State-of-the-art mechano-synthesis of substituted 1,2-naphthoquinones Kenneth Trejos-Cuadra 1,2 ; Guy Lamoureux 1,2 ; Katherine Chaves-Carballo 1,2 and Alice L. Perez 1,2 . 1 Natural Products Research Center (CIPRONA), Costa Rica, 2 University of Costa Rica, UCR, Costa Rica The molecular scaffold 1,2-naphthoquinone has many uses in industry, medicinal chemistry, materials, and REDOX chemistry. There are very few examples of 4-alkoxy and 4-phenoxy substituted 1,2-naphthoquinones, however, that have been synthetized and characterized in the literature. We present the synthesis of substituted 4-phenoxy-1,2-naphthoquinones, but utilizing a better environmental approach compared to classical synthesis. We compare the traditional aqueous synthesis to mechanochemistry, the latter which has the advantages of working with solid reagents, using less solvent, and requiring less time. This research combines state-of-the-art techniques in spectroscopy and new methods in synthesis. The preparation of a library of 4-substituted 1,2-naphthoquinones has proven to be a practical research project due to their crystallinity, coloration, and spectroscopic properties. The comparison of two different synthesis methods highlights the advantages and disadvantages of each and gives a better overview of which method is best suited for future work. The study of the spectroscopic and biological properties of a number of these compounds allows students to improve their analytical skills and increase their interest in research. The principles of green chemistry, as well as new techniques in synthesis, encourage others to follow green-chemistry practices, and to create a paradigm shift in chemical synthesis. We conclude with the importance of undergraduate research projects and the value of shared instrumentation for the chemistry program at the University of Costa Rica.
Figure 1. 1 H-NMR spectrum of 4-(p-methoxyphenol)-1,2-naphthoquinone. References
1. Elbashir, A. A.; Ahmed, A. A.; Ali, S. M.; Aboul-Enein, H. Y.; 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS) as an analytical reagent for the determination of pharmaceutical amine by spectrophotometry. Applied Spectroscopy Reviews. 2012, 47: 219-232. 2. López, L. I., Leyva, E., & García de la Cruz, R. F. Las naftoquinonas: más que pigmentos naturales. Revista mexicana de ciencias farmacéuticas. 2011, 42(1), 6-17. 3. Raymond, N. K.; Haberfield, P.; Solvation as a factor in the alkylation of ambident anions: The importance of the dielectric factor. JACS. 1962, 85: 1148-1154.
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