电化学氟化的新进展

电化学氟化是利用电极反应将氟直接引入有机或无机物的一种重要方法。有机物的电化学氟化方法有两种: 一是Simons于1941年发明的, 用镍作阳极, 在无水氟化氢溶液中, 电解制备全氟化合物的方法。此方法在近年来有不少改进。另一是1970年Rozhkov提出的, 以有机溶剂(如含Et3N.3HF的MeCN)为介质, 在铂阳极上,氧化得到单氟化产物的方法。本文全面地综述了这两种方法, 并着重于最新民发展。     

A new cell for electrochemical processes

A simple electrochemical reactor is described that fulfills most of the desired goals normally required. It is easy to construct and scale up. The main feature of the design is an electrode sandwich in which cloth separators are used to provide electrical insulation. They provide an inter-electrode space for the electrolyte and give good mass transfer characteristics. The ohmic drop in the solution is very low and the ratio of active electrode area to electrode volume is high. Operating properties have been determined and show that the cell may be applied to systems that might at first seem unfavourable for an electrochemical process, viz.: multi-phase (especially gas/liquid) mixtures and systems with very low concentrations of electroactive species. These proposals have been tested with some organic synthesis and with waste water purification (Cr(VI) reduction). The cell has been shown to perform well and to be inexpensive - both in construction and in operation.     

The electrochemical fluorination of acetyl fluoride

The electrochemical fluorination of acetyl fluoride in anhydrous hydrogen fluoride to produce trifluoroacetyl fluoride was investigated in a microprocessor-aided modified Simons' reactor. The product was recovered in acetic acid as trifluoroacetic acid. The experiments were carried out at a controlled anodic potential using a Cu/CuF₂ reference electrode. Product yields of 36 - 45%, current efficiencies of 30 to 50% and energy efficiencies of 11 – 23% were obtained.Experimental results of this investigation are presented and discussed.     

Detection of free radicals in electrochemical fluorination

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 255–256, January, 1991.     

A microfluidic flow-through electrochemical reactor for wastewater treatment: A proof-of-concept

In this work, a microfluidic flow-through electrochemical reactor for wastewater treatment is presented which simultaneously minimizes ohmic drop and mass transfer limitations, two of the most important bottlenecks in electrochemical wastewater treatment. A proof-of-concept comparison versus a state-of-the-art flow-by commercial reactor revealed that the proposed reactor greatly outperforms the commercial system. The novel system requires only 2.4 Ah dm^− 3 (vs. 11.4 Ah dm^− 3) and 12.5 kWh m^− 3 (vs. 75.0 kWh m^− 3) to completely mineralize 100 mg dm^− 3 of clopyralid spiked in a low-conductive (1 mS cm^− 1) matrix with both systems using diamond anodes. The microfluidic flow-through configuration represents a promising approach to the development of cost-effective electrochemical technologies for wastewater treatment.     

Selective fluorination of adamantanes by an electrochemical method

Selective fluorination of adamantanes was achieved by the electrochemical fluorination method, using Et 3N-5HF as electrolyte and a fluorine source. Mono-, di-, tri-, and tetrafluoroadamantanes were selectively prepared from adamantanes by controlling the oxidation potential, and the fluorine atoms were introduced selectively at the tertiary carbons. Adamantanes that have functional groups such as ester, cyano, and acetoxymethyl were also fluorinated selectively.     

The electrochemical fluorination of octanoyl fluoride with electrolyte circulation

A modification to the standard method of electrochemical fluorination is described which embodies a forced flow of electrolyte through the electrode pack. A preliminary study of flow characteristics through an electrode pack was carried out.Good yields of perfluorooctanoyl fluoride and associated perfluorinated products are reported. The nature of the anode surface was studied before and after fluorination by scanning electron microscopy.     

A general-purpose minicomputer system for electrochemical studies

A software system (SYS) is described for a 16-bit minicomputer interfaced to a potentiostat and electrochemical cells, as well as various display and signal devices. The software controls the functions common to all electrochemical experiments, such as applying cell voltage, timing, sampling signals, displaying these on graphic devices, and smoothing data; it also loads specific user programs into core, for experiments requiring these functions. In this way, a new experiment can quickly be programmed and running; the software also contains some debugging aids. While the system described is specific to the minicomputer used, its general structure should be capable of implementation on any mini- or micro-computer.     

Production of MoF6 via electrochemical fluorination

A new process for the electrochemical preparation of the fluorinating agent MoF₆ is described. Solutions fo MoF₄ in anhydrous HF are electrolyzed in a multielectrode cell at 20°C, 5.4÷5.7V cell voltage and 50÷100 A/m² current density, using nickel anodes and cathodes. A new modified Simons cell has been designed, equipped with a stirring system for the efficient recirculation of the electrolyte and with a condenser held at ?15°C.The reaction product MoF₆ (b.p. 35°C) dissolves in the electrolyte, contributing to its conductivity and in part is volatilized together with HF and some byproduct fluorine.Gaseous MoF₆ passing beyond the condenser can be easily collected and separated in a nickel trap held at low temperature.The process presents substantial advantages in comparison with known alternatives, such as the synthesis of MoF₆ from the elements Mo and F₂ at 250°C or the dismutation reaction: 2MoCl₅ + 10HF → MoF₄ + MoF₆ + 10 HClPreparation of the starting material MoF₄, operating conditions and experimental results are illustrated.     

Unique solvent effects on selective electrochemical fluorination of organic compounds

Recent studies on solvent effects on electrochemical partial fluorination are reviewed. At first, the historical background and some problems of electrochemical fluorination in organic solvents like acetonitrile (MeCN) are briefly mentioned. Ethereal solvents like dimethoxyethane (DME) and a mixture of DME and MeCN were found to improve both the yield and current efficiency for electrochemical fluorination since these solvent systems effectively suppress anode passivation and overoxidation of fluorinated products once formed during the electrolysis. It was also found that DME stabilizes radical cationic intermediates of 4-arylthio-1,3-dioxolan-2-ones and 3-phenylthiophthalide leading to α-fluorination while dichloromethane (CH₂Cl₂) destabilizes them leading to fluorodesulfurization. On the other hand, imidazolium ionic liquids and liquid fluoride salts like Et₄NF·4HF and Et₃N·5HF exhibited similar effects to CH₂Cl₂. Selective fluorination of hardly oxidizable phthalide was also achieved using a combination of two kinds of ionic liquids (imidazolium triflate and liquid fluoride salts).     

Novel electrochemical heterogeneous catalytic reactor for organic pollutant abatement

Taking nitrobenzene as a model, electrochemical heterogeneous catalytic degradation of organic pollutant is investigated using a novel electrochemical heterogeneous catalytic reactor coupled by three-dimensional electrode with heterogeneous catalytic reactor. The nitrobenzene removal efficiencies considerably depend on the applied potential, initial pH, and the concentration of the supporting electrolyte. The results show that, with catalyst the nitrobenzene removal efficiencies are higher than that of control (without catalyst). The efficiency of ferrous catalyst is the best for nitrobenzene removal especially. It is clear that the reaction of electro-oxidation is promoted by the catalyst. A possible mechanism of nitrobenzene degradation is deduced based on products. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 3, pp. 313–318. The text was submitted by the authors in English.     

A modified CCA model describing gelation processes

In order to simulate a gelation process that occurs by condensation-polymerization reactions in solution, the cluster–cluster aggregation (CCA) model is modified by introducing four- and two-functional units as monomers. The modified CCA model shows a clear dependence of the fractal dimension of the resulting gel structure on the ratio between the numbers of the four- and two-functional units. The model should be applicable to various real systems. For example, it explains the behavior of experimentally found fractal dimension that depends on the amount of water added in the sol–gel aggregation process of SiO₂ systems.     

Effect of surface fluorination on the electrochemical behavior of petroleum cokes for lithium ion battery

Surface structure change and electrochemical behavior of fluorinated petroleum coke samples (petroleum cokes: petroleum coke and those heat-treated at 1860 °C, 2300 °C and 2800 °C, abbreviated to PC, PC1860, PC2300 and PC2800, respectively) have been investigated. Surface oxygen of petroleum coke was decreased by the fluorination using elemental fluorine. Raman and EPR spectroscopies revealed that surface fluorination increased surface disorder and lattice defects. ¹⁹F NMR spectrum suggests that distribution of fluorine atoms in PC fluorinated 300 °C was similar to that in graphite fluoride with covalent CF bonds. Surface areas of fluorinated petroleum cokes were nearly the same as those of non-fluorinated ones or only slightly increased by fluorination, except PC fluorinated at 300 °C. It is noted that first coulombic efficiencies of PC2300 and PC2800 were highly increased to 80-84% by the fluorination at 300 °C. These values of 80-84% were 12-18% higher than those of non-fluorinated PC2300 and PC2800.     

Selective electrochemical fluorination of organic molecules and macromolecules in ionic liquids

This article provides an outline of recent studies on selective electrochemical fluorination in ionic liquid fluoride salts toward green sustainable chemistry. First, a brief historical background of electrochemical fluorination in organic solvents is provided, and some particular problems and unique solvent effects associated with this technique are briefly mentioned. Second, recent progress in selective fluorination and fluorodesulfurization of organic molecules and macromolecules in ionic liquids using direct and indirect electrolysis with recyclable mediators is reviewed.     

A new method for fluorination of sterols

Diethylaminosulfurtrifluoride (DAST) is a good fluorinating reagent for sterols. The fluorinating reactions proceed through SN₂ mechanism, while reactions through free carbonium ion are responsible for rearrangements and eliminations.     

A Born-Oppenheimer approach to adiabatic electrochemical charge transfer processes

An approach for the construction of the Hamiltonians and free energy surfaces for adiabatic electrochemical reactions accompanied by a considerable reorganization of the intramolecular structure is presented. For one-electron processes it reproduces the results of Koper and Voth (Chem. Phys. Lett. 282 (1998) 100) without an a priori introduction of a switching function transforming the bonding molecular potential into an antibonding one. The present approach is extended to two-electron processes, which are of importance for the dissociative adsorption and electrocatalysis.     

Ozone-based electrochemical advanced oxidation processes

Novel processes have recently been developed that provide for the enhancement of ozonation through combination with electrochemical treatments. These are processes that can be included among those defined as advanced oxidation processes as they proceed via electrogeneration of highly oxidizing radical species.These processes are generally carried out by sparging ozone in both divided and undivided electrochemical cells in order to promote its decomposition through different mechanisms, depending on the electrode materials adopted, and in some cases still debated.This mini review presents the most recent advances in the field of electrochemically assisted ozonation.In particular, the first section is focused on the process known as electroperoxone (EP) where the ozone decomposition is enhanced by the adoption of carbon-based cathodes, due to the electrogeneration of hydrogen peroxide, while the second section is focused on the process that implies ozonation in a cell adopting metal-based cathodes.