Carboxylic acid fluorides from 2 molecules

The carboxylic acid (10 g) was filled into a 250-mL autoclave made from Hastelloy C4. After evacuating and flushing with dry N2 twice, the reacior was cooled with liquid N2 and then tilled with SF4 and HF. The molar ratio of substrate/SF4/ HF was 1 (f x 4) (f x 5) f = number of COzH groups per molecule. This mixture was stirred for 20 h at rt. After completion of the reaction, the autoclave was connected to a battery of columns containing aq NaOH to absorb the excess SF4 and HF. Then N2 was passed through the mixture and the columns. Finally, potassium fluoride (5 g) was added in order to scavenge any residual HF. Solids (KF/KH2F) were separated by filtration. Extract and filtrate were combined and fractionated by distillation. 

Hydrolysis of each acid fluoride fraction and redistillation of the carboxylic acids allowed separation of mono- from dicarboxylic acids (Table III). Thus, the 1 1 dicarboxylic acid and the monocarboxylic acid formed from three molecules of hexafluoropropylene epoxide were isolated from the 1 1 oligomer acid fluoride fraction shown in Table II. The acids were converted to acid chlorides in high yields (about 90%) by prolonged refluxing with thionyl chloride (Table IV). A trace of pyridine was added as a catalyst. 

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