Trifluoromethyl benzene

To illustrate substituent effects on rate consider the nitration of benzene toluene and (trifluoromethyl)benzene... 

Nitration of (trifluoromethyl)benzene on the other hand yields almost exclusively m nitro(trifluoromethyl)benzene (91%) The ortho and para substituted isomers are minor components of the reaction mixture... 

Trifluoromethyl)benzene o Nitro(tnfluoro rn Nitro(tnfluoro p Nitro(tnfluoro... 

Because substitution m (trifluoromethyl)benzene occurs primarily at positions meta to the substituent we say that a trifluoromethyl group is a meta director... 

Turning now to electrophilic aromatic substitution in (trifluoromethyl)benzene we con sider the electronic properties of a trifluoromethyl group Because of their high elec tronegativity the three fluorine atoms polarize the electron distribution m their ct bonds to carbon so that carbon bears a partial positive charge... 

When we examine the cyclohexadienyl cation intermediates involved m the nitra tion of (trifluoromethyl)benzene we And that those leading to ortho and para substitu tion are strongly destabilized... 

All the ring positions of (trifluoromethyl)benzene are deactivated compared with benzene The meta position is simply deactivated less than the ortho and para positions The partial rate factors for nitration of (trifluoromethyl)benzene are... 

Figure 12 11 compares the energy profile for nitration of benzene with those for attack at the ortho meta and para positions of (trifluoromethyl)benzene The presence of the electron withdrawing trifluoromethyl group raises the activation energy for attack at all the ring positions but the increase is least for attack at the meta position... 

FIGURE 12 11 Comparative energy diagrams for nitro mum ion attack on (a) ben zene and at the (b) ortho (c) meta and d) para posi tions of (trifluoromethyl) benzene fact (ortho) > fact (para) > fact (meta) >... 

Because the carbon atom attached to the ring is positively polarized a carbonyl group behaves m much the same way as a trifluoromethyl group and destabilizes all the cyclo hexadienyl cation intermediates m electrophilic aromatic substitution reactions Attack at any nng position m benzaldehyde is slower than attack m benzene The intermediates for ortho and para substitution are particularly unstable because each has a resonance structure m which there is a positive charge on the carbon that bears the electron withdrawing substituent The intermediate for meta substitution avoids this unfavorable juxtaposition of positive charges is not as unstable and gives rise to most of the product... 

Trifluoromethyl-4-nitrophenol [88-30-2] M 162.1, m 81°, pK si 6.1. Crystd from benzene or from pet ether/ benzene mixture. 

At 320 °C, cesium tetrafluorocobaltate converts benzotrifluoride to /n-fluo-robenzotrifluoride, 2f/-heptafluorotoluene, octafluorotoluene, pertluoro-l -meth-ylcyclohexene, and perfluoromethylcyclohexane [29] l,3-Bis(trifluoromethyl)-benzene is convened at 420 °C to 4,5,6-trifluoro-l,3-bis(trifluoroethyl)bcnzene, perfluoro-l,3-dimethylbenzene, and perfluoro-l,3-dimethylcyclohexane [29], p-Xylene gives at 350 °C l,4-bis(difluoromethyl)tetrafluorobenzene, 1-di-fluoromethyl-3-trifluoromethyltetrafluorobenzene, perfluoro-1,3-dimethyl-benzene, and perfluoro-1,3-dimethyloyclohexane... 

Alkyl fluorides are more reactive than other alkyl halides under Friedel-Crafts conditions, whereas trifluoromethyl groups are less reactive than other trihalomethyl groups Thus, a bromoindane is prepared from 1-bromo-l-fluoro-2,2,3,3-tetramethylcyclopropane and benzene [5] (equation 8) whereas 3-tnfluo romethylphenyldiphenylchloromethane is obtained from 3-trifluoromethyl-benzotrichloride and benzene [9] (equation 9)... 

Amtnonolysis of tetrakis(l,2,3,5-trifluoromethyl)benzene with liquid ammonia in a sealed tube gives a tncyano derivative [99] (equation 85). 

Alkynes substituted with one or two trifluoromethyl groups are also highly reactive dienophiles [9] Indeed, hexafluoro-2-butyne is used increasingly as a definitive acetylenic dienophile in "difficult Diels-Alder reactions. It was used, for example, to prepare novel inside-outside bicycloalkanes via its reaction with cir,trnns -l,3-undecadiene [74] (equation 67) and to do a tandem Diels-Alder reaction with a l,l-bis(pyrrole)methane [75] (equation 68) Indeed, its reactions with pyrrole derivatives and furan have been used in the syntheses of 3,4-bis(tri-fluoromethyl)pyrrole [76, 77] (equation 69) and ],4-bis(trifluoromethyl)benzene-2,3-oxide [78] (equation 70), respectively. 

The use of trifluoromethyl-substituted a-pyrones in Diels-Alder reactions with all types of dienophiles provides an interesting route to trifluoromethyl-benzenes [I/Sj (equation 98)... 

Perfluorotetramethylthiadiphosphanorbornadiene and bis(trifluoromethyl) thiadiphosphole can be prepared by thermolysis of an adduct of methanol and hexakis(trifluoromethyl)-l,4-diphosphabarrelene with sulfur [113] (equation 23) Pyrolysis of the adduct of hexafluorinated Dewar benzene and phenyl azide results in ring expansion giving azepine, which photochemically yields an intramolecular 2-1-2 adduct, a good dienophile for the Diels-Alder reaction [114, //5] (equation 24) Thermolysis of fluonnated derivatives of 1,5-diazabicyclo-... 

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