Ephedrines determination

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. 

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. 

Imaz, C., Navajas, R., Carreras, D., Rodriguez, C., and Rodriguez, F.A., Comparison of various reversed-phase columns for the simultaneous determination of ephedrines in urine by high-performance liquid chromatography, /. Chromatogr. A, 870 (1 2), 23, 2000. 

In agreement with previous works, elimination of amphetamine-like compounds was diverse. Amphetamine and ephedrine are the best removed amphetamine-like compounds in the Ebro River basin. On the other hand, MDMA and methamphet-amine were poorly removed compared to other studies as they were found randomly at higher concentrations in effluents than in influents. Similar to these compounds and in contrast to previous studies, the only lysergic analyte determined in waste-waters, nor-LSD, was poorly or not eliminated during wastewater treatment processes (see Fig. 5). 

A spectrophotometric method for determination of primary and secondary amines requires development for each particular compound, determining the kinetics of reaction of the amine with sodium l,2-naphthoquinone-4-sulfonate (143) and the UVV absorption spectrum of the product, under a set of fixed conditions. The procedure was applied to determination of ephedrine (30) and amphetamine (28) in pharmaceutical samples339. Reagent 143 in a FLA. system was used for the fast determination of lysine (144) in commercial feed samples by multivariate calibration techniques, without need of chromatographic separation340. 

The competent authorities of India were successful in preventing diversions of such substances. Four large cases were uncovered in 2004. In three of the cases, one involving a shipment of 6 tons of ephedrine to Kenya and two further orders from a company in Indonesia, traffickers used falsified import documents. A further intended export of 4 tons of pseudoephedrine from India via the United States to Mexico was found to be a diversion attempt when investigations determined that 80 per cent of the customers claimed by the importer did not exist. All four shipments were stopped. 

Substituted chiral aldehydes can be derivatized with naturally occurring (1/ ,2S)-ephedrine to give oxazolidines, UC- and H-NMR analysis allows determination of the enantiomeric excess and in simple cases the absolute configuration of the analyzed aldehyde6. Very mild reaction conditions are required. 

Acids and bases. These can be converted to various salts. For example, the absolute configuration of dimethyl (M)-5,6,8,10-tetramethyl-l,2-heptalenedicarboxylate (p 404) was determined by X-ray analysis of its (+)-ephedrine salt84, and the absolute configuration of Troger s base (p 404) by X-ray analysis of a salt with an acid of known configuration87. 

Pig liver esterase (PLE, E.C. 3.1.1.1) is one of the most successful enzymes for the enantiotopos-differentiating hydrolysis of dicarboxylic diesters and diacetates of diols as exemplified by the two examples, dimethyl cv. y-4-cydohexene-l,2-dicaiboxylate (I)100 - " 2 and (l/ ,2.S,3S)-l,3-di-acetoxy-2-nitrocyclohexane (3)113. The monoester 2 is obtained with the same results when prepared on a 100 mol scale114. The ee values of the monoester 2 may be determined conveniently by H-NMR spectroscopy in the presence of (+)- or ( )-ephedrine and that of the monoacetate 4, after conversion to the corresponding Mosher ester, by 19F-NMR spectroscopy. 

Determined by two methods a) reduction with NaBH4 to the corresponding alcohol and acetylation, ee was then determined by 1H NMR using a chiral shift reagent, or b) the ephedrine method 29 using 13C-NMR spectroscopy on the derived oxazolidines. 

EXTENSIONS AND COMMENT ARY Here is another example of the presentation of a compound for which there has not yet been an effective level determined. Why For a very good reason. This is an example of a whole class of compounds that I have called the pseudos, or the -compounds. Pseudo- as a prefix in the literary world generally stands for false. A pseudopod is a thing that looks like a foot, but isn t one. A pseudonym is a fictitious name. But in chemistry, it has quite a different meaning. If something has a common name, and there is a second form (or isomer, or shape, or orientation) that is possible and it doesn t have a common name, it can be given the name of the first form with a pseudo- attached. Ephedrine is the erythro-isomer of N-methyl-13-hydroxyamphetamine. There is a second stereoisomer, the threo- isomer, but it has no trivial name. So it is called pseudoephedrine, or the Sudafed of sinus decongestant fame. 

A voltammetric MIP chemosensor for determination of an ephedrine stimulant has been fabricated using an immobilized MIP film overlaid with a polypyrrole film... 

N. Iwanami, Y. Ohtsuka, and H. Kubo, Determination of ephedrine alkaloids in Ephedra herb and Oriental pharmacceutical preparations by HPLC, Yaoxue Tongbao, 20 149 (1985). 

Y. M. Liu and S. J. Sheu, Determination of ephedrine and pseudo-ephedrine in Chinese herbal preparations by capillary electrophoresis, J. Chromotogr., 637 219 (1993). 

Limits of detection for many amino acids were enhanced considerably by pre-column derivatization with the achiral reagent dansyl chloride whose function it was to increase their specific rotation [17]. Determinations of the enantiomeric purities for mixtures of D-and L-tryptophan [18] and of isomeric ratios for mixtures of pseudoephedrine and its diastereomer ephedrine [19], were effected using diode-laser polarimetry and using OR detection in series with UV absorbance detection respectively. 

In recent years several sensitive and specific methods for the simultaneous determination of ephedrine alkaloids in plant material have been published. These include thin-layer chromatography (292,426), gas chromatography (251), straight-phase and reversed-phase high-performance liquid chromatography (253, 255, 302, 355, 427), isotachophoresis (303, 356), and 13C-NMR (304). Resolution of enantiomeric alkaloids by HPLC has been achieved on chiral stationary phases (417, 418) or after derivatization with a chiral agent on an achiral stationary phase (419). Chromatographic separation and analytical detection of... 

In summary, the efficiency of (-)-ephedrine supported on inorganic MTS in the model reaction is determined by two factors firstly, the activity of the mineral surface towards the formation of racemic 1-phenyl-propan-l-ol wich depends on the coverage of the surface by organics and secondly, the accessibility to the catalytic sites wich depends on the mesopore diameters of the support. 

The reaction of racemic A-phthalimido-S-p-tolyl-S-vinylsulfoximine with a deficiency (0.5 molar equiv) of enantiomerically pure (-)-ephedrine resulted in a kinetic resolution of the vinyl sulfoximine.113 When the reaction was conducted at -30 °C the unreacted vinyl sulfoximine could be recovered with an enantiomeric purity of 46%. (-)-Amphetamine and (+)-l-phenylethylamine were not effective for kinetic resolution. The analogous (Z)-propenyl sulfoximine also underwent kinetic resolution with (-)-ephedrine, but the extent of kinetic resolution was not determined. 

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