Fluorine gas

Continuous monitoring for the presence of fluorine gas in the workplace may be accompHshed using detectors available from Mine Safety Apphances (Pittsburgh, Pa.) or FIT (Exton, Pa.). 

Burns. Skin bums resulting from contact with pure fluorine gas are comparable to thermal bums and differ considerably from those produced by hydrogen fluoride (114). Fluorine bums heal much more rapidly than hydrofluoric acid bums. 

Fig. 5. Equipment foi surface treating plastic components. Parts ate loaded into one of the two lower chambers which is then evacuated to remove most of the air. This chamber is then flooded with a dilute mixture of fluorine and nitrogen which is made and stored in the upper chamber. After the treatment is completed, the fluorine mixture is pumped back up to the upper chamber for storage and the lower chamber repeatedly flooded with air and evacuated to remove any traces of fluorine gas. Two treatment chambers are cycled between the loading/unloading operation and the treatment step to increase equipment output. The fluorine—nitrogen blend may be used several times before by-products from the treatment process begin to interfere. AH waste...

An equiHbrium exists between chlorine trifluoride, chlorine monofluoride, and fluorine gas (38). The equiHbrium constant may be expressed as... 

In another process (105), fluorine gas reacts under pressure with Hquid I2 held above its melting poiat (113°C) but below a temperature (150°C) that would result ia the formation of significant amouats of IF. Fluorine is added coatiauously uatil all the iodiae has beea coaverted and yields of IF ia excess of 95% are reported. The reaction pressure is ca 300 kPa (3 atm) so that the IF produced ia the reaction is maintained as a Hquid. 

Direct Fluorination. This is a more recently developed method for the synthesis of perfluorinated compounds. In this process, fluorine gas is passed through a solution or suspension of the reactant in a nonreactive solvent such as trichlorotrifluoroethane (CFC-113). Sodium fluoride may also be present in the reaction medium to remove the coproduct hydrogen fluoride. There has been enormous interest in this area since the early 1980s resulting in numerous journal pubHcations and patents (7—9) (see Fluorine compounds, organic-direct fluorination). Direct fluorination is especially useful for the preparation of perfluoroethers. 

Direct fluorination involves the treatment of an appropriate hydrocarbon precursor dissolved in an inert Hquid with fluorine gas to yield a perfluorinated precursor to a long-chain carboxyflc acid. Equations 2 and 3 illustrate the process for perfluorooctadecanoic acid (17). 

Unlike ECF, direct fluorination does not alter the carbon backbone preparation of isomerically pure acids is possible (18). Both direct fluorination and ECF permit a great variety of stmctures to be made, but each method is better at certain types of stmctures than the other. Ether acids are produced in good yields, by direct fluorination (17), while ECF of ether-containing acids is fair to poor depending on the substrate. Despite much industrial interest, the costs and hazards of handling fluorine gas have prevented commercial application of this process. 

Manufacture. One commercial process features a three-stage saturation—rearomatization technique using benzene and fluorine gas as raw materials (73). Principal problems with this method are the complex nature of the process, its dependence on fluorine gas which is cosdy to produce, and the poor overall utilization of fluorine, because nearly one-half of the input fluorine is removed during the process. 

Silver(III) Compounds. No simple silver(Ill) compounds exist. When mixtures of potassium or cesium haUdes are heated with silver hahdes ia a stream of fluorine gas, yellow KAgF [23739-18-6] or CsAgF [53585-89-0] respectively, are obtained. These compounds are diamagnetic and extremely sensitive to moisture (21). When Ag2S04 is treated with aqueous potassium persulfate ia the presence of ethylenedibiguanidinium sulfate, the relatively stable Ag(Ill)-ethylenebiguanide complex is formed. 

Saturated hydrocarbons such as neopentane, notbomane, and cyclooctane have been converted to the corresponding perfluoro derivatives in 10-20% yield by gas-phase reaction with fluorine gas diluted with helium at —78°C. Simple ethers can be completely fluorinated under similar conditions. Crown polyethers can be fluorinated by passing an Fa/He stream over a solid mixture of sodium fluoride and the crown ether. Liquid-phase fluorination of hydrocarbons has also been observed, but the reaction is believed to be ionic, rather than radical, in character. A variety of milder fluorination agents have been developed for synthetic purposes and will be discussed in Chapter 6 of Part B. 

Fluorine is the most reactive of all elements, in part because of the weakness of the F—F bond (B.E. F—F = 153 kj/mol), but mostly because it is such a powerful oxidizing agent (E ed = +2.889 V). Fluorine combines with every element in the periodic table except He and Ne. With a few metals, it forms a surface film of metal fluoride, which adheres tightly enough to prevent further reaction. This is the case with nickel, where the product is NiF2. Fluorine gas is ordinarily stored in containers made of a nickel alloy, such as stainless steel (Fe, Cr, Ni) or Monel (Ni, Cu). Fluorine also reacts with many compounds including water, which is oxidized to a mixture of 02> 03> H202, and OF2. 

If an electrolytic cell producingfluorineusesacurrentof7.00 X 103 A (at 10.0 V), how many grams of fluorine gas can be produced in two days (assuming that the cell operates continuously at 95% efficiency) ... 

Any pure gas, when cooled sufficiently, will condense to a liquid and then, at a lower temperature, will form a solid. There is great variance in the temperature at which this condensation occurs. Apparently there is a corresponding variance of the forces in liquids and solids. For example, lithium fluoride gas at one atmosphere pressure condenses when cooled below 1949°K. When the temperature is lowered to 1143°K, the liquid forms a clear crystal. In contrast, lithium gas at this pressure must be cooled to 1599°K before it forms a liquid and this liquid does not solidify until the temperature reaches 453°K. The solid is a white, soft metal, not resembling crystalline lithium fluoride at all. Fluorine gas is equally distinctive. At one atmosphere pressure it must be cooled far below room temperature before condensation occurs, at 85°K. Then the liquid solidifies to a crystal at 50°K. Why do these three materials behave so differently Can we understand this great variation Let us begin by finding a common point of departure. 

The syn addition of pentafluoroethyl hypofluorite (CF3CF2OF), generated in situ by the action of anhydrous, hydrogen-fluoride-free fluorine gas on sodium trifluoroacetate, to 5-acetyl-5//-dibenz[/i,/]azepine (11) has been reported to yield 12.135... 

CF) is prepared by the reaction of carbon powder with fluorine gas at an elevated temperature. The properties of (CF) are similar to those of polytetrafluoroeth-ylene (PTFE) which is prepared by organic synthesis. 

There is also oxifluorination that is a process in which fluorine gas is thinned with nitrogen to which several percent of oxygen by volume have been added. Subjecting PE to fluorine and oxygen at the same time leads to functionalization of the PE, making it impermeable. This technique permits substantially reducing the required amount of fluorine, resulting in a cost-to-performance improvement. 

In recent years, fluorine bomb calorimetry has been used effectively. A number of substances that will not burn in oxygen will burn in fluorine gas. The heat resulting from this fluorine reaction can be used to calculate AfH°m. For example, Murray and 0 Hare have reacted GeS2 with fluorine and measured ArH°. The reaction is... 

As well as a bonding pair of electrons, a fluorine molecule also possesses lone pairs of electrons that is, pairs of valence electrons that do not take part in bonding. The lone pairs on one F atom repel the lone pairs on the other F atom, and this repulsion is almost enough to overcome the favorable attractions of the bonding pair that holds the atoms together. This repulsion is one of the reasons why fluorine gas is so reactive the atoms are bound together as F2 molecules only very weakly. Among the common diatomic molecules, only H2 has no lone pairs. 

C08-0076. Calculate the overall energy change for the formation of lithium fluoride from lithium metal and fluorine gas. hi addition to data found in Appendix C and Table 8-4. the following information is needed The bond energy of F2 is 155 kJ/mol, and lithium s enthalpy of vaporization is 159.3 kJ/mol. 

Accordingly, for decades scientific investigations have been carried out to achieve the direct fluorination which would be attractive as a one-step synthesis alternative. Although the early reports concerned gas-phase direct fluorinations, the most relevant work in the last three decades was based on contacting fluorine gas with the aromatic compound dissolved in a liquid phase. These attempts at gas/liquid... 

Many expensive reductions such as the Birch reduction of naphthalene to isotetralin, benzene to cyclohexene, with metallic sodium and liquid ammonia, or reduction with LiAlHa, can generally be carried out electrochemically at much lower cost and under safe conditions. Electrochemical processes allow fluorinations to be carried out without using fluorine gas. Conducting polymers have been made by electrochemical processes which operate under ambient conditions, and the polymer can be synthesized, doped and shaped in film form in a single step. 

Treatment of liquid air (containing condensed atmospheric moisture) with fluorine give a potentially explosive precipitate, thought to be fluorine hydrate [1], Contact of liquid fluorine with a bulk of water causes violent explosions. Ice tends to react explosively with fluorine gas after an indeterminate induction period [2],... 

Sodium ignites in fluorine gas but is inert in the liquefied gas [1]. Cold sodium ignites in moist chlorine [2] but may be distilled unchanged in the dry gas [1]. Sodium and liquid bromine appear to be unreactive on prolonged contact [3], but mixtures may be detonated violently by mechanical shock [4]. Finely divided sodium luminesces in bromine vapour [1], Iodine bromide or iodine chloride react slowly with sodium, but mixtures will explode under a hammer-blow [1]. Interaction of iodine pentafluoride with solid sodium is initially vigorous, but soon slows with film-formation, while that with molten sodium is explosively violent... 

La-Mar [Named after the inventors, R. J. Lagow and J. L. Margrave] A process for flu-orinating organic compounds, using fluorine gas at low partial pressures. Commercialized by the 3M company. 

Assume that 185.00 grams of fluorine gas and 4.0 moles of xenon gas are contained in a... 

In studying the reactivity of iV-fluoropyridinium fluoride 127 obtained from pyridine 126 by treatment with fluorine gas in chloroform at low temperature (Scheme 30), Kiselyov studied reactions with isocyanides in the presence of trimethylsilylazide <2005TL4851>. A mixture of products was obtained in which, besides tetrazolylpyr-idine 128 and a nicotinamide derivative 129 also tetrazolo[l,5-tf]pyridine 1 was obtained in very poor yield (5-10%). 

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