Use of nanoporous Na + -montmorillonite sulfonic acid (SANM) as an eco-benign, efficient and reusable solid acid catalys
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ORIGINAL PAPER
Use of nanoporous Na+-montmorillonite sulfonic acid (SANM) as an eco-benign, efficient and reusable solid acid catalyst for the one-pot synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes and 1,8-dioxo-dodecahydroxanthene derivatives Farhad Shirini • Manouchehr Mamaghani Seyyed Vahid Atghia
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Received: 18 December 2011 / Accepted: 3 October 2012 / Published online: 17 October 2012 Ó Iranian Chemical Society 2012
Abstract Nanoporous Na?-montmorillonite sulfonic acid was found to be an efficient and green catalyst for the synthesis of various 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-dodecahydroxanthene derivatives by the reaction of aldehydes with 2-naphthol and 1,3-cyclohexanedione, respectively. This novel synthetic method has the advantages of high yields, short reaction times and recyclability of the catalyst, simplicity and easy workup compared to the conventional methods reported in the literature. Keywords Xanthene Aldehydes b-Naphthol 1,3-Cyclohexanedione Na?-montmorillonite
Introduction In the past few decades, synthesis of xanthene derivatives has been of considerable interest to organic chemists because they posses various biological and pharmaceutical activities such as antiviral [1], antibacterial [2], and antiinflammatory [3] activities. Furthermore, these compounds can be used as leuco-dyes [4], in laser technology [5] and pH-sensitive fluorescent materials for the visualization of biomolecular assemblies [6]. It is also noteworthy that dibenzoxanthene derivatives are candidates as sensitizers in photodynamic therapy [7] (PDT; a method of treating tumors by combined use of a photosensitizer and light) and antagonists for the paralyzing action of zoxazolamine [8].
F. Shirini (&) M. Mamaghani S. V. Atghia Department of Chemistry College of Science, University of Guilan, Rasht zip code 41335, Islamic Republic of Iran e-mail: [email protected]
Many procedures have been investigated for the construction of these important intermediates, among which the reaction of aldehydes with 2-naphthol and/or 1,3cyclohexanedione via cyclodehydration in the presence of various Lewis and Bro¨nsted acid catalysts is the most important one. Some of the acidic catalysts which have been used earlier for this reaction included AcOH–H3PO4 and AcOH–HClO4 [9], AcOH–H2SO4 [10], sulfamic acid [11], p-TSA [12], Amberlist-15 [13], heteropolyacids [14, 15], Dowex-50W [16], HClO4–SiO2 [17], NH4H2PO4/SiO2 [18], silica sulfuric acid [19, 20], NaHSO4/SiO2 [21], montmorillonite K10 [22], PANI–PTSA [23], DBSA or SDS [24], n-Bu4NBr [25] and acidic ionic liquids [26, 27]. However, these methodologies suffer from one or more disadvantages such as low yield, prolonged reaction time (e.g., in the case of AcOH–H3PO4 and AcOH–HClO4, products obtained after 3–5 days or p-TSA catalyzed the reaction at 15–30 h in the refluxed 1,2-dichloroethane), use of toxic organic solvents, requirement of excess of reagents or catalysts, special apparatus (some of these methodologies were carried out in microwave or ultrasonic c
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