Preparation by Anodic Oxidation

Preparation by Anodic Oxidation.—When potassium hydrogen sulfate ionizes, we may consider the ions -°v 

A similar result is obtained with some other polybasic acids, though not with all. 

In the tube T, place a solution of potassium hydrogen sulfate saturated at about 0° or made by saturating a solution of sulfuric acid of density 1.3 with normal potassium sulfate, K2S04. Fill the beaker B with ice and water. Use three storage cells and secure a voltage across the terminals of about 6.75 volts and a current density of 1 amp. per square centimeter. 

A copious white crystalline precipitate soon settles from the anode to the bottom of the tube T. After an hour or so, interrupt the process, decant the electrolyte from the crystals, collect them on a small filter in a Gooch crucible, wash them with alcohol using a pump, and dry them in air. The decanted solution may be used for another run. 

Preparation by the Action of H202 on Acids or Their Salts.—By this more general method, a large number of per-acids or their salts have been prepared. 

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Perfluoroepoxides have also been prepared by anodic oxidation of fluoroalkenes (39), the low temperature oxidation of fluoroalkenes with potassium permanganate (40), by addition of difluorocarbene to perfluoroacetyl fluoride (41) or hexafluoroacetone (42), epoxidation of fluoroalkenes with oxygen difluoride (43) or peracids (44), the photolysis of substituted l,3-dioxolan-4-ones (45), and the thermal rearrangement of perfluorodioxoles (46). 

Thin films of photochromic silver complex oxides were prepared by anodic oxidation of silver metal films (15). Complex oxides, such as Ag2V04, Ag SiO, and Ag2P04, darkened by exposure to visible light, but required heating to 150—250°C for thermal bleaching. 

NHE (25 °C) or [Hg/HgO/ln NaOH in H2O] E = +140 mV versus NHE (25 °C) are, for example, interesting if chloride ions are not allowed. A problem of all mercury containing systems is the toxicity. A nontoxic system is [Ag/AgCl/sat. KCl in H2O] E = +197 mV versus NHE (25 °C). It is nearly temperature independent and insensitive against current flow. It can be easily prepared by anodic oxidation of a silver wire in KCl solution (coating with an AgCl layer, subsequently an excess of solid KCl is added to the electrolyte round the silver wire). But, diffusion of silver ions out of the partially soluble AgCl can be a problem. 

Radicals prepared by anodic oxidation of anions or by the Kolbe reactions can couple with other radicals or add to double bonds. For instance in Scheme 2 [4, 5], the... 

The diamagnetic red-brown Ru (aq) cation has been known since the 1950s. It has been prepared by anodic oxidation of [Ru(H20)6] + or [Ru(H20)6] ", or by reduction of RUO4 with H202. Results of Ru K-edge EXAFS are consistent with the formulation [Ru4(//-0)g-(1120)12]" (152) with an adamantine-like structure. 

Chemical vapor deposition [37,38], and thermal or anodic oxidation of Ti substrates [39,40,41] have been used to prepare polycrystalline thin films of Ti02. For example, thin films of Ti02 prepared by anodic oxidation of Ti, followed by electrodeposition of In20s from 0.5 M 102(504)3 show enhanced optical absorption up to 500 nm [42] with the In203 modified electrode showing enhanced photocurrent and photovoltage partially due to the low electrical resistance (10 Q) and reduced overvoltage of the photoanode. 

Gong D, Grimes CA, Varghese OK, Hu W, Singh RS, Chen Z, Dickey EC (2001) Titanium oxide nanotubes array prepared by anodic oxidation. J Mater Res 16 3331-3334... 

Fig. 9 Rate of hydrogen generation from nanotube arrays films of different lengths annealed at 530 °C. Electrode area of 1 cm 100 mW/cm visible light. In the inset FESEM cross-sectional image of 2.8 um long Xi02 nanotube array prepared by anodic oxidation of a titanium foil in an electrolyte containing potassium fluoride (KF 0.1 M), sodium hydrogen sulfate (1 M), trisodium citrate (0.2 M) and sodium hydroxide. Elaborated from Grimes et...

Deposition of metals may lead to well dispersed metal nanoparticles, as discussed in the previous section, but also to special metal structures. Using a Xi02 nanotube array prepared by anodic oxidation as a template and electrodepositing An onto the template. An nanonets could be prepared. 

Schemes 24 and 34. Not all specific examples follow these generalized pathways. Although 78h does decompose predominately into 99 (Scheme 44) at neutral pH, evidence suggests that it may not do so via an addition-elimination mechanism. This intermediate is detectable in reaction mixtures, but it has never been isolated due to its high reactivity. The N-benzoyl analogue 78h has been prepared by anodic oxidation of N-benzoyl-2-aminofluorene and has been shown by labeling experiments to generate 99 by an intramolecular pathway presumably involving the intermediate 100. ...

Similarly, NADH may be oxidized to NAD+ by a quinonoid 2-amino-dihydropteridone-4,18 prepared by anodic oxidation of the corresponding 5,6,7,8-tetrahydro derivative. 

The a-methoxylated derivatives are shown to be versatile synthons because of the reactivity of the methoxy group near the nitrogen atom, a-Methoxycarbamates, prepared by anodic oxidation, were used as key intermediates in the synthesis of a-amino acids,200 a new carbon-phosphorus bond-forming reaction,200 and in a new method of acylation of aliphatic amines at the -position.201 The application of this reaction to the synthesis of pyrrolidine, piperidine, and tropane alkaloids is also described.202... 

Deoxy-2-chloropyranosyl amide 10 was prepared by anodic oxidation of chloride ions in the presence of glucal 2 in acetonitrile however, the diastereoselectivity was modest and the 1/ ,2/ -adduct was prevalent ( H NMR)203. 

Mesoporous alumina membranes ( anodic aluminium oxide , or AAO) are prepared by anodic oxidation of aluminium metal [1,2]. The cylindrical pores, perpendicular to the membrane surface, form hexagonal arrays of straight non-intersecting channels with pore densities up to lO Vcm. Their diameters are controllable within the range 5 - 100 nm as a linear function of anodisation voltage. These membranes are used as molecular sieves, and have also found application as templates for metallic nanowires [3,4,5,6], metal elusters and colloids [7,8], and carbon nanotubes [9,10]. 

A material exhibiting high electrocatalytic activity in the HER was prepared by anodic oxidation of the amorphous alloy FegoCojoSiioBio in 30% aqueous KOH at 70°C (202). A dissolution-precipitation process involving the Fe is involved, giving an active surface oxide that is presumably reduced on subsequent evolution of Hj. A highly porous material results. 

In other studies, various complex ring systems useful in the synthesis of natural products have been prepared by anodic oxidation of electron-rich phenols bearing alkenyl side chains of varying substitution and stereochemistry [59-65]. In some instances, the... 

Yields in the range of 60-90% of unsymmetrical disulfides, RSSR, were obtained by reaction of a sulfenium cation, RS" ", prepared by anodic oxidation of several disulfides, RSSR, with thiols, R SH, in CH2CI2/BU4NCIO4 solutions using a Pt anode [44] ... 

Benzofuroxanes may be prepared by anodic oxidation of < -nitroaniline in MeCN containing iodide [126]. 

Aliphatic gem-dinitro compounds can be prepared by anodic oxidation of a nitro-paraffin in aqueous alkaline solution in the presence of an excess of N02 [201]. Yields are considerably better when Ag" is the oxidizing agent [202], so that an indirect oxidation process involving the generation of Ag" " at an Ag anode was found to give excellent results [203]. 

M.-J. Jeng and J.-G. Hwu, Enhanced nitrogen incorporation and improved breakdown endurance in nitrided gate oxides prepared by anodic oxidation followed by rapid thermal nitridation in N2O, Appl. Phys. Lett. 69(25), 3875, 1996. 

Figure 16, SEM image of Ti02 nanotubes prepared by anodic oxidation of Ti substrate in an acetic acid solution containing 1.0 vol % HF at 20 V for 45 min.(A) Amperometric response of (a) Th/HRP/ Ti02 and (b) Th/ Ti02 at-450 mV upon successive additions of 0.134 mM H202 into 0.1M PB at pH 6.8. (B) Plot of the reduction current versus the H202 (Adapted with permission from S. Liu, A. Chen, Langmiur 2005, 21, 8409-8413.Copy right 2000 American Chemical Society).

Anodic oxidation of metallic tungsten in methanol afforded a mixture of [W(OMe)s] and [WO(OMe)4]. After purification and treatment with MeOC2H4OH, crystals of [ LiW02(0C2H40-Me)3 2-2Li(IIOC2I I40Me)2][W60 9] were obtained.42 Single crystals of W(OMe)6 were also prepared by anodic oxidation and subsequent separation from by-product, [WO(OMe)4].43... 

Kavan L., Stoto T., Gratzel M., Fitzmaurice D. and Shklover V. (1993), Quantum size effects in nanocrystalline semiconducting titania layers prepared by anodic oxidative hydrolysis of titanium trichloride , J. Phys. Chem. 97, 9493-9498. 

The plant is to use the barrier prepared by anodic oxidation of aluminum whose properties are given in Table 14.6, in tubes 0.014 m in diameter and 4 m long. The plant is to be built as an ideal cascade of stages operating at the optimized conditions of Table 14.9. 

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