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Racemic compound formation-conglomerate formation

Part 4. Optical resolution and determination of the melting phase diagrams of 2′,6′-pipecoloxylidide and four 1-alkyl-2′,6′-pipecoloxylidides

Journal of Thermal Analysis and Calorimetry
Authors: Katalin Nemák, Mária Ács, D. Kozma, and E. Fogassy

The phenomena of conglomerate formation-racemic compound formation were investigated in a series of five (N-alkyl)-2′,6′-pipecoloxylidides. The optically active enantiomers were prepared by optical resolution of the racemates using 2R,3R-tartaric acid and 0,0′-dibenzoyl-2R,3R-tartaric acid as resolving agent. By DSC measurement of the racemates and the enantiomer the binary phase diagrams were determined.

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The phase diagram of R(+)-S(-) efaroxan hydrochloride (Tfus.(R)=245.10.3C. ΔHfus.(R)=119.63.0 J g-1) shows a racemic compound. The melting temperature and melting enthalpy of the compound are: Tfus.(RS)=247.80.2C and ΔHfus. (RS)=124.62.4 J g-1. A solid ↔ solid transformation takes place at Ttrs.=1801C, ΔHtrs.=15.00.4 J g-1. This transition is observed between 3 and 97% R(+). The stability of the racemic compound already established in a previous study was confirmed by the value of Petterson's coefficient (i=1.19). The two eutectic positions at 20 and 80% R(+) that define the range over which the racemic compound is found, exclude the use of resolution methods by preferential crystallization.

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This paper reports a number of original thin-layer chromatographic enantioseparations of chiral sulfoxides that are important for their use as drugs and drug metabolites, pesticides, or chiral auxiliaries, obtained by elution with alcohols or aqueous-alcoholic mixtures at different ratios on cellulose tribenzoate. Detection was performed by exposing the plates to iodine vapor, followed by densitometry at 410 nm. Under these experimental conditions, ten of the eighteen chiral aromatic sulfoxides investigated were baseline or partially resolved, thus providing useful chromatographic information for this important class of racemic compounds.Data obtained with cellulose tribenzoate were compared to those achieved with microcrystalline cellulose triacetate for the same group of chiral sulfoxides, evidencing an interesting complementary behavior of the two stationary phases.

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metastable melting points of the racemic compound and the eutectic invariant gives a rough estimation of the energetic advantage of the conglomerate over the racemic compound. Fast precipitation can, in accordance with the Ostwald rule of stage, lead to the

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Journal of Thermal Analysis and Calorimetry
Authors: A. Sykuła-Zając, E. Łodyga-Chruścińska, B. Pałecz, R. E. Dinnebier, U. J. Griesser, and V. Niederwanger

at above 60 °C. Statistical analyses show that only about 10% of racemates are conglomerates, while the vast majority of them are racemic compounds. Bupivacaine belongs to that 10% group of conglomerate compounds, which offers the possibility

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