A Green and Efficient One-Pot Synthesis of 2,3-Diphenylquinoxaline Using Sodium Hypochlorite as a Sustainable Oxidant

Abstract: Quinoxaline derivatives are a vital class of compounds, with 2,3-diphenylquinoxaline (DPQ) being particularly important for its applications in pharmacology and material science. However, traditional methods for its synthesis often rely on harsh conditions and environmentally harmful solvents, creating a need for greener alternatives. Addressing this challenge, we present a highly efficient, sustainable, and versatile one-pot method for synthesizing DPQ. This approach is centered on green chemistry principles, utilizing sodium hypochlorite (NaOCl·5H₂O) as an inexpensive and eco-friendly oxidant.

The synthesis involves the oxidation of benzoin and its subsequent condensation with o-phenylenediamine within a benign ethanol/water solvent system. A key strength of this method is its remarkable adaptability; the reaction performs exceptionally well under several conditions, affording excellent yields of 96% with a photochemical reactor, 92% under standard reflux, and 83% in an electrochemical cell. The successful synthesis and high purity of the DPQ product were confirmed through comprehensive characterization, including ¹H and ¹³C NMR spectroscopy.

To provide deeper mechanistic insight, the reaction was modeled using Density Functional Theory (DFT) calculations. These studies elucidated a favorable reaction pathway involving the formation of aminol and diaminol intermediates, identifying key energetic barriers for the proton transfer steps. By successfully integrating multiple green-by-design strategies with detailed computational validation, this research provides a robust and accessible blueprint for the clean production of valuable quinoxaline derivatives, championing the broader adoption of sustainable practices in modern organic synthesis.