Fluorine tetrafluoromethane

Tetrafluoromethane plasma modified polyethylenes indicate two mechanisms degradation and fluorination. These reactions are competitive and parallel [42]. 

Write the balanced chemical equation for the complete fluorination of methane to tetrafluoromethane. Using bond enthalpies, estimate the enthalpy of this reaction. The corresponding reaction using chlorine is much less exothermic. To what can this difference be attributed ... 

Fluorine derivs (cont d) sulfur hexafluoride 6 F147 sulfuric oxyfluoride 6 F148 sulfurous oxyfluoride 6 F148 tetrafluorohydrazine 6 FI 48 tetrafluoromethane see Carbon tetrafluoride 2C64... 

Another possibility for achieving attractive interactions due to fluorination could be provided by partial fluorination of aliphatic hydrocarbons. If H and F are combined at one C atom the highly polar nature of the C-F bond can cause polarization of the C-H bond at the same carbon, thus enabling attractive interactions with fluorine atoms at neighboring molecules. For example, difluoromethane has a significantly higher boiling point (—52°C) than either methane (—161°C) or tetrafluoromethane (—128°C) [59, 421],... 

The fluorine produced is either immediately used to prepare other final products or is first liquefied and delivered in steel cylinders where required. When fluorine is liquefied it is first led from the electrolyzer through a steel coil cooled to — 90 °C by dry ice. It then passes through a coil submerged in liquid oxygen, (— 183 °C) to separate the remaining traces of hydrogen fluoride, carbon dioxide and tetrafluoromethane. The product still contains a small... 

The fluorine thereby obtained is directly processed further (to uranium hexafluoride, sulfur hexafluoride) or liquefied (b.p. -188°C) and filled into pressure cylinders. Pressure cylinders with mixtures of fluorine and nitrogen, with 10 or 20% by volume of fluorine, are widely marketed (utilized, for example, for the surface fluorination of vehicle fuel tanks). The worldwide fluorine capacity is estimated to be ca. 7.5 10 t/a, of which 60% is in the USA, 25% in Europe and 15% in Japan. Ca. 75% of the fluorine manufactured is utilized in the manufacture of uranium hexafluoride, 22.5% in the manufacture of sulfur hexafluoride and 2.5% in the manufacture of tetrafluoromethane. In 1986 ca. 100 t of fluorine was utilized in the manufacture of fluorographite (high conductivity) for use in batteries. 

Our first example is tetrafluoromethane, CF4. The total number of available (outershell) electrons (32) is given by the carbon contribution of four electrons and the contribution of seven electrons from each fluorine atom. The structure we draw follows the octet rule (recall that the line represents two electrons in a bond) ... 

Figure 1.9 Resonance stabilization of the carbon—fluorine bond in tetrafluoromethane, and electrostatic and steric shielding against nucleophilic attack on the central carbon atom. The electrostatic potentials are mapped on the electron isodensity surface (calculation at the MP2/6-31+G level of theory [7, 14] red denotes negative, blue positive partial charges).

By-products. The presence in the products of small quantities of compounds which would arise from combination of free radical intermediates can provide evidence for a free radical process. For example, the explosive reaction of methane with fluorine gives mainly hydrogen fluoride and a mixture of mono-, di-, tri- and tetrafluoromethanes, but small quantities of fluorinated ethanes, including C2F6, are also produced. These two-carbon products cannot be readily explained on the basis of possible molecular reactions (see reaction 6.16), but would arise naturally as combination products of the fluorinated methyl radicals produced in a radical chain reaction sequence (reaction 6.17). 

The distributions of concentrations F and HF are shown on Fig. 1, a and Fig. 1, b correspondingly at 25 % fraction H2 mCF4/H2- The main part of fluorine atoms obtained from the dissociation of tetrafluoromethane are consumed in the reactions with hydrogen atoms to form an abundant component HF. As a result the fluorine concentration monotonous decreases along the flow direction whereas the concentration HF rises and reaches a maximum at the outlet of reactor. 

Although Antoine Lavoisier (1743-1794) had assumed the existence of a new element in hydrofluoric acid, it was not until 1886 when Henri Moissan (1852-1907) succeeded in synthesizing elemental fluorine. He electrolysed potassium fluoride dissolved in liquid hydrofluoric acid at —55°C in a platinum apparatus [5], and he was awarded the Nobel Prize for the same in 1906. As Moissan used graphite electrodes, the nascent fluorine reacted with carbon and produced a blend of perfluorocarbon compounds mainly containing tetrafluoromethane, CF4. Moissan noted that what he assumed to be pure CF4 would fiercely react with sodium to give carbon and sodium fluoride [6]. 

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