Acid-base titration in nonaqueous solvents

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

Fritz, J.S., Acid-Base Titration in Nonaqueous Solvents Allyn and Bacon Boston, 1973 Chapter 2. 

J. S. Fritz, Acid-Base Titrations in Nonaqueous Solvents (Boston Allyn Bacon, 1973) J. Kucharsky and L. Safarik, Titrations in Non-Aqueous Solvents (New York Elsevier, 1963) W. Huber, Titrations in Nonaqueous Solvents (New York Academic Press, 1967) I. Gyenes, Titration in Non-Aqueous Media (Princeton, NJ Van Nostrand, 1967). 

J. s. fritz Acid-Base Titrations in Nonaqueous Solvents, G. F. Smith Chemical, Columbus, Ohio, 1952 Acid-Base Titrations in Nonaqueous Solvents, Allyn and Bacon, Boston, 1973. 

Acid-Base Titrations in Nonaqueous Solvents. It is a fact that the apparent acidity or basicity of a compound is strongly dependent on the acid-base properties of the solvent. For example, very strong acids such as HCl and HNO3 cannot be individually titrated in water because water is sufficiently basic that these acids appear to be totally ionized. Very weak bases, such as amines, cannot be successfully titrated with strong acid in water. Many acids or bases that are too weak for titration in an aqueous medium, however, become amenable to titration in appropriate nonaqueous solvents. As a consequence, there are now many neutralization methods that call for solvents other than water [23-25]. 

J. Fritz, "Acid-Base Titrations in Nonaqueous Solvents", The G. Frederick Smith Chemical Comnany,... 

Table 1 Examples of acid-base titrations in nonaqueous solvents ...

J. A. Riddick, Anal. Chem., 24, 41 (1952). Acid-base Titrations in Nonaqueous Solvents. Extensive survey of theory and practice. 

Many cationic surfactants can be determined by direct acid-base titration in nonaqueous solvents according to general methods for determination of amines. Usually, perchloric acid titrant is used in a solvent of glacial acetic acid. Since such titrations are in no way specific for surfactants, they can only be used for solutions in which there are no unknown components. Details may be found in standard texts on nonaqueous titration. 

B. Chemical Reactions in Solvents and Melts, Pergamon Press, Oxford, 1969 Gyenes, 1. Titrationen in Nichtwdsserigen Medien, F. Enke, Stuttgart, 1970 Fritz, J.S. Acid-Base Titrations in Nonaqueous Media, Allyn Bacon, Needham Heights, MA, 1973 Kratochvil, B. 

Popov, A. I., Caruso, H. Acid-base equilibria and titrations in nonaqueous solvents. B. Amphiprotic solvents, in Ref. 1, pp. 303-348. 

Some of the reasons for considering coulometric titrations in nonaqueous solvents are that many organic compounds are not soluble in water, metals can exist in oxidation states that are not found in water, and advantage can be taken of the acidity or basicity of the solvent to improve the basic or acidic strength of a base or acid, respectively. 

Water is highly unusual in the extent of its interactions with solutes, but even minimal solvent-solute interactions can play a major role in the nature of chemical reactions. To calculate pH during acid-base titrations in a nonaqueous solvent, we must consider not only the equilibria discussed in Chapter 3 but also reactions discussed in Sections 4-2, 4-3, and 4-4. 

The analytical chemistry of redox reactions in nonaqueous solvents has received less attention than acid-base reactions in these solvents. It should be a fruitful subject for future study. Thus far the Karl Fischer titration for water has been the most... 

Many amines that ai e too weak to be titrated as bases in water are readily titrated in nonaqueous solvents, such as anhydrous acetic acid, which enhance their basicity. 

Use of potentiometry for pH titration allows analyses to be carried out in colored or turbid solutions. Also, it solves the problem of selecting the correct indicator for a particular acid-base titration. The endpoint can be determined more accurately by using a first or second differential curve as described earlier. It also permits pH titrations in nonaqueous solvents for the determination of organic acids and bases as described subsequently. In addition, it can be readily automated for unattended operation. 

Acid-base indicators for titrations in nonaqueous solvents are normally weak protolytes. For dissociation model I as given in Table 1, the acid-base equilibrium of a weak acid type of indicator in the pure solvent can be represented in water by the following reaction ... 

Reactions at the silicon nitride - solution interface - The use of potentiometric titrations in nonaqueous solvents indicates that there are possibly several different kinds of acid and base sites on the silicon nitride depending on the prior environmental history of the powd. The results are generally consistent with potentiometric titrations us d to evaluate the silicon dioxide surface. Future work will focus on further potentiometric as well as conductometric titrations on silicon nitride as well as model systems such as silicon dioxide. 

Aqueous titrations of amines are amply discussed elsewhere d. Nonaqueous titrations. Three main purposes may be served by carrying out titrations in nonaqueous solvents increased solubility, change of the pH scale, and resolution of mixtures. The prediction of a potentiometric titration curve in an arbitrary solvent is a difficult task, in which many factors intervene, such as dielectric constant, definition of acid and base in relation to the solvent, electrodes, actual structure of conjugate acids and bases, etc. Acetic acid, sulphuric acid, acetonitrile, and alcohol-water mixtures have been extensively studied and were reviewed elsewhere Some solvents will be treated here briefly ... 

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. 

QuaHty control in the production of organic solvent finish removers may be done by gas—Hquid chromatography, which allows the manufacturer to determine the actual ratio of volatile solvent present in the finished product. If the product does not meet specifications, solvents can be added to bring the product to an acceptable composition. A less expensive approach is to use a hydrometer to determine the specific gravity of the product. The specific gravity indicates if the proper blend has been reached. Nonaqueous acid—base titration may be used to determine the amount of acid or alkaline activator present in a remover. 

Acid-base potentiometric titration of phenol in aqueous solution is precluded because of its high pATa value (9.98), while 4-nitrophenol (7.41) and 2,4,6-trinitrophenol (0.71) can be directly titrated in that solvent. Nonaqueous titrations of phenol are possible however, difficulties are met when nitrophenols are also present in the system. The determination of carboxylic and phenolic groups in humic acids was carried out by acid-base potentiometric titrations in NaCl solutions up to 1 M. Titration data were processed by linear and nonlinear calculation techniques. ... 

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