A chiral bisthiourea as a chiral solvating agent for carboxylic acids in the presence of DMAP.
A simple chiral bisthiourea has been used as a highly effective and practical chemical solvating agent (CSA) for diverse α-carboxylic acids in the presence of DMAP. Excellent enantiodiscrimination based on well-resolved α-H NMR signals of the enantiomers of carboxylic acids can be obtained without interference from the chiral bisthiourea and DMAP. To check the practicality of the chiral bisthiourea/DMAP for enantiomeric determination, the ee values of mandelic acid (MA) samples over a wide ee range were determined by integration of the α-H signal of MA in (1)H NMR. A discrimination mechanism is proposed, that the formation of two diasteromeric ternary complexes between the chiral bisthiourea and two in situ formed enantiomeric carboxylate-DMAPH(+) ion pairs discriminates the enantiomers of carboxylic acids. Computational modeling studies show that the chemical shift value of α-H of (S)-MA is greater than that of (R)-MA in ternary complexes, which is consistent with experimental observation. 1D and 2D NOESY spectra demonstrate the intermolecular noncovalent interactions between the protons on the aromatic rings of chiral bisthiourea and α-H of the enantiomers of racemic α-methoxy phenylacetic acids in the complexes.
The State Key Lab of Structural Chemistry and The Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences , Fuzhou, Fujian 350002, P. R. China.
Guangling
G
Bian
Hongjun
H
Fan
Shiwei
S
Yang
Huifeng
H
Yue
Huayin
H
Huang
Hua
H
Zong
Ling
L
Song
D015761:4-Aminopyridine / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D008333:Mandelic Acids / Q000737:chemistry; D015394:Molecular Structure; D012995:Solubility; D013890:Thiourea / Q000031:analogs & derivatives / Q000737:chemistry*
D002264:Carboxylic Acids; D008333:Mandelic Acids; D015761:4-Aminopyridine; D013890:Thiourea; C037938:mandelic acid