Fluorination of toluene

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

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... 

Figure 5.18 Comparison of space-time yields of direct fluorination of toluene for the falling film micro reactor (FFMR), micro bubble column (MBC) and laboratory bubble column (LBC) referred to the reaction volume (a) and referred to an idealized reactor geometry (b) [38],...

Jahnisch K, Baerns M, Hessel V, Ehrfeld W, Haverkamp V, Lowe H, Wille C, Guber A (2000) Direct Fluorination of Toluene Using Elemental Fluorine in Gas/Liquid Microreactors. J Fluor Chem 105 117-128 Jahnisch K, Hessel V, Lowe H, Baerns M (2004) Chemistry in Microstructured Reactors. Angew Chem Int Ed 43 406 -46 Jensen KF (2001) Microreaction Engineering - is Small Better Chem Eng Sci 56 293-303... 

Fluorination of toluene gives a mixture of ortho- and para- uorotoluene, as expected for an electrophilic process (B), but the partial rate factors (Table 4) [139] show a very high ortho para ratio indicating that radical processes (A) must also be involved. Furthermore, fluorination of the methyl group, giving benzyl fluoride, also occurs in increasing yield as the reaction temperature is raised. 

The cobalt(III) fluoride fluorinations of toluene, the xylenes, and many similar compounds to give the corresponding perfluoroperhydro compounds are covered in Houben-Weyl, Vol. 5/3, pp 53-72. Rearrangement is again noted64 when butylbenzene is fluorinated Over cobalt(III) fluoride at 300 C the major products are, as well as the expected perfluoro(butylcyclohexane), perfluoro(decahydronaphthalene) and perfluoro(l-methylhexahydroindane). 

Oxidative fluorination of toluene derivatives to the corresponding fluoromethylben-zenes is possible using appropriate lead or nickel complexes in liquid hydrogen fluoride, but fluorination becomes more difficult as the reaction progresses because fluorine substituents increase the oxidation potential of the substrate [146] (Figure 3.20). Consequently, it seems unlikely that the ECF process (Chapter 2, Section III) could proceed to perfluorination by an analogous mechanism. 

Generally, anodic benzylic substitution reactions take place readily. However, anodic benzylic fluorination does not always occur. The major competitive reaction is acet-amidation when MeCN is used as a solvent [24-26]. In contrast to these cases, triphenylmethane is selectively monofluorinated in 80% yield [27]. When Et4NF-/7HF n = 3,4,5) is used in the absence of MeCN, anodic fluorination of toluene and mono-fluoromethylbenzene provides mainly mono- and difluoromethylbenzenes, respectively [22]. On the other hand, difluoromethylbenzene affords only products fluorinated in the benzene ring [Eq. (4)] [28]. 

Scheme 8.2 Fluorination of toluene in a falling-film microflow reactor...

K. Jahnisch, M. Baerns, V. Hessel, W. Ehrfeld, V. Haverkamp, H. Lowe, C. Wille, A. Guber, Direct fluorination of toluene using elemental fluorine in gas/liquid microreactors, J. Fluor. Chem. 105 (2000) 117. 

In another example, Hessel et al. [42] and Loewe et al. [43] studied the direct fluorination of toluene with F2 in a microsystem consisting of reaction channels as well as mass transfer and heat transfer in close proximity. They claim a change in the reaction mechanism from radical in nature to an electrophilic substitution, through careful control of the reaction conditions. This type of microreactor is well described in the literature and is commonly known as a falling film microreactor [44, 45]. 

Direct fluorination of toluene and nitrotoluene Falling film and bubble column MSR Jahnisch et al. [30]... 

The fluorination of toluene with 10% F2 in N2 by using the falling-film microreactor and the microbubble column has also been studied (Scheme 8.7) [11, 12]. Both the falling-film microreactor and the microbubble column offer advantages over conventional reactors in fluorination reactions. The selectivity of the formation of monofluorinated toluene in a falling-film microreactor is significantly higher than... 

Direct fluorination of toluene using elemental fluorine is not feasible since the heat release cannot be controlled with conventional reactors. So the process is deliberately slowed down. Hence, the direct fluorination needs hours in a laboratory bubble column. It can be completed within seconds or even milliseconds when using a miniature bubble column, operating close to the kinetic limit. The Bayer-Villiger oxidation of cyclohexanol to cyclohexanone with fluorine and aqueous formic acid (5% water) is done in miniature bubble column reactors at 60% conversion at 88% selectivity. 

Selective Electrochemical Fluorination, Scheme 14 Solvent-free electrochemical fluorination of toluene in poly HF salt... 

Momota K, Mukai K, Kato K, Morita M (1998) Electrochemical fluorination of aromatic compounds in liquid R4NF mHF. Part VI. The fluorination of toluene, monofluoromethyibenzene and difluoromethyibenzene. Electrochim Acta 43 2503-2514... 

Direct fluorination of toluene dissolved in acetonitrile Falling film microreactor Safer process. Yield in microreactor 2.5 times higher than in a lab bubble column... 

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