Plumbagin Extraction: A Green Study

Abstract

A green study was undertaken for the extraction of plumbagin, an important natural naphthoquinone, from the roots of Plumbago pulchella Boiss. In the first stage, four solvents were comparatively evaluated, acetone, n-hexane, ethyl acetate, and methanol; attending Principle #5, only green solvents (ethyl acetate and acetone) were underscored. In a second step, considering Principle # 6, various green alternative activating modes were assessed: two electromagnetic methods, microwave (MW) and near-infrared (NIR), in addition to mechanical approaches, ultrasound (US), and tribochemistry-mechanochemistry (TB-MCh). These green modes were studied in comparison to the classical mantle heating (MH) and finally with maceration (M). MW and US-MH ensued the better modes, and EtOAc (green) and n-hexane (non-green) displayed the best yields (0.027% and 0.025%, respectively). Focusing on Principle #11, the monitoring and quantification of the extractions were performed by GC-MS employing 8-hydroxyquinoline as a reference. Some other involved Principles (#1, #3, #7, #12) will be commented on in the discussion. As an important complement, a statistical technique based on the analysis of variance (ANOVA) and response surface methodology was used to establish the degree of dependence of the amount of plumbagin extracted with the parameters time and amount of root, in addition to a GC-MS validation process carried out according to ICH Q2 R2 2022 guidelines. Finally, it is convenient to highlight that the target plant is native to Mexico, and according to a profound literature search, no chemical information for Plumbago pulchella Boiss is accessible.