Chromium fluoride catalysts

It may also be prepared by pyrolysis of 1,1-difluoroethane at 725°C over a chromium fluoride catalyst in a platinum tube or by the action of zinc dust on bromodifluoroethane at 50°C. 

At atmospheric pressure vinyl fluoride (VF) is a colorless gas with an etheral odor. Its boiling point is — 72.2°C, its critical temperature Tc=54.7°C, and its critical pressure Pc = 51.7 atm. It is flammable at air between the limits of 2.6 and 21.7% VF by volume and an ignition temperature of 400 °C. A toxie effect is found at 20% VF by volume and above [456,457], The first reported preparation was by Swartz [451] in 1901. VF was found after the reaction between l,l-difluoro-2-bromoethane and zinc. Later the pyrolysis of 1,1-difiuoroethane at 725 °C over a chromium fluoride catalyst [462] or at 400 °C in the presence of oxygen [463] are described. 

Chromic Acid Electrolysis. Alternatively, as shown in Figure 1, chromium metal may be produced electrolyticaUy or pyrometaUurgicaUy from chromic acid, CrO, obtained from sodium dichromate by any of several processes. Small amounts of an ionic catalyst, specifically sulfate, chloride, or fluoride, are essential to the electrolytic production of chromium. Fluoride and complex fluoride catalyzed baths have become especially important in recent years. The cell conditions for the chromic acid process are given in Table 7. 

Trifluoroacetyl fluoride and hexafluoroacetone have been made commercially by reaction of their perchloro analogs with hydrogen fluoride and chromium oxide catalysts. 

Vapor-phase fluorination using hydrogen fluoride and, for example, a chromium or aluminum oxide/fluoride catalyst (i.e., the procedures used for manufacture of fluorochloroalkanes16) has also been applied (Eq. 7).17... 

These observations are in some respects contrary to the behavior of chromium oxide catalysts, which are quite active when supported on silica alone. But even the activities of chromium oxide/silica catalysts tend to improve when they are acidified by the addition of compounds of Ti, Al, F, or other ions. As noted in Sections 14.7-14.9, the addition of fluoride or sulfate or silica to Cr/alumina catalysts also increases the activity several fold. Being attached by two, rather than just one, oxide link could also decrease the electron density on chromium oxide catalysts, particularly after calcination at high temperatures when strain can be introduced [52,65,387],... 

Reaction of tiichloroacetaldehyde with hydrogen fluoride in the presence of chromium-based catalysts gives CFs-CHO.HF which, on treatment with an alkoxysilane (RO)4Si or with ROH-SiCU (R = Me, Et, Pr, or n-CsHu), yields the corresponding hemiacetals CF3-CH(OH)OR (69— 92%) the acetal I-----------------------1... 

Ferric acetylacetonate catalyst, H2S determination Cadmium sulfate catalyst, halogenation Chromium fluoride (ic) catalyst, high temp. polyester premix compounds... 

The gas-phase reaction of benzotrichloride with hydrogen fluoride over a chromium trifluoride catalyst is claimed to give a 93% yield of benzotri-fluoride, and pentafluorobenzaldehyde reacts with sulphur tetrafluoride to give a-jtf-heptafluorotoluene, C,Fj-CFjH (see also Vol. 1, p. 208), a better route to which apparently involves the fluorination of 2,3,4,5,6-pentafiuoro-benzal chloride. Bromination of the heptafluoro-compound gives perfluoro-... 

J. Krishna Murthy, U. GroB, St. Rudiger, E.Unveren, W. Unger and E. Kemnitz, Synthesis and characterization of chromium(lll)-doped magnesium fluoride catalysts, Appl. Catal., A., 282, 85-91 (2005). 

The fluorine titration of chromium oxide was carried out at the Elf-Atochem Research Center, Pieire-Benite.The catalyst mineralization was carried out in a Parr bomb by reaction with sodium peroxyde. Fluorine ions were then titrated by a potentiometric method with a specific fluoride electrode. 

Disproportionation of halogenatcd aliphatic hydrocarbons can also be accomplished using catalysts based on chromium oxides with the formula Cr01 2F2 1.18 This catalytic material is obtained by fluorination w ith hydrogen fluoride of an oxide hydrate of trivalent chromium with the formula Cr203 xH,0 (with x = 1-9). The chromium oxide hydrate is reacted with a mixture of hydrogen fluoride/nitrogen gas in a molar ratio of 1 10 in an externally heated nickel tubular reactor at 350 450 C. 

In addition to the traditional catalysts aluminum trifluoride, chromium oxyfiuoride and iron(III) fluoride, published references to chlorofluorocarbon disproportionation reactions describe zinc aluminate (ZnAl,04)l> and nickel(II) chloride on "/-aluminum oxide as carriers.20... 

The examples given demonstrate that l,3,5-trichloro-2.4,6-trifluorobenzene can be dispropor-tionated either with or without an additive. Aluminum trifluoride and chromium(III) fluoride act as catalysts and enhance the reaction boron trifluoridc, however, seems to act as an inhibitor. 

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