Influence of structural factors on the thermolysis of 2-alkoxytetrafluoropropionic acid salts

Abstract

2,2,2 Trifluoroethyl and phenyl trifluorovinyl ethers were obtained by the thermolysis of 2 substituted potassium tetrafluoropropionates ROCF(CF 3 )COOK (R = CF 3 CH 2 ; Ph). The reaction mechanism is analyzed.Key words: hexafluoropropylene oxide, 2 alkoxytetrafluoropropionic acids, 2 phenoxy tetrafluoropropionic acid, alkyl trifluorovinyl ethers, phenyl trifluorovinyl ether.Thermal decomposition of fluorocarboxylic acids is a universal method for the synthesis of higher linear fluo roolefins. 1,2 A particular case of this reaction is the thermolysis of 2 alkoxytetrafluoropropionic acid salts ROCF(CF 3 )COO -M + (R = alkyl, α,α dihydrofluoro alkyl, perfluoroalkyl; M is metal cation) (1) 3,4 resulting in trifluorovinyl ethers.However, in the case of perfluorinated salts 1, perfluo roalkyl vinyl ethers that found practical use as comono mers in the synthesis of fluoropolymers are formed in al most quantitative yields, 4 whereas the thermolysis of com pounds 1 with R = Me, Et, and CF 3 CH 2 leads to a com plicated mixture of products. 3 It was postulated 3 that the composition of the reaction products reflects the compe tition between the decarboxylation accompanied by the β elimination of the fluoride ion to form trifluorovinyl ethers and the intramolecular nucleophilic substitution of the α fluorine atom with the intermediate formation of 2 alkoxy 2 trifluoromethyl α lactones, whose rate is de termined by the influence of the alkoxy group. It was shown for the thermolysis of salts 1 (R = Me) as an example that the contribution of the latter direction of the process in creased from 75-80% in the case of the potassium and cesium salts to 100% for the sodium salt. This is due to the "higher energy of formation of the crystalline lattice of NaF." 3 However, reasons for the preferential (in the case of the sodium salts, exclusive) α elimination of the fluo ride ion during the thermolysis of salts 1 remained beyond the discussion.We do not contest the proposed 3 scheme of thermoly sis of salts 1 but believe that the influence of the nature of the alkoxy group and the counterion on the composition of the reaction products is determined by other factors, namely: (a) the anionoid mobility of the α fluorine atom that increases in parallel to the electron releasing ability of the RO group and (b) the ionic radius of the metal cation that exerts an electrophilic assistance of the elimi nation of F -within the frame of the five or six membered transition state.In order to confirm the above assumption, we syn thesized 2 alkoxytetrafluoropropionic acids 2 by the re action of the corresponding alcohols and an excess of alkali with hexafluoropropylene oxide (HFPO) in an ether-water system in the presence of Bu 4 N + Br -; the acidification of the reaction mixture affords acids 2 in 40-70% yield (this procedure is a simplified version of the synthesis of 2 alkoxytetrafluoropropionic acids described earlier 3,5 ) (Scheme 1). Potassium salts 1a-c were obtained by the treatment of acids 2 with aque ous KOH.The choice of alcohol was ba...

Pentafluorosulfanyldifluoroacetic Acid: Rebirth of a Promising Building Block

“…5 in the manuscript gives 70 °C/60 mmHg) yielded 7.42 g, 83% of pentafluorosulfanyldifluoroacetic acid. 1 H NMR (300 MHz, CDCl 3 ) δ 11.09 (s, 1 H). 19 F NMR (283 MHz, CDCl 3 ) δ 64.2 (n, J = 147 Hz, 1 F), 41.7 (dm, J = 147 Hz, 4 F), -92.3 (qn, J = 11 Hz, 2 F).…”

“…Removal of the solvent by distillation gave 0.164 g, 70% of compound 7d as a volatile oil. 1 H NMR (300 MHz, CDCl 3 ) δ 3.44 (q, J = 6 Hz, 2 H), 3.41 (q, J = 6 Hz, 2 H), 1.22 (t, J = 6 Hz, 3 H), 1.13 (t, J = 7.2 Hz, 3 H). 19 F NMR (283 MHz, CDCl 3 ) δ 67.2 (n, J = 148 Hz, 1 F), 40.7 (dm, J = 148 Hz, 4 F), -84.2 (qn, J = 11 Hz, 2 F).…”

“…mp 97 -98 °C. 1 H NMR (300 MHz, CDCl 3 ) δ 7.43 -7.31 (m, 5 H), 6.54 (bs, 1 H), 5.17 (qn, J = 7 Hz, 1 H), 1.60 (d, J = 7 Hz, 3 H). 19…”

“…mp 113 -114 °C. 1 H NMR (300 MHz, CDCl 3 ) δ 7.85 (bs, 1 H), 7.51 (q, J = 9 Hz, 4 H). 19 F NMR (283 MHz, CDCl 3 ) δ 65.78 (n, J = 144 Hz, 1 F), 41.55 (dm, J = 144 Hz, 4 F), -92.62 (qn, J = 14 Hz, 2 F).…”

“…Oil 1. H NMR (300 MHz, CDCl 3 ) δ 5.08 -5.00 (m, 1 H), 1.94 -1.32 (m, 10 H).19 F NMR (283 MHz, CDCl 3 ) δ 65.7 (n, J = 148 Hz, 1 F), 41.0 (dm, J = 148 Hz, 4 F), -91.3 (qn, J = 11 Hz, 2 F).13 C NMR (75.5 MHz, CDCl 3 ) δ 157.34 (t, J = 28 Hz), 118.54 (tqn, J = 308, 26 Hz), 78.50 (s), 30.62 (s), 24.94 (s), 23.11 (s).…”