Fluorine and chlorine

Fluorine occurs in waters largely in the form of the simple anion F, sometimes also as hexafluorosilicates SiFg and complex compounds with metals, particularly with Fe(III) and Al(III) (fluoroferrates and lluoroalumi-nates). The concentration of fluorides in waters is limited by the solubility of CaF2 and MgF2. As CaF2 is less soluble than MgF2 the equilibrium concentration of fluorides in water depends primarily on the concentration of calcium. 

The concentration of fluorides in natural waters ranges from hundredths to tenths mg 1. Concentrations exceeding 1 mg 1 are exceptional. 

Fluorine in waters is of special hygienic importance from the viewpoint of stomatology. Health disorders can occur in the case of both deficiency and excess of fluorine in drinking water. At higher concentrations a chronical disease occurs — fluorosis which is manifested by spots on the teeth dential fluorosis). Therefore, the limiting content of fluorides in drinking water is 

Mineral waters with a concentration of fluorides more than 2.0 mg 1 are called fluorine (fluoride) waters. 

Chlorine is present in waters primarily in the form of the simple Cl anion, and in some cases also in the form of chloro complexes, for example, [FeCl]+, [FeClj] , [FeCl] +, [FeClg] , [FeCl4] , etc. Of other forms of occurrence of chlorine, elementary chlorine, non-dissociated hypochlorous acid HCIO, CIO anion and different chloramines should be considered, followed by organically bonded chlorine which may originate from the waste-waters of chemical industry, and from chlorinated pesticides. However, it can also enter the water via the chlorination of polluted waters. 

Radiolysis and photodecomposition of chlorite and chlorate have been studied in aqueous solution. Reaction schemes, rate constants, and quantum yields are reported.The first stage in the reaction of chlorine with phenol is the second-order formation of [CI2 PhOH], with a rate constant 2 = 2.3 x 10 lmol- s at 5 °C. This [Clg-PhOH] intermediate, whose properties are similar to those of known charge-transfer compounds of halogens with aromatic compounds, decomposes by three parallel pathways. Chlorine reacts more slowly with chlorophenols than with phenol itself. The reaction of chlorine dioxide with phenol follows a comparable rate law  

Exchange between chloride ion and chlorine in aqueous solution can be monitored by n.m.r. spectroscopy below about —35 °C above this temperature linewidths are controlled by relaxation processes rather than by chemical exchange. The chemical exchange takes place via the equilibrium 

---

Seel M and Bagus P S 1983 Ah initio cluster study of the interaction of fluorine and chlorine with the Si(111) surface Phys. Rev. 28 2023-38... 

Barone M E and Graves D B 1995 Molecular dynamics simulations of direct reactive ion etching of silicon by fluorine and chlorine J. Appi. Phys. 78 6604-15... 

Evidence for the solvated electron e (aq) can be obtained reaction of sodium vapour with ice in the complete absence of air at 273 K gives a blue colour (cf. the reaction of sodium with liquid ammonia, p. 126). Magnesium, zinc and iron react with steam at elevated temperatures to yield hydrogen, and a few metals, in the presence of air, form a surface layer of oxide or hydroxide, for example iron, lead and aluminium. These reactions are more fully considered under the respective metals. Water is not easily oxidised but fluorine and chlorine are both capable of liberating oxygen ... 

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

Calculations for CHON Species. Journal of the American Chemical Society 97 1302-1306. i iiigliam R C, M J S Dewar and D H Lo 1975d. Ground States of Molecules. XXVIII. MINDO/3. -alculahons for Compounds Containing Carbon, Hydrogen, Fluorine and Chlorine. Journal of the -American Chemical Society 97 1307-1310. 

Compounds containing fluorine and chlorine are also donors to BF3. Aqueous fluoroboric acid and the tetrafluoroborates of metals, nonmetals, and organic radicals represent a large class of compounds in which the fluoride ion is coordinating with trifluoroborane. Representative examples of these compounds are given in Table 5. Coordination compounds of boron trifluoride with the chlorides of sodium, aluminum, iron, copper, 2inc, tin, and lead have been indicated (53) they are probably chlorotrifluoroborates. 

Chlorine Trifluoride. Chlorine trifluoride is produced commercially by the continuous gas-phase reaction of fluorine and chlorine ia a nickel reactor at ca 290°C. The ratio of fluorine to chlorine is maintained slightly in excess of 3 1 to promote conversion of the chlorine monofluoride to chlorine trifluoride. Sufficient time ia the reactor must be provided to maintain high conversions to chlorine trifluoride. Temperature control is also critical because the equiHbrium shift of chlorine trifluoride to chlorine monofluoride and fluorine is significant at elevated temperatures. 

Cooled dust-laden gas is dedusted in an electrostatic precipitator and sent to the cleaning unit to remove impurities such as arsenic, fluorine, and chlorine before being sent on to the sulfuric acid production plant. 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

A special precaution is imperative in handling elemental fluorine and chlorine tnfluoride. Both gases are extremely corrosive and so reactive that they are very seldom used without dilution with inert gases such as nitrogen, helium, or argon. Fluorine is now available in mixtures with nitrogen. Fluorine is very toxic in... 

Elements such as oxygen, nitrogen, fluorine, and chlorine are more electronegative than carbon, so a carbon atom bonded to one of these atoms has a partial positive charge ( -1-). Conversely, metals are less electronegative than... 

The fluoride and chloride ions are very difficult to oxidize (Elx F = —2.889 V E°x Cl- = —1.360 V). Hence the elements fluorine and chlorine are ordinarily prepared by electrolytic oxidation, using a high voltage. As pointed out in Chapter 18, chlorine is prepared by the electrolysis of aqueous sodium chloride ... 

Oxidation through electrolysis is used to make fluorine and chlorine. Chlorine, for example, is... 

C. Powdered osmium is slowly attacked by oxygen at room temperature, yielding 0s04 (though not below 400°C if in bulk). Osmium reacts with fluorine and chlorine at about 100°C. Both metals are attacked by molten alkalis and oxidizing fluxes. 

Comparative x-ray absorption measurements were used in the identification of various new compounds that could contain at most the following elements carbon, hydrogen, fluorine, and chlorine. The presumed composition of each compound, known in advance, was duplicated by properly blending carbon tetrachloride, benzotrifluoride, heptane, and benzene the latter also was used as solvent for the unknown. Under conditions intended to be identical, the amount of unknown... 

C03-0004. Write the chemical formula for each of the following substances (a) stearic acid, whose molecules contain 36 hydrogen atoms, 18 carbon atoms, and 2 oxygen atoms (b) silicon tetrachloride, whose molecules contain one silicon atom and four chlorine atoms and (c) Freon-113, whose molecules contain three atoms each of fluorine and chlorine and two atoms of carbon. 

C09-0136. Sulfur forms neutral compounds with oxygen, fluorine, and chlorine that display a variety of steric... 

Although they have the same bonding patterns, bromine and iodine differ from chlorine and fluorine in their macroscopic physical appearance and in their molecular behavior. As Figure 11-1 shows, at room temperature and pressure, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. 

Carbon electrodes are widely used in electrochemistry both in the laboratory and on the industrial scale. The latter includes production of aluminium, fluorine, and chlorine, organic electrosynthesis, electrochemical power sources, etc. Besides the use of graphite (carbons) as a virtually inert electode material, the electrochemical intercalation deserves special attention. This topic will be treated in the next paragraph. 

Farrar, R. L. et al., Some Considerations in Handling Fluorine and Chlorine Fluorides, Oak Ridge Rept. K/ET-252, 1979, 41pp... 

Both yellow and red phosphorus ignite on contact with fluorine and chlorine red ignites in liquid bromine or in a heptane solution of chlorine at 0°C. Yellow phosphorus explodes in liquid bromine or chlorine, and ignites in contact with bromine vapour or solid iodine [1]. Interaction of bromine and white phosphorus in carbon disulfide gives a slimy by-product which explodes violently on heating [2], Interaction of phosphorus and iodine in carbon disulfide is rather rapid [3], A less hazardous preparation of diphosphorus tetraiodide from phosphorus trichloride and potassium iodide in ether is recommended [4],... 

Typically, intense chemiluminescence in the UV/Vis spectral region requires highly exothermic reactions such as atomic or radical recombinations (e.g., S + S + M - S2 + M) or reactions of reduced species such as hydrogen atoms, olefins, and certain sulfur and phosphorus compounds with strong oxidants such as ozone, fluorine, and chlorine dioxide. Here we review the chemistry and applications of some of the most intense chemiluminescent reactions having either demonstrated or anticipated analytical utility. 

The usual oxidizer in the fire triangle is oxygen in the air. However, gases such as fluorine and chlorine liquids such as peroxides and chlorates and solids such as ammonium nitrate and some metals can serve the role of an oxidizer. Exothermic decomposition, without oxygen, is also possible, e.g., with ethylene oxide or acetylene. 

Fluorine and chlorine are the only important choices for the labile substituents on a heterocyclic reactive system but numerous other leaving groups have been patented, mostly as substituent on an s-triazine ring. These include sulpho, cyano, thiocyanato, azido and trichloromethyl [26], as well as more elaborate groupings (Figure 7.2). Such derivatives are... 

---