[79-01-6]  · C2HCl3  · Trichloroethylene  · (MW 131.38)

(starting material for the preparation of dichloroacetylene;1-4 reagent for the preparation of alkynic ethers;12 reagent for ethynylation and vinylation)

Alternate Name: trichloroethene.

Physical Data: bp 86.9 °C; d 1.464 g cm-3.

Solubility: practically insol water; miscible with ether, alcohol, chloroform. Drying: can be dried by distillation from phosphorus pentoxide.

Handling, Storage, and Precautions: is slowly decomposed (with formation of HCl) by light in the presence of moisture. Avoid prolonged exposure to excessive heat. Moderate exposures to humans can cause symptoms similar to alcohol inebriation. Higher concentrations can have a narcotic effect. Deaths occurring after heavy exposure have been attributed to ventricular fibrillation. Found to induce hepatocellular carcinomas in mice. Dichloroacetylene (see below) is known to be toxic and, in its pure form, explosive. Use in a fume hood.

Preparation of Dichloroacetylene.

A dichloroacetylene-ether complex is readily prepared from trichloroethylene with Lithium Hexamethyldisilazide in hexanes at -78 °C1 or with Potassium Hydride and catalytic methanol in THF at room temperature.2 Alternatively, the dichloroacetylene-ether complex can be obtained from a mixture of trichloroethylene and diethyl ether in an aqueous solution of Sodium Hydroxide in the presence of either a phase transfer catalyst3 or a catalytic amount of Dimethyl Sulfoxide.4

Dichloroacetylene reacts with tertiary ketone or ester enolates to give chloroethynyl adducts in 64-90% yields.5 The chloroethynyl group can be converted to the ethynyl derivative using Copper powder in HOAc/THF, or can be directly reduced (H2/Lindlar catalyst) to the vinyl derivative (eq 1).5 This method is limited to tertiary enolates.

Additional enolate addition/elimination reactions with chloroacetylenes that yield alkynyl derivatives have been reported for 1-Chloro-2-phenylacetylene5 and 1-chloro-2-phenylthioacetylene.5 Similar alkynylations have been reported for tertiary b-dicarbonyl enolates using alkynyllead triacetates6 or alkynyliodonium tetrafluoroborates.7 Direct vinylations have been reported using alkenyllead triacetates,8 vinyl halides and nickel catalysis,9 or enol ether iron complexes.10

Dichloroacetylene reacts with alkylthiolates under mild conditions to yield bis(alkylthio)acetylenes (eq 2).11

Preparation of Alkynic Ethers.

Secondary alcohols, on treatment in THF with 2 equiv of potassium hydride and trichloroethylene, followed by n-Butyllithium and a primary iodide (or water), are converted in 66-87% yield to alkynic ethers (eq 3).12 The potassium alkoxides react with trichloroethylene first to generate and then to add to dichloroacetylene. The resulting dichloro enol ethers on treatment with n-butyllithium are converted to the corresponding acetylides, which are then either alkylated or protonated.

Reaction with Other Nucleophiles.

Trichloroethylene reacts with the enolate of 2,6-dimethylcyclohexenone (Lithium Diisopropylamide, HMPA, in THF, -78 °C) to yield the dichlorovinyl adduct (1) in 60% yield.5,13 While the dichlorovinyl adduct may serve as a masked ethynyl group,13 the reagent of choice is the independently generated dichloroacetylene described above. Under more vigorous conditions (Sodium Hydride, HMPA, refluxing THF) the tertiary enolate of diethyl ethylmalonate reacts to give dichlorovinyl adduct (2) in 64% yield.5 These reactions have been demonstrated to proceed through the in situ generation of dichloroacetylene.14 Comparable reactions have been reported for CClF=CHCl,5 CF2=CHF,15,16 CF2=CH2,16 and Chlorotrifluoroethylene.16

Trichloroethylene reacts with Sodium Amide and excess dimethylamine to yield bis(dimethylamino)acetylene (eq 4).17 With lithium dialkylamides in ether as the base in the presence of excess dialkylamines, the intermediate 1,2-dichloro dialkyl enamines or chloro ketene aminals can be isolated (eq 5).18 Trichloroethylene also reacts with secondary aliphatic amines in the presence of an aqueous solution of NaOH and a catalytic quantity of Benzyltriethylammonium Chloride to give glycinamides (eq 6).19

Trichloroethylene will undergo palladium-catalyzed coupling with arylmagnesium halides to yield (Z)-1,2-dichloroethylenes (eq 7).20 Under alternate conditions with alkylmagnesium halides, 1,1-dichloroalkenes are obtained (eq 8).21

1. Kende, A. S.; Fludzinski, P. S 1982, 455.
2. Denis, J.-N.; Moyano, A.; Greene, A. E. JOC 1987, 52, 3461.
3. Pielichowski, J.; Popielarz, R. S 1984, 433.
4. Pielichowski, J.; Bogdal, D. JPR 1989, 331, 145.
5. (a) Kende, A. S.; Fludzinski, P. TL 1982, 23, 2373. (b) Kende, A. S.; Fludzinski, P.; Hill, J. H.; Swenson, W.; Clardy, J. JACS 1984, 106, 3551.
6. (a) Moloney, M. G.; Pinhey, J. T.; Roche, E. G. JCS(P1) 1989, 333. (b) Hashimoto, S.; Miyazaki, Y.; Shinoda, T.; Ikegami, S. CC 1990, 1100.
7. Ochiai, M.; Ito, T.; Takaoka, Y.; Masaki, Y.; Kunishima, M.; Tani, S.; Nagao, Y. CC 1990, 118.
8. Moloney, M. G.; Pinhey, J. T. JCS(P1) 1988, 2847.
9. Millard, A. A.; Rathke, M. W. JACS 1977, 99, 4833.
10. (a) Chang, T. C.; Rosenblum, M.; Samuels, S. B. JACS 1980, 102, 5930. (b) Chang, T. C.; Rosenblum, M.; Simms, N. OS 1988, 66, 95.
11. Riera, A.; Cabre, F.; Moyano, A.; Pericas, M. A.; Santamaria, J. TL 1990, 31, 2169.
12. (a) Moyano, A.; Charbonnier, F.; Greene, A. E. JOC 1987, 52, 2919. (b) Denmark, S. E.; Senanayake, C. B. W.; Ho, G.-D. T 1990, 46, 4857. (c) Almansa, C.; Moyano, A.; Pericas, M. A.; Serratosa, F. S 1988, 707. (d) Loffler, A.; Himbert, G. S 1992, 495.
13. (a) Kende, A. S.; Benechie, M.; Curran, D. P.; Fludzinski, P.; Swenson, W.; Clardy, J. TL 1979, 4513. (b) Kende, A. S.; Fludzinski, P. OS 1986, 64, 73.
14. Kende, A. S.; Fludzinski, P. TL 1982, 23, 2369.
15. Kende, A. S.; Fludzinski, P. JOC 1983, 48, 1384.
16. Crouse, G. D.; Webster, J. D. JOC 1992, 57, 6643.
17. Rene, L.; Janousek, Z.; Viehe, H.-G. S 1982, 645.
18. van der Heiden, R.; Brandsma, L. S 1987, 76.
19. Pielichowski, J.; Popielarz, R. T 1984, 40, 2671.
20. Minato, A.; Suzuki, K.; Tamao, K. JACS 1987, 109, 1257.
21. Ratovelomanana, V.; Linstrumelle, G.; Normant, J.-F. TL 1985, 26, 2575.

Pawel Fludzinski

Lilly Research Centre, Windlesham, UK

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