Microwave-Assisted and Thermal Synthesis of Calix[4]arene Derivatives
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icrowave-Assisted and Thermal Synthesis of Calix[4]arene Derivatives M. H. Al-Douha, Y. Alib,*, and S. Abd Hamidc,** a
Chemistry Department, Faculty of Science, Hadhramout University, Mukalla, Hadhramout, 50511 Yemen b
c
Department of Chemistry, Sarhad University of Science and Information Technology, Peshawar, 25000 Pakistan
Kulliyyah of Science, International Islamic University Malaysia, Bandar Indera Mahkota, Kuantan, Pahang, 25200 Malaysia e-mail: *[email protected]; **[email protected] Received February 07, 2020; revised February 16, 2020; accepted February 22, 2020
Abstract—Some tert-butylcalix[4]arene derivatives were synthesized by thermal and microwave methods. The microwave method was conducted in two ways: (1) all the reactants were added in one batch and (2) the reactants were added in two batches under different conditions. Tetrabutylammonium iodide (TBAI) was used in both methods, and its effect on the reaction rate was studied. In general, the duration of the microwaveassisted reactions in the presence of TBAI, especially in the two-batch method, was shorter, and the yields were higher, than in the thermal reaction. The highest yield of (S)-glycidyl calixarene derivative by the thermal method was obtained by using K2CO3 as a base with MeCN as a solvent in the presence of TBAI, while the lowest yield of the same compound was observed when using acetone in the absence of TBAI. All the synthesized calix[4]arene derivatives were characterized by 1H and 13C NMR experiments. Keywords: microwave synthesis, calix[4]arenes, tetrabutylammonium iodide
DOI: 10.1134/S1070428020070209 INTRODUCTION Thermal heating is an established method commonly used in organic synthesis. However, prolonged reaction time, formation of undesirable side products, and sometimes low yields are the common concerns associated with the conventional thermal procedure. In order to rationalize the organic synthesis and optimize the reaction process, researchers often look for new pathways and approaches [1, 2]. Introduction of new catalysts, use of an appropriate solvent system, and optimization of other reaction conditions such as pH and temperature, are some of the areas of interest in search of perfect synthesis. Microwave-assisted organic synthesis (MAOS) was introduced in the late 1990s as an alternative to the conventional heating procedure, and it showed comparable and sometimes superior results than its counterpart. This eco-friendly method is an attempt to reduce the time of chemical reactions and obtain the product(s) in quantitative yield [3]. Calixarenes are cyclic oligomers that are considered as the third generation of supramolecules, and they show a wide range of applications [4, 5]. The basic
core of calixarene is usually modified at the para position of the aromatic rings (upper rim) and the phenolic hydroxyl functional group region (lower rim). The mechanism of the reaction and geometry of calixarene derivatives are greatly influenced by the catalyst applied and solvent system used [6]. Both conventional and microw
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