Nitration of fluorobenzene

Smith and coworkers have screened the solid catalysts for aromatic nitration, and found that zeolite (3 gives the best result. Simple aromatic compounds such as benzene, alkylbenzenes, halogenobenzenes, and certain disubstituted benzenes are nitrated in excellent yields with high regioselectivity under mild conditions using zeolite (3 as a catalyst and a stoichiometric quantity of nitric acid and acetic anhydride.11 For example, nitration of toluene gives a quantitative yield of mononitrotoluenes, of which 79% is 4-nitrotoluene. Nitration of fluorobenzene under the same conditions gives p-fluoronitrobenzene exclusively (Eqs. 2.1 and 2.2)... 

Knowledge was accumulated systematically from the start of the present century, and has been summarized.9 A major contribution was made by Holleman and his group in the Netherlands in the period up to 1915. Various fluorobenzene derivatives having one or more substituents (N02, NH2, Me, C02H, OMe, SOsH or halo) were made and orientated. The ratio of isomers formed in the nitration of fluorobenzene was determined (mainly para some ortho). Also, fluorobenzene was itself resistant to attack by nucleophiles, but if a nitro group was present, particularly in the para position, fluorine was replaced much more readily. 

Germain, A., Akouz, T. and Figueras, F. Vapour-phase nitration of fluorobenzene with N204 over aluminosilicates. Effects of structure and acidity of the catalyst, Appl. Catal., A, 1996, 136, 57-68. 

The nitration of fluorobenzene was studied by a number of authors. Most of the earlier work was devoted to mononitration (Wallach [44], Holleman [45], Swarts [46]). 

For a preparation by nitration of fluorobenzene see Hudlicky4b and Zahn and Wiirz.820... 

Under conditions in which benzene and its homologues were nitrated at the zeroth-order rate, the reactions of the halogenobenzenes ([aromatic] = c. o-1 mol 1 ) obeyed no simple kinetic law. The reactions of fluorobenzene and iodobenzene initially followed the same rates as that of benzene but, as the concentration of the aromatic was depleted by the progress of the reaction, the rate deviated to a dependence on the first power of the concentration of aromatic. The same situation was observed with chloro- andjbromo-benzene, but these compounds could not maintain a zeroth-order dependence as easily as the other halogenobenzenes, and the first-order character of the reaction was more marked. 

Friedel-Crafts acylation of fluorobenzene with thiophene-l-carboxylic acid gives the ketone 7. Nitration proceeds ortho to the fluoro group to give the intermediate Nucleophilic displacement by means of... 

The method used at PicArsn for prepg TNFB involved foe nitration of 2,4-dinitro-fluorobenzene, but the attempts, based on literature references, were unsuccessful Refs 1) Beil, not found 2) L.G. Wesson, USP 2179605(1940) CA 34, 1852(1940)... 

Nitration of strongly deactivated aromatics was carried out with nitric acid mixed with triflatoboric superacid.482 The method is characterized by high yields (penta-fluorobenzene, 99%, 1,2,3,5-tetrafluorobenzene, 89% 2,3,4-trifluoronitrobenzene, 96% methyl phenyl sulfone, 78%), usually high regioselectivity, and mild reaction conditions (room temperature), and it also tolerates many functional groups. 

Trioitro derivatives of chlorobenzene Picryl chloride Ph> ical properties Chemical properties ] Ch]oro-2,4,5-irinitrobenzcnc Diagram of the nitration of chlorobenzene Thermochemical and explosive properties of chloronitrobenzenes Nitro derivatives of p-chlorobenzene Mononitro derivative ofp-chlorobenzene Dinitro derivative of p dichIorobenzene 2 4,6 Trinitroderivative of 1.3.S-trichtorobenzene Manufacture of l,3,5-trichloro-2.4.6-irinitrobenzenc Nitro derivatives of fluorobenzene Literature... 

Nitration of halogenobenzenes yields 12% of the ortho product for fluorobenzene, and 41% for the iodobenzene. 

Nitrobenzene was obtained from the nitration of benzene with yields of 32-61%, fluoronitrobenzeneB from fluorobenzene with 28-76% yields, the relative order of activity of the catalysts used being AsF > PF > BF3 > TiClij > BCI3. With the chloride catalysts used, a considerable amount of chlorobenzene also was formed in the reaction, as was the case with AlCl. ... 

It has been shown by studies of kinetic isotope effects that the deprotonation step is fast and does not influence the rate of nitration. The cases in which this has been demonstrated include, among others, nitration of benzene, toluene, nitrobenzene, and bromobenzene in nitric acid-sulfuric acid nitration of benzene, toluene, and fluorobenzene with nitronium tetrafluoroborate and nitration of toluene in nitric acid-nitromethane. The only exception, where primary isotope effects are observed, is in the case of substituted 1,3,5-tri-r-butylbenzenes. Here, steric hindrance to deprotonation is apparently sufficiently large to make deprotonation slow relative to the first two steps in the nitration mechanism. 

Fluoronitrobenzenes or Nitrofluorohenzenes, (ortho-, meta- and para-), F.C H NC ) mw 141.11, N 9-94%. Prepd by variety of nitration methods from fluorobenzene. Its para-compd is described in Ref 1, as pale yel... 

Fluorobenzene is hydroxylated in 90% yield with nitrous oxide (N,0) over a zeolite catalyst, but a mixture of regioisomers is formed (Table 7).1091,2,4,5-Tetrafluorobenzene is oxidized, instead of nitrated, by fuming nitrie acid to 2,5-difluoro-l,4-bcnzoquinone (1) in low yield.1,0... 

C o solubility increases in the similar sequence, from iodobenzene to chlorobenzene. The exception is fluorobenzene in which C6o solubility is lower than in iodobenzene. Apparently, in the case of interaction between fluorobenzene and C6o fullerene the factor of high fluorine electronegativity prevails. Moreover, as Table 3 indicates the fluorobenzene nitration gives rise to mainly para-isomer and very little ort/zo-isomers. Consequently, the entire negative charge is localized in the /jara-position in a fluorobenzene molecule. Therefore, as with Cgo solubility in alkyl derivatives of benzene (Table 2), one can anticipate that for the C6o molecule that is an electrophilic reagent, the ortho-position will be the more preferential location for electrophilic attack than the /w/ra-position. 

Dinitration to obtain 1,2,4-fluorodinitrobenzene was described by Holleman and Beekman [47] who nitrated p- fluoronitrobenzene. Zahn and A. Wurz [48] prepared the same dinitrocompound by nitrating fluorobenzene. 1,2,4,6-Fluorotrini-trobenzene (picryl fluoride) was prepared by Olah, Pavlath, J. Kuhn and Varsanyi [49] by acting on 1,2,4-fluorodinitrobenzene with a nitrating mixture composed of fuming nitric acid and 60% oleum. The yield was 36% of theoretical. 

With this in mind, how would you expect fluorobenzene to react Most election density is removed first from the ortho positions by induction, then from the meta positions, and then from the para position. Any conjugation of the lone pairs on fluorine with the tc system would increase the electron density in the ortho and para positions. Both effects favour the para position and this is where most substitution occurs. But is the ring more or less reactive than benzene This is hard to say and the honest answer is that sometimes fluorobenzene is more reactive in the para position than benzene (for example, in proton exchange and in acetylation—see later) and sometimes it is less reactive than benzene (for example, in nitration). In all cases, fluorobenzene is significantly more reactive than the other halobenzenes. We appreciate that this is a rather surprising conclusion, but the evidence supports it. 

The percentage of the ortho product increases from fluorobenzene to iodo-benzene. We might have expected the amount to decrease as the size of the halide increases because of increased steric hindrance at the ortho position but this is clearly not the case. The series can be explained by the greater inductive effect of the more electronegative atoms (F, Cl) withdrawing electron density mostly from the ortho positions The relative rates follow a U-shaped sequence fluorobenzene nitrates most quickly (but not as fast as benzene), followed by iodo-, then chloro-, and then bromo-benzenes. This is a result of two opposing effects electron donation by conjugation and electron withdrawal by inductive effect... 

We used HZSM-5 zeolites (Si02/AI203 = 40 - 120) and H[Ga]ZSM-5 zeolites (Si02/AI203 = 60) prepared by decationization of the Na-form with a 1 N aqueous solution of HCI. The preliminary activation of all catalyst samples was carried out at temperatures of 820 - 1120 K either in an Ar flow or in an air flow for 6 h. For comparison, we prepared the HZSM-5 zeolite modified by 2 wt % Cu (wet impregnation with a 1 M nitrate solution with further nitrate decomposition at 820 K in air) and tested this sample in the fluorobenzene oxidation by nitrous oxide. 

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