Porous anodization

Fluorocarbons are made commercially also by the electrolysis of hydrocarbons in anhydrous hydrogen fluoride (Simons process) (14). Nickel anodes and nickel or steel cathodes are used. Special porous anodes improve the yields. This method is limited to starting materials that are appreciably soluble in hydrogen fluoride, and is most useflil for manufacturing perfluoroalkyl carboxyflc and sulfonic acids, and tertiary amines. For volatile materials with tittle solubility in hydrofluoric acid, a complementary method that uses porous carbon anodes and HF 2KF electrolyte (Phillips process) is useflil (14). 

Fig. 15.1 Diagrammatic cross-section of porous anodic oxide film...

Figure C shows an electron photomicrograph of a broken planar SOFC. The thick portion on the left is the porous anode structure. This is an anode-supported cell, meaning that in addition to collecting current and supporting the anode reaction, the anode layer stiffens the whole cell. The layer on the right is the cathode, and the interface between the two is the thin electrolyte. One of the challenges of this design is to ensure that the rates of expansion of the cathode and the anode match. If the anode expands faster than the cathode, the planar cell tends to curl like a potato chip when the temperature changes.

Routkevitch D, Bigioni T, Moskovits M, Xu JM (1996) Electrochemical fabrication of CdS nanowire arrays in porous anodic aluminum oxide templates. J Phys Chem 100 14037-14047... 

I I Dense Anodic Oxid E23 Oxide Transition [Ml Porous Anodic Oxid... 

The trimethylsilyloxy (TMSO) group is stable under the coupling conditions in acetonitrile (Table 12, number 6). After oxidative dimerization the TMS-ether can be mildly hydrolyzed (H+ and H2O) to the phenol or converted to a dibenzofuran. 1,2-Dialkoxybenzenes have been trimerized to triphenylenes (Table 5, numbers 7, 8). The reaction product is the triphenylene radical cation, which is reduced to the final product either by zinc powder or in a flow cell consisting of a porous anode and cathode [188]. Anodic trimerization of catechol ketals yields triphenylene ketals, which can function as a platform for receptors, for example, in an artificial caffeine receptor [190]. 

A very early use of anodic alumina as a template involved colonization of the alumina by depositing nanometals in the pores [39]. Somewhat later, Kawai and Ueda templated cobalt and nickel in alumina by electrodeposition [40]. Other metals were deposited by Andersson et al. [41] and Patel et al. [42]. The use of anodic alumina as a template increased after Furneaux et al. developed a convenient voltage-reduction method for detaching the porous anodized alumina from the underlying aluminum [38]. 

Fuel cells are electrochemical devices that convert the chemical energy of a reaction directly into electrical energy. The basic physical structure or building block of a fuel cell consists of an electrolyte layer in contact with a porous anode and cathode on either side. A schematic representation of a fuel cell with the reactant/product gases and the ion conduction flow directions through the cell is shown in Figure 1-1. 

Hoar, T. P. and N. F. Mott. 1959. Mechanism for the formation of porous anodic oxide films on aluminum. J. Phys. Chem. Solids 9 97-99. 

Itaya, K., S. Sugawara, K. Arai and S. Saito. 1984. Properties of porous anodic aluminum oxide films as membranes. J. Cheim. Eng. Japan 17(5) 514-20. 

O Sullivan, J. P. and G. C. Wood. 1970. The morphology and mechanism of formation of porous anodic films on aluminum. Proc. Roy. Soc. London A317 511-43. 

Smith, A. W. 1973. Porous anodic aluminum oxide membrane. J. Electrochem. Soc. 120(8) 1068-69. 

Takahashi, H., M. Nagayama, H. Akahori and A. Kitahara. 1973. Electron-microscopy of porous anodic films on aluminum by ultrathin section technique. Part 1. The structural change of the film during the current recovery. J. Electron Microscopy 22(2) 149-57. 

Porous anodized alumina (plateshaped membranes), mean pore diameter 80-250 nm. Reactants enter the reactor from opposite membrane sides. 

Fumeaux, R. C., A. P. Davidson and M. D. Ball. 1987. Porous anodic aluminum oxide membrane catalyst support. European Patent Appl. 0,244,970A1. 

Imine intermediates can be trapped by an added nucleophile. However the only reactions of general preparative value are those in which a carbon-carbon bond is formed. In most other cases the product is unstable under the reaction conditions, reverting to the imine which reacts further. Reactions are best carried out in the flow through cell devised by Moinet and Raoult, illustrated in Figure 8.1 [87]. This cell permits total oxidation of tlie substrate in one pass through the porous anode, tlius exposing the product to further oxidation for only a short time, a-aminonitriles are obtained when cyanide ion is added to the electrolyte [88, 89]. In the case of piperidine ring oxidation, addition to the imine is from the less hindered... 

Imai H, Takei Y, Shimizu K, Matsuda M, Hirashima H (1999) Direct preparation of anatase Ti02 nanotubes in porous alumina membranes. J Mater Chem 9 2971-2972 Michailowski A, A1 Mawlawi D, Cheng GS, Moskovits M (2001) Highly regular anatase nanotubule arrays fabricated in porous anodic templates. Chem Phys Lett 349 1-5 Jung JH, Kobayashi H, van Bommel KJC, Shinkai S, Shimizu T (2002) Creation of novel helical ribbon and double-layered nanotube Ti02 structures using an... 

Michailowski A, Al-Mawlwai D, Cheng GS, Moskovits M (2001). Highly regular anatase nanotubule arrays fabricated in porous anodic templates. Chem Phys Lett 349 1-5... 

Thompson GE (1997) Porous anodic alumina fabrication, characterization and applications. Thin Solid Films 297 192-201... 

Eiu Y, Alwitt RS, Shimizu K (2000) Cellular porous anodic alumina grown in neutral organic electrolyte-I. Structure, composition, and properties of the films. J Electrochem Soc 147 1382-1387... 

The three principal electrochemical methods are described by which fluorine can be directly introduced into organic compounds, namely electrolysis in molten salts or fluoride ion solutions, electrolysis in molten potassium fluoride/hydrogen fluoride melts at porous anodes, and electrolysis in anhydrous hydrogen fluoride at nickel anodes. Using examples from the past decade, it is aimed to demonstrate that electrofluorination in its various forms has proved to be an increasingly versatile tool in the repertoire of the synthetic chemist. Each method is described in terms of its essential characteristics, reaction parameters, synthetic utility, advantages and disadvantages, patent protection, and potential for commercial exploitation. The different mechanisms proposed to explain each process are critically reviewed. 

Electrolysis in Molten Potassium Fluoride/Hydrogen Fluoride at a Porous Anode... 

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