Addition of carbonyl fluoride to organic and inorganic nitriles

TR Number



Journal Title

Journal ISSN

Volume Title


Virginia Tech


Carbonyl fluoride will add to alkyl and perfluoroalkyl nitriles and alkane dinitriles in anhydrous acids to form the corresponding α,α-difluoroalkyl isocyanate, perfluoroalkyl isocyanate, or α,α,ω,ω-tetrafluoro- α,ω-diisocyanatoalkane. With acetonitrile the reaction proceeded slowly in anhydrous hydrogen fluoride or hydrogen chloride to yield a clear colorless liquid which was identified by infrared, mass, proton NMR, and fluorine-19 NMR spectroscopies to be a,a-difluoroethyl isocyanate. Increasing yields based on the lesser reactant were achieved by making the ratio of acetonitrile to carbonyl fluoride greater or less than one, having the optimum amount of anhydrous acid, the presence of an alkali metal fluoride and/or an increase in reaction time. The a,a-difluoroethyl isocyanate reacted with anhydrous ethyl alcohol to form the carbamate which slowly decomposed by splitting out hydrogen fluoride. The addition reaction proceeded more rapidly, in comparison to acetonitrile, with propionitrile and less rapidly with trifluoroacetonitrile. Cyanamide yielded trifluoromethyl isocyanate and cyanuric acid. Adiponitrile produced 1,6-diisocyanato-1,1,6,6- tetrafluorohexane and 1-isocyanato-5-cyano-1,1-difluoropentane.

Carbonyl fluoride will add to arylformonitriles in the presence of anhydrous hydrogen fluoride and alkali metal fluorides to produce the corresponding aryl-α,α-difluoromethyl isocyanate. The reaction proceeded more rapidly in the presence of alkali metal fluoride and at elevated temperatures. Increasing yields were achieved by having carbonyl fluoride in excess of the nitrile and the optimum amount of anhydrous hydrogen fluoride. The aryl-α,α-difluoromethyl isocyanates reacted with two additional moles of aryl formonitrile to yield aryltrifluoromethanes and 2-hydroxy-4,6-diaryl-s-triazines. Alkali metal fluorides also enhanced this reaction and suppressed the formation of 2,4,6-triaryl-s-triazine. Hith an electron withdrawing substituent on the aromatic ring, the reactions did not yield any significant quantity of the aryltrifluoromethanes but stopped at the aryl-α,α-difluoromethyl isocyanate stage. In the case of o-tolunitrile, steric hindrance prevented the formation of the isocyanate as well as of the trimer.

Pentafluorosulfanyl isocyanate was prepared by the addition of carbonyl fluoride to thiazyl trifluoride in the presence of anhydrous acids. Increasing the concentration of anhydrous hydrogen fluoride resulted in decreasing yield of the isocyanate while without an acid no isocyanate was formed. Pentafluorosulfanyl isocyanate in an excess of anhydrous hydrogen fluoride yielded the starting products. Isolated from anhydrous hydrogen chloride-catalyzed reaction was pentafluorosulfanyl carbamoyl chloride. N,N'-bis(pentafluorosulfanyl)urea was synthesized from pentafluorosulfanyl isocyanate and pentafluorosulfanyl amine or from thiazyl trifluoride, anhydrous hydrogen fluoride, and carbonyl fluoride. The reaction was reversible in excess anhydrous hydrogen fluoride or when heated under vacuum to over 90° C. With triethylamine the urea decomposed.

Mercuric isocyanate does not produce mercuric imino sulfur difluoride by reaction with sulfur tetrafluoride. Thiazyl trifluoride and ammonia react at low temperature to produce a white unidentified compound, possibly NS(NH₂)₃. Thiazyl trifluoride and diacetamide react in triethylamine to produce a compound which apparently decomposes immediately to give unidentified products. The decomposition proceeds even at ice water temperatures.