A method of solvent sublation was developed for the enantioseparation of racemic ofloxacin (rac Oflx) and racemic tryptophan (rac Trp). In this method, dibenzoyl-L-tartaric acid (L-DBTA) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) and sodium lauryl sulfate (SDS) were used as chiral coextractants and foamer, respectively. Several important parameters influencing the separation performances, such as pH in aqueous phase, concentrations of rac mixtures, L-DBTA, D2EHPA, and SDS, were investigated. Under the optimal operation conditions, the enantiomeric excess and enantioselectivity were 60.08% and 5.58 for Oflx and 65.09% and 6.31 for Trp, respectively. The yields of D-enantiomer and L-enantiomer were 34.23% and 8.54% for Oflx and 18.59% and 3.93% for Trp, respectively. The results suggest that the enantioselectivities have been enhanced compared with the traditional chiral extraction. This technique is an efficient chiral separation method, with many advantages such as low expenditures of organic solvent, low consumption of chiral extractant, and easy realization of multistage operation.
The distribution behavior of ofloaxcin (OFLX) enantiomers in a two-phase system was examined using a new mixed complex chiral selector consisting of di(2-ethylhexyl) phosphoric acid (D2EHPA) and two tartaric acid derivatives with n-octanol as diluents. The influence of composition of mixed complex chiral selector, initial concentration of OFLX, pH of aqueous phase and temperature was investigated. A maximum enantioselectivity of 2.43 was obtained when the molar concentration ratio of L-(-)-DBTA to L-(-)-DTTA is 2:3 L-(-)-DTTA concentration 0.18 mol/L, L-(-)-DBTA concentration 0.12mol/L) and the pH of aqueous phase is 6.86 at 25°C, with D D and D L up to a relative high value of 10.2 and 4.20, respectively. The results indicated a useful way of searching new efficient chiral selectors and it was proved also helpful to optimize the extraction systems and realize the large-scale production of the pure isomer of racemic mixtures with extraction methods.
A method of bubble fractionation, with the help of solvent extraction, was developed for the resolution of racemic ofloxacin (rac OFLX). In this method, dibenzoyl-L-tartaric (L-DBTA), di-(2-ethylhexyl) phosphoric acid (D2EHPA) and sodium lauryl sulfate (SDS) were used as chiral collector, co-extractant and foamer, respectively. Several important parameters influencing the resolution performances, such as pH in aqueous phase, concentration of OFLX, concentration of L-DBTA, concentration of SDS and volume ratio of D2EHPA to n-octanol in solution, were investigated. The optimal resolution conditions were obtained with the aqueous phase pH 7, volume ratio of D2EHPA to n-octanol 6/14 in organic phase, concentration of SDS 0.42 mg mL -1 , concentration of OFLX 1.67 mg mL -1 , and concentration of L-DBTA 0.11 g mL -1 . Under the optimal extraction conditions, the enantiomeric excess value (e.e.%) was 60.08% and the enantioselectivity (a) was 5.58. It was found that the capacity of enantioselective separation can be greatly improved by the co-technology.
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