(735g) Acylation of 2-Methylfuran and Carboxylic Acid: Solvent Effects

Alkyl aryl ketones formed from acylation of aromatic substrates and carboxylic acid derivatives are important intermediates in the renewable chemical industry. Direct acylation using carboxylic acids forms only water as the by-product, whereas indirect acylation using an anhydride results in acid as the by-product. However, acylation using carboxylic acids has limitations such as lower activity compared to the anhydride, a side reaction of the formed water with furan leading to furan polymerization, and the self-ketonization reaction of acids at high temperatures. The catalyst pore structure, acid site density as well as the nature of the solvent (polarity and structure) influence the acylation catalytic activity and is not well understood. In this work, we evaluate the effect of different solid acid catalysts, carboxylic acid chain length, and the choice of solvent in enhancing 2-methylfuran acylation rates as well as the catalyst stability. The vapor phase reaction of acetic acid and 2-methylfuran was investigated using different zeolite structures and heteropoly acids. The parameters such as the Si/Al ratio, heteroatom, and the Bronsted acid strength were varied. The effect of the solvent chain length was evaluated for the reaction of 2-methylfuran and octanoic acid over HZSM5 (25) in a continuous flow fixed bed reactor setup. A non-polar alkane solvent such as heptane has been shown to be effective in reducing side reactions such as furan hydrolysis in the presence of water. The reaction under consideration was therefore investigated using non-polar linear alkanes as solvents to understand the partitioning of the components in the zeolite pores.