ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Monoterpenes etherification reactions with alkyl alcohols over cesium partially exchanged Keggin heteropoly salts: effects of catalyst composition

Márcio José da Silva, Neide Paloma Goncalves Lopes, Sukarno Olavo Ferreira, Rene Chagas da Silva, Ricardo Natalino, Diego Morais Chaves, and Milena Galdino Texeira

Chemistry Department, Federal University of Viçosa, Viçosa, Brazil

E-mail: silvamj2003@ufv.br

Received: 18 March 2020  Accepted: 14 July 2020

Abstract:

In this work, cesium partially exchanged Keggin heteropolyacid (HPA) salts were prepared, characterized, and evaluated as solid catalysts in monoterpenes etherification reactions with alkyl alcohols. A comparison of the activity of soluble HPAs and their insoluble cesium salts showed that among three different Keggin anions the phosphotungstate was the most efficient catalyst. Assessments on the effects of the level of the protons exchange by cesium cations demonstrated that Cs_2.5H_0.5PW₁₂O₄₀ solid salt was the most active and selective phosphotungstate catalyst, converting β-pinene to α-terpinyl methyl ether. The influences of the main reaction parameters such as reaction temperature, time, catalyst load, substrate nature (i.e., alcohols and monoterpenes) were investigated. We have demonstrated that the simultaneous presence of the cesium ions and protons in the catalyst plays an essential role, being the 2.5–0.5 the optimum molar ratio. The Cs_2.5H_0.5PW₁₂O₄₀ salt was efficiently recovered and reused without loss of catalytic activity.

Graphic abstract

Keywords: Cesium partially exchanged heteropoly salts; Monoterpenes; Etherification

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-020-01288-x

Chemical Papers 75 (1) 153–168 (2021)