Advantage of Using NaH₂PO₂ over Alkali Metal Formates as a Hydrogen Source for Pd-gC₃N₄ Catalyzed Hydro-Dehalogenation of Aryl Halides

Halogenated and polyhalogenated aromatic compounds are known for their toxicity and effect on human health and the environment. These aromatic hydrocarbons have been widely used in pesticides, flame retardants, pharmaceuticals, and other industrial chemicals. The substitution of halogen atoms of aromatic halides by hydrogen atoms in the presence of a metal catalyst is an important organic transformation and is known as a catalytic hydro-dehalogenation reaction. It is an important technique used for the treatment of halogenated industrial waste. Herein, we investigated the comparative hydro-dehalogenation of aryl halides in the presence of Pd-gC₃N₄ catalyst using various hydrogen transfer sources in an eco-friendly manner. We also investigated the advantage of using sodium hypophosphite (NaH₂PO₂) as a hydrogen source for hydro-dehalogenation in comparison to alkali metal formates. For hydro-dehalogenation of 1 mmol of aryl halide, 2 equivalents of NaH₂PO₂ are used while 4 equivalents of KHCO₂ are required in the presence of 3.8 wt % of Pd metal catalyst. The Pd-GCN catalyst was characterized by various microscopic and spectral techniques such as PXRD, FTIR, SEM, TEM, XPS, and TGA, etc. A gram scale reaction was performed to analyze the industrial potential of the proposed catalytic system. Finally, the recyclability of Pd-GCN was found excellent and the catalyst could run multiple cycles with sustained activity.