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Oxidation of oregano essential oil using zeolite-encapsulated Cr(salpn) complex
Flexible ligand (H2salpn, N,N´-bis(salicylidene)propane-1,3-diamine) was used to form complex with Cr(III) metal ion inside the cages of NaY-zeolite. The encapsulation of Cr(salpn) complex was confirmed with Fourier transform infrared (FT-IR). The encapsulated Cr(salpn) complex catalysed the liquid-phase oxidation of both carvacrol and thymol in the presence of hydrogen peroxide. The conversion range was found be between 35–39% for the oxidation of both carvacrol and thymol. A high yield of thymoquinone (TQ) was obtained along with other side-products such as, thymohydroquinone (THQ) and benzoquinones (BQ). Oxidation of carvacrol and thymol provided a TQ yield of 31.2 and 34.5%, respectively. Oxidation reaction did not occur in the absence of a catalyst. The Cr(salpn)-NaY catalyst was catalytically active with an acceptable leaching performance. Oxidation of oregano essential oil having carvacrol as major compound caused the formation of an essential oil rich in TQ. The carvacrol present in the oregano essential oil was converted into mainly TQ with 33.6% yield and 70% total conversion as a result of the side-products namely BQ, THQ, and several undefined products. © 2017 Scibulcom Ltd. All Rights Reserved.