Chloromethane production

Watling R, Harper DB (1998) Chloromethane Production by Wood-Rotting Fungi and an Estimate of the Global Flux to the Atmosphere. Mycol Res 102 769... 

Watling R. and Harper D. B. (1998) Chloromethane production by wood-rotting fungi and an estimate of the global flux to the atmosphere. Mycol. Res. 102, 769-787. 

All the above material confirm that the problem of industry electrolysis of pure hydrochloric acid is solved in general. Waste HCl from several chlororganic productions (for example, the chloromethane production [18] ) can be electrolyzed as well. Electrolysis of such acid cause no difficulties unless an organic phase appears, as its presence sharply reduces the diaphragm lifetime. Chlorine, the main purpose product, contains only tetraolorooarbon - the final product of methane chlorination. 

The secondary reactions are series with respect to the chloromethane but parallel with respect to chlorine. A very large excess of methane (mole ratio of methane to chlorine on the order of 10 1) is used to suppress selectivity losses. The excess of methane has two effects. First, because it is only involved in the primary reaction, it encourages the primary reaction. Second, by diluting the product, chloromethane, it discourages the secondary reactions, which prefer a high concentration of chloromethane. 

Consider the chlorination of methane to chloromethane The heats of formation of the reac tants and products appear beneath the equation These heats of formation for the chemical com pounds are taken from published tabulations the heat of formation of chlorine as it is for all elements IS zero... 

Methane is also used for the production of several halogenated products, principally the chloromethanes. Due to environmental pressures, this outlet for methane is decreasing rapidly. 

Chlorination of various hydrocarbon feedstocks produces many usehil chlorinated solvents, intermediates, and chemical products. The chlorinated derivatives provide a primary method of upgrading the value of industrial chlorine. The principal chlorinated hydrocarbons produced industrially include chloromethane (methyl chloride), dichloromethane (methylene chloride), trichloromethane (chloroform), tetrachloromethane (carbon tetrachloride), chloroethene (vinyl chloride monomer, VCM), 1,1-dichloroethene (vinylidene chloride), 1,1,2-trichloroethene (trichloroethylene), 1,1,2,2-tetrachloroethene (perchloroethylene), mono- and dichloroben2enes, 1,1,1-trichloroethane (methyl chloroform), 1,1,2-trichloroethane, and 1,2-dichloroethane (ethylene dichloride [540-59-0], EDC). 

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. 

Production and sales data for methyl chloride, as reported by the U.S. International Trade Commission for the years 1945 to 1989, are given in Table 3. Production grew tremendously in the 1960s and again in the late 1980s. Methanol hydrochlorination was used to produce about 64% of the methyl chloride in 1969 and about 98% by 1974. The principal U.S. producers and their capacities are shown in Table 4 (54). These capacities do not include the 100 + million kg per year used by The Dow Chemical Company, Occidental, and Vulcan to captively produce other chloromethanes. 

Table 3 Hsts the U.S. producers of methylene chloride and their rated yearly capacities. Since the product mix of a typical chloromethanes process is very flexible, production may be adjusted according to the demand for methylene chloride and chloroform. The demand for methylene chloride has taken a broad downturn as a result of the 1985 NTP carcinogenicity tests (Table 4). The 1988 and 1989 demands were 227,000 t and 216,000 t, respectively, with a forecast 1993 demand of 186,000 t. The historical growth rate (1979—1988) was —2.7% pet year. In the future this should decrease even further to —3 to...

Carbon tetrachloride [56-23-5] (tetrachloromethane), CCl, at ordinary temperature and pressure is a heavy, colorless Hquid with a characteristic nonirritant odor it is nonflammable. Carbon tetrachloride contains 92 wt % chlorine. When in contact with a flame or very hot surface, the vapor decomposes to give toxic products, such as phosgene. It is the most toxic of the chloromethanes and the most unstable upon thermal oxidation. The commercial product frequendy contains added stabilizers. Carbon tetrachloride is miscible with many common organic Hquids and is a powerhil solvent for asphalt, benzyl resin (polymerized benzyl chloride), bitumens, chlorinated mbber, ethylceUulose, fats, gums, rosin, and waxes. 

Chlorination of methane provides approximately one third of the annual U.S. production of chloromethane. The reaction of methanol with hydrogen chloride is the major synthetic method for the preparation of chloromethane. 

Methane is the most difficult alkane to chlorinate. The reaction is initiated by chlorine free radicals obtained via the application of heat (thermal) or light (hv). Thermal chlorination (more widely used industrially) occurs at approximately 350-370°C and atmospheric pressure. A typical product distribution for a CH4/CI2 feed ratio of 1.7 is mono- (58.7%), di-(29.3%) tri- (9.7%) and tetra- (2.3%) chloromethanes. 

Product distrihution among the chloromethanes depends primarily on the mole ratio of the reactants. For example, the yield of mono-chloromethane could he increased to 80% hy increasing the CH4/CI2 mole ratio to 10 1 at 450°C. If dichloromethane is desired, the CH4/CI2 ratio is lowered and the monochloromethane recycled. Decreasing the CH4/CI2 ratio generally increases poly substitution and the chloroform and carhon tetrachloride yield. 

Methyl chloride is primarily an intermediate for the production of other chemicals. Other uses of methyl chloride have been mentioned with chloromethanes. 

Chloromethane (CH3C1) is only one of the products dichloromethane (CH2C12), trichloromethane (CHCl3), and tetrachloromethane (CC14) also form, especially at high concentrations of chlorine. 

The oxidative addition of hexafluoroacetone to 221 gives 222 (X = CH) in which chloromethane has been eliminated in a ring-closing step to give a product with a bridgehead phosphorus center (Scheme 28). Analogous products 223 were obtained by treatment of 221 (X = N) with hexafluoroacetone (Scheme 29) <2000ZFA412>. The oxidative addition was found to be reversible. 

Relatively soon after the discovery that aqueous solutions containing PtCl - and PtClg- can functionalize methane to form chloromethane and methanol, a mechanistic scheme for this conversion was proposed (16,17). As shown in Scheme 4, a methylplatinum(II) intermediate is formed (step I), and this intermediate is oxidized to a methylplatinum(IV) complex (step II). Either reductive elimination involving the Pt(IV) methyl group and coordinated water or chloride or, alternatively, nucleophilic attack at the carbon by an external nucleophile (H20 or Cl-) was proposed to generate the functionalized product and reduce the Pt center back to Pt(II) (step III) (17). This general mechanism has received convincing support over the last two decades (comprehensive reviews can be found in Refs. (2,14,15)). Carbon-heteroatom bond formation from Pt(IV) (step III) has been shown to occur via nucleophilic attack at a Pt-bonded methyl, as discussed in detail below (Section V. A). 

Attempts to alkylate C6o with methyl iodide did not give an addition product, probably because of insufficient reactivity of this electrophile system, due to the low electronegativity of iodine. On the other hand, the use of liquified chloromethane at 60 °C in a stainless steel autoclave afforded the methylated product, which consisted of only the 1,2 isomer, as expected from the small steric requirement of the methyl group (29). 

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