Chlorofluorocarbons , DuPont

Several different solvents have been used. These include petroleum ether, diethyl ether, chloroform, and carbon tetrachloride. Of these, petroleum ether and diethyl ether are highly flammable, whereas chloroform (although a very good solvent) and carbon tetrachloride are toxic. Thus, these solvents are not recommended for use. Currently, 1,1,2 trichloro, trifluoroethane (Freon 113) is used when infrared (IR) absorbance is used for analysis. However, these solvents are being phased out because of potential interference with the ozone layer in the atmosphere. Studies are currently under way to find a replacement solvent. Potential candidates include hexane, cyclohexane, methylene chloride, perchloroethylene, and a commercial hydro chlorofluorocarbon (DuPont 123). When the gravimetric technique is used for analysis, 1,1,1-trichloroethane or dichloroethylene may also be used. 

As you know, most countries are phasing out certain refrigerants to lessen damage to the ozone layer. The chemicals being phased out are chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Replacements are hydrofluorocarbons (HFCs) and certain blends. The DuPont web site (www.dupont.com) gives the handy Table I of recommended replacement refrigerants for various applications. 

DuPont scientists researching the production of chlorofluorocarbons accidentally produce a white waxy substance that becomes Teflon. 

Of all the elements, fluorine is the most reactive and the most electronegative (a measure of tendency to acquire electrons). In its chemically combined form, it always has an oxidation number of -1. Fluorine has numerous industrial uses, such as the manufacture of UF6, a gas used to enrich uranium in its fissionable isotope, uranium-235. Fluorine is used to manufacture uranium hexafluoride, SF6, a dielectric material contained in some electrical and electronic apparatus. A number of organic compounds contain fluorine, particularly the chlorofluorocarbons used as refrigerants and organofluorine polymers, such as DuPont s Teflon. 

Fluoropolymers could not be prepared in hydrocarbon solvents and earlier routes to them had employed ozone-depleting chlorofluorocarbon (CFC) solvents. The C02-philic nature of both the monomers and the resulting polymers allowed a homogeneous polymerization reaction to be performed. DuPont now... 

Teflon was discovered by accident in 1938 by a DuPont chemist named Roy Plunkett (1911-1994). Plunkett was working on the development of chlorofluorocarbons (CFCs) for DuPont. He wanted to see what happened when one compound, tetrafluoroethylene, orTFE (C2F4), was mixed with hydrochloric acid (HCI). To carry out the experiment, he set up the equipment so that the gaseous TFE would flow Into a container of HCI. 

CFC s or chlorofluorocarbons are chemicals that cause ozone depletion in the stratosphere as well as the "Greenhouse Effect". They have been typically employed as blowing agent in foams. Since the initial proclamation, the mandate has been revised several times to accelerate the CFC phaseout schedule, with the latest revision resulting from the Copenhagen agreement in November 1992 where 87 nations resolved to move up total CFC phaseout by four years in January 1996. The recent Copenhagen revision induced major CFC manufacturers to accelerate their phaseout time table. DuPont announced recently that it plans to stop CFC production by 1994, almost 2 years ahead of plan. 

Freon is a DuPont trademark for certain chlorofluorocarbons other companies related products are known by other names. Typical freons are trichlorofluoromethane,... 

Chlorofluorocarbons (CFCs) are chemically inert, nonflammable, nontoxic compounds that are superb solvents and have been used in many industrial processes they are excellent coolants for air conditioners and refrigerators. Two CFCs that have been widely used are Freon-11 and Freon-12 (Freon is a DuPont trade name). 

Of particular relevance to this chapter is the use of CO2 in polymer synthesis, in the manufacture of polymethylmethacrylate and polystyrene (Xerox) and for the production of fluoropolymers (DuPont). One of the main drivers for the latter was the phasing out of the chlorofluorocarbons (CFCs) used in the original process. The main advantage to this application is not necessarily the avoidance of the use of CFCs (although this is important), but the superior polymer processing properties made possible by the relative volatility of CO2 and its ease of removal. 

Chlorofluorocarbons have been used as refrigerants for the past 50 years, but their use is now being phased out worldwide because of concerns about atmospheric ozone depletion. Draw the Lewis structure of dichlorodifluoromethane, CF2CI2, also known as DuPont s Freon-12. 

DuPont in USA disclosed a process for the preparation of expanded PE in 1942, using nitrogen as a blowing agent. In 1945 carbon dioxide was used instead of nitrogen. Commercial production of expanded PE as an electric cable insulation started in 1950s. In 1958 chlorofluorocarbons (CFC) were introduced, and foamed PE insulation was based on high pressure, low density PE (LDPE) [24]. 

In a repeat of a theme seen in many scientific discoveries, one of DuPont Chemical s most femous and profitable polymers was discovered by accident. Teflon, a fluo-ropolymer best known for use in cookware, is highly resistant to most solvents and acids 2ind is used in analytical chemistry in applications such as soil and acid digestion. Teflon was accidentally made for the first time by DuPont chemist Roy Plunkett in 1938. Plunkett had been working with refrigerants based on chlorofluorocarbons when he returned to the lab one momir to find a waxy solid in a container where none should have been. Thus was Teflon bom. 

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