Hexafluorobenzene reaction

Write equations describing the addition-elimination mechanism for the reaction of hexafluorobenzene with sodium methoxide clearly showing the structure of the rate determining intermediate j... 

An interesting variant in which nucleophilic aromatic substitution is carried out on the crown nucleus rather than using the crown as nucleophile was reported by Haines . In this approach, hexafluorobenzene was stirred in 1,2-dimethoxyethane at room temperature with pentaethylene glycol and sodium hydride. A double nucleophilic aromatic substitution occurred affording 2, 3, 4 ,5 -tetrafluorobenzo-15-crown-5 as an oil in 38% yield. The reaction is illustrated below. 

Reactions of the halogen iluorides with other unsaturated functional groups are generally reported only with highly fluorinated substrates Hexafluorobenzene and denvatives [118] and octaflvoronaphthalene [119] react with mixtures of bromine and bromine trifluoride by 1,4 addition of fluorine followed by addition of bromine fluoride across a reniatning double bond (equation 22)... 

Oxidative reactions of dienes are accomphshed under similar conditions as those of alkenes. Abicydic diene synthesized from hexafluorobenzene and 1,2-di-chloroethylene is monoepoxidized by triflnoroperoxyacetic acid [43] (equation 35). 

In 1966, a photochemical rearrangement by ultraviolet (UV) irradiation of hexafluorobenzene to hexafluorobicyclo[2 2 0]hexa-2,5-diene was achieved Since then, many reactions analogous to the valence tautomerism of benzene and bicy clo[2 2 0]hexadiene (1 e, Dewar benzene), as well as of fluonnated benzvalene and... 

The most common types of aryl halides in nucleophilic aromatic substitutions are those that bear- o- or p-nitro substituents. Among other classes of reactive aryl halides, a few merit special consideration. One class includes highly fluorinated aromatic compounds such as hexafluorobenzene, which undergoes substitution of one of its fluorines on reaction with nucleophiles such as sodium methoxide. 

Further lowering the dielectric constants has been achieved by preparing highly fluorinated polyethers without any sulfone, ketone, or other polarizable groups.239 241 Typically, the /jara-lluorinc atoms on highly fluorinated aromatic compounds, such as hexafluorobenzene and decafluorobiphenyl, are activated and thus can go through aromatic nucleophilic substitution with HFBPA under typical reaction conditions (Scheme 6.31).217... 

The choice of solvent may have a critical impact on efficiency too. In metathesis, dichloromethane, 1,2-dichloroethane and toluene are the solvents most commonly used. There are examples that show much higher yields in ring closing metathesis (RCM) when using fluorinated solvents [150]. An impressive effect of hexafluorobenzene as a solvent for CM is the modification of the steroid 93 the use of 1,2-dichloroethane leads to a very low yield and significant amounts of dimerisa-tion while the same reaction proceeds in 90% yield in C F (Scheme 3.14) [151]. 

The authors carried out theoretical calculations on this system as well as on the [ (PMej) ] system to compare their reactivity with hexafluorobenzene. They found that the barrier for [ (liPr) ] is approximately 10 kJ/mol lower in energy than the corresponding barrier for the phosphine-bearing system. This value was in agreement with the different reactivity of both complexes but could not fully explain the large difference in reaction times. Density functional Theory (DFT) calculations also showed that the trans product is more stable than the cis product (total energies are respectively -130.9 and 91.1 kJ/mol), which was in agreement with the experimental values. 

Reaction of hexafluorobenzene with MeIr(PEt3)3 results in C—F and P—C bond cleavage and P—F bond formation, according to reaction Scheme 28.504 An X-ray crystallographic study of (310) reveals a distorted square-planar arrangement of Ir. 

Reaction of hexafluorobenzene and silane under single pulse irradiation of a MW CO2 laser was explosive. 

The above reactions reinforce the diradical mechanism proposed for the BF3 reaction. Hexafluorobenzene and the various fluorinated ethylenes 73,74 however, react quite differently. The products in these reactions formally correspond to C-F bond insertion by an SiF2 monomer. 

Interestingly, in fluorinated solvents where the solubility of the reagents is not compromised, for example hexafluorobenzene, the rate of reaction is not increased (Figure 7.2). This implies that there is an inverse relationship between solubility of reagents and the rate of reaction, and that this relationship may be exploited by the use of either water or suitable perfluorinated solvents. 

Figure 3. Effect of water on the reaction of hexafluorobenzene and bisphenol-A in chlorobenzene in the presence of 18 crown-6 catalyst. Products of the catalyzed reaction were oligomeric materials. No reaction is observed under the experimental conditions in the absence of the 18-crown--6 catalyst. (Reproduced with permission from reference 14, Copyright 1985 John Wiley.)...

The reaction of the carbanion derived from diethyl methylphosphonate with perhalogenated aromatics may result in substitution of halide to yield perhaloaryl(hetaryl)methylphosphonates, which can be converted into tris- or bis-(perhaloaryl)methanes. Displacement of fluoride ion has been reported in the reaction of dimethoxycarbene with l-fluoro-2,4-dinitrobenzene and with hexafluorobenzene. The hydrodehalogenation of halogenated aryl ketones may be facilitated using hydrogen over a Pt/C catalyst. " ... 

Sensitivity to the magnetic held strength has also been observed in the process of photoisomerization of tran -stilbene (tS) into c -stilbene (cSt) in the presence of pyrene (P). The reaction was run in a solution with acetonitrile, DMSO, or hexafluorobenzene being a solvent. During the reaction, spin polarization was established (Lyoshina et al. 1980). The spin polarization was explained by the following sequence of the elementary acts ... 

In the reaction with hexafluorobenzene at 40"C exclusive 1,4-addition to give 18 is observed. In addition to higher regioselectivity, perfluoro-fcrf-butyl hypofluorite has higher reactivity as a reagent compared to trifluoromethyl hypofluorite (see Section 6.1.1.).14... 

Three recent papers directed toward the reaction of elemental fluorine with hexafluorobenzene (71), decafluorohexane (72), and pentafluoro-... 

A mixture of tetrafluoroethene (2.45 g, 24.5 mmol), 02 (24.5 mmol) and 03 (0.03 mmol) was condensed in a Pyrex tube (33 ml) with a long capillary neck containing hexafluorobenzene (8.3 g). After 5 d reaction in (he dark at 15 C, the ampule was opened and the volatile products were analyzed and separated by GC [He as carrier gas, —9 C, bis(2-ethylhcxyl) sebacate on kieselguhrl yields 17 (0.67 g, 24%), 21 (0.38 g, 23%). A highly viscous residue that contained 19 (1.5 g) was diluted with hexafluorobenzene and treated with a slight excess of 57% HI (1 part) and glacial HOAc (10 parts), usually at rt. The whole apparatus was swept with He and the C02 evolved during the reduction was absorbed by standard Ba(OH)2. 

The preparation of perfluoroazepines is more facile. Hexafluoro-l//-azepine-l-carbonitrile (6a) is prepared by the reaction of hexafluorobenzene with cyanonitrcne.15 Likewise, the 1-ethoxycarbonyl derivative 6 b is prepared in moderate yield by the reaction of hexafluorobenzene with ethoxycarbonylnitrene.16 In each case, a benzoazirine intermediate is presumably involved, which isomerizes to the azepine structure. Perfluoroazepines 6 isomerize photolytically to the corresponding 2-azabicyclo[3.2.0]hepta-3,6-dicncs 7 in high yield.17 Azepine 6c is obtained from 6a by acid hydrolysis.17... 

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