Neutralization titrations nonaqueous media

Acid value/H2S04a Potentiometric titration Acid amine neutralization in nonaqueous medium... 

Studebaker (63) studied the potentiometric titration of surface oxides in nonaqueous medium. Using sodium aminoethoxide in ethylene diamine, he found indications for the appearance of two breaks in the titration curves. The first break was attributed to carboxyl groups or groups of similar acidity, the second one to phenols. Only two-thirds of the acidity that was determined by NaOH neutralization could be titrated in nonaqueous medium. 

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]. 

A strong acid is released during the reaction. An important point to note is that the formed oxime does not exhibit any basic character also, the initial solution was neutral. This is easily explained by the fact that hydroxylamine is a strong base and, hence, its conjugate acid a very weak one. It is interesting also to note that the reaction medium is nonaqueous for the most part, since it only contains 10% water (in mass). Water is added essentially in order to dissolve the hydroxylamine hydrochloride. The medium also contains pyridine in order to displace the oxime formation equilibrium toward the right by formation of the pyridinium ion. The hydrochloric acid released is titrated with a methanolic sodium hydroxide solution. The indicator chosen is bromophenol blue, whose color-change interval is located on the acidic side. Actually, it is the pyridinium cation that is titrated with the methanolic sodium hydroxide solution. The pyridinium cation results from the protonation of the pyridine by the released hydrochloric acid. 

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