Hexachloroethane, reaction

Smoke-Generating Devices. Smoke generators are used by the military for daytime obscuration and signaling. For field use where portable stable systems ate requited, pyrotechnic devices are often employed. The primary composition since the 1940s has been HC smoke, which generates a cloud of zinc chloride, ZnCl, smoke by a series of reactions between hexachloroethane, C2Clg(HC), zinc oxide, and aluminum (3) (eq. 4—6). The zinc regenerated in... 

Miscellaneous Reactions. Chlorinolysis of mixtures containing 1,1,2-trichloroethane at 550°C was found to give primarily perchloroethylene and hexachloroethane (97). 

Physical properties of hexachloroethane are Hsted in Table 11. Hexachloroethane is thermally cracked in the gaseous phase at 400—500°C to give tetrachloroethylene, carbon tetrachloride, and chlorine (140). The thermal decomposition may occur by means of radical-chain mechanism involving -C,C1 -C1, or CCl radicals. The decomposition is inhibited by traces of nitric oxide. Powdered 2inc reacts violentiy with hexachloroethane in alcohoHc solutions to give the metal chloride and tetrachloroethylene aluminum gives a less violent reaction (141). Hexachloroethane is unreactive with aqueous alkali and acid at moderate temperatures. However, when heated with soHd caustic above 200°C or with alcohoHc alkaHs at 100°C, decomposition to oxaHc acid takes place. 

Photochlorination of tetrachloroethylene, observed by Faraday, yields hexachloroethane [67-72-1]. Reaction with aluminum bromide at 100°C forms a mixture of bromotrichloroethane and dibromodichloroethane [75-81-0] (6). Reaction with bromine results in an equiUbrium mixture of tetrabromoethylene [79-28-7] and tetrachloroethylene. Tetrachloroethylene reacts with a mixture of hydrogen fluoride and chlorine at 225—400°C in the presence of zirconium fluoride catalyst to yield l,2,2-trichloro-l,l,2-trifluoroethane [76-13-1] (CFG 113) (7). 

The nucleophilic reaction of bromotrifluoroethene with alkoxides yields not only the expected addition and addition-elimination products but also a product from a bromophilic reaction of the carbanion intermediate [6] (equation 3) Similar are the reactions of sodium phenoxide with perfluorovinyl ethers in the presence of hexachloroethane or selected vicinal dibromoperfluoroalkanes The intermediate carbanion is trapped in high yield by these sources of Cl or Br, which suggests a... 

Kattenberg and coworkers54 studied the chlorination of a-lithiated sulfones with hexachloroethane. These compounds may react as nucleophiles in a nucleophilic substitution on halogen (path a, Scheme 5) or in an electron transfer reaction (path b, Scheme 5) leading to the radical anions. The absence of proof for radical intermediates (in particular, no sulfone dimers detected) is interpreted by these authors in favour of a SN substitution on X. 

Humic acid and the corresponding fulvic acid are complex polymers whose structures are incompletely resolved. It is accepted that the structure of humic acid contains oxygenated structures, including quinones that can function as electron acceptors, while reduced humic acid may carry out reductions. These have been observed both in the presence of bacteria that provide the electron mediator and in the absence of bacteria in abiotic reactions, for example, reductive dehalogenation of hexachloroethane and tetrachloromethane by anthrahydroquininone-2,6-disulfonate (Curtis and Reinhard 1994). Reductions using sulfide as electron donor have been noted in Chapter 1. Some experimental aspects are worth noting ... 

Under anaerobic conditions, various reactions can occur, and the following are illustrative (a) trichlorofluoromethane -> carbon monoxide (b) hexachloroethane tetrachlo-roethene (c) l,l,l-trichloro-2,2,2-trifluoroethane l,l-dichloro-2,2-difluoroethene (Hur et al. 1994). 

It is well-known that 2- and 3-selenienyllithium derivatives are valuable synthetic intermediates for the preparation of various 2- and 3-substituted selenophenes. In this way, 2- and 3-chloroselenophenes have been obtained by reaction with hexachloroethane at — 70°C.76 Another example has already been shown in connection with inverted reactivity (Section VI,B), and many applications will be demonstrated in subsequent sections. 

Hexachloroethane is released to the air during military operations and training exercises when smoke-producing devices containing it are used. In a smoke pot or grenade, most of it is used up by the smoke-producing reaction. Only small amounts (5% or less) remain after the smoke has formed. 

Hexachloroethane is metabolized by the mixed function oxidase system by way of a two-step reduction reaction involving cytochrome P-450 and either reduced nicotinamide adenine dinucleotide phosphate (NADPH) or cytochrome b5 as an electron donor. The first step of the reduction reaction results in the formation of the pentachloroethyl free radical. In the second step, tetrachloroethene is formed as the primary metabolite. Two chloride ions are released. Pentachloroethane is a minor metabolic product that is generated from the pentachloroethyl free radical. 

In studies using liver microsomes, approximately 99.5% of the hexachloroethane was converted to tetrachloroethene at physiological pHs (Nastainczyk et al. 1982b). When the reaction occurred at higher pHs... 

Both tetrachloroethene and pentachloroethane undergo subsequent hepatic metabolism. Pentachloroethane is reductively dechlorinated by microsomes to yield trichloroethene. (Reductive dechlorination was favored when there were three chlorines on one carbon and at least one chlorine on the vicinal carbon [Thompson et al. 1984], a characteristic shared by hexachloroethane and pentachloroethane). Trichloroethene and tetrachloroethene were then oxidized by hepatic enzymes to form trichloroethanol and trichloroacetic acid as terminal reaction products. Apparently additional dechlorination reactions can occur since labeled dichloroethanol, dichloroacetic acid, monochloroacetic acid, and oxalic acid have been... 

Liver necrosis is another concern following hexachloroethane exposure. Hexachloroethane is metabolized in the centrilobular area of the liver by way of the microsomal mixed function oxidase system. The relatively nonpolar pentachloroethyl free radical is an intermediate in this pathway. The reaction of the free radical with unsaturated lipids in the cellular or organelle membranes could contribute to hepatocyte damage and necrosis. 

Environmental agents that influence microsomal reactions will influence hexachloroethane toxicity. The production of tetrachloroethene as a metabolite is increased by agents like phenobarbital that induce certain cytochrome P-450 isozymes (Nastainczyk et al. 1982a Thompson et al. 1984). Exposure to food material or other xenobiotics that influence the availability of mixed function oxidase enzymes and/or cofactors will change the reaction rate and end products of hexachloroethane metabolism and thus influence its toxicity. 

Neither the mechanism of absorption nor the mechanism of distribution for hexachloroethane has been established. There are indications that free radical reactions may be responsible for some of the toxic effects of hexachloroethane in the liver (Town and Leibman 1984), but the data are not conclusive. When additional data on absorption, distribution and mechanism are available, compound-specific studies on methods for mitigation of toxic effects can be designed. 

As an alternative to radical chlorination, use has been made of carbon tetrachloride and hexachloroethane in the presence of a quaternary ammonium salt, as source of the chloronium ion for reaction with activated alkylbenzenes [38], Benzyl chlorides need the additional activation of a nitro group for their conversion into the corresponding nitrobenzotrichlorides, whereas benzal chlorides do not need the extra activation for a similar conversion. The same synthetic protocol, using hexachloroethane, has been used for the conversion of allylic sulphones into the 1,1-dichloro derivatives [39],... 

Dichlorocarbene has also been generated by the reaction of tetrachloromethane, hexachloroethane, or bromotrichloromethane using 60% aqueous or solid potassium hydroxide in the presence of a tetra-n-butylammonium salt [15, 16]. Yields of insertion products are similar to those obtained by Makosza s procedure. 

In anoxic hypolimnion samples collected from Lower Mystic Lake, MA, hexachloroethane was abiotically transformed into tetrachloroethylene via reductive elimination and to pentachloro-ethane via hydrogenolysis. Tetrachloroethylene accounted for 70% of hexachloroethane in unaltered lake water and 62% in filter-sterilized water after 10 d. Trichloroethylene and pent-achloroethane accounted for <1 and 2% in unaltered lake water and filter-sterilized water, respectively. Disappearance rate constants for hexachloroethane were 0.33/d for unaltered water and 0.26/d for filter-sterilized water. At least 80% of the hexachloroethane disappearance in unaltered water was abiotic in origin due to the reactions with naturally occurring aqueous polysulfides, H2S and (Miller et al, 1998a). 

Butler and Heyes (1998) investigated the reductive dechlorination of hexachloroethane in water by iron sulfide. Tetrachloroethylene was the major product with pentachloroethane as a minor intermediate. Final reaction products were trichloroethylene, c/s-1,2-dichloroethylene, and acetylene. The rate of reaction increased with increasing iron sulfide concentrations and pH. At pH 7.8, first-order rate constants were 0.0726, 0.086, and 0.533/h at iron sulfide concentrations of 10, 25, and 100 g/L, respectively. At an iron sulfide concentration of 100 g/L, first-order rate... 

The original HC smoke mixtures (Type A) contained zinc metal and hexachloroethane, but this composition is extremely moisture- sensitive and can ignite spontaneously if moistened. An alternative approach involves adding a small amount of aluminum metal to the composition, and zinc oxide (ZnO) is used in place of the moisture-sensitive metal. Upon ignition, a sequence of reactions ensues of the type [6]... 

Exhaustive chlorination of quinoline over antimony pentachloride leads to fragmentation into perchlorobenzene and hexachloroethane (1882JCS412). Direct uncatalyzed chlorination of quinoline at 160-190 °C gives at least five chloroquinolines (Scheme 29) among the ten products of reaction detected by gas chromatography (70JHC171). Substitution at position... 

The triphenylphosphine-hexachloroethane system was also used to form oxazolo[5,4-3]pyridines (Equation 62). The reaction conditions tolerated a wide variety of substituents in the 2-position, and even a sterically bulky group did not decrease dramatically the yield of desired products <2005TL9001>. 

Heteropolyacids Hi4[NaPsW29MoOno] and H3PMO12O4 have been shown to be efficient catalysts for consecutive condensation of aldehydes with 5-aminopyrazole -carboxamide and cyclization into pyrazolo[3,4-t4pyrimidines <2007MI1467>. The reaction of ethyl 5-acylaminopyrazoles with hexachloroethane and triphenylphosphine in the presence of a base has been recently reported to afford an imidoyl chloride that reacted in situ with ethylamine yielding an amidine in 71% yield that cyclized readily in DMF in the presence of potassium carbonate to yield pyrazolopyrimidines in 65% yield <2007TL3983>. 

For munitions contg HC (hexachloroethane) smoke fillings, the reaction should be hot and preferably produce Some slag, but only little gas... 

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