Synthesis of Octafluoronaphtalene by Perfluorodecalin Defluorination
S.M. Igoumnov, K.G.Narinyan, E.V. Igoumnova
Previously, Octafluoronaphtalene was obtained by passing Perfluorodecalin over Ni and Fe at 460 oC (1) by interaction of Octachloronaphtalene with anhydrous potassium fluoride in sulfolane at 235 oC in 50-60 % yield (2) and without solvent at 300-330 oC in 30% yield (3) by defluorination of Hexafluorobicyclo [4.4.0]dec-1(6)-ene over Zn in DMF at 80 oC (in 65% yield) [4]. It was supposed that the existence of at least one double bond is necessary for such defluorination.
Recently Octafluoronaphtalene synthesis from Perfluorodecalin in the presence of excess Al activated by HgCl2 in THF at ambient temperature (in 40% yield) was described , but the reaction was realized only with metallocene catalysis [5].
It is shown that Perfluorodecalin containing no double bond can be easily defluorinated to perfluoronaphtalene by Al or Zn activated with M(II) salts (M=Pb, Sn, Cu, Hg). The yield and conversion are 73% and 55-60%, respectively. Low conversion can be explained by formation of metal fluoride layer on the surface by Al or Zn.
The reaction is accompanied by formation (up to 3%) of heptafluoronaphtalene (the structure is confirmed by spectrum 19F NMR and mass-spectra) that indicate to a reaction scheme of reductive defluorination.
Experimental
In a four-necked flask fitted with a stirrer , dropping funnel, reflux condenser and a thermometer, a suspension of Al powder(9.45, 0.071 mol) and Pb (OAc)2 (4g, 0.012 mol) was placed and mixed for 10 minutes. The mixture was heated to 110oC, then the heating bath was removed and perfluorodecalin (46.2 g) was performed visually through formation of aluminum fluoride slurry. After finishing the process ( approximately 5 hours), the mixture was refluxed for 3 hours and treated with hot octafluoronaphtalene (14.0g). Both fractions contained some water. The crude product was filtered off and recrystallized from light petroleum to afford 12g ( 73%yield, 60% conversion) of octafluronaphtalene. Boiling point 207-209 oC, melting point 84.5-86.0 oC. Calculated for C10 F 8 , %:C, 44.12: F, 55.08. Found, %:C,44.92; F, 55.08.
19 F NMR (acetone -d 6 , external TFA): 78.0 (4F,S) and 69.0 (4F,S) chemical shifts.
Analogous results were obtained for Al/HgCl2 , Al/SnCl2, and Zn/Cu(OAc)2 in DMF and N,N,-dimethylacetamide
Conclusions
Octafluoronaphtalene is obtained from Perfluorodecalin in aprotic polar solvents with the use of M/M+2 system where M=Al, Zn, and M= Al, Zn, à Me+2 =Pb+2, Sn+2, Cu+2, Hg+2.
It is shown that along with the main reaction the reductive defluorination of Perfluorodecalin with Heptafluoronaphtalene formation is taken place.
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