Solutions, Nonaqueous

In nonaqueous media, the polarography of Th(IV) tends to display more defined and reproducible reduction wave(s). Astheimer and Schwochau proposed a two-step reduction of ThCU in dimethylsulfoxide according to the equations Th(IV) + 2e  

Electrochemical reduction of CO2 in nonaqueous solutions is significant from the following viewpoints Firstly, hydrogen evolution reaction can be suppressed. Secondly, the concentration of water as a reagent can be accurately regulated and the reaction mechanism may be more easily studied. Thirdly, the solubility of CO2 in organic solvents is much liigher than in water. Various metal electrodes have been tested for CO2 reduction in some nonaqueous solvents, such as propylene carbonate (PC), acetonitrile (AN), DMF, and dimethyl sulfoxide (DMSO), as tabulated in Table 5. Methanol is also used for CO2 reduction, and mentioned in the next Section. 

Haynes and Sawyer conducted a chronopotentiometric study of CO2 reduction at Au and Hg electrodes in DMSO. They showed that CO and formate are the reaction products from CO2. Tyssee et al. reported that oxalic acid is exclusively formed from CO2 reduction at Hg in DMF.  

Kaizer and Heitz employed Cr-Mo-Ni steel as a cathode in AN and PC electrolytes with tetraalkyl ammonium salt as the electrolyte.They showed that oxalic acid is the main product. Addition of slight amount of water to die electrolyte gives formate as the main product. 

Saveant and his coworkers studied the electrochemical reduction of CO2 at Pb and Hg in H2O-DMF solutions. The main products were CO, HCOOH and (COOH)2, the product distribution depending upon the operational conditions. They discussed the reaction schemes with an assumption that a presumed intermediate CO2 is adsorbed on neither Pb nor Hg electrode and that no specific interaction exists between intennediates or products and the electrodes. 25 The details are discussed later. 

and Pt predominantly yield CO from CO2. Fe, Cr, Mo, Pd, and Cd form both C2O42 and CO in comparable yields. The product selectivity by Ito et al. is mostly confirmed by other workers results with exceptions mentioned below. 

Although aqueous solutions have been the main object of interest, X-ray diffraction can also be used to study nonaqueous solutions, and to investigate, for example, the influence of a solvent on the structure of a specific complex. A summary of results of structure determinations of complexes in nonaqueous solvents is given in Table VII (180-199). 

By isostructural substitution, using the Er3+—Y3+ pair, the structures of chloride and nitrate complexes of Er3+ in DMSO solution have been determined and can be compared with the structures of corresponding complexes in aqueous solution (37). The deconvoluted RDFs for 1 M erbium(III) nitrate and chloride solutions, calculated from difference curves, are shown in Fig. 27. The structures for the complexes were derived from these RDFs and the final parameter values were obtained by least-squares refinements using the intensity difference curves. The bonding of the ligands and a comparison between experimental values and values calculated for the derived models are shown in Fig. 27. 

In comparison to the other actinides the electrochemical behavior of uranium 

The electrochemical behavior of UCI4 in THF with [(n-C4H9)4N][B(Ph)4] as supporting electrolyte was studied to determine the fate of the electrogenerated U(III) species [85]. The voltammograms are not straightforward and a number of additional U(IV) chloride species 

Cyclic voltammetric studies were employed to determine the stability of electrogenerated U (V) derivatives for several bis (alkoxido)-uranium-triamidoamine complexes of the general formula U(NN3)(OR)(OR )Li(THF) , in which NN3 = N(CH2CH2NSiMe3)3 and R, R = 

U(III) species and a second three-electron reduction to give U(0) metal. The first reduction, U(IV)/U(III) couple, is elec-trochemically and chemically irreversible except in hexamethylphosphoramide at 298 K where the authors report full chemical reversibility on the voltammetric timescale. The second reduction process is electrochemically irreversible in all solvents and only in dimethylsulfone at 400 K was an anodic return wave associated with uranium metal stripping noted. Electrodeposition of uranium metal as small dendrites from CS2UCI6 starting material was achieved from molten dimethylsulfone at 400 K with 0.1 M LiCl as supporting electrolyte at a platinum cathode. The deposits of uranium and the absence of U CI3, UCI4, UO2, and UO3 were determined by X-ray diffraction. Faradaic yield was low at 17.8%, but the yield can be increased (55.7%) through use of a mercury pool cathode. 

FIGURE 6.32. Cathodic current on n-Si in 0.1M TBAP, ACN and in 20% HF aqueous solution. After Kaser and Bard,  

FIGURE 6.33. Cyclic voltammogram on ap-Si electrode in liquid ammonia (water C 10 M). a V= 80 mV/s, etched crystal and b on p-Si, nonetched, with added water (C = 10 M). After Amerongen et (Reproduced by permission of The Electrochemical Society, Inc.) 

IM KBr as electrolyte. The anodic current observed above 0.6V is due to the solvent oxidation through hole capture from the valence band  

The electrode behavior of silicon in nonaqueous solvents strongly depends on the presence of water. The presence of a very small amount of water will cause the formation of silicon oxide at anodic potentials and cause reduction of water at large cathodic potentials. The presence of a thin oxide layer due either to native oxide or to water presence affects the electrode behavior by acting as a physical barrier and source of interface states. It has been found that with 10 ppm water in organic electrolytes the silicon surface is oxidized slowly via formation of oxide islands which grow to 0.6 nm thick and cover about 60% of the surface after 1 week of immersion. 

The two principal etching solution systems for silicon are HE solutions and alkaline solutions. This is because silicon is inert in aqueous solutions due to the formation of an insoluble surface oxide except for HE solutions or alkaline solutions in which the oxide is soluble. Various chemical agents can be added to these two solutions so as to 

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Popvych O and Tomkins R P T 1981 Nonaqueous Solution Ohemistry (New York Wiley)... 

Electroplated Metals and Alloys. The metals electroplated on a commercial scale from specially formulated aqueous solutions iaclude cadmium, chromium, cobalt, copper, gold, iadium, iron, lead, nickel, platinum-group metals, silver, tin, and ziac. Although it is possible to electroplate some metals, such as aluminum, from nonaqueous solutions as well as some from molten salt baths, these processes appear to have achieved Httie commercial significance. 

In general, the surface tension of a Hquid mixture is not a simple function of the pure component surface tensions because the composition of the mixture surface is not the same as the bulk. For nonaqueous solutions of n components, the method of Winterfeld, Scriven, and Davi is apphcable ... 

Organic polymer materials may be analyzed by ashing at relatively high temperatures. This involves oxidation of the carbon containing matrix, leaving an inorganic residue that is taken up in acid. An alternadve in some cases is to dissolve the polymer in solvent and analyze the nonaqueous solution direcdy. Nonaqueous media will be discussed in a later secdon. 

Numerous tetrahedral halogeno complexes [T1" X4] (X = Cl, Br, I) have been prepared by reaction of quaternary ammonium or arsonium halides on TIX3 in nonaqueous solution, and octahedral complexes TI "X< ] (X = Cl, Br) are also well established. The binuclear complex Cs3[Tl2"Cl<)J is an important structural type which features two TlCls octahedra sharing a common face of 3 bridging Cl atoms (Fig. 7.9) the same binuclear complex structure is retained when Tl " is replaced by Ti ", V ", Cr " and Fe " and also in K3W2CIS and CssBiily, etc. 

V. Gutmann (ed.), in Halogen Chemistry, Vol. 2, p. 399, Academic Press, London, 1967 and V. Gutmann, Coordination Chemistry in Nonaqueous Solutions, Springer-Verlag, New York, 1968. 

In very strongly acidic nonaqueous solutions (such as HF/8bF5) H28 acts as a base (proton acceptor) and the white crystalline... 

Several mixed species have been identified in nonaqueous solutions by Se nmr spectroscopy. These include BrSeSeCl. Sc3X2 and Se4X2 " and ClSeSCl, BrSeSCl, ClSeSBr and... 

However, solubility, depending as it does on the rather small difference between solvation energy and lattice energy (both large quantities which themselves increase as cation size decreases) and on entropy effects, cannot be simply related to cation radius. No consistent trends are apparent in aqueous, or for that matter nonaqueous, solutions but an empirical distinction can often be made between the lighter cerium lanthanides and the heavier yttrium lanthanides. Thus oxalates, double sulfates and double nitrates of the former are rather less soluble and basic nitrates more soluble than those of the latter. The differences are by no means sharp, but classical separation procedures depended on them. 

Chemistry of nonaqueous solutions current progress (G. Mamantov and A.I. Popov eds.), VCH, Weinheim,... 

The electrical double layer at BiDER has been studied in various nonaqueous solutions MeOH,677,678 DMF,679,680 AN,480,681,682 DMSO,475 EtOH, 3-690 1-prOH,691 2-prOH,692 isomers of BuOH,693 96 and ethylene glycol (EG)697... 

First attempts to study the electrical double layer at A1 electrodes in aqueous and nonaqueous solutions were made in 1962-1965,182,747,748 but the results were not successful.190 The electrical double-layer structure at a renewed Al/nonaqueous solution of surface-inactive electrolytes such as (CH3)4NBF4) (CH3)4NC104, (CH3>4NPF6, and (C4H9)4NBF4, has been investigated by impedance.749-751 y-butyrolactone (y-BL), DMSO, and DMF have been used as solvents. In a wide region of E [-2.5 [Pg.128]

Electrical Double-Layer Parameters of Al in Nonaqueous Solutions... 

Barthel, J. Temperature Dependence of Conductance of Electrolytes in Nonaqueous Solutions 13... 

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