Thermally unstable fluorides

In general, high reactivity of compounds is associated with high sensitivity. Thermally unstable fluorides may still be prepared under fluorine pressure, if their formation takes place already at moderate temperatures. Hexafluorides of the platinum metals are very strong oxidizers and volatile, but also thermally quite unstable, in particular those that are most reactive. Nevertheless, RuF6 and RhF6 were obtained via pressure fluorination of their respective pentafluorides [92] ... 

The fluorine dissociation pressure over thermally unstable fluorides increases exponentially with temperature. Accordingly, even in a rather narrow temperature... 

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

Thiazyl fluoride is a moisture-sensitive, thermally unstable gas. It is conveniently generated by decomposition of compounds which already... 

Of the 6 possible oxide fluorides of Cl, 5 have been characterized they range in stability from the thermally unstable FCl "0 to the chemically rather inert perchloryl fluoride FCl "03. The others are FC1 02, F3C1 0 and F3C1 "02-... 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

Attempted syntheses of trifluoromethyl derivatives of germanium, tin, and lead by thermal decarboxylation either resulted in decomposition of the trifluoroacetate without forming carbon dioxide (22,39,40) or gave carbon dioxide but no trifluoromethyl organometallic (22). In the latter case, the metal fluoride was detected. This suggests that the trifluoromethyl compound is thermally unstable and decomposes by fluoride abstraction. 

Pentafluorophenyllithium is thermally unstable and decomposes to generate tetrafluorobenzyne by / -elimination of lithium fluoride. The benzyne can be trapped by a variety of dienes to give the corresponding Diels-Alder adducts [193,196,197,206] (Scheme 71). 

Tris[fluoroalkoxy] tellurium fluorides are thermally unstable, moisture-sensitive liquids. 

The great power of the general synthetic procedure proposed by Zemva, Bartlett et al. lies in the ability to prepare marginally thermally stable and even thermodynamically unstable fluorides at low temperatures. Originally [67], they... 

These compounds range from the thermally unstable FCIO to the rather chemically inert perchloryl fluoride FCIO3. The structure and properties of this family of compounds resemble those of the halogen fluorides. Therefore, they have to be handled with the same care as elemental fluorine and its chemically reactive fluorides. The halogen oxide fluorides can be prepared by fluorination of halogen oxides with elemental fluorine or with halogen fluoride. 

Chlorine Oxide Fluoride. The only member of the halogen oxide fluoride class is chlorine oxide fluoride (6). It forms a solid that melts to a red liquid at —70 °C. In the gaseous state, it is thermally unstable and decomposes to give FCIO2 and CIF. It can be made by the hydrolysis of CIF3 with substoichiometric amounts of H2O in a flow reactor. It is also produced by photolysis of a mixture of CIF and O3 in Ar at 4 15K. 

Beside XeOs and Xe04, some xenon oxyfluorides are also thermally unstable compounds. They may detonate, particularly at higher temperatures. Other derivatives of the xenon and krypton fluorides involving ligands less electronegative than fluorine should also be assmned to be of low thermodynamic stability. Many derivatives such as perchlorates and trifluoroacetates are known to be explosive. 

Thiazyl fluoride is a moistme-sensitive, thermally unstable gas. It is conveniently generated by decomposition of FC(0)NSP2 or Hg(NSF2)2- It may also be obtained from [NSJjAsFe] andCsF orfrom(NSCl)3 andKF intetramethylene sulfone at 80 °C. The microwave spectrum of NSF indicates a bent structure. Thiazyl fluoride can be stabilized by coordination to a transition metal and such complexes, for example, [M(NSF)6] [AsFe] (M = Co, Ni), are conveniently prepared in liquid SO2. ... 

This procedure has been used to prepare many other chlorides, e.g., tungsten hexachloride, vanadium tetrachloride, and the pentachlorides of niobium and tantalum. However, it is normally much easier to prepare chlorides than fluorides. This method will therefore find application only where this generalization is not applicable. In particular, it will find application where the chloride is thermally unstable under normal chlorination conditions and must be prepared at or below room temperature. This method has been used to advantage for the preparation of ReCle and the new compound osmium pentachloride. ... 

Weinstock, Malm, and Weaver have shown that platinum hexafluoride is thermally unstable and dissociates to a lower fluoride and fluorine. In view of this capacity of the hexapositivc platinum to oxidise combined fluorine to the elemental furm. it is not surprising that it is also capable of oxidising the oxygen molecule. A similar oxidation by ruthenium and rhodium hexafluorides is to be looked for. 

The first effective synthesis of CgFgAsFfi employed 02AsF as the oxidizer of C F dissolved in liquid WPg. This solvent not only provided the desirable diluent effect for this hot reaction but its relatively high heat capacity also aided in preservation of a lower temperature. These are essential requirements for high-yield syntheses of C5F(AsF and its monocyclic relatives, since all are thermally unstable at ordinary temperatures. In more recent work sulfuryl chloride fluoride has been used as the diluent and moderator and the low working temperatures have resulted in greatly improved yields. Nevertheless, even with SO2CIF, pyrolysis products from the salts are always observed and a quantitative yield has never been obtained for any of the monocyclic cation salts. For these and other reasons the salt composition in each Case has been determined from the stoichiometry of the salt pyrolysis products and other reaction stoichiometries. 

As the alcohol is not formed, there is no need to use sterically hindered alkoxides. This reaction is usually carried out in pentane or in an excess of alkene at 0 to 10 °C and is recommended for the preparation of thermally unstable 1,1-dichlorocyclopropanes. An interesting modification for the synthesis of 1,1-dichlorocyclopropanes which eliminates strongly alkaline medium, utilizes trimethylsilyl trichloroacetate and potassium fluoride in the presence of a catalyst (a quaternary ammonium salt or a crown ether),... 

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