Ephedrine titration

You may wonder why we did not use the titration curve to determine the pH at the stoichiometric point of the ephedrine titration, as we did to find the pH at the midpoint. Notice from Figure 18-6 that near the stoichiometric point, the pH changes very rapidly with added H3 O. At the stoichiometric point, the curve is nearly vertical. Thus, there Is much uncertainty in reading a graph to determine the pH at the stoichiometric point. In contrast, a titration curve is nearly fiat in the vicinity of the midpoint, minimizing uncertainty caused by errors in graph reading. 

For the estimation of ephedrine in its salts or simple solutions, titration methods and a Kjeldahl estimation have been described by various authors. The formation of iodoform from ephedrine has been proposed as a method of estimation by Sanchez, and biological methods have been used by several authors. ... 

Schematic profile of the titration curve for a weak base B titrated with hydronium ions. The pH values are those for titration of ephedrine, a weak base that is the active ingredient in many decongestants.

Ephedrine, a weak base, is the active ingredient in many commercial decongestants. To analyze a sample of ephedrine dissolved in 0.200 L of water, a chemist carries out a titration with 0.900 M HCl, monitoring the pH continuously. The data obtained in this titration are shown in Figure 18-6. Calculate Zj, for ephedrine and determine the pH of the solution at the stoichiometric point. 

The association constants for CyD complexes with chiral guests are generally different and mostly quantitatively determined by the chemical shift titration experiments. However, as mentioned above, other NMR parameters, such as relaxation rates [10, 70] or self-diffusion coefficients, may also be used. Both those parameters were successfully applied for the enantiodifferentiation and determination of association constants in complexes of the trifluoroacetate salts of the enantiomers of amphetamine, ephedrine, and propranolol with 2,6-di-O-dodecyl-a-CyD and its p analogue [71]. The DOSY technique was employed for the determination of diffusion coefficients of enantiomers of cyclohexanone derivatives complexed with a-, j8-and y-CyDs as well as with their per-O-methylated analogues [72]. 

Treatment of 8 (derived from (-l-)-ephedrine) with two equivalents of a toluenic solution of HCI (previously titrated) produced 30 in 90% yield, with inversion of configuration at the P atom. Purification by column chromatography, although... 

A variation on these titrations consists of adding hydrochloric acid to the hydroalcoholic solution of the solute and then titrating them with a sodium hydroxide solution. The equivalence point is detected by pH-metry. Ephedrine, bupivacaine, de-sipramine, chlorprothixene, and amantadine hydrochlorides are titrated in this way. Using pH-metry is necessary in this variation since we must detect the successive equivalence points with an optimal precision. The first equivalence point corresponds to the end of the neutralization of hydrochloric acid, the second to that of the cation. The addition of hydrochloric acid facilitates the detection of the beginning of the cation neutralization reaction. It can be inferred from all these results that the addition of ethanol to water permits a satisfactory detection of the equivalence point of this kind of products, even of those that exhibit the higher pK values, such as the amantadine hydrochloride (pK = 10.68). This means that the reaction between the base of the titrant couple and the cation is more quantitative in these mixtures than in water. In other words, the couple BH+/B is farther from the couple H20/0H in these mixtures than it is in water. Actually, the titrant is a mixture of the couple H2O/OH- andC2H50H/C2Hs0. ... 

To an aqueous acid solution containing approximately 0-1 g of alkaloid, the volume of solution being kept low, add excess of solution of ammonia and extract with liberal portions of ether. As the alkaloid is very soluble in water, do not wash the ether extracts but dry them with anhydrous sodium sulphate before evaporating carefully. Dry the alkaloid in a desiccator. As a check after weighing the alkaloid, titrate as usual, using methyl red as indicator. 1 ml 0-lN = 0 01652 g of ephedrine ephedrine x 1 221 = ephedrine hydrochloride,... 

Sanchez" determined ephedrine by its reaction with alkaline iodine solution at 50 to form iodoform and titration of excess iodine in acid solution. Application of this method to standard solutions of ephedrine... 

Commercially, preparations are encountered with anhydrous ephedrine, in an oily base, usually containing eucalyptol, camphor and menthol. The ephedrine in such preparations can readily be determined by mixing a suitable volume with glacial acetic acid and toluene and carrying out a direct non-aqueous titration with perchloric acid in glacial acetic acid. 

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