Fluoromethane substitution

In a series of comparative studies Dolle et al. examined the nucleophilic aromatic substitution of a number of nitropyridine derivatives [104—106], The results, as summarized in Scheme 13.14, show that under microwave-enhanced conditions the 2-N02 and 2-+NMe3 groups led to excellent fluorine incorporation whilst the 2-iodo compound was virtually unreactive. Under thermal conditions no fluorination was observed for the 2-chloro and 2-bromo compounds. In a separate study Banks et al. [107] again observed the beneficial effects of nitro and trimethylamino substitution (Scheme 13.15). The authors also developed a novel microwave-enhanced method of producing [18F]-fluoromethane [108]. 

In the United States, suppression systems using Halon 1301 (bromotri-fluoromethane) (NFPA 69,1986) to quench the flames in industrial equipment are popular because damage to the product and to electrical components and other equipment is minimized. Halon 1301 is also used for flame suppression in areas occupied by people such as in computer rooms. Extinguishing flames successfully can usually be achieved at Halon 1301 concentrations of 5% for about 10 min., which usually allows people time to escape the area without harm. Halon 1301 is colorless and odorless and has minimal, if any, central nervous effects to people below a 7% concentration for exposures of 5 min. However, the decomposition products of Halon 1301 that may result from a fire are quite toxic. They have a characteristic sharp, acrid odor that provides a built-in warning system to people. Halon compounds are fluorocarbons which are being phased out of use because of environmental concerns. Substitutes are being developed and should be considered as they become available. 

Similarly, the fluoromethanes have F—C bonds that shorten128 as the number of fluorines increases from one in 2.87 to four in 2.90, and the number of generalised anomeric effects accumulates. The bond-strengthening represented by these bond-shortenings contributes to the reduced reactivity towards nucleophilic substitution seen in polyhalogenated alkanes. 

Fluoro-2-pyridone is readily prepared by reaction of 5% fluorine in nitrogen and 2-trimethylsiloxypyridine in trichloro-fluoromethane at -78°C the pyridone is a selective fluorinating reagent. 5 The novel 3-substituted pyridine (43) is formed when... 

The hydrogen affinities of fluoromethanes increase with increasing fluorine substitution ... 

A substitution reaction between fluoromethane (CH3F) and potassium bromide (KBr) trades elements in the following reaction ... 

TFE undergoes free radical addition reactions typical of other olefins. It readily adds Br, Cl, and I, halogen halides IBr and ICl, and nitrosyl halides such as NOCl and NOBr. Additional reactions of chloro-fluoromethanes and chloromethanes in the presence of catalysts like aluminum chloride have been reported [48]. A variety of other compounds such as alcohols, primary amines and ammonia can be reacted with TFE to prepare tetrafluoroethers (HCF CF OR), difluoroacetamide (HCF CONHR) and substituted triazines. Oxygen can be added to TFE to produce polymeric peroxide or TFE epoxide. In the absence of hydrogen, sodium salts of alcohols will react with TFE to yield trifluorovinylethers (ROCF = CF ), which can be homo- and copolymerized. 

Hie formation of CH F and CF F following ener tlc F atomic substitution reactions in fluorinated methanes (71-75) and ethanes 60. 66) has been well documented. Lindner and Pauwels obtained direct evidence for C0F F production in unpublished recoil F experiments with fluoromethanes (7. 75). Although CF F was identified as the C0F F precursor through competitive experiments with C3F6 scavenger, the detailed mechanism for process 28 was not established. 

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