Anodic Treatments

Magnesium Alloys, Anodic Treatment Of, MUitary Specification MIL-M-45202, Dept, of the Army, Army Materials and Mechanics Research Center, Watertown, Mass., Oct. 3, 1968. 

Aluminum is suitable for contact with cold dilute sulfuric acid solutions, especially if an anodizing treatment has been applied. As the H2SO4 concentration increases, rates of attack also increase. This is illustrated in Figure 3.6. Aluminum may be used for handling oleum however, the passivity of the metal with sulfuric acid is soon destroyed as the temperature rises, and the boiling solutions of an acid of any concentration attacks rapidly. 

The beneficial effects of the graphite oxide film on the adsorption and oxidation of DNA on GC(ox) seem to be strongly dependent on the thickness of this film, obfained under different conditions (supporting electrolyte, applied voltage, duration of the anodization treatment and pH). 

Webster DA, Spadaro JA, Becker RO, et al. 1981. Silver anode treatment of chronic osteomyelitis. Clinical Orthopedics and Related Research 161 105-114. 

Deposition of boron-doped diamond films and their anodic treatment for the oxygen-terminated diamond sensor... 

The direct electrochemical methoxylation of furan derivatives represents another technically relevant alkoxylation process. Anodic treatment of furan (14) in an undivided cell provides 2,5-dimethoxy-2,5-dihydrofuran (15). This particular product represents a twofold protected 1,4-dialdehyde and is commonly used as a C4 building block for the synthesis of N-heterocycles in life and material science. The industrial electroorganic processes employ graphite electrodes and sodium bromide which acts both as supporting electrolyte and mediator [60]. The same electrolysis of 14 can be carried out on BDD electrodes, but no mediator is required The conversion is performed with 8% furan in MeOH, 3% Bu4N+BF4, at 15 °C and 10 A/dm2. When 1.5 F/mol were applied, 15 is obtained in 75% yield with more or less quantitative current efficiency. Treatment with 2.3 F/mol is rendered by 84% chemical yield for 15 and a current efficiency of 84% [61, 62]. In contrast to the mediated process, furan is anodically oxidized in the initial step and subsequently methanol enters the scene (Scheme 7). 

Anodic treatment of 1,2- or 1,4-dihydroxy-substituted benzenes to form the corresponding quinones or masked congeners is well known, since they represent valuable synthetic intermediates [64]. Benzoquinone ketals of electron rich arenes like 18 can be challenging since the oxidative aryl-aryl coupling reaction usually competes. When using BDD anodes the benzoquinone ketal 19 is obtained in an almost quantitative manner, demonstrating the superior properties of this electrode material. Despite the basic conditions, no deblocking of the silyl-protected phenol moiety is observed [65] (Scheme 9). 

A variety of organic transformations in aqueous media using BDD anodes have been studied. The pronounced stability of the BDD material in the presence of water makes it obvious that is should be used in oxidation processes. However, the yields are usually low and therefore less attractive for synthetic purposes. The BASF company investigated the anodic oxidation of butyn-l,4-diol 32. The anodic treatment in an electrolyte of dilute sulfuric acid gave small amounts of the monoacid 33 and the acetylene dicarboxylic acid 34. The moderate product efficiency might be attributed to electrochemical incineration processes (Scheme 15). 

Anodic treatment of 3,5-lutidine (35) on BDD electrodes also turned out to be challenging. Only traces of the desired pyridine-3,5-dicarboxylic acid (36) could be detected. As electrolyte a dilute NaOH solution was employed. The mineralization and decomposition seem to be the dominant reaction pathways (Scheme 16). 

Table 2 Anodic treatment of 37 with different additives...

Anodic treatment of 4-methyl guaiacol (51) by the elaborated protocol using HFIP at BDD anodes yields exclusively the ortho-meta coupled product 52. Based on the previous results a selective ortho coupling to symmetric products was anticipated. 

The current density has a dramatic influence on the yield of 52 and reveals that more than one electrode reaction is involved in the sequence. When the current density is in the range of 2.8. 7 mA/cm2, 52 is directly obtained in about 30% yield. The rationale for the formation of 52 starts with the direct or indirect generation of phenoxyl radicals at the BDD anode. Since the used conditions will provide concentrations of oxyl spin centers, which exclude a recombination, the transformation has to follow a different mechanistic course. The anodic treatment will cause an Umpolung effect because the electron rich phenol is oxidized [110-113]. Such phenoxyl species are still electrophilic despite the liberation of a proton [114-119]. The electrophilic attack occurs at the most electron rich position of the reaction partner which provides the observed connectivity in 52 (Scheme 21). 

The observed chemoselectivity is unique. Anodic treatment on BDD of 3,4,5-trimethoxy toluene results in the exclusive formation of the mixed biaryl 56. This method can be further performed with benzo[l,3]dioxole-containing arenes as reaction partners, giving biaryls 57 and 58 in acceptable yields. Furthermore, naphthalene moieties can be directly located onto 4-methyl guaiacol as the products 59 and 60 reveal. This novel cross-coupling can be expanded to other phenolic reaction partners as well [28]. The displayed selection of mixed biaryls 53-60 is accessible in a single step. In the workup protocol, HFIP is almost quantitatively recovered since it represents the most volatile component in the electrolyte. In addition, nonconverted starting materials can be recycled by short path distillation with approximately 80% efficiency (Scheme 23). 

Kirste A, Nieger M, Malkowsky IM, Stecker F, Fischer A, Waldvogel SR (2009) ortho-Selective phenol-coupling reaction by anodic treatment on boron-doped diamond electrode using fluorinated alcohols. Chem-Eur J 15 2273-2277... 

Minford, J. D., Comparison of Aluminum Adhesive Joint Durability as Influenced by Etching and Anodizing Treatments of Bonded Surfaces, Journal of Applied Polymer Science, Applied Polymer Symposia, vol. 32, 1977, pp. 91—103. 

Military Specification, MIL-M-45202C, Magnesium Alloy, Anodic Treatment of April 1981. 

Eickner, H. W., Adhesive Bonding Properties of Various Metals as Affected by Chemical and Anodizing Treatments of die Surfaces, Forest Products Laboratory Reports 1842 and 1842-A, February 1955 and August 1960, Forest Products Laboratory, Madison, WI. 

Light anodic treatment and various corrosion preventive treatments have been developed by magnesium producers. 

Fig. 5.15 SEM images (top view and cross section) of BDD/Si anodes (from CSEM, Switzerland) used under different conditions, (a) Electrode surface after electrolysis in Me0H/H2S04. No degradation of the diamond layer, (b) Electrode surface after anodic treatment ( 36 h) in 0.1 M aq. NaOH, containing 3,5-dimethylpyridine. Obvious signs of degradation of the diamond layer, but use in electrosynthesis was still possible, (c) Cross section of electrode (a), film thickness 1.2 p m as determined by EPMA. (d) Cross section of electrode (b), film thickness 0.84 p,m...

Duo, I., Levy-Clement, C., Fujishima, A. and ComnineUis, Ch. (2004) Electron transfer kinetics on boron-doped diamond Part 1 Influence of anodic treatment. J. Appl. Electrochem. 34,935-943. 

The effectiveness of the anodic treatment at BDD was also tested with an insoluble dye-like dispersed indigo (Bechtold et al. 2006), a typical dye used for cotton work clothes and blue jeans. Also in this case the treatment was effective leading to the complete decolourisation of the solution. The current yield was found to decrease with the applied current indicating a direct oxidation at the electrode interphase under diffusive control. The addition of NaCl up to 144mgL 1 did not enhance the rate of the decolourisation, as well as persulphate, eventually formed from sulphate present in the supporting electrolyte, resulted ineffective. 

Another study (Polcaro et al. 2002) showed mat when different substances were present in the waste, the selectivity of anodic treatment at BDD towards the different compounds may be low, and a significant enhancement of biodegradation was achieved only for high COD removal, requiring a high amount of current. 

In this work, the efTect of anodic oxidation treatments on activated carbon fibets (ACFs) was studied in the context of Cr(Vl), Cu( II), and Ni( II) ion adsorption behaviors. Ten wt% phosphoric acid and sodium hydroxide were used for acidic and basic electrolytes, respectively. Surf properties of the ACFs were determined by XPS. The specific surface area and the pore stnicture were evaluated from nitrogen adsorption data at 77 K. The heavy metal adsorption rates of ACFs were measured by using a UV spectrometer and 1C P. As a result, the anodic treatments led to an increase in the amount of total acidity by an increase of acidic functional groups such as carboxyl, lactone, and phenol, in spite of a decrease in specific surface area, due to the pore blocking by increased acidic functional groups. 

Preparation of CuC=CPh-L (L=l,10-phen, bipy) occurs by oxidation of HC=CPh in acetone or CH3CN at a Cu anode". Treatment of CuBH4(PPh3)2 with HC=CPh and KOH affords tetranuclear [CuC CPhfPPhj)] in high yield. ... 

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