Background and overview[1]
Many salts are ionic liquids. Due to their properties, ionic liquids represent efficient alternatives to traditional volatile organic solvents for organic synthesis in modern research. The use of ionic liquids as new reaction media is also a practical solution to problems in solvent evaporation and catalyst reprocessing. Trihexyltetradecylphosphorus tetrafluoroborate can be used as the ionic liquid. Ionic liquids containing tetrafluoroborate anions are generally produced as follows: In the second step, a halide, such as 1-ethyl-3-methylimidazole chloride or bromide, can be mixed with NaBF4 according to the S.Par method. In acetone; with NaBF4 in water; with AgBF4 or HBF4 in water; with NH4BF4 in acetone; with HBF4 in methanol; or react with NH4BF4 by microwave irradiation. However, all known methods have disadvantages, especially for large-scale industrial synthesis.
Preparation[1]
Trihexyltetradecylphosphonium tetrafluoroborate is prepared as follows: 54.35g (0.105mol) trihexyl(tetradecyl)phosphonium chloride is reacted with 18.90g of approximately 50% HBF4 aqueous solution. Then add 40ml of 1,4-dioxane, and distill out 48ml of HCl-containing water/dioxane azeotrope under atmospheric pressure (85~90°C). Then add 30 ml of dioxane, and distill out 30 ml of HCl-containing water/dioxane mixture under atmospheric pressure (85°C to 101°C). After another azeotropic distillation with 30 ml of dioxane, the content of chloride ions in the residue was so low that it could not be detected by the silver nitrate test. The distillation residue was dried under reduced pressure of 1.3 Pa and 70°C to obtain liquid trihexyltetradecyltetrafluoroborate phosphorus. The yield is approximately quantitative. A microtitration was performed with a solution of silver nitrate in a non-aqueous medium. The end point was determined by potentiometric analysis using a Cl-selective electrode. The chloride content in the ionic liquid was 12 ppm.
1HNMR spectrum, ppm (acetonitrile-D3; reference reverse osmosis fungicide: TMS): 0.91t (CH3); 0.93t (3CH3); 1.28～1.40m (16CH2); 1.40～1.62m (8CH2); 2.07 ~2.20m (4pvc stabilizer CH2); 3JH, H=7Hz.
11BNMR spectrum, ppm (acetonitrile-D3; reference: BF3·OEt2-external)-1.22s (BF4-).
19FNMR spectrum, ppm (acetonitrile-D3; reference: CCl3F-internal)-149.22br.s(BF4-)
