Amines, titration perchloric acid/glacial acetic

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. 

Glacial acetic acid, pure or mixed with other solvents, is one of the most attractive solvents for the titration of amines. Commercial acetic acid containing not more than 1% of water (Karl Fischer titration check) can be used in normal practice for the highest accuracy, however, the water content must be lowered to about 0.01% by addition of acetic anhydride and standing for 24 h not more than the stoichiometric amount of acetic anhydride should be used in order to avoid possible reactions with active hydrogen-containing analyte components such as primary or secondary amines or alcohols. A similar procedure is followed in the preparation of perchloric acid titrant from the commercial... 

The secondary amine function of dobutamine hydrochloride may be determined by potentiometric titration with perchloric acid using glacial acetic acid as a nonaqueous solvent. Mercuric acetate is used to tie up the chloride ion. 

Analysis. The amine oxide picrates were determined according to the procedure of Clark and Wang. A sample of 0.2 to 0.4 meq. of the picrate was dissolved in 10 ml. of glacial acetic acid. About 3 drops of methyl violet indicator were used. The color change from deep to light blue was used as the end point. The solutions were titrated with standard O.IV perchloric acid in glacial acetic acid with a microburet. 

The amides present are the ethanolamide itself and the amide ester(s). The amines are the ester amine(s), the mono- or diethanolamine, and possibly DHEP. Amines only are titrated with perchloric acid in glacial acetic acid. In acetic anhydride the same titrant titrates amides as well [23, 24]. 

Amines dissolve a 5g sample in glacial acetic acid (caution irritant vapour) and titrate potentiometrically with 0.1 M perchloric acid in glacial acetic acid. Or use 1% methyl violet in glacial acetic acid as indicator. The colour change is from violet to a light blue-green. 

That approach is useless for SW amphoterics BEC titration measures the total active and SDS titration in acid solution measures nothing. Acid-base titration measures both the acid group of the carboxylate and the basic group of the amphoteric. If the sample is dried and dissolved in glacial acetic acid, the amine function of the SW amphoteric can be titrated with perchloric acid in glacial acetic acid, but it is likely that other weak bases will be present. Extraction of the carboxylic acid is the simplest way. 

Suppose we consider some very weakly basic compounds, such as ketimines, phosphines, and oxiranes. A very interesting method of dealing with oxiranes was developed by Durbetaki. The oxirane was reacted with hydro-bromic acid to form the bromohydrln. This type of reaction has long been known using hydrochloric acid, but in that medium the reaction takes approximately three hours. In glacial acetic acid, the reaction is enough to allow you to titrate directly at normal speed. You can get an end point potentiometrically or with an indicator. In fact, if you have a mixture of amine and oxirane, you can get two potentlometric breaks, the first for the amine and the second for the oxirane. Amides, phosphene oxides, triphenyl methanol, and amine oxides are very weak bases and cannot be titrated in glacial acetic acid under ordinary conditions. However, they can be titrated if one uses acetic anhydride as solvent, or if one uses a solvent that is mixed with acetic anhydride. Why does acetic anhydride work There are two reasons. First, it removes the last trace of water from the solution secondly, perchloric acid in the presence of acetic anhydride forms the ion CHsCO". Since this is an extremely reactive substance, one can titrate very weak bases. 

Another method of analyzing a mixture of bases is to utilize the difference in the basicity of its components. As an example, let us take a mixture of aromatic and aliphatic amines. Since aliphatic amines are more strongly basic, one would expect to get a titration curve with two breaks, one for the aliphatic amine and one for the aromatic amine. However, you must not use glacial acetic acid for this titration because you will get a curve similar to curve B in Fig. 1. In other words, you get one potentiometric end point for the sum of the two. The reason is that glacial acetic acid reacts with aliphatic amines to form the acetate ion, which has about the same basic strength as the aromatic amine. Glacial acetic acid levels these two amines to the same strength. What you have to do is employ a nonaqueous solvent like acetonitrile and titrate with perchloric acid dissolved in dioxane. If you do this. 

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