Composition in nonaqueous solvents

In nonaqueous solvents. Exact composition depends on the manufacturer, usually propylene carbonate—dimethyl ether for ... 

Figure 7.13 Dependence of the mechanism (Tafel slope) of O2 evolution on the composition of Ir02 + RUO2 mixtures depending on the procedure of mixture preparation. (1) Thermal decomposition, precursors dissolved in water (2) thermal decomposition, precursors dissolved in nonaqueous solvents (3) reactive sputtering [62].

In analyzing polysaccharide hydrolyzates, some workers have assumed that, because mutarotation in pyridine is slow and the tri-methylsilylation reaction is fast, no change in the composition occurs during trimethylsilylation. Others have equilibrated the monosaccharides in pyridine, before trimethylsilylation.172,255 In nonaqueous solvents, the mutarotation may be catalyzed by lithium perchlorate172 or, more conveniently, by 2-pyridinol,256,257 which is volatile, but does not interfere with subsequent analyses. 

Fusion with Alkali and Cupric Oxide in Nonaqueous Solvents. Alkali lignin was fused with potassium hydroxide and cupric oxide in methanol under conditions suggested by Tiemann (20) and in n-amyl alcohol as suggested by Klages (4). These procedures were very effective in earlier model compound studies in our laboratories (12). Ether extracts obtained were less than those from corresponding experiments in aqueous solution, and qualitative compositions were essentially the same. In the case of the amyl alcohol experiments, artifacts with the cupric oxide were obtained. Again, experiments were conducted under more dilute conditions in a bomb under superatmospheric conditions, but results were no better. 

Lamivudine is an example of the effect of hydrates in nonaqueous solvents (Jozwiakowski et al., 1996). In distilled water at 25D, the anhydrate free base (form II) is 1.2 times as soluble as the 0.2 hydrate (form I). In ethanol at 26, the hydrate is 1.6 times as soluble as the anhydrate. The maximum solubility in ethanol-water mixtures was found to be at 40-60% water in ethanol, when form I is the most stable solid phase. The transition composition was with 18-20% water in ethanol in binary mixtures with more than 20% water, only the hydrate was found at equilibrium, and with less than 18% water, only the anhydrate was found at equilibrium. 

The meaning to be attached to pH values obtained in different solvents and under different conditions needs interpretation. For example, solutions of pH 5 in the three solvents water, ethanol, and acetonitrile do not denote the same acidity (acidity defined as a measure of the tendency for protons to be donated to basic substances). In view of what is known about transfer activity coefficients (Section 4-1), an acetonitrile solution of pH 5 is far more acidic (higher absolute activity) than an ethanol solution of pH 5 and, in turn, one in ethanol is more acidic than one in water. The significant point is that a solution of, say, pH 5 in a given solvent has an acidity 10 times the acidity of another solution of pH 6 in that same solvent. A single universal scale of pH for all solvents does not exist instead there is a different scale for every solvent of differing composition. To denote pH values in nonaqueous solvents, the... 

The oxyhydrochlorination catalyst was prepared according to the procedure of Conner et al. [9]. The material was prepared in nonaqueous solvents by successive impregnation of metal chloride salts onto a silica support. A saturated solution of copper (I) chloride in acetonitrile was sorbed into fumed silica (325 mVgram). The acetonitrile was then removed under reduced pressure. A solution of potassium chloride and lanthanum chloride 1n formic acid was added to the cuprous chloride coated silica. The formic acid was removed under reduced pressure to produce the layered oxyhydrochlorination catalyst. The weight composition of the final catalyst was 41.7% CuCI, 37.5% Si02, 11.5% KC1, and 9.4% LaClj. The catalyst could be activated in a stream of hydrogen chloride at 300°C for ten minutes. 

Autoxidation of iron(II) chloride in nonaqueous solvents is much faster than in water. The rate is first order in oxygen, and under controlled conditions, second order in iron(II). Various additives have powerful catalytic or inhibitory effects. The inhibition by iron(III) disappears in the presence of excess lithium chloride, so inhibition is attributed to competition between iron(II) and iron(III) for chloride ions. Induced autoxidation of benzoin to benzil has the same rate-limiting step as the autoxidation of iron(II) without cosubstrate. The data can be accommodated by a mechanism in which the rate-limiting step is production of iron(IV) by dissociation of a binuclear complex having the composition Cl FeOOFeCl. In the presence of excess lithium chloride, intermediates containing more chloride bound to iron become involved. 

The thermodynamic affects of complexation of 25, its monomeric component and 23 with metal ions monitored through NMR studies in nonaqueous solvents also show that in these conjugates, the positions of the pyridyl nitrogen and ethereal oxygen play a primary role in their hosting abilities for metal cations and as the distance of N and O increases, the ability of the ligand to coordinate decreases. Thus, 23 was able to interact with alkali metal cations, but this ability is lost for 25. The conductance measurements show that for all cations except Hg°, the composition of complexes of 25 is 1 1. However, 25 hosts two Hg° cations (2005JPC(B)14735). 

Bis[tris(2,4-pentanediono)titanium(IV)] hexachlorotita-nate(IV) is soluble in nonaqueous solvents, such as benzene and chloroform, but only slightly soluble in cold glacial acetic acid. It is completely decomposed by water into acetylacetone, hydrous titanium oxide, and hydrochloric acid. When a glacial acetic acid solution of the titanium compound is added to one of iron(III) chloride, a red crystalline compound having the composition [Ti(C6H702)j]-FeCh is precipitated. 

Solvents containing buffers or modifiers prepared from solids must be filtered prior to use. For the best reproducibility, the buffer solutions should be made up separately as individual components of the mobile phase and then filtered separately. For example, a mobile phase having a composition of 50/50 methanol/water (50 mM sodium acetate at pH 4.5 buffer) should have the acetate buffer prepared separately and then combined with the methanol. Avoid adjustments of the pH in nonaqueous solvents, since pH meters are designed to repond to hydrogen ion activity in an aqueous solution only ... 

---