Nonaqueous

The location and shape of the entire electrocapillary curve are affected if the general nature of the medium is changed. Fawcett and co-workers (see Ref. 126) have used nonaqueous media such as methanol, V-methylformamide, and propylene carbonate. In earlier studies, electrocapillaiy curves were obtained for O.OIA/ hydrochloric acid in mixed water-ethanol media of various compositions [117, 118]. The surface adsorption of methanol, obtained from... 

The traditional association colloid is of the M R" type where R" is the surfactant ion, studied in aqueous solution. Such salts also form micelles in nonaqueous and nonpolar solvents. These structures, termed inverse micelles, have the polar groups inward if some water is present [198] however, the presence of water may prevent the observation of a well-deflned CMC [198,199]. Very complex structures may be formed in nearly anhydrous media (see Ref. 200). 

Filins at Liquid-Liquid Interfaces and on Nonaqueous Liquid Surfaces... 

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

Friberg S E and Liang Y-C 1987 Nonaqueous microemulsions Microemulsions Structure and Dynamics ed S E Friberg and Bothorel (Booa Raton, FL Chemioal Rubber Company) pp 79-91... 

Kose A and Hachisu S 1974 Kirkwood-Alder transition in monodisperse latexes. I. Nonaqueous systems J. Coiioid interface Sc/. 46 460-9... 

Gast A P, Flail C K and Russel W B 1983 Polymer-induced phase separations in nonaqueous colloidal suspensions J. Colloid Interface Sol. 96 251 -67... 

Nadimi S, Oliver S, Kuperman A, Lough A, Ozin G A, Garces J M, Olken M M and Rudolf P 1994 Nonaqueous synthesis of large zeolite and molecular sieve crystals Stud. Surf. Sol. Catal. 84 93-100... 

Grote s reagent is useful for the determination of 2-aminothiazoie in blood and wine (145), This thiazole may be extracted from its aqueous solution and then titrated in nonaqueous medium (MeOH) with HCIO4 in the presence of a mixed methyl red-methylene blue indicator (146). 

Mention must be made of the u.se of o- or p-hydroxystyryl thiazolo dyes as indicators for protolytic titrations in nonaqueous media (145). and of the hypotensive action of some neotrinuclear thiazolo cyanines in experiments on animals (146). 

Aldehydes are more easily oxidized than alcohols which is why special reagents such as PCC and PDC (Section 15 10) have been developed for oxidizing primary alco hols to aldehydes and no further PCC and PDC are effective because they are sources of Cr(VI) but are used m nonaqueous media (dichloromethane) By keeping water out of the reaction mixture the aldehyde is not converted to its hydrate which is the nec essary intermediate that leads to the carboxylic acid... 

Table 8.11 pK, Values for Proton-Transfer Reactions in Nonaqueous Solvents 8.81... 

FIGURE 8.1 Approximate potential ranges in nonaqueous solvents. 

Solubility can often be decreased by using a nonaqueous solvent. A precipitate s solubility is generally greater in aqueous solutions because of the ability of water molecules to stabilize ions through solvation. The poorer solvating ability of nonaqueous solvents, even those that are polar, leads to a smaller solubility product. For example, PbS04 has a Ks of 1.6 X 10 in H2O, whereas in a 50 50 mixture of H20/ethanol the Ks at 2.6 X 10 is four orders of magnitude smaller. 

The majority of titrations involving basic analytes, whether conducted in aqueous or nonaqueous solvents, use HCl, HCIO4, or H2SO4 as the titrant. Solutions of these titrants are usually prepared by diluting a commercially available concentrated stock solution and are stable for extended periods of time. Since the concentrations of concentrated acids are known only approximately,the titrant s concentration is determined by standardizing against one of the primary standard weak bases listed in Table 9.7. 

The NH3 is removed by distillation and titrated with HCl. Alternatively, N03 can be titrated as a weak base in an acidic nonaqueous solvent such as anhydrous acetic acid, using HCIO4 as a titrant. 

Many pharmaceutical compounds are weak acids or bases that can be analyzed by an aqueous or nonaqueous acid-base titration examples include salicylic acid, phenobarbital, caffeine, and sulfanilamide. Amino acids and proteins can be analyzed in glacial acetic acid, using HCIO4 as the titrant. For example, a procedure for determining the amount of nutritionally available protein has been developed that is based on an acid-base titration of lysine residues. ... 

Another important example of a redox titration for inorganic analytes, which is important in industrial labs, is the determination of water in nonaqueous solvents. The titrant for this analysis is known as the Karl Fischer reagent and consists of a mixture of iodine, sulfur dioxide, pyridine, and methanol. The concentration of pyridine is sufficiently large so that b and SO2 are complexed with the pyridine (py) as py b and py SO2. When added to a sample containing water, b is reduced to U, and SO2 is oxidized to SO3. 

A more thorough discussion of nonaqueous titrations, with numerous practical examples, is provided in the following text. 

Fritz, J. S. Acid-Base Titrations in Nonaqueous Solvents. Allyn and Bacon Boston, 1973. 

The concentration of anionic surfactants at the sub-ppm level in natural waters and industrial waters are determined spectrophotometrically. The anionic surfactants are extracted into a nonaqueous solvent following the formation of an ion association complex with a suitable cation. 

Potcntiomctric Titrations In Chapter 9 we noted that one method for determining the equivalence point of an acid-base titration is to follow the change in pH with a pH electrode. The potentiometric determination of equivalence points is feasible for acid-base, complexation, redox, and precipitation titrations, as well as for titrations in aqueous and nonaqueous solvents. Acid-base, complexation, and precipitation potentiometric titrations are usually monitored with an ion-selective electrode that is selective for the analyte, although an electrode that is selective for the titrant or a reaction product also can be used. A redox electrode, such as a Pt wire, and a reference electrode are used for potentiometric redox titrations. More details about potentiometric titrations are found in Chapter 9. 

Protonic acids dissociate to some extent in the nonaqueous reaction mixtures to produce an equilibrium concentration of protons ... 

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