Synthesis of cis-Cinnamic Acid from trans-Cinnamaldehyde over Ag+-Exchanged Beta-Zeolite in Toluene

Abstract

With a view to promoting green chemistry, cis-cinnamic acid (cis-CA) has been synthesized by using Ag-exchanged zeolites (AGZ). cis-CA [(Z)-3-phenyl-2-propenoic acid] and derivatives are physiologically active substances having plant growth regulatory activity, and have recently been isolated from plants[1,2]. Methods of synthesizing cis-CA reported up to now include photoisomerization of trans-cinnamic acid [the (E)-form, trans-CA], the method of reacting (Z)-2-bromostyrene with carbon monoxide in the presence of a palladium triphenylphosphine phasetransfer catalyst[3], and the method of electrolytic carboxylation of 2-bromostyrene using a nickel catalyst[4]. On the other hand, silver ion (Ag) -exchanged zeolite, silver ion supported on porous material[5] and complex membranes made up of amino acids and silver polymers[6] and the like have been utilized as olefin separation agents. In the present study, cis-CA was prepared in one pot synthesis using AGZ in toluene by novel methods of isomerization and oxidation of trans-cinnamaldehyde (TCA) to cis-CA exploiting the fact that Ag soft Lewis acid on AGZ forms a π -complex with the olefin double bond of TCA and reacts as the oxidant. (Scheme 1)