorption of a pure sample of the cyclic trimer within ferrierite, a reaction occurs to produce acetaldehyde as the only product with the same equilibrium distribution of the cyclic trimer and acetaldehyde as that obtained from the reaction of acetaldehyde in ferrierite. The role of Brønsted acid catalysis in the transformation between acetaldehyde and the cyclic trimer in ferrierite is confirmed from the fact that no reaction occurs on adsorption of acetaldehyde within sodium-exchanged ferrierite.