Xenon tetrafluoride preparation

Survey and account for the group characteristics and trends in the elements of Group O (He-Rn). Outline the preparation and stereochemistry of xenon tetrafluoride. 

Stable noble-gas compounds have no industrial uses as of this writing but are frequently utilized in laboratories as fluorinating and oxidizing agents. Xenon difluoride and xenon tetrafluoride are relatively mild oxidative fluorinating agents and have been used for the preparation of phosphoms, sulfur, tellurium. 

FIGURE 15.27 Crystals of xenon tetrafluoride, XeF4. This compound was first prepared in 1062 by the reaction of xenon and fluorine at 6 atm and 4(J(J C. 

The starting point for the synthesis of xenon compounds is the preparation of xenon difluoride, XeF2, and xenon tetrafluoride, XeF4, by heating a mixture of the elements to 400°C at 6 atm. At higher pressures, fluorination proceeds as far as xenon hexafluoride, XeFfi. All three fluorides are crystalline solids (Fig. 15.27). In the gas phase, all are molecular compounds. Solid xenon hexafluoride, however, is ionic, with a complex structure consisting of XeF< + cations bridged by F anions. 

The xenon fluorides are used to prepare the xenon oxides and oxoacids and, in a series of disproportionations, to bring the oxidation number of xenon up to +8. First, xenon tetrafluoride is hydrolyzed to xenon trioxide, Xe03 in a disproportionation reaction ... 

In the preparation of xenon difluoride dioxide from caesium nitrate and xenon tetrafluoride oxide, the latter must always be used in excess to prevent formation of explosive xenon trioxide. 

Interaction of the yellow hexafluoride with silica to give xenon tetrafluoride oxide must be interrupted before completion (disappearance of colour) to avoid the possibility of formation and detonation of xenon trioxide [1]. An attempt to collect the hexafluoride in fused silica traps at — 20°C after separation by preparative gas chromatography failed because of reaction with the silica and subsequent explosion of the oxygen compounds of xenon so produced [2],... 

It is a powerful explosive [1] produced when xenon tetrafluoride or xenon hexafluoride are exposed to moist air and hydrolysed. Some tetrafluoride is usually present in xenon difluoride, so the latter is potentially dangerous. Although safe to handle in small amounts in aqueous solution, great care must be taken to avoid solutions drying out, e.g. around ground stoppers [2], Full safety precautions have been discussed [2,3,4], Precautions necessary for use of aqueous solutions of the trioxide as an epoxidation reagent are detailed [5,6], A safe method of preparation,... 

Xenon tetrafluoride also can be prepared by oxidizing xenon with dioxygen difluoride, O2F2, or by photolysis of xenon-fluorine mixture. 

Xenon also forms many fluoroanions and their salts, mostly prepared from xenon tetrafluoride and hexafluoride. Such compounds include Na+XeFs and Cs" XeF7- formed by reactions of xenon fluorides with sodium fluoride or cesium fluoride. The dicesium xenon octafluoride, Cs2XeFs, is a stable yellow solid that decomposes above 400°C. 

The preparation of xenon tetrafluoride is carried out by heating a 1 5 mixture of xenon to fluorine under a pressure of several atmospheres ... 

Both of these rules follow in a straightforward way from the properties of enthalpy changes. The first rule can be explained by recalling that the sip7i of AH indicates the direction of the heat flow at constant pressure. If the direction of the reaction is reversed, the direction of the heat flow is also reversed. To see this, consider the preparation of xenon tetrafluoride, which was the first reported binary compound made from a noble gas ... 

Less than a year after Bartlett s report, a group at Argonne National Laboratory near Chicago prepared xenon tetrafluoride by reacting xenon and fluorine gases in a nickel reaction vessel at 400°C and 6 atm ... 

Physical properties of the Xe-PtFt adduct.—The adduct is yellow when deposited in thin films but in bulk is deep red. The solid becomes glassy in appearance when heated to 115°, but does not melt below 165°, when it decomposes to produce xenon tetrafluoride. X-ray powder photographs of the adduct of composition XePtFe show no diffraction pattern. Complex patterns are observed with samples of material richer in platinum. The plasticity of the material made the preparation of good powder samples difficult. Even well-cooled samples did not grind well. 

Within a few weeks of the discovery ( > of xenon tetrafluoride by Claassen, Selig and Malm, they and their collaborators at the Argonne National Laboratory, had also prepared and characterized a difluoride < > and a hexafluoride (2 ). These compounds were soon confirmed in a number of other laboratories. Ali thee fluorides, which are white crystalline solids at room temperature are preparable from fluorine and xenon, the nature of the product depending upon the ratio of the reactants and the temperature, the tetrafluoride being thermally more stable than the hexafluoride... 

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. 

Fia. 10. Apparatus for preparation and purification of xenon tetrafluoride. A. 30,000-p.s.i. valve, Monel body, Teflon packing. 

The apparatus used for the preparation and purification of xenon tetrafluoride is shown in Fig. 10. The total volume of the manifold including the U-tubes, but excluding all reaction and storage vessels, is about 105 ml. All parts are fabricated of nickel or Monel and are pretreated by... 

Xenon hexafluoride may be prepared in essentially the same way as xenon tetrafluoride (synthesis 66), except for increasing the fluorine-to-xenon ratio and the final pressure at reaction temperature.Variations of temperature, pressure, mol ratio, and time make possible the formation of xenon difluoride, xenon tetrafluoride, or xenon hexafluoride. The conditions described below have been found to give good yields and purity for xenon hexafluoride. 

The purity of the xenon difluoride can be checked by measuring the absorption in the infrared (synthesis 66). Samples prepared as described above, with continuous trapping, contain less than 1 % xenon tetrafluoride, even if the initial fluorine-to-xenon ratio is varied from 0.1 to over 6. 

Xenon trioxide may also be prepared by hydrolysis of xenon tetrafluoride, but in that case the yield cannot exceed 33%. ... 

How many grams of xenon oxide tetrafluoride, XeOF4, and how many liters of HF at STP could be prepared, assuming complete reaction of 10.5 g of xenon tetrafluoride, XeF4, with a stoichiometric quantity of water according to the equation below ... 

Preparation by hydrolysis of either xenon tetrafluoride or xenon hexafluoride. Oxidizing action,2 Xenic acid reacts readily with u/c-diols in neutral or alkaline solution the products are xenon (gas) and carboxylic acids. 

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