1.2- Dichloroethylenes

Interestingly, 1,2-dichloroethylene can be used for coupling without activation of the chlorides. The reaction of c -1.2-dichloroethylene (331) has wide... 

A trialkylsilyl group can be introduced into aryl or alkenyl groups using hexaalkyidisilanes. The Si—Si bond is cleaved with a Pd catalyst, and trans-metallation and reductive elimination afford the silylated products. In this way, 1,2-bis-silylethylene 761 is prepared from 1,2-dichloroethylene (760)[625,626], The facile reaction of (Me3Si)2 to give 762 proceeds at room temperature in the presence of fluoride anion[627]. Alkenyl- and arylsilanes are prepared by the reaction of (Me3Si)3Al (763)[628],... 

Halogenation and Hydrohalogenation. Halogens add to the triple bond of acetylene. FeCl catalyzes the addition of CI2 to acetylene to form 1,1,2,2-tetrachloroethane which is an intermediate in the production of the industrial solvents 1,2-dichloroethylene, trichloroethylene, and perchloroethylene (see Chlorocarbons and chlorohydrocarbons). Acetylene can be chlorinated to 1,2-dichloroethylene directiy using FeCl as a catalyst... 

Dehydrochlorination 1,1,2-Trichloroethane is easily dehydrochloriaated by a number of catalytic reagents to give 1,1-dichloroethylene and some 1,2-dichloroethylene. Refluxing with aqueous and methanolic solutions of NaOH, Ca(OH)2, and Mg(OH)2 and water gives 1,1-dichloroethylene... 

The only significant use of 1,1,2,2-tetrachloroethane is as a feedstock in the manufacture of trichloroethylene, tetrachloroethylene, and 1,2-dichloroethylene. Although it is an excellent solvent, its use should be discouraged in view of its high toxicity. 

Dichloroethylene consists of a mixture of the cis and trans isomers, as manufactured. The physical properties of both isomeric forms are Hsted ia Table 1. Biaary and ternary a2eotrope data for the cis and trans isomers are given ia Table 2. 

Table 1. Physical Properties of the Isomeric Forms of 1,2-Dichloroethylene...

Dichloroethylene can be produced by direct chlorination of acetylene at 40°C. It is often produced as a by-product ia the chlorination of chloriaated compounds (2) and recycled as an iatermediate for the synthesis of more useful chloriaated ethylenes (3). 1,2-Dichloroethylene can be formed by contiauous oxychloriaation of ethylene by use of a cupric chloride—potassium chloride catalyst, as the first step ia the manufacture of vinyl chloride [75-01-4] (4). 

The trans isomer is more reactive than the cis isomer ia 1,2-addition reactions (5). The cis and trans isomers also undergo ben2yne, C H, cycloaddition (6). The isomers dimerize to tetrachlorobutene ia the presence of organic peroxides. Photolysis of each isomer produces a different excited state (7,8). Oxidation of 1,2-dichloroethylene ia the presence of a free-radical iaitiator or concentrated sulfuric acid produces the corresponding epoxide [60336-63-2] which then rearranges to form chloroacetyl chloride [79-04-9] (9). 

The unstabiUzed grade of 1,2-dichloroethylene hydrolyzes slowly ia the presence of water, produciag HCl. Although unaffected by weak alkaUes, boiling with aqueous NaOH may give rise to an explosive mixture because of monochi oroacetylene [593-63-5] formation. 

Dichloroethylene is usually shipped ia 208-L (55 gal) and 112-L (30 gal) steel dmms. Because of the corrosive products of decomposition, inhibitors are required for storage. The stabilized grades of the isomers can be used or stored ia contact with most common constmction materials, such as steel or black iron. Contact with copper or its alloys and with hot alkaline solutions should be avoided to preclude possible formation of explosive monochloroacetylene. The isomers do have explosive limits ia air (Table 1). However, the Hquid, even hot, bums with a very cool flame which self-extiaguishes unless the temperature is well above the flash poiat. A red label is required for shipping 1,2-dichloroethylene. 

Dichloroethylene is toxic by inhalation and ingestion and can be absorbed by the skin. It has a TLV of 200 ppm (10). The odor does not provide adequate warning of dangerously high vapor concentrations. Thorough ventilation is essential whenever the solvent is used for both worker exposure and flammabihty concerns. Symptoms of exposure include narcosis, dizziness, and drowsiness. Currently no data are available on the chronic effects of exposure to low vapor concentrations over extended periods of time. 

Dichloroethylene was selected in April 1990 for National Toxicological Program (NTP) carcinogenesis studies there is no data available as of summer 1992. 

Dichloroethylene appeared frequently in the 1980s Hterature largely because of its presence at ground water cleanup sites. The continued presence of 1,2-dichloroethylene may be a result of the biotransformation of tetrachloroethylene and trichloroethylene, which are much more common industrial solvents and are likely present because of past disposal practices (11,12). 

Dichloroethylene can be used as a low temperature extraction solvent for organic materials such as dyes, perfumes, lacquers, and thermoplastics (13—15). It is also used as a chemical intermediate in the synthesis of other chlorinated solvents and compounds (2). 

Recently several patents have been issued (16—18) describing the use of 1,2-dichloroethylene for use in blends of chlorofluorocarbons for solvent vapor cleaning. This art is primarily driven by the need to replace part of the chlorofluorocarbons because of the restriction on their production under the Montreal Protocol of 1987. Test data from the manufacturer show that the cleaning abiUty of these blends exceeds that of the pure chlorofluorocarbons or their azeotropic blends (19). 

Chlorocarbons and Chlorohydrocarbons-Dichloroethylenes" under "Chlorine Compounds, Organic", in ECT 1st ed., VoL 3, pp. 786—787, byj. Werner, General Aniline Film Corp., Aniline Works Division "Chlorocarbons and Chlorohydrocarbons-Dichloroethylenes" in ECT 2nd ed., VoL 5, pp. 178—183, by D. W. F. Hardie, Imperial Chemical Industries, Ltd "1,2-Dichloroethylene" under "Chlorocarbons, -Hydrocarbons" in ECT 3rd ed., Vol. 5, pp. 

Trichloro- and tetrachloroethylene are important organic solvents. These are produced by further chlorination of 1,2-dichloroethylene ia the gas phase with simultaneous dehydrochloriaation ia the preseace of a suitable chloride catalyst (see Chlorocarbonsandchlorohydrocarbons). 

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