Mixed Water-Organic Solvents

A typical approach, in which the ionic strength is established by a 1-1 salt, and the pH is adjusted by an acid or base that has an ion in common with the inert electrolyte and is measured by means of a glass electrode, was used to study the following systems by titration, electrophoresis, and electroacoustics. A purely aqueous system was usually studied as a reference. The physical properties of solvents relevant to the interpretation of electrokinetic data (viscosity and permittivity) may be very different from those of water, and they have to be taken into account in the interpretation of results. 

Alumina was studied in aqueous alcohols [925], aqueous dioxane [666,963], aqueous dimethylsulfoxide (DMSO), aqueous glycerol, and aqueous heavy water [963]. Fe2O3 was studied in aqueous alcohols [1375,1386,1434,1456], aqueous dioxane [1388], and aqueous DMSO [1411]. Goethite was studied in aqueous acetone and aqueous methanol [1521]. Silica was studied in aqueous alcohols [1838, 1910,1911] and in other water-organic mixtures [1838]. Silica capillary was studied by electro-osmosis in 50 50 mixtures of organic solvents with water in the presence of a phosphate buffer [2927]. Surface charging of silica in mixed solvents is reviewed in [3110]. Titania was studied in aqueous alcohols [220,550,1986, 1988,2059,2115], aqueous dioxane [666,963], aqueous DMSO, aqueous glycerol, and aqueous heavy water [963]. Yttria was studied in aqueous alcohols [220]. 

Different oxides were studied in aqueous I-propanol [350], Controlled pore glass was studied in aqueous alcohols [2603], 

In another series of publications, the solids were dispersed in pure mixed solvents or the concentrations of various inorganic components (which may include acid or base) was adjusted, but the pH was not measured. Hematite was studied in a 50 50 ethanol-water mixture at different concentrations of NaOH and UNO, [3111]. Silica was studied in aqueous acetone (0-100%) at constant Nal concentration [3112]. Quartz was studied in ethanol-water mixtures in the presence of alkali bromides [3113]. Anatase was studied in 25% and 50% methanol [1984] at different NaCI concentrations. Glass was studied in a 50 50 ethanol-water mixture at different concentrations of NaOH and HNO, [3111]. 

Polystyrene latex was studied in water-alcohol mixtures in the presence of 0.0001-0.1 M KBr [3114], in aqueous ethanol and aqueous 1-propanol in the absence of electrolyte [3115], and in aqueous methanol and ethanol in the absence of electrolyte [3116]. 

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Figure 2. Viscosity B coefficients for salt solutions in mixed water-organic solvents, as a function of the mole fraction of the organic component in the solvent. O, this work , Ref. 18 Q Ref. 16 Ref. 6.

Timasheff SN and Inoue H. Preferential Binding of Solvent Components to Proteins in Mixed Water-Organic Solvent Systems. Biochemistry 1968 7 2501-2513. 

Basic hydrolysis of [Ru(NH3)jX]X (X = Cl, Br, or I) at 0.03—0.02M-OH " concentrations shows deviations from first-order plots early in the reaction the rate data fit a combination of two exponential decays, thought to be competing Sis,2cb and Sn2 processes. The kinetics of aquation of [Ru(NH3)5Cl]Cl2 and m-[RuCl2(en)2]CI,-H2O in mixed water-organic solvent media indicate processes. Hg catalyses the aquation of the former complex [(NH3)5Ru—Cl—Hg]" is formed in a preequilibrium and dissociates to form HgCl. [Ru(phen)3] and [Ru(bipy)3] oxidize cyclohexanone in IM-H2SO4 by outer-sphere processes. In 0.1M-OH with excess RCHO (R = Me or Ph), [Ru(NH3)g] is rapidly converted into [(NH3)5Ru(NCR)]. In basic conditions, the cation reacts with oxygen to form [Ru(NH3)sNO] in the presence of [Ru(NH3)5 NO] is still formed,... 

A wide range of organic compounds can dissolve in the mixed water-organic solvent phases and be separated, so RPC is by far the most popular form of HPLC. For those that can be separated either by NPC or RPC, the elution order is generally reversed, although not always exactly. Of course, if a sample is very nonpolar and insoluble in water mixtures, normal-phase chromatography is used. Otherwise, reversed-phase chromatography is used. 

The pK values, considered as acidity constants, refer mainly to aqueous solutions (pKj = pK ), and - more rarely - to the solutions in organic or mixed, water+organic solvents. In turn, the papers on changes in pK values, resulting from changes in the solvent composition in binary-solvent systems, are scarce. The main aim of this issue is the elaboration of a simple methodology that enables the binary-solvent electrolytic systems to be studied, with use of mathematical modeling applied. 

Bimolecular rate constants (k p = k bs/[R]x where [R]x represents the total concentration of one of the two reactants and whose concentration is larger than that of the second reactant, S, by a factor of more than 5) for 1,3-dipolar cycloaddition reactions of benzonitrile oxide (18) with a series of Af-substituted maleim-ides (19a-19c) in micelles of nonionic surfactants, C,2Eg, C,2E23, Cj Ejo, and CigE2o, fit reasonably well to a kinetic equation similar to Equation 3.61 (Chapter 3)." The calculated values of vary from 0.30 to 0.39 for all four nonionic micelles. Nearly 3-fold micellar deceleration effects have been shown to be similar to the effect of mixed water/1-propanol solvent with [H2O] about 15 M on k pp. However, a comparison of k with k pp in such water-organic solvents does not provide detailed information about the exact nature of the reaction environment in the micellar pseudophase. Instead, it provides information about the question insofar as the micellar reaction environment is satisfactorily mimicked by such mixed water-organic solvents. 

German N, Armalis S (2012) Voltammetric determination of naphthalene, fluorene and anthracene using mixed water-organic solvent media. Chemija 23 86-90... 

For some elements, there are a variety of possible precursors, sulfur for instance (Figure 11). Use of metal-organic precursors, used in MOMBE or MOVPE, are possible if they are soluble in water, or a nonaqueous solvent is used. Mixed aqueous-organic solvents could improve solubility. Overall, there would be an increased probability of carbon contamination, however. One of the benefits of using inorganic salts in aqueous solutions is that the number of constituents is limited, and thus the... 

Other methods start from crude indanthrone, which is dissolved in sulfuric acid or oleum (sometimes mixed with organic solvents). The product may be precipitated with water. It is more advantageous to separate the precipitated crude pigment, to reslurry it in water, and to heat the resulting aqueous suspension in the presence of a cationic surfactant. Subsequent treatment of the sulfuric acid solution with nitric acid, manganese dioxide, or chromium trioxide is followed by transfer into a solution containing sodium sulfite or iron(II)sulfate. 

A further complication that sets in when organic or mixed aqueous-organic solvents are used, which is aggravated when the relative permittivity of the medium, e, falls below 40, is ion pairing. This phenomenon does occur in purely aqueous solutions, mainly with higher-valence-type electrolytes 2 2 and higher, and with 2 1 or 1 2 electrolytes only at high concentrations. Ion pairs may also form in aqueous solutions of some 1 1 electrolytes, provided the ions are poorly hydrated and can approach each other to within <0.35 nm. Such ion pairs are of major importance in solvents that are relatively poor in water or that are nonaqueous. 

Semiaqueous or Nonaqueous Solutions. Although the measurement of pH in mixed solvents (e.g., water/organic solvent) is not recommended, for a solution containing more than 5% water, the classical definition of a pH measurement may still apply. In nonaqueous solution, only relative pH values can be obtained. Measurements taken in nonaqueous or partly aqueous solutions require the electrode to be frequently rehydrated (i.e soaked in water or an acidic buffer). Between measurements and after use with a nonaqueous solvent (which is immiscible with water), the electrode should first be rinsed with a solvent, which is miscible with water as well as the analyte solvent, then rinsed with water. Another potential problem with this type of medium is the risk of precipitation of the KC1 electrolyte in the junction between the reference electrode and the measuring solution. To minimize this problem, the reference electrolyte and the sample solution should be matched for mobility and solubility. For example, LiCl in ethanol or LiCl in acetic acid are often used as the reference electrode electrolyte for nonaqueous measurements. 

We have recently devised a rapid and convenient method for determination of the ionization constant for water in mixed aqueous organic solvents (11-16). The method utilizes glass electrodes and gives results in satisfactory agreement with earlier work. 

Hefter, G., Marcus, Y., and Waghome, W. E. (2002) Enthalpies and entropies of transfer of electrolytes and ions from water to mixed aqueous organic solvents, Chem. Rev. 102, 2773-2835 and references cited therein. 

The efficiency of molecular recognition may be improved by creating additional hydrogen bonding sites in the Ti02-gel. As an example, a composite gel film was prepared from trimethoxysilane with a urea unit (TMS-PU) and Ti(0 BU)4. TMS-PU and Cbz-(3-Ala were mixed in organic solvent in the presence of water. After aging and addition of Ti(0 Bu)4, the stock solution was subjected to the surface sol gel process, and the template molecule was removed... 

The authors of this article have studied the properties of a series of complexes of alternating9, 52 54,66"711 and random72" 1 copolymers with nonionic polymers (Tables 4, 5) by means of the potentiometric, viscometric and conductometric methods. In some cases, when the copolymer is insoluble in water the complex formation has been studied in water-organic solvent mixtures. Thus, the water-DMSO (90 10 vol-%) mixed solvent for the PVP-MAA/St system761 and water-ethanol (70 30 wt-%) mixed solvent for the PVP (PEG) - MAA/MMA (MAA/BMA)771 systems have been used. 

As an example we mention the dependence of the free energy of transfer of man-ganese(II) ions from water to water-acetonitrile mixtures on the parameter [85]. It is a complicated nonlinear dependence, which suggests that the interaction of /7-nitroaniline (used in determination of nd manganese(II) with aqueous solutions of acetonitrile is totally different. One may expect that complicated dependences of AG,r or E° EI/2) potentials on parameters of the Lewis basicity or acidity of mixed solvents will be observed for other ions also. Such relationships of the solvation abilities of water-organic solvent mixtures in respect to different cations are determined by several factors ... 

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