Reactivity of linear alkyl carbonates toward metallic lithium: Infrared reflection-absorption spectroscopic studies in ultrahigh vacuum

摘要

The reactivity of symmetric and asymmetric alkyl linear carbonates of the type ROCO2R', where R and R' represent methyl or ethyl groups, toward metallic Li was studied by infrared reflection-absorption spectroscopy (IRAS) in ultrahigh vacuum. Comparison of the IRAS spectra of clean Li surfaces exposed to dimethyl, diethyl (DEC), and ethyl-methyl carbonates (EMC) with those obtained in very similar experiments involving judiciously selected alcohols provided unambiguous evidence that the products of such reactions are primarily Li alkoxides (ROLi and R'OLi). Spectral evidence was also found for the presence of Li ethyl carbonate for experiments involving DEC and EMC. No changes in the IRAS spectra could be discerned upon exposure of RCO2R'-reacted Li surfaces to large doses of CO2 at ca. 300 K. Furthermore, predosing Li surfaces with CO2 at 300 K to form small amounts of Li2CO3 prior to exposure to ROCO2R' did not alter the nature of the reaction products. The conclusions emerging from this study support by and large the mechanism proposed by Aurbach et al. for reactions between Li and condensed phase linear and cyclic alkyl carbonates. [References: 23]