Claisen rearrangement with a novel solid superacid UDCaT-5: atom economical and selective conversion of allyl-4-methoxyphenyl ether into 2-allyl-4-methoxyphenol

Abstract

The Claisen rearrangement of allyl aryl ethers provides a convenient route to obtain allyl phenols which are precursors to a variety of natural products. All uncatalyzed Claisen rearrangements are energy intensive requiring temperatures above 200 °C whereas those using homogeneous acid catalysts leads to a loss in yield and selectivity, in addition to pollution problems. In the current work, the Claisen rearrangement of allyl-4-methoxyphenyl ether to 2-allyl-4-methoxyphenol was investigated at 90 °C using chlorobenzene as a solvent over several solid acid catalysts such as dodecatungstophosphoric acid/hexagonal mesoporous silica (HMS), Cs_2.5H_0.5PW₁₂O₄₀/K10 clay, sulfated zirconia and a new mesoporous solid superacid UDCaT-5. 2-Allyl-4-methoxyphenol is used in perfumes, flavors, soaps, detergents, air fresheners, and cosmetic materials. UDCaT-5 was found to be superior, robust and recyclable and 100% selective. A complete theoretical and experimental analysis is also presented. This is a 100% atom economical and efficient process.