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View Preview. Detail surveys of them have been provided by several reviews. In , General Motors Corporation, manufacturers of refrigerators, appointed McNary, Midgley and Henne to the task of finding inert refrigerants. Until then, available conventional refrigerants had serious drawbacks: some were flammable, others like SO 2 were corrosive and toxic, and still others like NH 3 combined all three hazards.
In the meantime, General Motors had approached E. In , a joint corporation, Kinetic Chemicals Inc. Application of the new compound was successful, and by the end of , Kinetic Chemicals had expanded its facilities, and begun manufacture of anhydrous hydrofluoric acid, a basic raw material Eq. In , this reaction was improved and employed for the synthesis of chlorofluoromethanes, the fluorinated derivatives of chloroform Eq.
This compound later became very important as the precursor of tetrafluoroethylene TFE. He weighed the cylinder and it was the same as before. Plunkett then cut the cylinder open and discovered a waxy substance formed inside. Plunkett realized that the exact combination of pressure and cold temperature, along with the age of the gas in a cylinder, had allowed the TFE gas molecules to polymerize to give this product PTFE with such potentially useful characteristics.
Chemists and engineers in the Central Research Department of DuPont investigated the substance further. Although PTFE is the best known fluoropolymer nowadays, it was not the first of the fluoroplastics to be prepared. At that time, fluoropolymers were so expensive to produce that all believed they would never find a market.
Their features were striking in fulfilling the requirements of the gaseous diffusion process of the Manhattan project at Columbia University in New York City during World War II and the fluoropolymers were first used as materials that could tolerate fluorine or its derivative uranium hexafluoride UF 6.
Even after the isolation of fluorine by Moissan in , the difficulties in research using fluorine discouraged most chemists, and it was not until World War II when development was undertaken. The first large-scale production of fluorine was carried out for the atomic bomb Manhattan project which needed UF 6 as a gaseous carrier of uranium to separate the U and U isotopes of uranium.
UF 6 was almost as reactive as elemental fluorine. In order to use it in a gas-diffusion plant, a wide range of materials which would not react with UF 6 remained to be developed. These would include relatively low molecular weight liquids for coolants; higher molecular weight materials for lubricants; and polymers that could be fabricated into gaskets, valve packings and tubing.
A 2 mL sample of liquid fluorocarbon was sent from Simons to Urey at Columbia University and tested to show that it had the desired properties. Several methods were subsequently developed. The first major process was a catalytic fluorination process using fluorine. However, it was found extremely difficult to extend this process to large-scale production. Another and principal method was the metallic fluoride process, which employs cobalt trifluoride CoF 3 , in particular. Ruff et al. Cobalt difluoride CoF 2 is co-produced but is converted with elemental fluorine to cobalt trifluoride.
An entirely different approach was also carried out: the electrochemical fluorination ECF process for producing fluorocarbons. ECF was invented by Simons, 46 but was not reported until for security reasons associated with the Manhattan project. Further study of ECF was carried out after the launch of fluorocarbons, and product line was extended to production of fluorocarbon derivatives possessing functional groups: perfluoroethers, perfluoroacyl fluorides, perfluoroalkanesulfonyl fluorides, and perfluorinated amines. Perfluoroalkyl iodides, which are synthesized by the telomerization method Eq.
However, it cannot be processed by conventional melt techniques. This difficulty was overcome by FEP. Polymers with partially-fluorinated monomers, that is, PVdF poly vinylidene fluoride was developed in DuPont in and commercialized in The monomers are produced by a route shown in Scheme 2.
The majority of commercial homopolymers nowadays are produced from only four monomers discussed above: tetrafluoroethylene TFE , chlorotrifluoroethylene CTFE , vinyl fluoride VF , and vinylidene fluoride VdF. Perfluorinated polymers are prepared by a free-radical polymerization reaction in water or in a fluorinated solvent.
ETFE is mainly used for insulation of electric cable, and also provides tough and flexible film which is used for architectural area. However, perfluorinated vinyl ethers were found to react with TFE to give copolymers. It is made of the polymer prepared by copolymerization of TFE and the functional perfluorovinyl ether, which is derived from HFPO as shown in Scheme 4.
The sea around Kyushu, Japan, turned out to be the site of an outbreak of Minamata Disease, said to be one of the worst cases of mercury poisoning in history. This incident caused deep concern about chemical production processes. The key was a central membrane that allow only specific ions to pass through. When sodium chloride NaCl is electrolyzed to produce sodium hydroxide NaOH , a violent situation to the membrane with strong alkali occurs.
Only a membrane made from fluoropolymer could withstand this reaction. The perfluorinated carboxylic acid membrane consists of a copolymer of TFE and perfluorinated vinyl ether, which has a carboxylic acid group in the side chain. The manufacturing process is shown in Scheme 5.
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Moreover, the energy consumption of electrolysis processes was dramatically reduced by developing an advanced electrode. Common plastics are made from a variety of organic materials, but the use of these materials should be minimized for reducing environmental burden. One way is to ensure products last longer. For example, for outdoor coating products that are exposed to outdoor environment, durable fluorinated materials are used.
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The added fluorinated structure enabled to create surprisingly durable coating materials. The outstanding resistance to violent chemicals in ion-exchange membranes and the excellent weatherability are derived from high stability of C-F bonds. Any oxidants or chemicals hardly attack the fluorine-substituted carbons. However, this stability was backfired in chlorofluorocarbons CFCs. Studies have shown that in the deep blue sky, CFCs and other substances released into the atmosphere are causing damage to the ozone layer.
CFCs are so stable substances that they moved far into the upper atmosphere, causing the destruction of the ozone layer. Carbon—chlorine bond cleavage of CFCs by UV light generates radical species, which cause ozone depletion, whereas C-F bonds are stable even in the stratosphere.
It was therefore necessary to find alternative CFCs that possess carbon-hydrogen bonds, which are cleaved before they reach the stratosphere. CFCs had three main applications: Refrigerants for air conditioners and refrigerators, blowing agents for urethane foaming, and precision equipment cleaning agents. The innovative development was assisted by not only conventional experimental chemistry but computer chemistry technologies and the most appropriate alternative to CFC was selected from thousands of candidate materials, then actually synthesized by modified Prins reaction of TFE and CHCl 2 F HCFC Eq.
Thus, organofluorine chemistry plays important roles in minimization of environmental impact and in production of various materials for industrial use such as thermoplastics, elastomers, membranes, textile finishes, coatings. Fluorine is the most electronegative element in the periodic table. When bound to carbon, it forms the strongest bonds in organic chemistry.
This makes introduction of fluorine attractive for the development of material science. Although highly polarized, the C-F bond gains stability from the resultant electrostatic attraction between C and F atoms. Therefore, normal metabolism in a living body is easily inhibited as well block effect by such strong bonds. On the other hand, the van der Waals radius of fluorine is similar to that of hydrogen. Accordingly, organofluorine compounds are similar in steric size to non-fluorinated ones but quite different in electronic nature. As a living body can not sterically distinguish fluorinated molecules from the corresponding non-fluorinated one, fluorinated molecules are incorporated into metabolic sequences in a manner similar to that of non-fluorinated one mimic effect.
However, since the C-F bond in the fluorinated molecule resists the metabolism common with the parent compound due to opposite polarization, the normal metabolism in a living body is inhibited to cause various biological effects. This makes fluorine substitution attractive for invention of pharmaceuticals and agrochemicals. There are many applications.
For examples, inhalation anesthetics 15 are synthesized by classical halogen exchange reactions. Elemental fluorine was first prepared in small quantities by Henri Moissan in by electrolysis of anhydrous hydrogen fluoride. However, only decomposed products resulted and, occasionally, explosions occurred. In the early 20th century, it was very difficult to control the reactions with fluorine because of the violence in nature. For example, in , Bancroft and Jones reported explosions during attempted fluorination of benzene and toluene with molecular fluorine.
In , Bancroft and Wherty tried the fluorination of benzene again using fluorine diluted with nitrogen. The explosion was avoided, though they obtained only tarry products. During World War II, the first sample of fluorocarbons, found to be inert towards UF 6 , had been made by direct reaction between carbon and elemental fluorine catalyzed by mercury. It was used on a semi-technical scale for production of perfluoropropane, which is used as a dry plasma etchant in microelectronics industry.
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The concentration of fluorine and the reaction temperature are slowly increased over a period of several days to permit perfluorination. This batch process requires relatively long reaction times to obtain perfluorinated material. Some years later, Adcock invented a flow version, an aerosol fluorination process. This process has an advantage that it is a continuous flow method and the control of reaction parameters are easier.
In fact, in the liquid-phase direct fluorination process, the reactant is injected at a very slow constant rate into an inert fluorocarbon solvent saturated by fluorine. It is pointed out to be very important that a large excess of F 2 relative to hydrogen atoms to be replaced in a substrate should be maintained. This method is, however, only suitable for the perfluorination of substrates, such as partially fluorinated ethers and amines, both soluble in a perfluorocarbon solvent and can withstand such vigorous reaction conditions.
Almost the same time, Exfluor Corporation claimed that various ethers and esters are perfluorinated without UV irradiation Exfluor-Lagow method.
The Exfluor-Lagow method involves slow addition of both a hydrocarbon substrate and fluorine in excess into a vigorously stirred chlorofluorocarbon CFC or a perfluorinated inert solvent. If required, the reaction is accelerated by adding a small quantity of a highly reactive hydrocarbon such as benzene, which reacts spontaneously with fluorine to produce a very high concentration of fluorine radicals that ensure perfluorination of substrates. The Exfluor-Lagow elemental fluorine process can give products of the liquid-phase fluorination process in high yields.
However, reaction solvents are limited to now-regulated CFCs, particularly for direct fluorination of substrates which contain functional group s in the structure because of solubility problem. Partially fluorinated substrates are more stable towards the fluorination process, since solubility increases, and presence of a polyfluoroalkyl group significantly lowers the oxidation potential of the substrates. Consequently, perfluorinated compounds are generally produced in higher yields than the corresponding non-fluorinated compounds.
This method was applied to preparation of perfluoro ethers. Considering these results, it is suggested that direct fluorination method had almost reached an adequate standard level for monomer synthesis in industry. Okazoe et al. However, it was found hard to reproduce the results.
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In order to solve this problem, they have developed an entirely new method that involves combination of direct fluorination and organic synthesis, perf luorination of e sterified c ompounds followed by t hermolysis, abbreviated as PERFECT Scheme 7. This contrasts sharply to that of non-fluorinated compounds. Thus, available perfluoro alkoxyalkanoyl fluorides such as perfluoro 2-propoxypropionyl fluoride can be multiplied by use of the hydrocarbon counterpart alcohols and fluorine gas as raw materials Scheme 7.
In the case that the desired perfluoro alkoxyalkanoyl fluoride is not readily available, it can be obtained from its hydrocarbon counterpart alcohol and an available perfluoroacyl fluoride Scheme 8. The PERFECT method was applied to the synthesis of perfluorinated diacyl fluorides, which are used for the carboxylic acid type ion exchange membrane Scheme 9.
Synthesis of monomers for perfluoalkanesulfonic acid type membrane was achieved through direct fluorination of the substrate which possesses a sulfonyl group at the end Scheme The application of the PERFECT method to non-fluorinated secondary alcohols as a starting material Scheme 11 enabled to synthesize perfluorinated ketones. Because raw materials are inexpensive hydrocarbons, and the synthesis from hydrocarbon components makes it possible to create entirely new fluorinated compounds at will.
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Theoretically, by-product of the process is hydrogen only, because HF, which is formed in the process, can be converted electrochemically back to hydrogen and fluorine; fluorine can be used again in the process. In that sense, it contributes to reduce environmental burden. Nowadays, organofluorine compounds are essential materials especially in recent IT, electronics, and medical applications.
They are based on the history over 80 years. Among them, recent development of direct fluorination with elemental fluorine is promising to prepare versatile materials both in creating comfortable life and in reducing environmental burden.