Chloroaromatics remediation: Insights into the chemical reduction and hydrodechlorination of chlorobenzenes

Abstract

Chloroaromatic compounds—including not only chlorobenzenes, but alsochloroanilines, chlorophenols and others—are chemicals widely used for decades as industrial solvents, synthetic intermediates, and pesticides. However, many of these compounds are classified as persistent organic pollutants due to their biaccumulative nature, additionally having toxic and neurotoxic effects to humans and animals. Significant stocks of obsolete chloroaromatics, along with numerous heavily contaminated sites worldwide—including air, surface water, groundwater, and soil—underscore the urgent need for efficient remediation strategies. Chemical reduction has emerged as a well-stablished and effective approach for the transformation and/or valorization of chloroaromatics, particularly chlorobenzenes, into less toxic and higher-value compounds, such as cyclohexane and benzene. This approach may also yield other specific products such as methane, polyaromatics, and carbon-based nanomaterials.In this review, we provide the first comprehensive and also critical assessment of all hydrodechlorination and chemical reduction methods applied to the transformation, remediation, and valorization of chlorobenzenes. All the available literature has been analyzed in terms of practical feasibility, limitations, cost-effectiveness, and scalability. Reduction strategies are categorized by the type of reducing agent, distinguishing between stoichiometric and catalytic methods. The performance of various reductants—including metals, metal sulfides, hydrogen gas, hydrides, and water—in combination with a long series of organic and inorganic hydrogen donors (e.g. hydrocarbons, alcohols, formates, silanes, hydrazine) is thoroughly evaluated. Finally, insights into the electrochemical and photochemical reduction of chlorobenzenes in both polluted water and soil are also provided.