1,2-Dichloroethylene isomerization

C15-0057. Under the appropriate conditions, czs-dichloroethylene isomerizes to frans-dichloroethylene ... 

Pretreatment of rats with Aroclor 1254 protected against hepatotoxicity due to inhalation of 1,1-dichloro-ethylene, suggested that MFO induction by PCBs may be responsible for detoxification of 1,1-dichloro-ethylene (Reynolds et al. 1975). This detoxification might occur if the epoxide of 1,1-dichloroethylene isomerizes rapidly to an aldehyde before reacting with tissues. 

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...

Another approach to the synthesis of polyimides from chloral derivatives involves the use of dianhydrides of isomeric tetracarboxylic acids containing central carbonyl or 1,1-dichloroethylene groups and two ether bonds as the starting electrophilic compounds [31-33] (Scheme 3.8). 

Over a period of years Dainton and his co-workers have studied intensively photochlorination processes. Their work also indicated (31) that at temperatures below 150°C. the kinetics of photochlorination of trichloroethylene and tetrachloroethylene are explainable in terms of reactions (l)-(6). Above a characteristic limiting concentration the observed rates are in agreement with eq. (C). However, in a more recent work Ayscough et al. (6) have compared the rates of geometrical isomerization (Ri) of pure cis- and trans-1,2-dichloroethylene with the rates of the simultaneously occurring photochlorination. This work is of... 

Equations (2) and (3) could permit a simple determination of fc 2/A-B, and the authors started their experimental work with this objective in mind. The values of Ez and A3 for the C2H2CI3 radicals were known from the work of Ayscough et al. (7) in which they applied the rotating sector technique to the photochlorination of cis-l,2-dichloroethylene and found logio A3 (1. mole"1 sec.-1) = 8.7 0.3 and i 3 = 2.7 0.6 kcal. mole-1. In view of these values, and Howlett s conclusion, based on thermal dehydrochlorination studies, that for C2H3CI2 radical A 2 = 1013 sec.-1 and f 2 = 22 kcal. mole-1, no detectable isomerization was expected below 200°C. However, in contrast to this, a concurrent isomerization was easily detectable at 30°C even at a chlorine pressure of 200 mm. A detailed investigation was therefore necessary to explain the reasons for the discrepancy. 

The trans —> cis isomerization of 1,2-dichloroethylene proceeds if supplied with the energy of activation of 55.3 kcal mol-1. AH associated with the reaction is l.Okcal. What do you predict is the value of Ea for the reverse isomerization, cis transl From equation (20-6),... 

As shown in Figure 1.17, there are three possible dichloroethylene compounds, all clear, colorless liquids. Vinylidene chloride forms a copolymer with vinyl chloride used in some kinds of coating materials. The geometrically isomeric 1,2-dichloroethylenes are used as organic synthesis intermediates and as solvents. Trichloroethylene is a clear, colorless, nonflammable, volatile liquid. It is an excellent degreasing and dry-cleaning solvent and has been used as a household solvent and for food extraction (for example, in decaffeination of coffee). Colorless, nonflammable liquid tetrachloroethylene has properties and uses similar to those of trichloroethylene. Hexachloro-butadiene, a colorless liquid with an odor somewhat like that of turpentine, is used as a solvent for higher hydrocarbons and elastomers, as a hydraulic fluid, in transformers, and for heat transfer. 

Describe how the two forms of 1,2-dichloroethylene can be used to illustrate cis-trans isomerism. 

As shown in Figure 16.2, there are three possible dichloroethylene compounds, all clear, colorless liquids. Vinylidene chloride forms a copolymer with vinyl chloride, used in some kinds of coating materials. The geometrically isomeric 1,2-dichloroethylenes are used as organic synthesis intermediates and as solvents. 

In 1928 Bonino had opened the March 31 issue of Nature and read about the Raman effect for the first time. Soon afterward, he ended his long series of papers on infrared spectra by publishing two articles that dealt with the new Raman spectroscopy. [34] These were written in German and published in Zeitschrift fur Physik in 1929. In the first of these two papers, dated May 1929, Bonino reported on the Raman spectra of dichloroethylene and tetrachloroethylene and discussed their relationship with the infrared spectra. The second paper was written with his coworker Briill and appeared in the fall of 1929. In it they studied the relationships between Raman spectra and geometrical isomerism. [35]... 

The effect of pressure on equilibrium constants has been explored in a number of instances, and the Van t Hoff equation (XV.5.8) has been verified from independent studies of the partial molar volumes. This has been reported for the isomerization of cis-dichloroethylene with reasonable accuracy and qualitatively for N2O4 dissociatioiF and the ionization of weak electrolytes. ... 

Low reactivity was noted for Linde 5A, and the relative yields of isomeric dichloroethylenes varied greatly with the catalyst. More acidic sieves (HY, MgX) generally showed lower 1,1/1,2 and trans/cis ratios, Le., cis > trans > 1,1,- others (NaX, KX) gave unusually high (greater than equilibrium) trans/cis ratios. 

There are various methods by which the unsymmetrical dichloroethylene, vinylidene chloride, can be produced commercially. The first process is based on the chlorination of acetylene carried out in acetylene tetrachloride (tetrachloroethane). In the presence of ferric chloride, which acts as a catalyst, acetylene and chlorine combine at 135°C and yield vii lidene chloride. Another method of vinylidene chloride production starts from ethylene, which is chlorinated under controlled conditions to yield, 1,1,2-tri-chloroethane. On heating the latter substance in the presence of an alkali, hydrochloric acid is split off and a mixture of isomeric dichloroethylenes is obtiuned. They can be separated by fractional distillation. 

Two important cases in rotational isomerism may be distinguished by considering the nature of the central bond. When it is a double bond, rotation of one form into another is hindered by a very high potential barrier. This barrier may be so high that the two rotational isomers will be stable enough to make their physical separation possible. An example is 1,2-dichloroethylene (3-4). 

Dichloroethylene (C2H2CI2) has three forms (isomers), each of which is a different substance, (a) Draw Lewis structures of the three isomers, aU of which have a carbon-carbon double bond, (b) Which of these isomers has a zero dipole moment (c) How many isomeric forms can chloroethylene, C2H3CI, have Would they be expected to have dipole moments ... 

A mixture of iodine pentafluoride, slightly more than 2 moles of iodine, pure iron-free Al-shavings, and Al-iodide preheated in a rocking Monel autoclave at 130-135 for 2.5 hrs., cooled in Dry Ice, evacuated, charged with 1,1-difluoro-2,2-dichloroethylene, and shaken 17 hrs. in an ice bath l,l-dichloro-2,2,2-trifluoro-l-iodoethane. Gonversion ca. 80% based on maximum theoretical IF isomeric purity 95-98%. F. e. s. M. Hauptschein and M. Braid, Am. Soc. 83, 2383 (1961). 

We will discuss here two generalizations of the simple example treated in the preceding section. First, consider again an isomerization reaction. This could be a cis-trans conversion in dichloroethylene or a helix-coil transition in a polypeptide, symbolically... 

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