Practical method for PCB degradation using Pd/C-H2-Mg system

Mechanochemical treatment of hexachlorobenzene-contaminated soil with additives

The use of mechanochemistry for the remediation of hexachlorobenzene (HCB)-contaminated soil was investigated. Additives such as alkaline materials, neutral materials, natural minerals, and solid waste were studied to explore their effect on the degradation of hexachlorobenzene in soil with single or combined addition by mechanochemical method. The best combination of materials were determined based on HCB destruction percentage by considering the impact on soil quality, the treatment cost, and the availability of additives. Scanning electron microscope (SEM) images and X-ray photoelectron spectrometer (XPS) analysis were conducted for the mechanism studies. The combination of albite and ferric oxide (Fe₃O₄) was found to achieve the best performance in the degradation of HCB with the destruction percentage from 74.3 to 92.5% after 2-h and 6-h reaction, respectively. The developed fracture structure and complex compositions of albite provided abundant reaction sites for mechanochemical degradation of HCB in soil.

Degradation of PCB67 in soil using the heterogenous Fenton process induced by montmorillonite supported nanoscale zero-valent iron

Montmorillonite supported nanoscale zero-valent iron (MMT-nZVI) was prepared and proved to be able to induce the heterogenous Fenton process for better removal of 2,3',4,5-tetrachlorobiphenyl (PCB67) in a long-term polluted soil. PCB67 removal depended highly on the dosages of MMT-nZVI and H₂O₂, and the initial pH, with the highest removal rate of 76.38% at conditions of H₂O₂ 45.99 g·kg^-1, MMT-nZVI 29.88 g·kg^-1 and initial pH 3.5 after 80 min of reaction. Furthermore, PCB67 could be removed in a wider pH range (from 3.5 to near neutrality), with a loss of 13.6% in removal rate at neutral pH. With an activation energy of 21.4 kJ·mol^-1, the degradation of PCB67 was an endothermic and diffusion-controlled process and followed the pseudo-first-order kinetics. That Fe²⁺ was supplied through aerobic corrosion of MMT-nZVI to activate H₂O₂ for·OH production was the possible mechanism of PCB67 degradation, leading to complete mineralization of PCB67 through two proposed pathways, with the intermediates of ethylbenzene and 3-hepten-2-one, as well as dibutyl phthalate and butyl acetate respectively.

Defunctionalisation catalysed by boron Lewis acids

Selective defunctionalisation of organic molecules to valuable intermediates is a fundamentally important transformation in organic synthesis. Despite the advances made in efficient and selective defunctionalisation using transition-metal catalysis, the cost, toxicity, and non-renewable properties limit its application in industrial manufacturing processes. In this regard, boron Lewis acid catalysis has emerged as a powerful tool for the cleavage of carbon-heteroatom bonds. The ground-breaking finding is that the strong boron Lewis acid B(C6F5)3 can activate Si-H bonds through η1 coordination, and this Lewis adduct is a key intermediate that enables various reduction processes. This system can be tuned by variation of the electronic and structural properties of the borane catalyst, and together with different hydride sources high chemoselectivity can be achieved. This Perspective provides a comprehensive summary of various defunctionalisation reactions such as deoxygenation, decarbonylation, desulfurisation, deamination, and dehalogenation, all of which catalysed by boron Lewis acids.

Metal catalyzed defunctionalization reactions

The chronological development of metal assisted defunctionalization reactions is discussed from the stoichiometric to the catalytic stage with their application in synthetic organic chemistry.

Practical remediation of the PCB-contaminated soils

A practical method for the elimination of PCBs from PCB-contaminated soil has been developed by the combination of Soxhlet extraction using a newly-developed modified Soxhlet extractor possessing an outlet valve on the extraction chamber with the chemical degradation. Various types of PCBs contaminated in soils could be completely extracted in refluxing hexane, and the subsequent hydrodechlorination could also be completed within 1 h in a hexane-MeOH (1 : 5) solution in the presence of Pd/C and Et3N under ordinary hydrogen pressure and temperature without the transfer of the extracted PCBs to other reaction container (a complete one-pot procedure). The present system is quite useful as a simple, safe, mild and reliable remediation method of PCB-contaminated soil.