Hexafluorothioacetone

Hexafluoropropene and sulfur react at 425 °C in the vapor phase to give hexafluorothioacetone and its dimer [/]. In dimethylformamide, it reacts with potassium fluoride and sulfur to give hexafluorothioacetone dimer, which further reacts with hexafluoropropene to give the E and Z isomers of perfluoro-2,4,6-tris(trifluoromethyl)-5-thia-3-heptene [2] (equation 1). 

Hexafluorothioacetone, 50, 83 Hexamethylbicyclo[1.1.0]butane, from 1,3-dibromohexamethyl-cyclo butane and sodium-potassium alloy, 51, 58 Hexamethylphosphoramide, 50,... 

Thioketones, such as thiofluorenone, hexafluorothioacetone and perfluorocyclobutanone, add to a variety of 1,3-dienes to give dihydrothiapyrans (e.g. equation 24)25. Styrene yields a 1 2 adduct with hexafluorothioacetone (equation 25)25. The reactions of thioace-tophenone and thiobenzophenone with isoprene and 2-chlorobutadiene yield mixtures of regioisomers in quantitative yields (e.g. equation 26)26. 

A-(l-Adamantyl)hexafluorothioacetone S-imide, (F3C)2C=S=NAd, undergoes a range of dipolar cycloadditions with aromatic and aliphatic thiones. ... 

By this method of addition of chlorine to fluorothiocarbonyl chloride, thiocarbonyl difluoride 109), or hexafluorothioacetone 120), the respective sulfenyl chlorides are obtained ... 

The effect of halogens on reactivity is also seen for fluorothiocarbonyl monomers. Thiocarbonyl fluoride is polymerized at —78°C by a trace of mild base such as dimethylforma-mide. The polymerization of hexafluorothioacetone is an extreme example of the effect of... 

Thioureas (211) combine with hexafluorothioacetone (212) to give 1,2,4-dithiazoline derivatives (213). The proposed mechanism involves nucleophilic attack by the nitrogen atom of thiourea on the carbon atom of the thione group in (212) (Equation (24)) <90CB69l). 

Many cycloaddition reactions have been carried out with ketenes and thioketones. The products are thiolactones (52). Hexafluorothioacetone and diphenylketene, however, do not undergo cycloaddition even after prolonged heating at 100°C. Good results can be obtained when the more stable dimer of this fluorinated thioketone (53) is used. Anionic monomer 54 could be released by the action of potassium fluoride in an aprotic solvent. Two-step cycloaddition to diphenylketene yields ketone 55. 

With slight modification, the methods used to prepare fluorothioacyl fluorides can also be used for synthesis of fluorothioketones. Hexafluorothioacetone, the member of this class that has been studied most extensively, is readily obtained by high-temperature reaction of hexafluoropropylene and sulfur (53). The thio-ketone is a deep-blue liquid, bp 8° C, that dimerizes on standing to 2,2,4,4-tetrakis-(trifluoromethyl)-l,3-dithietane. 

It is best to store the thioketone as the dithietane, which is a white solid melting at 23.6° C and boiling at 110°C. When needed, hexafluorothioacetone can be obtained from the dithietane by pyrolysis in a hot tube at 600° C (44). Pyrolysis gives a quantitative yield of monomer. The thioketone so prepared is purified by distillation at 200 mm at which pressure it boils at — 20° C. 

The reaction of a perfluoromercurial with sulfur is particularly well suited to synthesis of hexafluorothioacetone. The first step is addition of mercuric fluoride to hexafluoropropylene in liquid HF which gives bis(hexafluoroiso-propyl)mercury. 

Passage of the mercurial through the vapor of boiling sulfur results in its conversion to hexafluorothioacetone in 60% yield (56). 

The hexafluorothioacetone is isolated as its dimer, 2,2,4,4-tetrakis(trifluoro-methyl)-f,3-dithietane, which forms immediately. In the case of the tri- and tetrasulfides, excess triphenylphosphine is used to remove the extra sulfur atoms by formation of triphenylphosphine sulfide. 

Fluorothioketones are more difficult to polymerize. There are two reasons. First, agents that promote polymerization also catalyze dimerization to dithi-etanes, which is a very fast reaction. Second, ceiling temperature of polymerization is low with the result that polymer decomposes back to monomer as it is being isolated. However, poly(hexafluorothioacetone) can be formed at very low temperatures by initiation with dimethylformamide or BF3 etherate, even though at — 78° C the only product isolated is 2,2,4,4-tetrakis(trifluoromethyl)-l,3-di-thietane. 

The dithiazolidine ring is of moderate stability, depending on its substitution. Some dithiazolidine derivatives, obtained by 1,3-dipolar cycloaddition of the thionc-.S -imide 113 and thiones 114, are indefinitely stable at room temperature as compounds 115 (R1, R2 = Ar). Others decomposed during recrystallization affording the corresponding imines 118, and some, such as the sterically crowded 115 (R1, R2 = 2-adamantyl), are so unstable that they spontaneously decompose, affording hexafluorothioacetone 116 and finally the more stable compound 117 (Scheme 16) <1998EJ0459>. 

Earlier methods of preparing 2,2,4,4-tetrakis(trifluoromethyl)-l,3-dlthletane (hexafluorothioacetone dimer, HFTA dimer) include the reaction of hexafluoropropene (HEP) and sulfur over a carbon bed at 425< C,3 and the reaction of HFP and sulfur in tetramethylene sulfone at 120°C 1n the presence of potassium fluoride (autoclave). Dimethylformamide appears to be a far superior solvent for this reaction, permitting the use of atmospheric pressure and modest temperatures, as well as affording a cleaner product. 

Perfluoro-2-diazopropane and hexafluorothioacetone react at temperatures as low as -30°C to give the tetrakis(trifluoromethyl)-substituted 1,3,4-thiadiazoline in nearly quantitative yield (69JOC3201) (Scheme 78). 

Hexafluoroacetone imine has been prepared by the reaction of hexafluoroacetone with triphenyl phosphine imine,2 by the pyrolysis of N-phenyl-2,2-diaminohexafluoropropane,23 by the reaction of hexafluorothioacetone with hydrazoic acid,4 and by the reaction of ammonia and phosphorus oxychloride with hexafluoroacetone.4,5 The latter method, which is described here, is the most convenient for it does not require preparation of several intermediates or use of pressure equipment. This method has also been used to prepare the imines of other Huoroketones, including the imines of chloropentafluoroacetone, dichlorotetrafluoroacetone, and perfluorodiethyl ketone.5 Substitution of methylamine for ammonia in this procedure gives the N-methyl imine.5... 

The most reactive of the fluoroalkyl thioketones is hexafluorothioacetone which provides cycloadducts with numerous helerodienophiles, including butadiene and some aromatic compounds at low temperature. In the case of the aromatic compounds 2 1 cycloadducts are obtained (Table 6). ... 

Buta-1,3-diene (10.8 g, 0.2 mol) was condensed into a flask cooled to —78 C with a dry icc/acetone bath. Hexafluorothioacetone was then distilled rapidly into the flask until a faint blue color persisted. Themixture was allowed to warm to ri and was then distilled to give (he product as a colorless oil yield 42.4 g (90 %) bp 65 C/.30 Torr. 

Hexafluorothioacetone does not readily form a hydrate, but dimerises readily, particularly in the presence of base high temperatures are then required to reverse the process [258] (Figure 8.97). 

The dimer of hexafluorothioacetone may also be obtained from hexafluoropropene [259] and the former has now been used in a route to a sulphene [260] (Figure 8.98). 

Other electrophiles that react with in situ-generated perfluorocarbanions in elude epoxides [226] equation 47), carbon dioxide [227] (equation 47) acyl halides [228, 229, 230, 20, 232, 233] (equation 48), fluoroformates [23d] car bonyl fluonde [23S, 236, 237] hexafluorothioacetone (generated from its dimei) [238] (equation 48), an a-fluoroalkylamine f2J9] (equation 48), cyanuric fluoride [240], and reactive alkyl halides [247, 242 243, 244, 245] (equation 49) Interestingly, an in situ-generated carbanion will also react with dibromodifluoromethane ia a mechanism involving difluorocarbene [246] (equation 50)... 

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