Halocarbons methylene chloride

This binuclear photooxidative addition reaction is general for a number of halocarbons (Figure 3). While DCE and 1,2-dibromoethane react cleanly to give the dihalide metal dimers and ethylene, substrates such as bromobenzene or methylene chloride react through an alkyl or aryl intermediate. This intermediate reacts further to yield the dihalide d2-d2 metal complexes. 

The mechanism of this reaction has been investigated in some detail. RX must be an activated halide, such as a benzyl halide, a-halo ether, or a 1,1-dihalocarbon where at least one of the halides is Br or L Simple halocarbons do not react, nor does methylene chloride. Reaction with chloroform is slow, while reaction with carbon tetrachloride is instantaneous at room temperature. The (pseudo) first-order rate constant is linearly correlated to the polarographic reduction potential of the halide thus electron transfer from (38) to RX (equation 57) is the rate-determining step, followed by rapid cleavage of the RX radical anion into R and X . 

Certain halocarbons such as methylene chloride, trichloroethylene, (TCE) and fluorocarbons can be used as a secondary cooling medium at temperatures lower than — 50°C. These fluids are nonflammable and non-corrosive under normal operating conditions. However, chlorinated compounds such as methylene chloride or TCE are very toxic and regulated by the Environmental Protection Agency (EPA). So, these fluids will be removed from the existing systems in the next few years. 

Some of the more important industries that produce solvent-contained air streams are printing dry cleaning and the manufacture of paints, polymers, adhesives, celluloid, rubber (e.g., rubber-coated fabrics), rayon, and gunpowder and extraction processes. The main solvents recovered by activated carbon adsorption are benzene, toluene, xylene, alcohols, acetone, petrol, ether, carbon disulfide, halocarbons (e.g., chloroform, carbon tetrachloride, trichloroethylene, methylene chloride, chlorobenzene, etc.). The major production facilities and the solvents recovered are listed in Table 5.3. In many cases the concentration of the organic solvent in waste gases is of the order of 1 to 2%. 

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