Uses
2,2-Difluoro-2-(fluorosulfonyl)acetic acid, is used as an important raw material and intermediate used in organic Synthesis, pharmaceuticals, agrochemicals and dyestuff. It is also used as an important reagent in the synthesis of difluorocarbenes and difluorocyclopropanes.
Synthesis
1. The 600 mL autoclave was cooled in an ice water bath, evacuated, and hexamethyldisiloxane (294 mL, 220 g, 1.36 mol) and compound (CAS: 677-67-8, 255.3 g, 1.42 mol) were added sequentially.
2. the autoclave was heated to 100 °C and maintained for 18 hours with a maximum pressure of 100 psig (0.79 MPa) during the reaction.
3. after completion of the reaction, the reaction was cooled to room temperature and the black liquid product (471.4 g) was collected from the autoclave.
4. The above product was combined with another batch prepared under the same conditions in a 2 L flask fitted with a water-cooled condenser for distillation. A dry ice trap was installed between the vacuum source and the distillation unit to capture the by-product trimethylfluorosilane.
5. The distillation conditions and results are shown in Table 1.
6. The data in Table 1 show that Fractions 2 and 3 contained 8.4 mol% of 2-fluorosulfonyl difluoroacetic acid (RSUA) and the main product, trimethylsilyl ester of 2,2-difluoro(2-fluorosulfonyl)acetic acid (RSUTMS), with an 86.9% yield of RSUTMS based on hexamethyldisiloxane (HMDS).
7. In another experiment, hexamethyldisiloxane (243.5 g, 1.50 mol) was added to a 1 L autoclave, purged with nitrogen and then cooled and evacuated. Compound (CAS: 677-67-8, 286 g, 1.59 mol) was then added.
8. The autoclave was heated to 100.6 °C with stirring at 600 rpm for about 1 hour up to a maximum pressure of 69 psig (0.58 MPa). Stirring was continued at 100 °C for 6 hours and then cooled to room temperature and the crude product (521 g) was collected, in which the molar concentration of RSUA relative to RSUTMS was about 7.7%.
9. The conversion of HMDS was shown to be about 97% by 1H NMR analysis.
10. The crude product was transferred to a 500 mL flask fitted with a vacuum-jacketed Vigreux column and a cold-finger distillation head, and the volatile components (including unreacted compounds and trimethylfluorosilane) were removed by distillation, first at atmospheric pressure, until the kettle temperature reached 127.6 °C. The product was cooled by adding chlorotrisilane to a vacuum-jacketed Vigreux column and a cold-finger distillation head.
11. After cooling, chlorotrimethylsilane (CTMS, 41.7 g, 0.384 mol) was added and again heated to a maximum of 107.8 °C at atmospheric pressure and distilled to remove excess CTMS.
12. the pressure was reduced for decompression distillation and the RSUTMS main fraction (320.6 g) was collected, which contained about 3.3 mol% RSUA, giving a yield of 85% RSUTMS based on HMDS converted over a 6 hour reaction time.
13. Under similar conditions, the compound (CAS: 677-67-8, 428 g, 2.38 mol) was reacted with HMDS (361.8 g, 2.25 mol) at 95 °C for 6 hours. 1H NMR analysis of the crude product showed that the conversion of HMDS was about 99.6%, and the product contained 48.1 mol% trimethylfluorosilane (FTMS) and 51.7 mol% RSUTMS. 19F NMR analysis showed that the molar ratio of RSUA relative to RSUTMS was about 3.0%.
14. The crude products of the two reactions (total 1558 g) were combined and after distillation at atmospheric pressure to remove the low-boiling components, chlorotrimethylsilane (126.04 g) was added and stirred overnight.
15. Subsequent distillation was carried out at a pressure of 370-380 mbar (37-38 kPa) and the pressure was further reduced to 33-36 mbar (3.3-3.6 kPa) and the product (1008 g) was collected with an RSUA content of 1.4 mol%, giving a yield of 87.7% of RSUTMS based on the added HMDS.
