Reactivity of metallic lithium toward γ-butyrolactone, propylene carbonate, and dioxalane

The nature of the reaction products generated by exposure of a model cyclic ester, γ-butyrolactone (γ-BL), two cyclic ethers, dioxalane (DIOX) and tetrahydrofuran (THF), and a cyclic alkyl carbonate, propylene carbonate (PC), toward metallic Li at room temperature was examined in ultrahigh vacuum by infrared reflection absorption, Auger electron (AES), and X-ray photoelectron (XPS) spectroscopies. The features observed in the spectra were consistent with Li butyrate and Li β-keto ester in the case of γ-BL, and a dialkoxide derivative of Li with small amounts of Li oxide for experiments involving PC as the main reaction products. The behavior of both these solvents differs greatly from that found of the cyclic ethers DIOX and THF, for which the XPS spectra yielded small amounts of Li oxide and Li carbide as the only reaction products. These two species are most likely not derived from reactions involving DIOX or THF but rather from reactions between metallic Li and CO desorbed from the walls of the chamber during prolonged dosings. The extent of the reaction involving γ-BL, as evidenced by the loss of the AES peak at 52 eV characteristic of metallic Li, far exceeded that observed with PC and the linear alkyl carbonates reported previously in this laboratory, for which the aforementioned feature could be discerned clearly even after extensive exposure. All these findings agree with those reported by Aurbach et al.¹ for experiments involving Li metal exposure to the same solvents in liquid phase, which suggests that conclusions drawn from ex situ experiments of the type originally devised by our research group may also be applicable to reactions in condensed phase, including electrochemical environments.