Halogens, elemental fluorination

Halides are compounds that include one of the halogen elements fluorine, chlorine, bromine, or iodine. The simplest halides are combinations of one element, such as sodium (Na), with a halogen element, such as chlorine (Cl). Complex halides combine two or more elements with a halogen, and some contain water. Some halides are economically important minerals, such as halite (common salt), fluorite (fluorine), and chlorargyrite (silver ore). 

Carbon atoms form bonds readily with hydrogen, oxygen, and nitrogen. Carbon also may combine with halogen elements (fluorine, chlorine, bromine, iodine), with phosphorus and sulfur, and, less often, with other elements. 

Figure 7 The halogen element fluorine has seven electrons in its outer energy level.

Chemical Properties. A combination of excellent chemical and mechanical properties at elevated temperatures result in high performance service in the chemical processing industry. Teflon PEA resins have been exposed to a variety of organic and inorganic compounds commonly encountered in chemical service (26). They are not attacked by inorganic acids, bases, halogens, metal salt solutions, organic acids, and anhydrides. Aromatic and ahphatic hydrocarbons, alcohols, aldehydes, ketones, ethers, amines, esters, chlorinated compounds, and other polymer solvents have Httle effect. However, like other perfluorinated polymers,they react with alkah metals and elemental fluorine. 

The tetrahedrally bonded materials, such as Si and Ge, possess only positional disorder however, materials of this type exhibit high density of defect states (DOS). It is only with the addition of elements such as hydrogen and/or a halogen, typically fluorine, that the DOS is reduced to a point such that electronic device appHcations emerge. These materials contain up to - 10 atomic % hydrogen, commonly called hydrogenated amorphous siHcon (i -Si H). 

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]... 

Now let s slide to the left in the periodic table and consider the column of elements fluorine, chlorine, bromine, iodine, and astatine. Each of these elements has one less electron than does its neighboring inert gas. These elements are called the halogens. (The discussion that follows does not include astatine because this halogen is very rare.)... 

The halogens include fluorine, chlorine, bromine and iodine and all have been used in CVD reactions. They are reactive elements and exist as diatomic molecules, i.e., F2, CI2, etc. Their relevant properties are listed in Table 3.2. 

Of all the elements, fluorine is the most chemically reactive. It combines directly with other elements. Chlorine is slightly less reactive. Both are gases at room temperature which is an important advantage in delivery and metering. Because of their reactivity, they form halides readily, but also attack most materials which makes them difficult to handle and requires equipment designed with inert materials such as Monel or Teflon. Halogens are also toxic, fluorine more so than chlorine by an order of magnitude. 

Halogens The elements—fluorine, chlorine, bromine, iodine, and astatine—that make up Group 17 of the periodic table. 

The introduction of the halogens onto aromatic rings by electrophilic substitution is an important synthetic procedure. Chlorine and bromine are reactive toward aromatic hydrocarbons, but Lewis acid catalysts are normally needed to achieve desirable rates. Elemental fluorine reacts very exothermically and careful control of conditions is required. Molecular iodine can effect substitution only on very reactive aromatics, but a number of more reactive iodination reagents have been developed. 

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... 

Halon is a halogenated compound that contains elements from the halogen series - fluorine, chlorine, bromine and iodine. Halogen atoms from noncombustible gases when they replace... 

PTFE, FEP and PFA are attacked only by alkaline metals and their organic derivatives elemental fluorine and chlorine trifluoride alkali and alkaline earth metals with their oxides and carbonates above 350°C. The other halogens, aqua regia, nitrosulfuric acid mixtures, oleum (fuming sulfuric acid) and solvents are without significant effects. 

A good fuel will react with oxygen (or a halogen like fluorine or chlorine) to form a stable compound, and substantial heat will be evolved. The considerable strength of the metal-oxygen and metal-halogen bonds in the reaction products accounts for the excellent fuel properties of many of the metallic elements. 

Elemental fluorine, which is a member of the halogen family, is a pale yellow-green, irritating gas with a sharp odour and atomic mass of 18.998. Fluorine is chemically most reactive of all the elements and does not therefore occur naturally in the free state. In combination it comprises 0.065% of the earth s crust, being the 13th element in abundance [1], and is an inevitable part of the biosphere and human life. The term fluorine is, in this report, used to denote the element in any of its forms and fluoride to denote free inorganic fluoride to which a fluoride ion-selective electrode (ISE) responds. 

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. 

Attempts to manufacture anhydrous mercury(II) fluoride by methods more conventional than the action of elemental fluorine upon mercury(II) chloride (vide supra) showed that aqueous reagents invariably yielded a dihydratc salt which could not be converted into anhydrous mer-cury(II) fluoride, because it always eliminated hydrogen fluoride in preference to water. In an effort to circumvent this, mercury(II) fluoride generated in situ has been used as the reagent for the substitution of one or several halogens by fluorine in various types of compounds (see Houben-Weyl, Vol. 5/3, p202 for pre-1959 reports). 

Free-radical halogenation of hydrocarbons induced thermally or photochemically can be performed with all four halogens, each exhibiting certain specificities. Because of the thermodynamics of the process, however, only chlorination (and bromination) are of practical importance.31,106-108 Fluorination with elemental fluorine is also possible. This reaction, as discussed above (see Section 10.1.1), follows an electrophilic mechanism in the solution phase.109,110 Under specific conditions, however, free-radical fluorination can be performed. 

As towards hydrogen so towards sulphur the affinity of the halogen elements rapidly decreases on passing from fluorine to iodine. Sulphur hexafluoride, SF6, is a stable substance, whereas the highest chlorine derivative which has been isolated is the unstable tetrachloride, SC14 sulphur monobromide, S2Br2, is the only bromide of sulphur known, whilst sulphur and iodine do not form any definite compound. 

All the halogen elements combine with tellurium. The powdered crystalline form is inflamed by fluorine in the cold 1 and by warm chlorine, the product in the latter case being the tetrachloride.2 With bromine the product is the dibromide, whilst iodine reacts only at a higher temperature, giving a tetra-iodide. Hydrogen chloride does not affect the element. 

The halogens (except fluorine) exhibit both electron-accepting and electron-re-leasing behaviors. Since they resemble the noble gas elements only in regard to electron releasing, this aspect of the chemistry of the two families will be discussed first. The more familiar acceptance of electrons by halogens is discussed later in the chapter. 

A very diversified art has been developed utilizing certain metal fluorides, inorganic fluorides, halogen fluoride, or electrochemical cells as media for fluorination. The more important approaches which have been developed to produce fluorocarbons and yet avoid the great reactivity of elemental fluorine are ... 

Reduction of the carbon-halogen bond is an important synthetic reaction in organic chemistry. The importance of the reduction has been enhanced in recent years by the application of a wide range of newly available reductants. However, in the case of fluorine, the reduction is of less importance than for the other halogens. Reviews on the reduction of fluorine bonds have appeared mainly in the more specialized literature,1 4 though some aspects of the subject have formed parts of reviews of the broader topic of hydrogenation, reduction, or substitution.5,6 This section does not include patent literature and all literature data. It is thus selective, not exhaustive, and includes representative examples of the most commonly used procedures for the reduction of C-F and element-fluorine bonds. 

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