Perfluoro , formation

An unusual 1,4-migration of a trifluoromethyl group was observed when azomethine imines were synthesized from hexafluoroacetone azine and alkoxy-acetylenes The rearrangement, which occurs at temperatures as low as 0 "C, results in the formation of A-(perfluoro-ferf-butyl)pyrazoles [207] (equation 46)... 

A mixture of nitromethane and hexafluorobenzene, when thermolyzed at 550 °C, yields pentafluorotoluene and pentafluorophenol as major products- The formation of nitrosyl and mtryl fluondes is probably a dnving force in this transfor-madon [705] A potential general preparative route to various perfluorovmyl amines is pyrolytic decarboxylation of potassium salts of perfluoro-2-(dialky-... 

Banks and co-workers found that gas-phase pyrolysis of pentafluorophenyl azide yields a diazaheptafulvalene (Scheme 16).50 The formation of the product was viewed as dimerization of the perfluoro analogue of 4b, although it is possible that it could, instead, have been formed by dimerization of the corresponding cyclic ketenimine. 

Micelle formation of our block copolymers in fluorinated solvents indicates that these polymers might act as stabilizers or surfactants in a number of stabilization problems with high technological impact, e.g., the surface between standard polymers and media with very low cohesion energy such as short-chain hydrocarbons (isopentane, butane, propane), fluorinated solvents (hexafluoroben-zene, perfluoro(methylcyclohexane), perfluorohexane) and supercritical C02. As... 

In another study the kinetics and mechanism of an unprecedented T/2-vinyl isomerization of a highly fluorinated tungsten(II) metalla-cyclopropene complex was studied (92). Photolysis of a tungsten(II) tetrafluoroaryl metallacycle 1 and perfluoro-2-butyne results in the formation of the kinetic rf -vinyl complex 2 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. Upon heating 2 is converted to the thermodynamic rf -vinyl complex 3 in which the fluoride ligand is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand as shown in Scheme 1. 

Photolysis of the carbon-iodine bond in iodo-perfluoroalkyl compounds has been employed to enable the formation of the corresponding pefluoroalkyl radical [37]. Different perfluorinated alkyl chains can thus be covalently bound to the CNT. Interestingly, the authors reported that no change in solubility of the nanotubes was noted after the perfluoro-alkylation. 

Rate constants and Arrhenius parameters for the reaction of Et3Si radicals with various carbonyl compounds are available. Some data are collected in Table 5.2 [49]. The ease of addition of EtsSi radicals was found to decrease in the order 1,4-benzoquinone > cyclic diaryl ketones, benzaldehyde, benzil, perfluoro propionic anhydride > benzophenone alkyl aryl ketone, alkyl aldehyde > oxalate > benzoate, trifluoroacetate, anhydride > cyclic dialkyl ketone > acyclic dialkyl ketone > formate > acetate [49,50]. This order of reactivity was rationalized in terms of bond energy differences, stabilization of the radical formed, polar effects, and steric factors. Thus, a phenyl or acyl group adjacent to the carbonyl will stabilize the radical adduct whereas a perfluoroalkyl or acyloxy group next to the carbonyl moiety will enhance the contribution given by the canonical structure with a charge separation to the transition state (Equation 5.24). 

The possibility of obtaining real improvements in the industrial production of perfluorooctanoic acid by using perfluorohexyl acetyl chloride in place of octanoyl chloride as starting material has been investigated [136]. In particular, the effect of blocking the formation of cyclic ethers on the yield of the perfluoro-acid was examined this was, however, less than expected due to the increased formation of perfluoro- -heptane. 

It was shown later that this reaction, and also pyrolyses of tetrafluoroethene (3) and of PTFE, can be adapted36 to give hexafluoropropene and also perfluoro(2-methylpropene), the key stage being formation of difluorocarbene. 

Several extraordinarily large perfluoro crown ethers have been synthesized examples are given by the formation of 6 and 7.24... 

Perfluoro-tert-butyl hypofluorite [perfluoro(2-fluoroxy-2-methylpropane), 14], readily prepared by the low-temperature fluorination of potassium or sodium perfluoro-/cr/-butoxide,812 reacts with hexafluoropropenc at low temperature to give 15 with more than 95 % regiosclcctivity, which may be explained by electrophilic attack and the formation of a fluorocarbeniuni ion, whose intervention is suggested in order to explain the production of perfluoro(l-/m-butoxy-propane) (15).12... 

Fluorination of perchloro bis(imine) 4 with sodium fluoride in tetramethylene sulfone at 120 JC takes place with ring formation to give the perfluoro imidazole derivatives 5-7.13... 

The energy of activation for the addition of trifluoroinethyl radical to the C=0 double bond of hexafluoroaeetone was calculated to be 9.7 0.26 kcal. mol.-1 and that for the decomposition of the perfluoro tert-butoxy radical was found to be 30.6 1.3 kcal. mol.-1, so that AH for the formation of the perfluoro ferf-butoxy radical is —20.9 kcal. mol.-1. Thus at high light intensities and elevated temperatures, the contributions of these reactions cannot be neglected. 

Analogous reactions with perfluoro(isopropyl-l,3,5-triazine) and per-fluoro(diisopropyI-l,3,5-triazine) with CsF yielded adducts 116 and 117, respectively, which were detected by 19F-NMR. Use of potassium fluoride, either alone or associated with 18-crown-6, did not lead to the formation of the adducts. In contrast, from tris(perfluoroisopropyl)-l,3,5-triazine no adduct was detected. This is quite interesting because it would indicate the importance of the gem-difluoro substitution to stabilize the adduct,160 in analogy with the effect of gem-dimethoxy substitution.76... 

Frequently substantially more than catalytic amounts of a Lewis acid metal halide are required to effect Friedel-Crafts alkylation. This is due partly to complex formation between the metal halide and the reagents or products, especially if they contain oxygen or other donor atoms. Another reason is the formation of red oils. Red oils consist of protonated (alkylated) aromatics (i.e., arenium ions) containing metal halides in the counterions or complexed with olefin oligomers. This considerable drawback, however, can be eliminated when using solid acids such as clays,97 98 zeolites (H-ZSM-5),99,100 acidic cation-exchange resins, and perfluoro-alkanesulfonic acid resins (Nafion-H).101-104... 

Several further experimental results lend support to the mechanisms postulated to explain the formation of the photoproducts. Thus irradiation of thiophene and substituted thiophenes in the presence of -propylamine leads to pyrroles, presumably via cyclopro-penylthiocarbonyl, or Dewar thiophene, intermediates (75T785). An extremely interesting development is the isolation of l,2,3,4-tetrakis(trifluoromethyl)-5-thiabicyclo[2.1.0]pent-2-ene, or perfluoro(tetramethyl Dewar thiophene) (2) by vapor-phase irradiation of perfluorotetramethylthiophene (81ACR76) the yield is about 58%. The half-life of thermal rearomatization of (2) at 160 °C is 5.1 h. The fluxional behaviour of the Dewar thiophene... 

Base-catalyzed trimerizations are facile also for example, trifluoromethyl cyanide trimer-izes in the presence of ammonia, presumably through the formation of the amidine intermediate (139 Scheme 77) (67JOC231). Similarly, perfluoro-n-propyl cyanide forms the 1,3,5-triazine in the presence of sodium methoxide, probably via the imidate (140 Scheme 78) (52JA5633). 

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