Fluorination flow-system

Iron(III) fluoride [7783-50-8] prepared from FeCl and anhydrous HF or other fluorinating agents ia a flow system at elevated temperature. 

Titanium Tetrafluoride. Titanium tetrafluoride [7783-63-3] is a white hygroscopic soHd, density 2798 kg/m, that sublimes at 284°C. The properties suggest that it is a fluorine-bridged polymer in which the titanium is six-coordinate. The preferred method of preparation is by direct fluorination of titanium sponge at 200°C in a flow system. At this temperature, the product is sufficiently volatile that it does not protect the unreacted sponge and the reaction proceeds to completion. The reaction of titanium tetrachloride with cooled, anhydrous, Hquid hydrogen fluoride may be used if pure hydrogen fluoride is available. 

Ring transposition processes are well established in six-membered heteroaromatic systems. Recent studies have centered on perfluoro systems in which bicyclic and tricyclic intermediates are sufficiently stable to permit isolation or at least detection. Thus, on irradiation in CF2C1CFC12, the perfluoropyridine 207 is converted into the azabicyclo[2.2.0]hexa-2,5-diene 208 and the two azaprismanes 209 and 210.154 An azabicyclo[2.2.0]hexa-2,5-diene has also been shown to be an intermediate in the photorearrangement of substituted 2-methylpyridines to o-substituted anilines.155 Diaza-bicyclo[2.2.0]hexa-2,5-dienes have similarly been shown to be intermediates in the conversion of fluorinated pyridazines (211) into the corresponding pyrazines (212)156 the proposed pathway is outlined in Scheme 7. Photoproducts which are formally dimers of intermediate azetes have been obtained when analogous reactions are carried out in a flow system.157... 

When carbon with low crystallinity and a large surface area is fluorinated, the reaction rate is normally very high as a result, deflagration decomposition of the product can occur with only a slight temperature increase. For the fluorination of such carbons, the flow system is recommended because it is convenient to remove the heat of reaction effectively. This type of process is used on an industrial scale. The static bed system is used for the preparation of small amounts of custom fluorinated products on a development scale with a wide variety of carbons and various degrees of fluorinations.6 In both systems, fluorine gas is diluted with an inert gas such as nitrogen to improve control of reaction exotherms. 

The only fluoropentaborane known is the 2-substituted derivative which was obtained by the reaction of 2-IB5H8 with antimony trifluoride in a flow system at low pressure 184). The compound is a liquid which is moderately stable at room temperature. No boron-fluorine spin coupling is evident in the boron-11 nmr spectrum, but a poorly resolved quartet (Jpb = 60 hz) is observed in the fluorine-19 nmr spectrum. The analogous reaction of I-IB5H8 with antimony trichloride gave a product which was too unstable to characterize 184>. 

A major decision that must be made is whether to carry out the experiment in an open or, better, a flow system, or alternatively in a closed or pressure system. Both reactions are equally well suited to be carried out in a flow system, as solid and non-volatile starting compounds react with the fluorine gas to form the desired non-volatile product together with volatile by-products. The latter are swept away by excess fluorine. In case of a closed system example (Eqn. (11)) turns out less favorable, as C1F will react with F2 to form C1F3, which in turn may also compete for the potassium component to form KC1F4. Under these conditions therefore a pure product is not expected. No such complications are to be expected with the second reaction (Eqn. (12)), which results in a very clean product. This very simple example is intended to demonstrate that, although for many experiments a flow system or a closed reaction vessel are mutually exchangeable, characteristic... 

The use of elemental fluorine in the preparation of main group fluorides is carried out in batch and flow systems... 

Bis(fluoroformyl)peroxide, a diacyl peroxide, is a sublimable solid. It can be made in good yields in a flow system from carbon monoxide, fluorine, and oxygen at room temperature (equation 58). 

Until recently, no selenium monohalide could be isolated only the short-lived radicals SeF, SeCl, and SeBr were identified in the gas phase. SeF, can be produced by reaction of fluorine atoms (by passing CF4 through a microwave discharge) with carbonyl selenide in a flow system. It has been detected by ESR spectroscopy and the Se-F bond length (1.742 A) is close to the value reported for SeF2 (1.69 A), deduced from infrared spectra. ... 

Vanadium Pentafluoride, VFs. Vanadium pentafluoride is the only pentahalide so far reported. It is best prepared by direct reaction between metallic vanadium and fluorine in a flow system at 300 °C under moisture free conditions. It is an extremely reactive white solid at room temperature and an extremely powerfiil oxidizing and fluorinating agent. 

Since it was observed that fluorine contamination was a possibility and had potentially detrimental effects as described in Chapter 10, the excellent primer adhesion achieved with Tfs/(Ar) and Tcs/(Ar), shown in Table 31.3, has significant importance in the practical application of the plasma technique without any of the potentially deleterious effects of fluorine-based systems. Argon plasma treatments on both flow system TMS (Tfs) and closed system TMS (Tcs) polymers were then investigated as an additional system modification that could provide strong adhesion without the incorporation of fluorine-containing monomers in the quest to produce chromate-free coatings systems. 

Xenon tetrafluoride has been prepared by a number of methods. Irradiation of a mixture of xenon and fluorine with ultraviolet light produces xenon difluoride if the reaction product is immediately condensed from the gas phase. However, if the di fluoride is allowed to remain in the reaction zone, the tetrafluoride is produced. Passage of an electric discharge through a mixture of xenon and fluorine also produces xenon tetrafluoride. Perhaps the best method is the one in which xenon and fluorine are heated together either in a closed system or in a flow system. The method which uses a closed system allows a somewhat better control of purity and is described below. 

One of the best-known thermal reactions of fluorine compounds is the pyrolysis of chlorodifluoromethane to tetrafluoroethylene as used in the production of Teflon polymer. This reaction was described by Park et in 1947, and Nor-ton" in 1957 reported an activation energy of 49 kcal.mole for the decomposition over silica at 425-525 °C. More recently, Gozzo and Patrick have made a kinetic study of the process using a helium flow system at 670-750 °C with a surface conditioned platinum tubular reactor. HCl is found to retard the raction and the following mechanism has been proposed... 

Carbon bromide fluoride is formed in a flow system with a yieid of 30% when a mixture of dinitrogen (saturated with dibromine), molecular fluorine, and carbon monoxide are passed simultaneously through a copper tube [1751]. No further details of this preparation are available, but if it is probably consistent with the stoicheiometry shown in Equation (16.7). 

The decay of fluorine atoms in the other reactions was estimated to be less than 1%.229,241 Pulse radiolysis combined with UV absorption was employed by Jodkowski et al.229 at pressures of 500 - 1000 mbar (M = SF6), while a fast-flow system with a quadruple mass spectrometer was applied at pressures in the range of 0.7 - 5.1 mbar (M = He). The influence of other homogeneous reactions on the reaction kinetics was also analyzed by computer simulation and found to be negligible. The rate constant ki = (1.3 + 0.3) x 10 10 cm3molecule"1s 1 at 298 K has been estimated at pressures of 500 - 1000 mbar of SF5.229 The theoretical analysis of the reaction kinetics was based on the approach developed by Troe et al.17 23 The fall-off curves for the reaction CH3... 

Agp2 is readily prepared from AgCI or AgF and elemental fluorine in a flow system (prefluor-inated Cu tube) at 100-250°. The residue of this reaction might be recycled under these conditions. Silver(ll) fluoride is available commercially from Ozark-Mahoning Inc. 

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