Continuous photocatalytic redox-neutral hydrohalogenation of unsaturated C-C bonds to mono-halides under mild conditions

<title>Abstract</title> <p>Halogenation is foundational to organic synthesis, but the synthesis of mono-halides, especially with regioselectivity, remains a largely unmet challenge in modern organic chemistry 1,2. Here we report the photocatalytic redox-neutral hydrohalogenation of unsaturated hydrocarbons as a new general approach that enables highly efficient and selective production of various organic mono-halides under mild conditions. Using RuO2/TiO2 nanosheet and photocatalytic acetylene hydrochlorination as the photocatalyst and benchmark reaction, this photocatalytic approach can achieve continuous vinyl chloride monomer production with production rate 53.9 mmol gcat−1 h−1, and can remain stable for over 104 hours with incredibly high selectivity (99.99%). No sacrificial reagents are required and hydrohalic acid serves as the ideal hydrogen and halogen sources with 100% atomic utilization efficiency. This photocatalytic redox-neutral approach impels the concurrent generation of hydrogen and halogen radicals and their tandem dual-addition into the same unsaturated C-C bond, and steers hydrohalogenation towards the anti-Markovnikov’s rule. The methodology shows generality for various unsaturated hydrocarbons and halide ions.</p>