Abstract
Na(1s, 2s, 2p) X-ray photoelectron (XPS) spectra of sodium L-tartrate, which is used as an asymmetric modifier of a catalyst that efficiently produces only one of the enantiomers during the asymmetric reduction synthesis of prochiral methyl acetoacetate (MAA), were measured. In addition, those of various sodium compounds were measured as the related compounds, and the electronic states of sodium ions in these compounds were clarified. The Na KLL Auger electron (AES) spectra were also measured to determine the Auger parameters of the sodium compounds. The value of Auger parameter of sodium L-tartrate was the largest among the measured sodium compounds. On the other hand, when MAA was added to sodium L-tartrate, its value of Auger parameter greatly decreased, and became nearly the same as those of other sodium compounds. Furthermore, C and O K-edge X-ray absorption (XANES) spectra were measured for L-tartaric acid and its alkali metal salts (Li, Na), and the L-tartrate-complexes with MAA. Though the energy resolution of the XANES spectra is much higher than that of the XPS spectra, C and O K-edge XANE spectra of the L-tartrate-complexes with MAA were very similar to the corresponding L-tartrates, respectively. There are no big changes not only in the XPS, but also XANES spectra between L-tartrates and L-tartrates-complexes with MAA, regarding the peak positions and peak shapes. On the other hand, in Ni (2p) XPS and Na KL23L23 AES spectra, the shifts of 0.6 and 2.1 eV were observed, respectively. These results suggest that the addition of MAA slightly changes the electronic state of the outermost shell of sodium ion, which could be confirmed from the Na (2p) XPS and Na KL23L23 AES spectral peaks.
