Toluene, fluorination

GL 1] [R 1] [P la] Using acetonitrile as solvent, the conversions ranged from 14 to 50% at selectivities of33-57% [38] (see also [3]). This corresponds to yields of 5-20%. The highest yield was found for a liquid volume flow of 11.6 ml h using a 1.1 mol toluene concentration at -20 °C. The fluorine/toluene molar ratio was 0.925. 

GL 1] [R 4] [P 2] Selectivities of up to 36% at 33% conversion were achieved using acetonitrile as solvent (1.0 fluorine-to-toluene equivalent) [13]. When including multi-fluorinated toluenes and chain-fluorinated toluenes, in addition to the mono-fluorinated toluenes, in the selectivity balance, the value increases to 49%. The remainder is lost in other side reactions such as additions or polymerizations. 

GL 1] [R 1] [R 3[ [P la-d[ A ratio of ortho-, meta- and para-isomers for mono-fluorinated toluene amounting to 5 1 3 was found for the falling film micro reactor and the micro bubble column at a temperature of -16 °C (3, 38]. This is in accordance with an electrophilic substitution pathway. The relatively high amoimt of ortho-isomers is due to the small size of the fluorine moiety as the ortho position is amenable to steric effects. 

GL 1] [R 4] [P 2] Variation of solvent affects also the substitution pattern to a certain extent [13], A ratio of ortho-, meta- and para-isomers for mono-fluorinated toluene amounting on average to 3.5 1 2 was found in the dual-channel micro reactor at room temperature, using acetonitrile as solvent [13]. Using methanol as solvent, the ratio was on average 5.5 1 2.4. Hence more products referring to an electrophilic substitution were formed [13]. 

Of a series of fluorinated benzenes and fluorinated toluenes tested with and without... 

Nitrogen dioxide Cyclohexane, fluorine, formaldehyde, alcohols, nitrobenzene, petroleum, toluene... 

Like many organic solvents, including hexane, heptane, ben2ene, xylene, toluene, gasoline, and particularly some of the other chlorinated and fluorinated solvents, methylene chloride may cause cardiac arrhythmias in the presence of elevated epinephrine when inhaled at concentrations as high as 20,000 ppm (36). 

Table 2. Fluorination of Toluene with Potassium Tetrafluorocobaltate at 340 °C [25] and Cesium Tetrafluorocobaitate at 360 C [29]...

A recently discovered variant of the Wallach technique is the silver ion cata lyzed fluorination of aryl diazo sulfides in hydrogen fluonde-pyridine-toluene solvent [57] (equation 12) Electron withdrawing substituents such as acetyl give higher yields of aryl fluoride (71%) than electron donating groups (butyl 39%, methoxy, 2-14%), reductive dediazoniation competes with fluorination... 

Reductive removal of fluorme from alk I fluorides requires a potent reducing agent and so is not noimally encountered However, hydrogenolysis of an unacuvated carbon-fluorine bond in, for example, 3 (3-fluorocholestane has been efficiently accomplished in 88% yield with a solution of potassium and dicyclohexyl 18 crown-6 in toluene at 25 C [/] Similarly, sodium naphthaiene in tetrahydrofuran converts 6 tluorohexene-1 and 1-fluorohexane to hydrocarbons in 50% yield at 25 C over a 7-h penod [2]... 

The mfluoromethyl group activates the fluorine in position 4 ofperfluorotolu ene toward reaction with carbon nucleophiles Examples on che use of perfluoro-toluene as an arylation agent abound, and in all cases, the 4-fluonne atom is replaced predommantly or exclusively [% 87,88,89, 90 (equation 48) In perjluoromesity-lene, the aromatic fluorine atoms are activated toward Ar reaction, and a reaction... 

Intense molecular ions are observed in the mass spectra of fluorinated benzene, ethyl benzene, toluene, and xylene. Most fluorinated aromatics lose 19 Daltons from the molecular ion. and some lose 50 Daltons (e.g., CF2). The chlorofluoroaromatics can easily be identified by examining the isotope ratios in the vicinity of the molecular ion. 

FIGURE 9.27 Transformation of fluorinated substrates by toluene 2,3-dioxygenase and yields (%). (From Neilson, A.H. and Allard, A.-S., The Handbook of Environmental Chemistry, Vol. 3R, Springer Verlag, 2002, pp. 1-74. With permission.)... 

As examples of micro-channel process intensification and the respective equipment, in particular gas/liquid micro reactors and their application to toluene and various other fluorinations and also to carbon dioxide absorption can be mentioned [5]. Generally, reactions may be amenable to process intensification, when performed via high-temperature, high-pressure, and high-concentration routes and also when using aggressive reactants [5]. 

Figure 1.31 Electrophilic and radical paths in direct-fluorination chemistry leading to substitutions, additions and polymerizations with the example of toluene as substrate.

Jahnisch, K., Baerns, M., Hessel, V, Haverkamp, V, Lowe, H., Wille, C., Selective reactions in microreactors -fluorination of toluene using elemental fluorine in a falling film microreactor, in Proceedings of tlie 37tli ESF/EUCHEM Conference on Stereocliemistry (13-19 April 2002), BUrgenstoclc, Switzerland. 

Cas/liquid reaction [CL 1] Direct fluorination of toluene using elemental fluorine... 

The temperature was set to -15 °C [38] (see also [3]). The molar ratio of fluorine to toluene spans the range from 0.20 to 0.83 hence under-stochiometric fluorine contents were employed. The concentration of toluene in the solvent was 1.1 mol As liquid volume flow always 13 ml h was applied. Acetonitrile was used as solvent for the aromatic compound. In the gas phase, 10% fluorine in nitrogen was used. The gas volume flow was varied from 12.1 ml min to 50.0 ml min . ... 

The number of fluorine equivalents (to toluene) was varied the gas and liquid flow velocities were kept constant to maintain the same flow pattern for all experiments. Liquid products were collected in an ice-cooled roimd-bottomed glass flask containing sodium fluoride to trap the hydrogen fluoride. The flask is connected to a cooling condenser to recover the solvent. Samples were typically collected for 1 h. Waste gases were scrubbed in aqueous 15% potassium hydroxide solution. Samples were degassed with nitrogen and filtered before analysis. 

Complete toluene conversion is achieved when using 5.0 fluorine-to-toluene equivalents [13], but at a much decreased selectivity of 11%. 

The highest yield of 14% was foimd at 2.5 fluorine-to-toluene equivalents (58% conversion 24% selectivity) [13]. This yield was obtained using acetonitrile as solvent slightly lower yields were obtained for methanol (Figiue 5.16). The selectivities were as high as for acetonitrile, the conversion being lower. Still lower yields (7%)... 

Figure 5.16 Influence of the fluorine-to-toluene equivalents (0.1 M toluene in acetonitrile) on conversion, selectivity and yield [13].

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