Abstract

This review summarizes recent applications of nickel as a nonprecious metal catalyst in hydrodehalogenation (HDH) reactions of halogenated aromatic compounds (Ar–Xs). Nickel-based HDH catalysts were developed for reductive treatment of both waste containing concentrated Ar–Xs (mainly polychlorinated benzenes) and for wastewater contaminated with Ar–Xs. Ni-catalyzed HDH enables the production of corresponding nonhalogenated aromatic products (Ar–Hs), which are principally further applicable/recyclable and/or Ar–Hs, which are much more biodegradable and can be mineralized during aerobic wastewater treatment. Developed HDH methods enable the utilization of both gaseous hydrogen via the direct HDH process or other chemical reductants as a source of hydrogen utilized in the transfer of the hydrodehalogenation process. This review highlights recent and major developments in Ni-catalyzed hydrodehalogenation topic since 1990.

Highlights

  • Ar–Xs are commercially important chemicals that are used as inert solvents, end products and intermediates in the manufacture of plastics, dyes and a diversity of agrochemicals, flame retardants or other specialty fine chemicals.Ar–Xs are xenobiotic, highly stable in the environment, resistant to biodegradation, often exhibit considerable toxicity and have long been regarded as a major source of environmental pollution [1]

  • Scrivanti et al later even published the complete HDH of 1,2,3-trichlorobenzene using an excess of NaBH4, the catalytic amount of Ni(Ph3P)2Cl2 salt with the co-action of an extra two equivalents of Ph3P in ethanol/pyridine solution at 70 °C after several hours of action

  • HDH of hardly reducible chlorinated compounds such as 4-chloroaniline or other polychlorinated aromatic compounds is not promoted by the addition of glucose, as we described earlier [91]

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Summary

Introduction

Ar–Xs are commercially important chemicals that are used as inert solvents (chlorobenzene or o-dichlorobenzene), end products and intermediates in the manufacture of plastics, dyes and a diversity of agrochemicals, flame retardants or other specialty fine chemicals. HDH involves hydrogenolysis of C–X bonds, lowering the toxicity and generating biodegradable or even reusable raw material Ar–H from Ar–X. It requires an external source of hydrogen and is typically promoted using hydrogenation catalyst (Pd, Pt, etc.) [1]: Licensee MDPI, Basel, Switzerland. From an economic viewpoint, considering incineration as the principal means of halogenated organic waste treatment, a move to a catalytic hydrodehalogenation-based treatment represents immediate cost saving in terms of fuel and/or possible chemical recovery [1]. Effective HDH enables the application of halogen as the protective and/or directive group in aromatic substitution reactions in syntheses of specialty organic fine chemicals, for example of herbicide Dicamba [3]. Direct HDH using excess of H2 gas and transfer HDH are the two employed strategies for reductive treatment of Ar–Xs

Ni-Catalyzed HDH Using Gaseous H2
Gas Phase HDH Catalyzed by Nickel on Alumina
It was their catalytic properties in the gas-phase HDH
HDH Catalyzed by Nickel on Silica
Raney Nickel Based HDH
Hydrogentransfer in Ni-Catalyzed Hydrodehalogenation Reactions
14. Ni-based produces polyphenylene
Solutions Methods
18. Dissolution
Utilization of Raney Al–Ni Alloy in HDH Processes
21. Raney Al–Ni
22. Al–Ni-based
23. Raney based HDCisofaccompanied
Ni-Based Bimetals Applied in Transfer HDH
The Role of HDH for Application of Halide as Protecting and Directing Group
Methods for for Recycling
Findings
Conclusions

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