Chloroethane, dehydrochlorination

Carbon tetrachloride can be reduced to chloroform using a platinum catalyst (10) or zinc and acid. With potassium amalgam and water, carbon tetrachloride can be totally reduced to methane. It is widely employed as an initiator in the dehydrochlorination of chloroethanes at 400—600°C ... 

The catalytic dehydrochlorination of tetra-chloroethane has been studied by Shvets, Lebedev, and Aver yanov [Kinetics and Catalysis, 10 (28), 1969]. 

Mochida, I. Yoneda, Y. Dehydrochlorination and dechlorination of chloroethanes on chromia catalyst. 

Order of reactivities in the dehydrochlorination of chloroethanes on different catalysts [186]... 

The catalysts which operate by means of an E2 mechanism give a high proportion of reaction products which are formed by the anti-elimination. This fact has been discussed in Sect. 2.1 and only few remarks need to be added here. Quantum chemical calculations [73] on the transition state of the dehydrochlorination of chloroethane, initiated by an attack of a basic species, confirmed the preference of the anti-elimination over the syn-mode. On the contrary, calculations on the transition state for non-catalytic (homogeneous) thermal elimination [201,202] confirmed the syn-elimination path. 

Another major chlorinated hydrocarbon is vinyl chloride. For many years acetylene was the sole raw material for the production of vinyl chloride by a catalytic fixed bed vapor-phase process. This process is characterized by high yields and modest capital investment. Nevertheless, the high relative cost of acetylene provided an incentive to replace it in whole or in part by ethylene. The first step in this direction was the concurrent use of both raw materials. Ethylene was chlorinated to di-chloroethane, and the hydrogen chloride derived from the subsequent dehydrochlorination reacted with acetylene to form additional vinyl chloride. 

This process is shown schematically in Figure 7. The ethylene part of the feed reacts with chlorine in the liquid phase to produce 1,2-di-chloroethane (EDC) by a simple addition reaction, in the presence of a ferric chloride catalyst (9). Thermal dehydrochlorination, or cracking, of the intermediate EDC then produces the vinyl chloride monomer and by-product HC1 (1). Acetylene is still needed as the other part of the over-all feed, to react with this by-product HC1 and produce VCM as in the all-acetylene route. 

From the temperature dependence of MC consumption shown in Fig. 8.17, an apparent activation energy for the reaction is estimated to be ca. 70 kJ mol-1. This kind of dehydrochlorination reaction from chloroethanes has previously been shown to occur on solid acids and bases.,8) Since the Ti02 surface has Lewis acid sites, the dehydrochlorination reaction may proceed on these acid sites. It is suggested that some of the HC1 produced remains on the Ti02 surface and may inhibit this reaction, but under photoillumination HC1 would be removed by a photocatalytic action of Ti02 as discussed below. 

In Fig. 25, we give scale diagrams for syw-periplanar, cmli-periplanar, and syn-cyclic dehydrochlorination of chloroethane with potassium alkoxide. The standard expression for an ion-dipole interaction is given in (194) (Amis, 1966), in which the negative and positive signs are... 

CH3CF2CI + 2HC1 1,1-Difluoro-l-chloroethane is then dehydrochlorinated CH3CF2CI CH2—CF2 + HQ... 

Pyrolysis of 1,1 -difluoroethane in the presence of a catalyst results in dehydrofluorination and yields Another method is comprised of dehydrochlorination of 1 -fluoro-2-chloroethane at 500°C in the presence of 1,2-diethylene chloride.f l f ] This reaction has a selectivity of 100% and a conversion yield of 15%. 

Vinyl chloride dehydrochlorination 1,2-dichlorethane chloromethanes, chloroethanes, chloroethylenes... 

The unimolecular gas-phase elimination kinetics of 2-methoxy-l-chloroethane, 3-methoxy-l-chloropropane, and 4-methoxy-l-chlorobutane has been studied using density functional theory (DFT) methods. Results calculated for 2-methoxy-l-chloroethane and 3-methoxy-l-chloropropane suggest that the corresponding olefin forms by dehydrochlorination through a concerted nonsynchronous four-centered cyclic transition state. In the case of 4-methoxy-l-chlorobutane, in addition to the 1,2-elimination mechanism, anchimeric assistance by the methoxy group, through a polar five-centered cyclic transition state, provides 4-methoxybutene, tetrahydrofuran, and chloromethane. Polarization of the C-Cl bond is rate limiting in these elimination reactions. 

---