Fluorine, elemental halogen oxides

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. 

Fluorine is the most energetic oxidizing element and as such is of prime importance in advanced oxidizers. The fluorine-based oxidizers discussed here include elemental fluorine, compounds containing oxygen and fluorine, nitrogen-fluorine compounds, halogen fluorides, and noble gas fluorides. 

The rules discussed so far allow us to make educated guesses about possible compounds formed by elements. However, not all compounds deduced by application of the rules actually exist. Moreover, some elements have more oxidation numbers than the rules identify. Nitrogen, for example, exhibits every integral oxidation number from -3 to +5, as well as a fractional oxidation number, -5, in HN3 and its salts. Except for fluorine, the halogens also exhibit most of the integral oxidation numbers from -1 to +7. Detailed study of the chemistry of the elements and their compounds is necessary to know which compounds actually exist. 

Halogen name for the group of elements comprised of fluorine, chlorine, bromine, and iodine. These elements are oxidizers and form acidic solutions in water. 

A classic reaction for preparing a molecular halogen (other than fluorine)—indeed, the reaction that led to the discovery of chlorine as an element—involves oxidation of a hydro-halic acid with manganese dioxide ... 

Hydrogen peroxide, HjOj Interhalogen compounds such as OF and BrF3 Halogen oxides such as OFj, QjO, and QjO, Elemental fluorine, chlorine, and bromine (F2, CI2, Br2)... 

Table 6.2 also includes the redox potentials, QX2 X"), which confirm that the oxidizing strength of the elemental halogen decreases from fluorine to iodine. Finally, there is the standard enthalpy of formation of the gaseous molecules, X2(g). The values are zero for fluorine and chlorine because these substances are already gaseous at 25 °C. However, bromine is a red liquid and iodine a dark solid, so for the reaction... 

When the elemental halogens act as oxidizing agents, they are converted into X"(aq) ions. In the process, we imagine first a step in which X2 is converted into X (g). The energy of this step is most favourable for fluorine, but it is quite similar for all the halogens the values of AH (X", g) in Table 6.4 illustrate the point. 

The elemental halogens are usually obtained by the oxidation of halide ions. Chlorine, bromine and iodine are made industrially by the oxidation of the aqueous halides in brines or seawater. With chlorine, the oxidation is electrolytic with bromine and iodine, chlorine is the oxidizing agent. Industrial fluorine is made by the electrolytic oxidation of a conducting, liquid blend of KF and HF. 

Many of the reactions of halogens can be considered as either oxidation or displacement reactions the redox potentials (Table 11.2) give a clear indication of their relative oxidising power in aqueous solution. Fluorine, chlorine and bromine have the ability to displace hydrogen from hydrocarbons, but in addition each halogen is able to displace other elements which are less electronegative than itself. Thus fluorine can displace all the other halogens from both ionic and covalent compounds, for example... 

Halogens can act as ligands and are commonly found in complex ions the ability of fluorine to form stable complex ions with elements in high oxidation states has already been discussed (p. 316). However, the chlorides of silver, lead(Il) and mercury(l) are worthy of note. These chlorides are insoluble in water and used as a test for the metal, but all dissolve in concentrated hydrochloric acid when the complex chlorides are produced, i.e. [AgCl2] , [PbC ] and [Hg Clj]", in the latter case the mercury(I) chloride having also disproportionated. 

Perfluorinated organic bromides can be oxidatively fluonnated with elemental fluorine to derivatives containing tn- [124] and pentavalent [/25 126 127] bromine in yields up to 42% Perfluoroheptylbromine tetrafluoride has been used to fluonnate double bonds in halogenated alkenes [127]... 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

The (compositionally) simplest mineral class comprises the native elements, that is, those elements, either metals or nonmetals that occur naturally in the native state, uncombined with others. Native gold, silver, and copper, for example, are metals that naturally occur in a ductile and malleable condition, while carbon - in the form of either graphite or diamond -and sulfur are examples of nonmetallic native elements. Next in compositional complexity are the binary minerals composed of two elements a metal or nonmetallic element combined with oxygen in the oxides, with a halogen - either fluorine, chlorine bromine, or iodine - in the halides, or sulfur, in the sulfides. The oxide minerals, for example, are solids that occur either in a somewhat hard, dense, and compact form in mineral ores and in rocks, or as relatively soft, unconsolidated sediments that melt at moderate to... 

In order to minimize the degradation of macromolecules, the choice of solvent is not a trivial matter. Hydrogen-containing solvents are obviously not suitable, but even halogenated ones such as CFC13 or CC12FCF2C1, usually stable to fluorine, can react violently with this element when irradiated at temperatures near 0°C. We chose two perfluorinated solvents that have been proven safe and suitable for radical fluorination perfluoro-2-(butyl)-tetrahydro-duran (FC-75 Fluorinert from 3M) and hexafluoropropylene oxide (HFPO) oligomers known as Krytox +... 

Thus one can draw the conclusion that there is no element in the periodic table, including other halogens and oxygen, that possesses stronger oxidizing properties than fluorine, which is really at the head of the oxidants series ... 

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