Photoelectrochemical Tandem Chlorination of sp3 C–H Bond in Seawater/Chloroform Two-Phase Electrolyte System by Ti-Doped Fe2O3 Photoanode

C-H bond activation is a fundamental challenge in organic synthesis, and various routes have been explored. Among them, halogenation has played an important role in producing valuable intermediates. We report a novel photoelectrochemical (PEC) tandem C-H chlorination using a Ti-doped Fe2O3 (Ti:Fe2O3) photoanode in a two-phase electrolyte system consisting of natural seawater and a chloroform organic phase. This system enables the in situ generation of Cl2 via the chlorine evolution reaction (CER) with near 100% Faradaic efficiency (FE) while suppressing the competing oxygen evolution reaction (OER). The generated Cl2 undergoes photolytic cleavage, forming chlorine radicals that selectively chlorinate sp3 C-H bonds in toluene, cyclohexane, and ethylbenzene with 100% regioselectivity. This work demonstrates the feasibility of seawater-based PEC halogenation and provides a sustainable strategy for selective C-H functionalization in organic synthesis.