Resolution, optical isomers

Pre-lab 8.2.b Optical Isomer Resolution Using Tartrate Salts5,6... 

Because they are similar, the aLkanolamines often can be used interchangeably. However, cost/perfomiance considerations generally dictate a best choice for specific appHcations. AMPD is manufactured in very low volumes for use as a reagent in certain medical diagnostic tests, although some is used in certain cosmetic products. 2-Ainino-1-butanol is used primarily as a taw material for the synthesis of ethambutol [74-55-5] an antituberculosis dmg. The first step in the synthesis of this dmg is the resolution of AB into its optical isomers because only (i)-2-amino-l-butanol, [5856-62-2] is utilized in this synthesis. 

J. Jaques, A. CoUet, and S. WiUen, Enantiomers, Racemate, and Resolutions,]o m Wiley Sons, Inc., New York, 1981 The Chemical Society of Japan, eds., Kikan Kagaku Sosetsu (No. 6, Resolution of Optical Isomers), Gakkai Shuppan Senta, Tokyo, Japan, 1989 G. C. Barrett ia Ref. 1, Chapt. 10, pp. 338—353 S. Otsuka and T. Mukaiyama, Progress of ylsymmetric Synthesis and Optical Resolution (ia Japanese), Kagaku Dojia, Kyoto, Japan, 1982. 

N. Oi ia Chemical Society of Japan, eds., Kagaku Sosetsu (No. 6, Resolution of Optical Isomers), Gakkai Shuppan Senta, Tokyo, Japan, 1989,... 

Crystallization continues to be the most widely used method of separating or resolving enantiomers (optical resolutions). The manufacture of chemicals and pharmaceuticals as purified optical isomers, or enantiomers, has taken on a pivotal importance in the pharmaceutical, agricultural and fine chemicals industries over the past 15-20 years. Crystallization has been and continues to be the most widely used method of separating or resolving enantiomers (optical resolutions), and is particularly well suited to separations at large scale in manufacturing processes (Jacques etal., 1981 Roth etai, 1988 Wood, 1997 Cains, 1999). 

Where unidentate ligands are present, the ability to effect the resolution of an octahedral complex (i.e. to separate 2 optical isomers) is proof that the 2 ligands are cis to each other. Resolution of [PtCl2(en)2] therefore shows it to be cis while of the 2 known geometrical isomers of [CrCl2en(NH3)2] the one which can be resolved must have the cis-cis structure since the trans form would give a superimposable, and therefore identical, mirror image ... 

Enantiomeric separations have become increasingly important, especially in the pharmaceutical and agricultural industries as optical isomers often possess different biological properties. The analysis and preparation of a pure enantiomer usually involves its resolution from the antipode. Among all the chiral separation techniques, HPLC has proven to be the most convenient, reproducible and widely applicable method. Most of the HPLC methods employ a chiral selector as the chiral stationary phase (CSP). 

Fanali, S., Ossicini, L., Foret, F., and Bocek, R, Resolution of optical isomers by capillary zone electrophoresis study of enantiomeric and distereoisomeric cobalt (III) complexes with ethylenediamine and amino acid ligands, /. Microcol. Sep., 1, 190, 1989. 

Ligand (69) coordinates to nickel such that the four donors and the metal ion form a planar array whereas (68) coordinates around one face of an octahedral arrangement. Each complex type exhibits a characteristic kinetic inertness which no doubt arises from the operation of the macro-cyclic effect. Indeed, because of the inertness of the cation [Ni(tri)(H20)3]2+, its resolution into optical isomers has been possible... 

Treatment of either the sc or the ap atropisomer of the diester (97) with potassium hydroxide effected the hydrolysis of only one of the ester groups for steric reasons, to afford monocarboxylic acid sc-98 and ap-98, respectively. The sc isomer was converted into a nienthyl ester (99) for resolution into optical isomers. Thus the three rotameric forms of the monocarboxylic acid ( + sc, -sc, ap) were isolated (142). 

The optical activity of biologically-active chemicals is important to their activity and toxicology. Pure enantiomers, or optical isomers, of pharmaceuticals and agrochemicals can in many cases be made by enantiospecific synthesis. An alternative method is to use a less complicated synthesis followed by chromatographic resolution of the racemic mixture into its enantiomers. 

A number of Co(III) complexes, such as Co(edta) and Co(phen)3, can be resolved into optical isomers and are extremely stable towards racemization. The Co(II) analogs are configurationally labile and resolution has proved impossible. Suggest how with a double mixing apparatus it might be possible to measure half-lives in the 10 -1 s range for the first-order racemization of the Co(Il) complexes. 

Most of the studies of the reactivity of this oxidation state have been carried out with these types of complexes. The low spin d Ni(IV) resembles Co(III) in being diamagnetic, substitution inert and capable of resolution into optical isomers. Reductions are outer-sphere when Co(edta), ascorbate and Co(phen)3+ Ref. 269 are used, intermediate Ni(III) species are detected and characterized. Oxidation of Co(edta) by Ni (S-Me2L) + or Ni (S-MejL), L = 12, R = R]=CH3i R2 = H, produces a =10% excess of (+)-... 

An effect observed with a number of compounds which have apparent chiral centers on elements other than carbon. Eor example, secondary and tertiary amines have a pyramidal structure in which the unshared pair of electrons is at the top of the pyramid. If the three substituents hnked to the nitrogen are all different, one might suspect that the tertiary amine would give rise to optical activity and be resolvable. However, rapid oscillation of the unshared pair of electrons on one side of the nitrogen to the other (hence, pyramidal inversion) in effect causes interconversion of the two enantiomers and prevents resolution. If the nitrogen is at a bridgehead, this umbrella effect is inhibited and optical isomers can be isolated. 

Under all applied conditions only C 0F4g is formed, probably as three different optical isomers [24—26] (Figure 9.1). Gakh and co-workers determined the correct structure on the basis of F NMR spectroscopy [24]. The structure was confirmed by resolution of the X-ray crystal structure [25, 26]. This shows that, probably, all three optical isomers - namely the two enantiomeric forms with Dj-symmetry and the mesoform with Sg-symmetry- can be foimd in the crystal (Figure 9.1, structures 11 and 12). 

The synthesis of optically active polyamides, or nylons, is a growing area of interest. From 1980 to 1991 there have been many citations in Chemical Abstracts on this subject. For example, optically active polyamides have been prepared for the resolution of optical isomers. The polyamides are prepared from optically active amines or dicarboxylic acids. One polyamide was prepared from (-)-(ram-l,2-diaminocyclohexane and terephthaloyl chloride and was used to resolve 2,2 -dihydroxy-6,6 -dimethylbiphenyl [31]. These optically active polyamides can be used in chromatography applications to resolve other optically active compositions. 

The d or L configuration of the two en rings about the Co atom then decides which optical isomer of the N—CH3en coordinates stereospecific-ally. The detection of optical forms of this type has been accomplished by the resolution of the fCo(NH3)4sarcosine]2+ ion (29), In dilute acid the rate of exchange of the proton on the coordinated sarcosine N atom is very slow, and the optical configuration of the asymmetric N moiety is preserved. In... 

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