Methane, chlorination

Like the chlorination of methane chlorination of ethane is carried out on an industrial scale as a high temperature gas phase reaction... 

Fig. 5. Effects of product recycle on methane chlorination product distributions where 1 = methyl chloride, 2 = methylene chloride, 3 = chlorine, and...

Methane, chlorine, and recycled chloromethanes are fed to a tubular reactor at a reactor temperature of 490—530°C to yield all four chlorinated methane derivatives (14). Similarly, chlorination of ethane produces ethyl chloride and higher chlorinated ethanes. The process is employed commercially to produce l,l,l-trichloroethane. l,l,l-Trichloroethane is also produced via chlorination of 1,1-dichloroethane with l,l,2-trichloroethane as a coproduct (15). Hexachlorocyclopentadiene is formed by a complex series of chlorination, cyclization, and dechlorination reactions. First, substitutive chlorination of pentanes is carried out by either photochemical or thermal methods to give a product with 6—7 atoms of chlorine per mole of pentane. The polychloropentane product mixed with excess chlorine is then passed through a porous bed of Fuller s earth or silica at 350—500°C to give hexachlorocyclopentadiene. Cyclopentadiene is another possible feedstock for the production of hexachlorocyclopentadiene. 

Like many radical reactions in the laboratory, methane chlorination requires three kinds of steps initiation, propagation, and termination. 

A methane/chlorine mixture detonates if the chlorine concentration is greater than 20%. 

Here, we have used single-headed curly arrows or fishhook arrows to indicate. the movement of single electrons. The tail of the curly arrow shows the source of the electron and the head shows its destination. Using single-headed curly arrows, the mechanism for the methane/chlorine chain reaction is completed below. 

In the process of methane chlorination coproducts of lower chlorine content than... 

In the manufacture of methyl chloride a mixture of methane and chlorine is mixed with recycled gas and fed into a reactor. The CH4 Cl2 ratio is 4-5. The reactor temperature is maintained by regulating the gas feed rate. In methane chlorination plants, 95-96% chlorine yields and 90-92% methane yields are typical.176 All four chloromethanes are formed with a typical composition of 35 wt% methyl chloride, 45 wt% methylene dichloride, 20 wt% chloroform, and a small amount of carbon tetrachloride.178 The reaction, however, may be regulated so that either mono- or tetrachlorination predominates.177 179 180... 

Methane Chlorine Methyl chloride Hydrogen Chloride... 

Tables of AG° values for formation of particular compounds (at various temperatures and states) from the elements are available in handbooks and the literature. With these, we can calculate equilibrium constants quite accurately. For example, handbooks give the following data, which are useful for methane chlorination ...

One might ask whether dissociation into ions would provide viable mechanisms for methane chlorination. Part of the answer certainly is Not in the vapor phase, as the following thermochemical data show ... 

Chain reactions may be considered to involve three phases. First, chain initiation must occur, which for methane chlorination is activation and conversion of chlorine molecules to chlorine atoms by light. Second, chain-propagation steps convert reactants to products with no net consumption of atoms or radicals. The propagation reactions occur in competition with chainterminating steps, which result in destruction of atoms or radicals. Putting everything together, we can write ... 

Exercise 4-13 Calculate AH0 for each of the propagation steps of methane chlorination by a mechanism of the type... 

To illustrate, suppose that methane chlorination appeared to proceed by way of a one-step concerted mechanism ... 

In practice, one can control the degree of substitution to a considerable extent by controlling the methane-chlorine ratio. For example, for monochlorination to predominate, a high methane-chlorine ratio is necessary such that the chlorine atoms react with CH4 and not with CH3Cl. 

Write a mechanism analogous to that usually written for methane chlorination that would lead to production of hexachloroethane as in Exercise 4-20a. (This reaction is used for commercial production of hexachloroethane.)... 

See Bromine pentafluoride Hydrogen-containing materials Chlorine trifluoride Methane Chlorine Hydrocarbons Fluorine Hydrocarbons Iodine heptafluoride Carbon, etc. 

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