Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
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Article Citation - Scopus: 7Oxidation of Oregano Essential Oil Using Zeolite-Encapsulated Cr(salpn) Complex(SCIBULCOM, 2017) Bayraktar, Oğuz; Yerkesikli, Alev GüneşFlexible 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.Article Citation - WoS: 11Citation - Scopus: 13Liquid-Phase Oxidation of Carvacrol Using Zeolite-Encapsulated Metal Complexes(American Chemical Society, 2006) Güneş, Alev; Bayraktar, Oğuz; Yılmaz, SelahattinWe report here the use of zeolite-encapsulated metal (salpn) complexes as catalysts in the oxidation reaction of the natural compound carvacrol in acetonitrile with hydrogen peroxide as the oxidant. No previous studies on the oxidation of carvacrol in the presence of metal salpn complexes have been reported. By using a general flexible ligand method, Cr(III), Fe(III), Bi(III), Ni(II), and Zn(II) complexes of N,N′-bis(salicylidene)propane1,3-diamine (H2salpn) encapsulated in NaY zeolite were prepared. All catalysts were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses to confirm the complex encapsulation. The activities of all prepared catalysts for the oxidation of carvacrol and hydrogen peroxide were tested. The performances of all catalysts were compared on the basis of the leaching test results and carvacrol conversions. Thymohydroquinone and benzoquinones were observed as byproducts at high conversions of carvacrol. No product was formed in the absence of a catalyst. Fe(salpn)-NaY catalyst exhibited the highest carvacrol conversion of 27.6% with a yield of 22.0%, followed by Cr(salpn)-NaY catalyst with 23.5% carvacrol conversion and a yield of 17.6%. Other catalysts have shown relatively lower performances in terms of carvacrol conversion and leaching. The Cr(salpn)-NaY catalyst was found to be a more efficient catalyst than others on the basis of leaching and activity tests. With the selected catalyst Cr (salpn)-NaY, the effects of temperature and carvacrol/hydrogen peroxide molar ratio on carvacrol oxidation reactions were investigated. Increasing the temperature from 40 to 60 °C caused an increase in the thymoquinone yield from 6.2% to 16.0%. An increase in carvacrol/hydrogen peroxide molar ratio from 1 to 3 resulted in a decrease in the thymoquinone yield.