Tributylmethylphosphonium Bis(trifluoromethanesulfonyl)imide was prepared as follows: 500 g (2.48 mol) of tributylphosphine and 800 mL of dimethyl carbonate were placed in a pressure vessel (the air in the pressure vessel was replaced with nitrogen beforehand), and reacted at 145 °C and 1.4–1.5 MPa for 8 hours to obtain a light yellow to brown solution. After cooling, a white solid precipitated out. 418.69 g (1.49 mol) of bis(trifluoromethanesulfonyl)imide in 400 mL of methanol solution was slowly added while stirring at room temperature, generating a large amount of gas. Then, 1.00 g of lithium bis(trifluoromethanesulfonyl)imide was added every 10 minutes until no more white precipitate was formed. The solution was filtered, and the filtrate was distilled under reduced pressure to remove low-boiling-point substances. The solution was dried at 80 °C and under vacuum for 6 hours to obtain 727.94 g (yield of about 59% in the two-step reaction) of colorless to light yellow Tributylmethylphosphonium Bis(trifluoromethanesulfonyl)imide salt.
