Synthesis of branched naphthoquinones from castor oil

Adriano Olímpio da Silva, Dênis P. de Lima, Rosangela da Silva Lopes, Ricardo Vieira de Lima, Roberto da Silva Gomes

Abstract


The naphthoquinones are cyclic aromatic α,β-dienonas with a basic framework derived from naphthalene. They are also found in many higher plants, algae, fungi and as the product of the  metabolism  of some  bacteria  having large biologica activity described in the literature such as antibacterial, anti-inflammatory, antitumor, anticancer and trypanocidal [1-3]. Castor oil is an abundant raw material in Brazil of great versatility and, it is present in biodiesel production, surfactants, cosmetics and others. Considering the importance of naphthoquinones and, the availability of the ricinoleic acid from castor oil, the aim of this study was the preparation of new branched naphthoquinones in order to test their trypanocidal activity. Castor oil was submitted to saponification with sodium hydroxide, ethanol and water under reflux for 6 h. We then carried out an acid hydrolysis with hydrochloric acid and the formed ricinoleic acid was extracted with ethyl acetate. Following, through Kochi-Anderson addition reaction it was performed the alkylation of a naphthoquinone 1 and 2, using ammonium persulfate, silver nitrate, acetonitrile and water, under heating at 70-80 ° C during 3 h, to give the branched naphthoquinones 4 and 5 (scheme 1). The naphthoquinone 3 will be similarly submitted to this procedure. The naphthoquinones 4 and 5 were purified by column chromatography on sílica gel using hexane as the eluent. The compounds were characterized by mass spectrometry and 1H and 13CNMR spectroscopy.


Keywords


alkylation; naphthoquinones; ricinoleic acid

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Orbital: The Electronic Journal of Chemistry (e-ISSN 1984-6428) is a quarterly scientific journal published by the Institute of Chemistry of the Universidade Federal de Mato Grosso do Sul, Brazil. Orbital is a peer-reviewed, open-access journal.