Propylene carbonate , reduction

ZnTe The electrodeposition of ZnTe was published quite recently [58]. The authors prepared a liquid that contained ZnGl2 and [EMIM]G1 in a molar ratio of 40 60. Propylene carbonate was used as a co-solvent, to provide melting points near room temperature, and 8-quinolinol was added to shift the reduction potential for Te to more negative values. Under certain potentiostatic conditions, stoichiometric deposition could be obtained. After thermal annealing, the band gap was determined by absorption spectroscopy to be 2.3 eV, in excellent agreement with ZnTe made by other methods. This study convincingly demonstrated that wide band gap semiconductors can be made from ionic liquids. 

The structure and composition of the lithium surface layers in carbonate-based electrolytes have been studied extensively by many investigators [19-37], High reactivity of propylene carbonate (PC) to the bare lithium metal is expected, since its reduction on an ideal polarizable electrode takes place at much more positive potentials compared with THF and 2Me-THF [18]. Thevenin and Muller [29] found that the surface layer in LiC104/PC electrolyte is a mixture of solid Li2C03 and a... 

The pc-Au/propylene carbonate (PC) + NaC104 interface has been studied by Nguyen Van Huong.481 A flame-annealed (02 + H2) pc-Au sphere was used. Before each experiment the pc-Au electrode was cleaned in an NaC104 aqueous solution by a few potential cycles involving oxidation-reduction of the surface until the i,E and C,E curves exhibited stable character. The C,E curves were recorded in the interval 15 150... 

Figure 1 shows how acid-gas-bearing process gases can be generally treated in industrial processes. The sulfur compounds and CO2 may be absorbed in a liquid medium, such as amines, alkali salts (NaOH, K2CO3), physical solvents (methanol, propylene carbonate), or water (3). The absorbed acid gases are released by reduction of pressure and/or by application of heat. Alternatively, the H2S and CO2 may chemically combine with the absorbent (as in NaOH scrubbing) to form salts which are removed in a liquid treatment unit. This requires continual and expensive makeup of sodium to the system. 

The ECMS method has been used effectively in such studies as electrolytic reduction of carbon dioxide and electrolytic oxidation of methanol. The example in Fig. 9.8 is for the electrolytic oxidation of propylene carbonate (PC) in the electrolyte solution... 

The impurity gives a signal that disturbs the measuring system. An example is shown in Fig. 10.1 [10], The residual current-potential curves were obtained with a platinum electrode in propylene carbonate (PC) containing various concentrations of water. Because water is amphiprotic, its cathodic reduction and anodic oxidation are easier than those of PC, which is aprotic and protophobic. Thus, the potential window is much narrower in the presence of water than in its absence. Complete removal of water is essential for measuring electrode reactions at very negative or positive potentials. 

A vacuum spectroelectrochemical cell that also contains an optically transparent thin-layer electrode (OTTLE) is shown in Figures 18.16 and 18.17. The cell can function either as a spectroelectrochemical cell employing an OTTLE or as an electrochemical cell for voltammetric measurements. This low-volume cell is useful for UV/Vis spectral studies in nonaqueous solvents when the reduction product is sensitive to traces of molecular oxygen present in the solvent. The cell is physically small enough to fit inside the sample compartment of the spectrophotometer. The performance of such a cell was evaluated from visible spectroscopy and coulometry of methyl viologen in propylene carbonate [45]. 

Two parallel routes for the elimination of glycol formate are suggested, involving either reaction with H2 or with cocatalyst water. The detection of formic acid in the reaction products suggests another mechanism, with initial production of formic acid from H2 and C02, followed by reaction with the oxirane. This mechanism is not favored however since the yields of glycol formates varied substantially when various substituted oxiranes were reacted. This would not have been expected in a mechanism with formic acid as an intermediate. A third mechanism, not considered by the authors, could proceed through initial production of propylene carbonate, followed by reduction to the mono- or di-formate. 

Eggins and McNeill compared the solvents of water, dimethylsulfoxide (DMSO), acetonitrile, propylene carbonate, and DMF electrolytes for C02 reduction at glassy carbon, Hg, Pt, Au, and Pb electrodes [78], The main products were CO and oxalate in the organic solvents, while metal electrodes (such as Pt) which absorb C02 showed a higher production for CO. In DMF, containing 0.1 M tetrabutyl ammonium perchlorate and 0.02 M C02 at a Hg electrode, Isse et al. produced oxalate and CO with faradaic efficiencies of 84% and 1.7%, respectively [79], Similarly, Ito et al. examined a survey of metals for C02 reduction in nonaqueous solution, and found that Hg, Tl, and Pb yielded primarily oxalate, while Cu, Zn, In, Sn, and Au gave CO [80, 81]. Kaiser and Heitz examined Hg and steel (Cr/Ni/Mo, 18 10 2%) electrodes to produce oxalate with 61% faradaic efficiency at 6 mA cm-2 [82]. For this, they examined the reduction of C02 at electrodes where C02 and reduction products do not readily adsorb. The production of oxalate was therefore explained by a high concentration of C02 radical anions, COi, close to the surface. Dimerization resulted in oxalate production rather than CO formation. 

When Desilvestro and Pons used in situ IR reflection spectroelectrochemistry to observe the reduction of C02 to oxalate at Pt electrodes in acetonitrile [83], two different forms of oxalate were observed. Similarly, Aylmer-Kelly et al. studied C02 reduction in acetonitrile and propylene carbonate at Pb electrodes [84], by using modulated specular electroreflectance spectroscopy. Subsequently, two radical intermediates were observed which they determined to be the C02 radical anion, C02, and the product of the radical anion and C02, the (C02)2 adduct (see Equations 11.9 and 11.10). Vassiliev et al. also studied the reduction of C02 in... 

Dimethyl sulfoxide (Me2SO). The applications of Me2SO in electrochemistry have been thoroughly reviewed.93 It is a particularly useful solvent because it has a high dielectric constant and is sufficiently resistant to both oxidation and reduction to provide a fairly wide potential range. It is, however, not as resistant as acetonitrile or propylene carbonate to oxidation and these latter two solvents are preferred over Me2SO for this purpose. 

ZnTe is usually applied in switching devices and in solar cells. It is one of the II—VI compound semiconductors with a direct band gap of 2.3 eV at room temperature. The electrodeposition of ZnTe was investigated by Sun et al. in the Lewis basic ZnCl2/l-ethyl-3-methylimidazolium ionic liquid containing propylene carbonate as a cosolvent at 40 °C [37]. 8-Quinolinol was added to the solution to shift the reduction of Te(IV) to more negative potential, thus facilitating the codeposition. The composition of the ZnTe deposits is dependent on the deposition potential and... 

Table 11 Limiting Reduction and Oxidation Potentials of Propylene Carbonate Electrolytes Containing 0.65 mol dm-3 Quaternary Ammonium or Phosphonium Tetrafluoroborate at 25°C (glassy carbon W.E.)... 

Details of the electrochemical reduction of 36 and the possible existence of the monoanionic intermediate (36) (R = Ph) are not yet settled. The neutral dimer is reported to undergo a single, chemically reversible, two-electron reduction at a mercury electrode (E = -1.26 V in CH3CN) (79), although the process was less reversible (R = Ph or Me) in propylene carbonate (81) and totally irreversible at platinum (79). The peak separation of 45 mV (at mercury), which contrasts with the expected value of 30 mV for a reversible two-electron reduction, is reported to be essentially independent of the cyclic voltammetric scan rate (79). Although this seems to imply that the overall process may consist of two closely spaced one-electron waves, mixing solutions of [36] (R = Ph) and 36 (R = Ph) did not produce a sufficient concentration for [36] (R = Ph) to be detected by ESR spectroscopy. Thus, the high disproportionation constant for the reaction ... 

The complexes [ Fe(CO)3(/i-SR) 2] are reduced in a single two-electron step (R = Me, E° = -1.22 V) much like the isoelectronic phosphido-bridged compounds 36. The resulting dianions are apparently more stable in DME (62) than in propylene carbonate (5i). The mixed-bridged compound [Fe2(CO)6(/i-SMe)(jn-PMe2)] behaves similarly (57), but two one-electron reductions, separated by 400 mV, were observed for... 

No crystal structure of derivatives containing the [U02(dik)2] anion is available. Like Th(acac)4, the uranium analogue, U(acac)4, in thf solution exhibits the U(IV) U(III) reduction at very negative potential values E° = —2.2 V, vs. SCE), which is partially chemically reversible. A previous report stated that in propylene carbonate or MeCN solution, U(acac)4 exhibited two reduction steps at about —0.8 V and —1.2 V, vs. SCE, respectively , but the purity of the sample has been questioned ". The presence of chemical complications following the U(IV) U(III) step has been also pointed out for the unsymmetric U(dik)4 with dik = MefC(0)CHC(0)Bu-f in dmso or dmf solution =. 

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