Fluoroacetyl fluoride

Fluoroacetyl fluoride, 46, 6 2-Fluoroalkanoic acids from 1-alkenes, 46, 39... 

It is interesting to compare the toxicity of fluoroacetyl chloride with the isomeric chloroacetyl fluoride. The former possessed a toxicity comparable to that of methyl fluoroacetate, whereas the latter was relatively non-toxic. This is readily understandable in that fluoroacetyl chloride gives the toxic fluoroacetic acid, whereas chloroacetyl fluoride hydrolyses to chloroacetic acid and the relatively non-toxic (at the concentrations employed) hydrogen fluoride. Fluoroacetyl fluoride also possessed a toxicity comparable with that of fluoroacetyl chloride or of methyl fluoroacetate, again showing that the COF group contributed practically nothing. Acetyl fluoride was also non-toxic. 

Chloromethyl esters are obtained quite readily by the action of paraformaldehyde on the appropriate acid chloride in the presence of a small quantity of zinc chloride as catalyst.1 It therefore seemed worth while to try the action of paraformaldehyde on fluoroacetyl fluoride, but the only product which could be isolated was a low-melting solid which appeared from its reactions to be methylene bisfluoroacetate, CH2(0 CO CH2F)2. The compound was submitted for physiological tests, and it was shown that the l.d. 50 subcutaneous injection into mice was about 10 mg./kg. Subcutaneous injection into rats with doses of 2-5, 5 and 10 mg./kg. all killed 1/1. 

The primary oxidation product, chlorotrifluoroethylene oxide (compound K), can isomerize either to trifluoroacetyl chloride, or to chlorodi-fluoroacetyl fluoride (compound L). It is unfortunate that the isomerization occurs in this way, because the other possibility would lead to a very coveted compound, trifluoroacetic acid [18,19, 20],... 

Treatment of I with a catalytic amount of triethylamine causes a quantitative rearrangement to 2-(fluorosulfonyl)-2-(pentafluoro-X6-sulfanyl)-2-fluoroacetyl fluoride. A mechanism for the formation and rearrangement reaction is described (260). 

Figure 1 Far-infrared spectra of (A) water vapour and (B) tri-fluoroacetyl fluoride.

Figure 2 Far-infrared spectrum of fluoroacetyl fluoride, FCH2CFO.

---