Zirconia Supported on Rice Husk Silica from Biowaste: A Novel, Efficient, and Recoverable Nanocatalyst for the Green Syn
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irconia Supported on Rice Husk Silica from Biowaste: A Novel, Efficient, and Recoverable Nanocatalyst for the Green Synthesis of Tetrahydro-1-benzopyrans M. Mishraa, K. R. S. Devia, D. Pinheiroa, and A. Nizama,* a
Department of Chemistry, CHRIST (Deemed to be University), Bangalore, Karnataka, 560029 India *e-mail: [email protected] Received May 15, 2020; revised May 25, 2020; accepted May 31, 2020
Abstract—Zirconia supported silica from rice husk (an agricultural waste) has been utilized as a novel and efficient heterogeneous catalyst for the synthesis of bioactive tetrahydro-1-benzopyran derivatives via multicomponent condensation of various aldehydes with dimedone and malononitrile. This protocol offers various advantages such as high yields, simple experimental work-up procedure, short reaction time, no by-products, economic availability, easy purification, and reusability of the catalyst. Keywords: tetrahydro-1-benzopyrans, rice husk silica-supported zirconia, multicomponent reactions (MCR), heterogeneous reusable catalyst
DOI: 10.1134/S107042802010019X Multicomponent reactions (MCRs) have become an emerging field of research, since they facilitate multibond formation and provide new chemical scaffolds in a single step. Moreover, MCRs offer advantages in terms of operational simplicity, easy work-up and purification procedures, atom economy, energy efficiency, and environmental friendliness and have proven to be a valuable tool in organic and medicinal chemistry [1]. An example of such MCRs is the one-pot synthesis of tetrahydro-1-benzopyran derivatives that are significant heterocyclic compounds exhibiting a broad range of biological activities such as anticancer, spasmolytic, diuretic, anti-coagulant, and anti-anaphylactic activity [2]. Furthermore, they are used as cognitive enhancers and for the treatment of neurodegenerative disease, amyotrophic lateral sclerosis, AIDS associated dementia, Down’s syndrome, and Parkinson’s, Huntington’s and Alzheimer’s diseases [3]. Considering the importance of such compounds, various methods have been reported for the synthesis of tetrahydro-1-benzopyrans using different catalysts such as amino functionalized silica gel (AP-SiO2) [4], potassium phthalimide [5], PEG-1000-based dicationic ionic liquid (PEG1000DAIL) [6], [PAPEG1000-DIL][BF4] [7], RuBr2(PPh3)4 [8], sodium selenate [9], CeMgxZr1–xO2 [10], diammonium sodium hydrogen phosphate [11] and RE(PFO)3 [12]. Most of the aforementioned techniques have one or more drawbacks such as high reaction temperature,
prolonged reaction time, expensive catalysts, etc. Therefore an alternative, efficient, inexpensive, and green methodology for the synthesis of tetrahydro-1benzopyran derivatives is highly desirable. In order to circumvent these obstacles, we decided to reconsider the synthetic routes using a modified silica catalyst. Silica can be obtained from rice husk (RHSi) in a very short time. Moreover, rice husk is the major waste product in the rice industry of the developing countries, which is usually disc
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