Tetrafluoroethylene decomposition

Hydroxymethylmethyldiazirine (209 unprotonated) formed propionaldehyde as the sole product by thermal nitrogen extrusion 4-hydroxy-l,2-diazaspiro[2.5]oct-l-ene (218) formed a mixture of cyclohexanone (73%), cyclohexenol (21%) and cyclohexene oxide (5%). Thermal decomposition of difluorodiazirine (219) was investigated intensively. In this case there is no intramolecular stabilization possible. On heating for three hours to 165-180 °C hexafluorocyclopropane and tetrafluoroethylene were formed together with perfluorofor-maldazine 64JHC59). 

Thermal decomposition is a major route to smaller perfluonnated molecules Tetrafluoroethylene pyrolyzed at 1100-1300 °C with carbon dioxide gives a mixture of tetrafluoromethane (19 9%), hexafluoroethane (61 3%), and carbonyl fluoride (18 6%) [87]... 

Methyl trifluorovinyl ether, b.p. 10.5- 12.5°C, prepared from tetrafluoroethylene and sodium methoxide [1], has considerable explosive potential. On ignition, it decomposes more violently than acetylene and should be treated with extreme caution [2], Other trifluorovinyl ethers are similarly available from higher alkoxides [1], and although not tested for instability, should be handled carefully. Presence of fluoro-haloalkanes boiling lower than the ether stabilises the latter against spark-initiated decomposition in both fluid phases [3],... 

Siu and Berman [163] determined selenium in marine sediments in amounts down to 0.2pg (or 20ng g 1 of sediment) with a precision of 7%. This method is based on the fact that 1,2 diaminobenzene (o-phenylene diamine) and its derivatives react selectively and quantitatively with selenium IV (average accuracy 94 5%) to form piazselenols that are both volatile and stable. Piazselenols can be determined by electron capture gas chromatography. The sediments were digested as follows. A 0.5g sample was placed in a poly(tetrafluoroethylene) pressure decomposition vessel. A... 

The decomposition products, up to a temperature of 500°C, are principally the monomer, tetrafluoroethylene, but also include perfluoropropene, other perfluro compounds containing four or five carbon atoms, and an unidentified particulate waxy fume. From 500°C to 800°C, the pyrolysis product is carbonyl fluoride, which can hydrolyze to form HE and CO2. 

Hanford and Joyce placed great emphasis on the precautions which are required for the safe handling of tetrafluoroethylene, particularly at elevated pressures. Failure to provide for the adequate control of temperature and efficient agitation may lead to an increasingly rapid reaction and eventually a violent explosive decomposition of the monomer to carbon and CF4 (Kiyama, Osugi, and Kusuhara Teranishi). 

TG-IR has also been used to examine the thermally induced decomposition products of polyvinyl chloride (PVC), polyacrylamide, tetrafluoroethylene-propylene, styrene-... 

S = generally satisfactory NR = not recommended NS = not suitable owing either to decomposition or to adverse effects ofthe solution on the material of construction. b Onlyupto650C c PTFE=poly(tetrafluoroethylene)... 

Thermal degradation does not occur until the temperature is so high that primary chemical bonds are separated. It begins typically at temperatures around 150-200 °C and the rate of degradation increases as the temperature increases. Pioneering work in this field was done by Madorsky and Straus (1954-1961), who found that some polymers (poly (methyl methacrylate), poly(oc-methylstyrene) and poly (tetrafluoroethylene)) mainly form back their monomers upon heating, while others (like polyethylene) yield a great many decomposition products. 

The first reported polymerization of fluoroolefins in carbon dioxide was by Fukui and coworkers [39,40]. Tetrafluoroethylene, chlorotrifluoroethylene,and other fluoroolefins were polymerized in the presence of CO2 using ionizing radiation [39, 40] and free-radical initiators [40]. DeSimone and coworkers reported the homogeneous telomerization of tetrafluoroethylene [41] and vinylidene fluoride [42] in CO2 using AIBN as an initiator. The kinetics of AIBN decomposition in CO2 is well understood [4]. However, peroxide initiators are preferred over azo initiators for producing stable endgroups in fluoroolefins... 

Difluorocarbene can be generated by high-temperature reaction of chlorodifluoromethane in the production of tetrafluoroethylene (TFE) (equation 48). Another method of in situ generation of the carbene is thermal decomposition of... 

AICI3), O3, CCI4, CI2, NOx, tetrafluoroethylene trifluorohj pofluorite. When heated to decomposition it emits acrid smoke and irritating fumes. 

Slow decomposition of PTFE occurs above the application temperature of 260°C. However, for a noticeable decomposition to occur, temperatures above 400°C are needed. The primary decomposition products are tetrafluoroethylene (TFE) and difluorocarbon diradicals (CF2). Further products are formed by secondary reactions, depending on temperature, reaction pressure and reaction atmosphere. The typical main products are TFE, hexafluoropropene (HEP), cyclo-perfluorobutane (C-C4F8) and other fluorocarbons. Most of these substances are nontoxic, but highly toxic substances such as perfluoroisobutene or fluorophosgene are also formed under some reaction conditions. 

Chemically, difluorodiazirine appears to be remarkably inert. Like diazirine itself, however, it is explosive. It undergoes thermal decomposition above about 160°C. Photolysis of this compound at room temperature produces only tetrafluoroethylene and nitrogen, presumably by the reactions... 

Atkinson et a/. - - have reported that the thermal decomposition of tetra-fluoroethylene can be divided into three temperature phases (see also ref. 454). At temperatures below 550 °C perfluorocyclobutane is the main product above 550 °C the equilibrium mixture of tetrafluoroethylene and perfluorocyclobutane decomposes to form perfluoropropene by a first-order reaction, and perfluoro-propene decomposes in turn by a 1.5-order process to perfluoroisobutene above 700 °C the perfluoroisobutene decomposes by a first-order reaction to perfluoro-ethane and non-volatiles. The observations are shown to be consistent with a reaction scheme involving CFj radicals in Phases 1 and 2, and CFj radicals in Phase 3, as follows... 

Analysis of the kinetics yielded Arrhenius parameters for the reversible cyclic dimerisation reaction involving tetrafluoroethylene and perfluorocyclobutane (see Table 1) and for the decomposition of perfluoroisobutene (A — 1.1 x 10 see E = 82.7 kcal.mole ). The dimerisation reaction has also been studied by Lacher et and the reverse process by Gray and Pntchard, and by Butler . These reactions appear to be elementary however. Gray and Pritchard have argued that the reverse (dissociation) reaction is not a simple unimolecular process. 

The decomposition of tetrafluoroethylene to difluorocarbene in a shock-tube with argon and nitrogen at 900-1500 °C has been reported by Modica and La Graff . The decomposition reaction was stated to be in the second-order region and in the presence of argon followed the rate equation... 

One of the best-known thermal reactions of fluorine compounds is the pyrolysis of chlorodifluoromethane to tetrafluoroethylene as used in the production of Teflon polymer. This reaction was described by Park et in 1947, and Nor-ton" in 1957 reported an activation energy of 49 kcal.mole for the decomposition over silica at 425-525 °C. More recently, Gozzo and Patrick have made a kinetic study of the process using a helium flow system at 670-750 °C with a surface conditioned platinum tubular reactor. HCl is found to retard the raction and the following mechanism has been proposed... 

The thermal stability of polytetrafluoroethylene oxide and PTFE have been compared under the same conditions by Donato et al. [263] between 450 and 600°C. The decomposition rate has a maximum at 628°C for the oxide and at 568°C for PTFE. The activation energy for the first-order degradations are 98 kcal mole"1 between 8.5 and 85% for the oxide polymer and 85 kcal mole-1 between 523 and 571°C for PTFE. The rate of weight loss is less than 1.2% per min for both polymers below T = 550°C for the oxide and T = 590°C for PTFE. The oxide, however, loses weight below 390° C whereas PTFE does not. The main components of the volatile material are trifluoroacetyl fluoride, carbonyl fluoride and tetrafluoroethylene. An end-initiated thermal degradation with small zip length is proposed. 

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