Ethylene anodic oxidation

Anodic Oxidation. The abiUty of tantalum to support a stable, insulating anodic oxide film accounts for the majority of tantalum powder usage (see Thin films). The film is produced or formed by making the metal, usually as a sintered porous pellet, the anode in an electrochemical cell. The electrolyte is most often a dilute aqueous solution of phosphoric acid, although high voltage appHcations often require substitution of some of the water with more aprotic solvents like ethylene glycol or Carbowax (49). The electrolyte temperature is between 60 and 90°C. 

The procedure described is essentially that of Belleau and Weinberg and represents the only known way of obtaining the title compound. One other quinone acetal, 1,4,9,12-t6traoxadispiro[4.2.4.2]tetradeea-6,13-diene, has been synthesized by a conventional method (reaction of 1,4-cyclohexanedione with ethylene glycol followed by bromination and dehydrobromination ) as well as by an electrochemical method (anodic oxidation of 2,2-(l,4-phenylenedioxy)diethanol ). Quinone acetals have been used as intermediates in the synthesis of 4,4-dimethoxy-2,5-cyclohexadienone,. syw-bishomoquinone, - and compounds related to natural products. ... 

GP 2] [R 3a] A nearly constant selectivity of up of about 60% at conversions ranging from 20 to 70% was determined for sputtered silver on anodically oxidized (porous) aluminum alloy (AlMg3) with two different ethylene loads (4 or 20 vol.-% ethylene, 80 or 96 vol.-% oxygen 0.3 MPa 230 °C) [44]. The highest yield... 

The transformation of 7,7-diMeO-CHT to a-, and y-tropolones is also achievable by using anodic oxidation in the key step (equation 18), namely the electrochemical oxidation of an isomeric mixture of diMeO-CHTs prepared by the thermal rearrangement of 7,7-diMeO-CHT yields a mixture of methyl ethers of ji- and y-tropolones. On the other hand, the thermal rearrangement of the ethylene acetal of tropone gives 3,4-dioxyethylene-CHT as a single product due to the difficulty of formation of other isomers, and it yields the ether of a-tropolone upon anodic oxidation. 

The anodic oxidation of ethylene in a low temperature aqueous electrolyte electrochemical cell has been studied by Holbrook and Wise (24). It was found that product selectivity (carbonate, vs. ethylene glycol) depends on the potential of the silver anode. 

The preparative electrochemical oxidation of silyl-substituted sulfides results in the cleavage of the C Si bond [36-38]. For example, the anodic oxidation of 1-phenylthio-l-trimethylsilylalkanes takes place smoothly in methanol in an undivided cell equipped with a carbon rod anode and a carbon rod cathode. Although 1-methoxy-l-phenylthioalkanes are formed as the initial products, they are converted into 1,1-dimethoxyalkanes during the course of the reaction (Scheme 8). The electrochemical reaction in the presence of diols such as ethylene glycol affords the corresponding cyclic acetals. 

Elsewhere in this book, White and Sandel [7] discuss the integration of chlorine and ethylene dichloride (EDC) processes. The oxygen content of the chlorine fed to an EDC unit must be kept within the process specification. This can be achieved by liquefying at least part of the chlorine in order to reject non-condensables or by acidifying the brine fed to the cells. Oxygen results from the anodic oxidation of hydroxide ions free acid in the feed brine will neutralise those ions and so reduce the amount of oxygen formed. 

The growth rates of anodic oxides depend on electrolyte composition and anodization conditions. The oxide thickness is reported to increase linearly with the applied bias at a rate of 0.5-0.6 nm V-1 for current densities in excess of 1 mA cnT2 and ethylene glycol-based electrolytes of a low water content [Da2, Ja2, Crl, Mel2] (for D in nm and V in V) ... 

A wide variety of electrolyte compositions used for anodic oxidation of silicon can be found in the literature. The electrolytes can be categorized in inorganic or organic solutions. In the latter case electrolytes like ethylene glycol [Ja2, Me6, Ma5, Mel3], methanol [Ma2] or tetrahydrofuryl alcohol [Be3] are used, with salts such as KN03 added in order to improve the conductivity. Studies with pure water [Ga2, Mo3, Hu3] as an electrolyte were performed, as well as with additions... 

EtMgBr solutions in poly(ethylene oxide) containing a small amount of THF or Et20 are electrically conducting. Best conductivity is achieved for an ethylene oxide-Mg ratio of 4, e.g. 0.1 mS cm at 40 °C was found. In contrast, PEO solutions of MgCla, Mg(C104)2 or Mg(SCN)2 show only low electrical conduction below 100 °C. Furthermore, in the presence of EtMgBr solutions Mg can be deposited by cathodic reduction or dissolved by anodic oxidation. Practical apphcation of these solutions are limited by their low thermal and electrochemical stabihty . ... 

From what has been described so far, there can be a flow of cathodic current, or of anodic current at an electrode/solution interface, according to the value (and particularly the sign) of the overpotential, i.e., of the displacement from equilibrium of the electric potential of the electrode. The equilibrium referred to is that of some specific interfacial electron transfer reaction (e.g., the cathodic reduction of 02 (02 + 4H+ + e —> 2H20)) or the anodic oxidation of ethylene, C2H4 + 4H20 — 2C02 + 12H+ + 12e. 

Electrochemical Nitrations. A method developed in 1956 in Sweden by Ohman for prepn of nitric acid esters has been described in several patents. The method consists in anodic oxidation (using a bright platinum anode) in presence of nitric acid, or its salts (such.as Ca nitrate). The compds to be nitrated areunsaturated hydrocarbons (such as ethylene, propylene, butylene, etc), which can be dissolved in nonaqueous solvents (such as acetone). The OH concn is maintained low during the reaction by adding either coned nitric acid or glacial acetic acid. Water should be absent to prevent the formation of various by-products... 

Electroorganic synthesis deals with conversion of organic compounds into useful products by anodic oxidation or cathodic reduction. Today there exist literally thousands of published examples of electrosynthesis reactions but only a very small number—certainly not more than several tens—are really exploited commercially, the best known example being the cathodic hydrodimerization of acrylonitrile to adipodinitrile, a precursor to hexam-ethylene diamine, which is the aminoconstituent of nylon 6,6 (779) ... 

A very recent paper by Cerrai and coworkers came to our attention after most of this review had been written, but its importance calls for inclusion in this chapter. Indeed the authors question the very nature of the initiating process in the classical electrolytic polymerisation. They reached this conclusion after a very thorough study of the electrochemical polymerisation of cyclohexylvinyl ether in ethylene chloride with tetra-butylammonium tetrafluoroborate and perchlorate, having shown that initiation could not be attributed to the anodic oxidation of the electrolyte anion, of the solvent, or of the monomer. The acid formed at the anode compartment was therefore throught to originate from the electrolysis of residual moisture in the system. This conclusion was supported by the fact that under the most rigorous experimental conditions the rates of polymerisation were considerably lower than when the runs had been performed un-... 

The oxidation of acetate by peroxodisulphate is much slower than that of formate. Glasstone and Hickling showed that the products, which include carbon dioxide, methane, ethane, and ethylene, are similar to those produced by the anodic oxidation of acetate ions (Kolbe electrolysis), and they inferred that the same organic radicals are formed as intermediates. Similar results are reported by Eberson et al. for the oxidations of ethyl terf.-butyl-malonate, tert.-butyl-cyanoacetate, and ferl.-butyl-malonamate ions. The oxidations of these ions and of acetate by peroxodisulphate are first order with respect to peroxodisulphate and zero order with respect to the substrate. Mechanisms involving hydroxyl radicals are excluded because the replacement of peroxodisulphate by Fenton s reagent leads to different products, so Eberson et al. infer that the initial attack on the substrate is by sulphate radical-ions. Sengar and Pandey report that the rate of the silver ion-catalysed oxidation of acetate is independent of the peroxodisulphate concentration. 

In a similar way, l-nonyl-3-oxocyclohexanecarboxylic acid ethylene ketal (VI) has been ring opened [37] to methyl 5-nonyl-5-hexenoate (VII) by anodic oxidation at a C anode in methanol containing K2CO3 ... 

FIGURE 3.5. Thickness of anodic oxide in methanol (with 0.01% HjO and 0.04N KNO3) and in ethylene glycol (with 2% H2O and 0.04N KNO4). After Madou et (Reproduced by permission of The Electrochemical Society, Inc.)... 

E. F. Duffek, E. A. Benjamini, and C. Mylroie, The anodic oxidation of silicon in ethylene glycol solutions, Electrochem. Tech. 3(3-4), 75, 1965. 

An interesting study examined the anodic oxidation of EDTA at alkaline pH on a smooth platinum electrode (Pakalapati et al. 1996). Degradation is initiated by removal of the acetate side chains as formaldehyde, followed by deamination of the ethylene diamine that is formed to glyoxal and oxalate. Oxalate and formaldehyde are oxidized to C02, and adsoption was an integral part of the oxidation. 

Pakalapati, S.N.R., B.N. Popov, and R.E. White. 1996. Anodic oxidation of ethylene-diaminetetraacetic acid on platinum electrode in alkaline medium. J. Electrochem. Soc. 143 1636-1643. 

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