Synthesis Of Chiral Chelating Extractants And Extraction Resolution D/L-amino Acid

In this article, two types of new chiral chelating extractants were synthesized, including chiral bisamide extractants, 2,6-pyridinedicarboxyl-L-Phenylalanine methyl ester (PhePyDA) and 2,6-pyridinedicarboxyl-L-Leucine methyl ester (LeuPyDA), and also chiral asymmetric secondary amine extractants, N-(2-Pyridylmethyl)-L-Phenylalanine methyl ester (PyMPhe) and N-(2-Pyridylmethyl)-L-Leucine methyl ester (PyMLeu). Their extractability for metal ions was studied. The preliminary study on the extraction separation of D/L-phenylalanine was conducted. The extraction performance of a new chiral bisamide extractants to extracting Ln (â…¢) and Cu (â…¡) ion was studyed. And also the extraction behavior were investigated with a new type of chiral asymmetric secondary amines extracting Cu (â…¡) ion from sodium chloride or acetate buffer solution and a preliminary study was conducted on the extraction separation of D/L-phenylalanine. The new extractants were characterized by infrared spectrum, nuclear magnetic resonance, element analysis and high performance liquid chromatography and etc. The main contents were as follows:1. 2,6-pyridinedicarboxylic acid and L-amino acid methyl ester as the raw material, PhePyDA and LeuPyDA were synthesized. The results showed that PhePyDA was the white solid and the yield was about 80%. m.p. 130-131℃. [α]D13.5 -96.0°(ethanol, c=1). HPLC >99%, e.e.%>99%; LeuPyDA was obtained by the yields of about 75%. m.p. 141-142℃. [α]D13.5 -17.0°(ethanol, c=1). HPLC >99%, e.e.%>99%.2. The single crystal of 2,6-pyridinedicarboxyl-L-Phenylalanine methyl ester was developed. The crystal is orthorhombic system, space group, P212121, a=9.155(8) nm, b=9.932(9) nm, c=27.83(2) nm,α=90.00°,β=90.00°,γ=90.00°, V=2530(4) nm3, Z =4, F(000)=1032, Dx=1.282 g·cm^-3, Mr=489.53,μ=0.091mm-1. The final R[I>2σ(I)]: R1=0.0497, wR2=0.1593.3. PyMPhe and PyMLeu were prepared by the reductive amination of Aldehydes, 2-pyridinecarboxaldehyde and L-amino acid methyl esters as raw materials, reducting with hydrogen on Pd/C catalyst. The results showed that PyMPhe was obtained with the yield of 77%. m.p. 130-131℃. [α]D14 -13.6°(ethanol, c=1). HPLC >96%; PyMLeu was obtained (76.5%, yield). m.p. 141-142℃. [α]D13.5 -25.1°(ethanol, c=1). HPLC >97%.4. The performance of PhePyDA and LeuPyDA to extract Ln (â…¢) and Cu (â…¡) ion was researched. We found that The extraction distribution ratio is very low. Under the conditions of adding a certain amount of salting-out agent, the extraction ratio was not significantly improved. The lower extraction performance was analyzed through the spatial structure of 2,6-pyridinedicarboxyl-L-Phenylalanine methyl ester.5. The performance of PyMPhe and PyMLeu to extract Cu(Ac)2 was researched. The effect of the diluent, acid concentration, extractant concentration, temperature and other factors on The extraction distribution ratio were studied. The conclusions were as follows:(1) In different diluents, the extraction distribution ratio of PyMLeu and PyMPhe in chloroform both are the largest, and the extraction ratio is much larger than other diluents. It showed that the extraction ability of amine extractants was greatly influenced by the diluent.(2) Under the conditions of a fixed buffer solution concentration, the influence of aqueous phase pH on the extraction distribution ratio is more complex and specific rules have yet to be further studied.(3) The extraction distribution ratio increases as extractant concentration increasing. The organic phase compositions of extracting Cu(Ac)2 are Cu(Ac)2·PyMLeu and Cu(Ac)2·PyMPhe, respectively. The reaction mechanism is as follows: Cu²⁺+2Ac-+PyMLeu=Cu(Ac)2·PyMLeu Cu²⁺+2Ac-+PyMPhe=Cu(Ac)2·PyMPhe(4) The extraction distribution ratio decreases with increasing on the temperature.This shows that the extraction reaction is an exothermic reaction, and increasing the temperature for the reaction was adversed. The calculated thermodynamic enthalpy value of extraction reaction isΔrHmθ= -51.025 kJ·mol-1.(5) Under the same extraction conditions, the extraction ability of extractants is in the order: PyMPhe> PyMLeu. This showed that the extraction ability was greatly influenced by the structure of extractants.6. The performance and mechanism of PyMPhe and PyMLeu on extracting CuCl₂ was studied. The conclusions were as follows:(1) As the NaCl concentration increasing the extraction distribution ratio increases rapidly, and it is much higher than the system of the same CuCl₂ concentration. When the NaCl concentration is 2 mol·dm^-3, the extraction ratio is more than 95%. It can meet the requirements of extractant with high affinity to metal ions, being combinated to metal ions strengthly and keeping the most small amount of metal in the the aqueous phase.(2) The extraction distribution ratio on extracting CuCl₂ increases as PyMPhe concentration increasing. The complex composition of organic phase is CuCl₂·PyMPhe. The reaction mechanism is as follows: Cu²⁺+2Cl-+PyMPhe=CuCl₂·PyMPhe(3) Analysis on the infrared spectra of organic phase of PyMPhe extractants before and after extraction of metal ions, the structure of the extracted complex we suggested is [Cu(PyMPhe)(H2O)2]Cl₂.7. The study on the determination of the amino acids in the aqueous solution after extraction showed that the use of UV and HPLC for the direct determination of amino acids can not be avoided the interference of Cu (â…¡). The method of Ninhydrin color reaction by using of appropriate experimental blank can eliminate various factors of extraction system which impacts the determined results. So it was considered a more ideal way to determine amino acids in the aqueous solution.8. Using the complex formed of PyMPhe and PyMLeu with transition metal Cu (â…¡) ion as the extraction separation agent, we conducted a preliminary study on the extraction separation of D/L-phenylalanine. The results showed that the new type of chiral asymmetric secondary amine extractants have a better extract separation performance. The conclusions were as follows:(1) The extraction distribution ratio was greatly influenced by the Cu (â…¡) ion concentration, as the Cu (â…¡) ion concentration increasing the extraction distribution ratio became larger. But if copper ion concentration is too high, it can exceed the load capacity of the organic phase. So the extraction rate of D/L-phenylalanine can be improved by controlling a amount of copper ions.(2) The extraction capacity of chiral extractants for L-phenylalanine is higher than D-phenylalanine. The extraction result of PyMPhe extractant is better than PyMLeu extractant, and the extraction distribution ratio is much larger than 1. The extractability is much larger than the current extraction reported in the literature, which can provides an important theoretical and experimental basis in further study on chiral solvent extraction separation technology in future.