Solvents, non-aqueous

Non-aqueous Solvents.—Mention has already been made of the evidence for an associative (/a) mechanism for the exchange of DMSO with the [Cr(DMSO) ] + ion. Both the entropy and volume of activation are large and negative. A recent study of the exchange process by n.m.r. in DMSO-MeNOj mixed solvents (nitro-methane is an inert, non-co-ordinating diluent which is known to have very little rate effect) shows that the exchange rate is approximately constant above 0.2 mole fraction of DMSO, but drops off sharply below this concentration. On the other hand the fraction of DMSO molecules in the solvation shell of the [Cr(DMSO) J + ion decreases immediately with the decrease in the DMSO mole fraction. This difference in concentration effects is postulated to arise from a unique outer-sphere solvation site which preferentially binds DMSO molecules and preferentially participates in the exchange reaction. 

Catalysis.—Acid- and base-catalysed reactions have already been mentioned [equation (27)] and will not be dealt with further in this section. c -Activation by coordinated oxoanions has also been discussed in the section dealing with the effects of non-leaving groups. Addition of sulphite, acetate, and nitrate ions to [Cr(H20)5X] + complexes (X = F, N3, or AcO) is also reported to accelerate the rate of aquation by the facile formation of oxoanion complexes. Rate data are reported for sulphite labilizations of the acetato- and azido-complexes and the nitrate labilizations of acetato- and fluoro-complexes. The catalysed reactions are characterized by a rate law of the type 

In the case of sulphite ion as a catalyst equation (34) is equivalent to attack by HSOs . This process is readily understood since formation of 0-bonded sulphito- 

Chelation by the 0-bonded sulphite ion is postulated to involve the formation of a seven-co-ordinate intermediate (or transition state) which readily loses the cis-ligand (X ). Catalysis by nitrate ion is also found to obey equation (34) and a mechanism for the loss of X analogous to that described above is favoured. 

The facile formation of nitrato-complexes and subsequent rapid loss of X is postulated to occur by the following mechanism (X = OAc)  

Non Aqueous Solvents. Several ll-VI compounds have also been electrodeposited from non-aqueous solvents. The first report was by BaranskI and Fawcett (60) in i960. Their approach was to deposit cationic species eiectrochemically from a solution containing elemental chalcogenide, dimethylsulfoxide (DMSO), dimethylformamide (DMF) and ethylene glycol (EG). A typical CdS deposition utilized a solution of 6 gm/l of sulfur and 10 gm/l of cadmium chloride. This was electrolyzed at 110°C with a current density of 2.5 mA/cm . The quality of the CdS deposit was independent of both the sulfur and cadmium chloride concentration used and was not affected by the addition of 10% water. The deposit composition was solution temperature dependent, however, becoming highiy non-stoichlometric below 90°C. X-ray diffraction data showed that the crystallites In the film were all oriented with their [ill] planes parallel to the electrode surface. The resistivity of these films was about 10 n cm which could be lowered by addition of sodium iodide to the solution. 

The sulfides of lead, bismuth, nickel, cobalt and thallium were also produced by changing the salt In solution. CdTe was obtained from a DMF solution saturated with tellurium containing 10 gm/l cadmium chloride and 10 gm/l potassium iodide. 

The photochemicai properties of the films were determined in a cell using 1 M sodium sulfide and 1 M sodium hydroxide astheeiectrolyte. The sulfides of cadmium and bismuth were n-type while that of thallium was p- 

Plots of the average thickness of the film versus time at constant current density were compared to the thickness expected from Faraday s law and the deposition efficiency was calculated to be 81 %. A similar plot of depth versus current density at constant time indicated a more rapid deposition at higher current densities which was attributed to increased deposition of cadmium. 

Addition of thaliium ions to the deposition solution changed the conductivity of the films as evidenced by a lowering of the necessary deposition potentiai as the thallium concentration was increased. It was thus possible to tailor the electrical characteristics of the film by the selective addition of various ions. 

The use of non-aqueous solvents in wet photovoltaic devices has been carefully investigated by a number of workers in recent years. The major impetus for this work has come from the observation by Lewis and coworkers that highly efficient photovoltaic devices can be obtained by the use of reversible one-electron couples such as ferrocene or cobalticinium carboxylic acid in anhydrous aprotic solvents such as acetonitrile (ACN) or propylene carbonate (PC) [21, 22], 

The main difference between aqueous and non-aqueous solutions in the case of p-GaAs is that there is no sign, in the latter case, of the large density 

The electroreflectance spectrum of p-GaP in PC is shown in Fig. 32 it clearly differs both in size and magnitude from that found in aqueous solution. A detailed analysis along the lines developed above suggests that a spectrum of this shape could only arise from a sample with very little potential dropped across the depletion layer, in agreement with the a.c. data, and the magnitude of the spectrum is consistent with the suggestion that the magnitude of the potential drop in the depletion layer is only a few tens of mV. 

The detailed interpretation of electroreflectance spectra is still in its infancy, but enough has already been learnt to indicate that the technique will form a most valuable adjunct to other methods that have recently been developed to study the semiconductor/electrolyte interface. The next few years should see this technique become a standard weapon in the armoury of the semiconductor electrochemist. 

A D mechanism is proposed for the solvolysis of the [Cr(NCS)6] ion in non-aqueous solvents (S = DMSO, DMF, or Me2NCOMe), and for the reactions of the product ion [Cr(NCS)5(S)] with pyridine or thiocyanate ion in sulpholan. Rate data for solvent exchange reactions of [Cr(NCS)5(S)] ions are collected in Table 20. 

Catalysis.—cis Activation by co-ordinated oxoanions and the catalytic effect of CO2 and N02 upon the rate of reaction of HjO and DMSO with the [Cr(H20) -(DMSO)6 m ions were discussed in previous sections. The catalytic effect of chloride and bromide ions upon the rate of hydrolysis of [Cr(NH3)6(ONO)] + was also noted earlier.  

IBr can be used to catalyse the removal of alkyl groups (R) from the [Cr(H20)6R] + ions in an S b2 reaction  

Many studies, theoretical as well as experimental, were devoted toward the understanding of the parameters of the carbons, such as pore volume, surface area, void utilization, effective carbon mass, and so on. Nevertheless, it is very difficult to trace out which factor affects the cell performance significantly. Zhang et al. examined single-wall carbon nanotube (SWNT) and carbon 

The cations present in the supporting electrol5Ae show a strong influence on the reversibility of oxygen reduction and evaluation reactions, as their presence leads to different reaction mechanisms of oxygen reduction at air cathodes. 

Early investigation of Li-air batteries showed that the air cathode was the most important challenge for their development, although lithium anode side needs another challenging endeavor in the hybrid configuration. Prabaharan et al recently reported on their proprietary lithium metal/SE monolithic cassette as the protected lithium anode.  

Catalysed Aquation.—Sulphite ion catalyses the rate of water exchange between [Cr(H20)6] ion and bulk solvent by a factor of 2.5 x 10 at 298.2 K, 7=0.65 mol Formation of [Cr(Ha0)50S02]+ ion by nucleophilic attack of co-ordinated HgO at is involved, the rate increase arising from the reduction in overall charge and probably cis-activation as well. 

The catalytic elfect of anions (Cl, Br ) and weak acids (HF, MeCOgH) on the rate of aquation of thiolato-chromium(iii) complexes [Cr(H20)6SR] + (R=EtNH3+ or J7-C6H4NH3+) involves the formation of /ra j-[Cr(H20)4(L)(SR)] ions (L= catalyst).  

A number of examples of acid- and metal-catalysed reactions were also discussed 

Oprescu, C. Vdrhelyi, and I. Ganescu, Russ. J. Inorg, Chem., 1972, 17, 1705. 

188 G Thomas, Wiss, Z. Martin-Luther-Univ., Halle-Wittenberg, Math. Naturwiss. Reihe, 1970, 19, 93 Chem. Abs., 1971, 75, 67 886k). 

In dimethyl sulphoxide solutions of cis- and of trans-[Cr cr x + both isomerization and solvolysis are important  

The rate law for aquations of complexes containing ligands which can be protonated is usually 

Complexes whose aquation kinetics conform to this pattern include [Cr(NH3)5(N3)] +, [Cr(NHs)6(03CCCl3)] +, and [CrCOH ) - 

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Acids can also exist in non-aqueous solvents. Since ammonia can also solvate a proton to give the ammonium ion. substances... 

SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

The alkali metals have the interesting property of dissolving in some non-aqueous solvents, notably liquid ammonia, to give clear coloured solutions which are excellent reducing agents and are often used as such in organic chemistry. Sodium (for example) forms an intensely blue solution in liquid ammonia and here the outer (3s) electron of each sodium atom is believed to become associated with the solvent ammonia in some way, i.e. the system is Na (solvent) + e" (sohem). 

The biologiccJ function of a protein or peptide is often intimately dependent upon the conformation(s) that the molecule can adopt. In contrast to most synthetic polymers where the individual molecules can adopt very different conformations, a protein usually exists in a single native state. These native states are found rmder conditions typically found in Uving cells (aqueous solvents near neutred pH at 20-40°C). Proteins can be unfolded (or denatured) using high-temperature, acidic or basic pH or certain non-aqueous solvents. However, this unfolding is often reversible cind so proteins can be folded back to their native structure in the laboratory. 

METHOD 2 Speed chemists have used hydroiodic acid (HI) for years to reduce ephedrine to meth. So when the government placed HI on the restricted list, speed chemists took to making the HI themselves. One of the ways they used was to make Hi in DMSO (dimethylsulfoxide, a common solvent) by reacting Nal or Kl with sulfuric acid. This a standard way to make both HBr or Hi in water (see the Chemicals section of this book) except these speed chemists were using the non-aqueous solvent DMSO instead of water. 

Calculate or sketch (or both) the titration curves for 50.0 ml of a 0.100 M solution of a monoprotic weak acid (pfQ = 8) with 0.1 M strong base in (a) water and (b) a non-aqueous solvent with ffg = 10 . You may assume that the change in solvent does not affect the weak acid s pfQ. 

No attempt should be made to purify perchlorates, except for ammonium, alkali metal and alkaline earth salts which, in water or aqueous alcoholic solutions are insensitive to heat or shock. Note that perchlorates react relatively slowly in aqueous organic solvents, but as the water is removed there is an increased possibility of an explosion. Perchlorates, often used in non-aqueous solvents, are explosive in the presence of even small amounts of organic compounds when heated. Hence stringent care should be taken when purifying perchlorates, and direct flame and infrared lamps should be avoided. Tetra-alkylammonium perchlorates should be dried below 50° under vacuum (and protection). Only very small amounts of such materials should be prepared, and stored, at any one time. 

D. Rosenthal and P. Zuman, Acid-base equilibria, buffers and titrations in water. Chap. 18 in I. M. Kolthoff and P. J. Elving (eds.). Treatise on Analytical Chemistry, 2nd edn., Vol. 2, Part 1, 1979, pp. 157-236. Succeeding chapters (pp. 237-440) deal with acid-base equilibria and titrations in non-aqueous solvents. 

W. L. Jolly and C. J. Hallada, Liquid ammonia. Chap. 1 in T. C. WaDDINGTON (ed.), Non-aqueous Solvent Systems, pp. 1-45, Academic Press, London, 1965. J. C. Thompson, The physical properties of metal solutions in non-aqueous solvents. Chap. 6 in J. Lagowski (ed.). The Chemistry of Non-aqueous Solvents, Vol. 2, pp. 265-317, Academic Press, New York, 1967. J. Jander (ed.). Chemistry in Anhydrous Liquid Ammonia, Wiley, Interscience, New York, 1966, 561 pp. 

Copper(II) also forms stable complexes with O-donor ligands. In addition to the hexaaquo ion, the square planar /3-diketonates such as [Cu(acac)2l (which can be precipitated from aqueous solution and recrystallized from non-aqueous solvents) are well known, and tartrate complexes are used in Fehling s test (p. 1181). 

The solid disulfide reacts explosively with chlorine or bromine. At low temperatures in certain non-aqueous solvents, e.g. chloroform, CISCSN3 and BrSCSN3 are probably formed, but the extreme instability of these compounds has precluded their exact analysis and description. However, the reaction between cyanogen bromide and the potassium salt of the thiol yields the well-defined cyanide NCSCSN3,... 

The Contact between Solvent and Solute Particles Molecules and Molecular Ions in Solution. Incomplete Dissociation into Free Ions. Proton Transfers in Solution. Stokes s Law. The Variation of Electrical Conductivity with Temperature. Correlation between Mobility and Its Temperature Coefficient. Electrical Conductivity in Non-aqueous Solvents. Electrical Conduction by Proton Jumps. Mobility of Ions in D20. 

Electrical Conductivity in Non-aqueous Solvents. Let us now discuss the random motion of an atomic ion dissolved in methanol or ethanol. It will be seen from Table 41 that the value of the dipole moment on the OH group of these molecules differs little from that of the... 

In contrast to the above resins, the chelating resin Amberlite IRC-718 is based upon a macroreticular matrix. It is claimed to exhibit superior physical durability and adsorption kinetics when compared to chelating resins derived from gel polymers and should also be superior for use in non-aqueous solvent systems. 

Also under this heading must be included titrations in non-aqueous solvents, most of which involve organic compounds. 

The Bronsted-Lowry theory of acids and bases referred to in Section 10.7 can be applied equally well to reactions occurring during acid-base titrations in non-aqueous solvents. This is because their approach considers an acid as any substance which will tend to donate a proton, and a base as a substance which will accept a proton. Substances which give poor end points due to being weak acids or bases in aqueous solution will frequently give far more satisfactory end points when titrations are carried out in non-aqueous media. An additional advantage is that many substances which are insoluble in water are sufficiently soluble in organic solvents to permit their titration in these non-aqueous media. 

Determinations in non-aqueous solvents are of importance for substances which may give poor end points in normal aqueous titrations and for substances which are not soluble in water. They are also of particular value for determining the proportions of individual components in mixtures of either acids or of bases. These differential titrations are carried out in solvents which do not exert a levelling effect. 

As indicated in Section 2.4 the strength of an acid (and of a base) is dependent upon the solvent in which it has been dissolved, and in Sections 10.19-10.21 it has been shown how this modification of strength can be used to carry out titrations in non-aqueous solvents which are impossible to perform in aqueous solution. Potentiometric methods can be used to determine the end point of such non-aqueous titrations, which are mainly of the acid-base type and offer very valuable methods for the determination of many organic compounds. 

Many of the non-aqueous solvents used must be protected from exposure to the air, and titrations with such materials must be conducted in a closed vessel such as a three- or four-necked flask. It must also be noted that organic solvents have much greater coefficients of thermal expansion than has water, and every effort must therefore be made to ensure that all solutions are kept as nearly as possible at constant temperature. 

As indicator electrodes glass and antimony electrodes are commonly used, but it must be noted that in benzene-methanol solutions, a glass-antimony electrode pair may be used in which the glass electrode functions as reference electrode. Glass electrodes should not be maintained in non-aqueous solvents for long periods, as the hydration layer of the glass bulb may be impaired and the electrode will then cease to function satisfactorily. 

The polarographic determination of metal ions such as Al3 + which are readily hydrolysed can present problems in aqueous solution, but these can often be overcome by the use of non-aqueous solvents. Typical non-aqueous solvents, with appropriate supporting electrolytes shown in parentheses, include acetic acid (CH3C02Na), acetonitrile (LiC104), dimethylformamide (tetrabutyl-ammonium perchlorate), methanol (KCN or KOH), and pyridine (tetraethyl-ammonium perchlorate), In these media a platinum micro-electrode is employed in place of the dropping mercury electrode. 

Titanium, D. of as oxide, via tannic acid and phenazone complexes, (g) 470 by hydrogen peroxide, (s) 696 Titan yellow 692 Titrand 257 Titrant 257 Titration 257 classification of, 258 in an inert atmosphere, 376, 629 in non-aqueous solvents, 281 aniline (and ethanolamine), D. of, 307 indicators for, 283 solvents for, 283... 

The traditional areas of wet chemistry came under very close scrutiny and it was felt that whilst the overall size of Part D could be justifiably reduced, the chapter on titrimetry required modification to include a section on titrations in non-aqueous solvents as these are of particular application to organic materials. It was also felt that environmentally important titrations such as those for dissolved oxygen and chemical oxygen demand should be introduced for the first time. By way of contrast to this we considered that gravimetry has greatly diminished in application and justified a substantial reduction in volume. This in no way undermines its importance in terms of teaching laboratory skills, but the original multitude of precipitations has been substantially pruned and experimental details abbreviated. 

The specificity of enzyme reactions can be altered by varying the solvent system. For example, the addition of water-miscible organic co-solvents may improve the selectivity of hydrolase enzymes. Medium engineering is also important for synthetic reactions performed in pure organic solvents. In such cases, the selectivity of the reaction may depend on the organic solvent used. In non-aqueous solvents, hydrolytic enzymes catalyse the reverse reaction, ie the synthesis of esters and amides. The problem here is the low activity (catalytic power) of many hydrolases in organic solvents, and the unpredictable effects of the amount of water and type of solvent on the rate and selectivity. 

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