Chemistry:Tetrachlorocyclopropene
Tetrachlorocyclopropene is a chemical compound with the formula C3Cl4. A colorless liquid, the compound is a reagent used to prepare acetylene derivatives and in organic synthesis.[1] It was first reported by Tobey and West.[2] It is prepared by addition of dichlorocarbene to trichloroethylene and then further treating the resultant pentachlorocyclopropane with base to perform dehydrochlorination.[3]
Treatment with a good chloride-accepting Lewis acid affords trichlorocyclopropenium (C
3Cl+
3) salts, a carbocation that is aromatic like other cyclopropenium ions, as predicted by Hückel's rule. Aluminum trichloride is most commonly used as the Lewis acid, giving the tetrachloroaluminate salt:[1][4]
- C
3Cl
4 + AlC
3 → [C
3Cl+
3][AlCl−
4]
The structure of trichlorocyclopropenium has been confirmed by X-ray crystallography of this salt.[5] Salts of hexachloroantimonate (SbCl−
6), tetrachloroferrate (FeCl−
4), and tetrachlorogallate (GaCl−
4) have also been prepared from other Lewis acids.[4] Tetrachlorocyclopropene appears inert towards boron trifluoride and trichloride, but reacts with boron tribromide to give tetrabromocyclopropene, with gaseous boron trichloride leaving solution:[2]
- 3 C
3Cl
4 + 4 BBr
3 → 3 C
3Br
4 + 4 BCl
3
Arylpropiolate esters may be prepared from trichlorocyclopropenium by reacting with arenes, followed by hydrolysis in alcohols.[1] This can be done without isolating the trichlorocyclopropenium ion.
Trichlorocyclopropene is also used to prepare arylcyclopropanones by a two-step, one-pot procedure beginning with a Friedel-Crafts-like arylation, with trichlorocyclopropenium as an intermediate prepared in situ:[1]
- C
3Cl
4 + ArH → ArC
3Cl
3 + HCl (ArH = arene)
The aryltetrachlorocyclopropenes are then hydrolyzed to give the keto-alcohol:
- ArC
3Cl
3 + 2 H
2O → ArC
3O(OH) + 3 HCl
References
- ↑ 1.0 1.1 1.2 1.3 Oliver Reiser; Armin de Meijere; Brittany M. Klootwyk; Gregory R. Boyce (2019). "Tetrachlorocyclopropene". EEROS. doi:10.1002/047084289X.rt028. ISBN 978-0-471-93623-7. https://onlinelibrary.wiley.com/doi/10.1002/047084289X.rt028.pub2.
- ↑ 2.0 2.1 Tobey, S. W.; West, R. (1963). "Tetrachlorocyclopropene and Hexachlorocyclopropane from Pentachlorocyclopropane". Tetrahedron Letters 4 (18): 1179–1182. doi:10.1016/S0040-4039(01)90799-3. https://www.sciencedirect.com/science/article/pii/S0040403901907993.
- ↑ Tobey, S. W.; West, R. (1966). "Tetrachlorocyclopropene, Tetrabromocyclopropene, and Some Fluorinated Cyclopropenes and Cyclopropanes". Journal of the American Chemical Society 88 (11): 2481–2488. doi:10.1021/ja00963a023. Bibcode: 1966JAChS..88.2481T. https://pubs.acs.org/doi/10.1021/ja00963a023.
- ↑ 4.0 4.1 West, R.; Sadô, A.; Tobey, S. W. (1966). "Synthesis of Trihalocyclopropenium Salts and Normal Coordinate Analysis of C3Cl3+". Journal of the American Chemical Society 88 (11): 2488–2494. doi:10.1021/ja00963a024. https://pubs.acs.org/doi/10.1021/ja00963a024.
- ↑ Clark, George R.; Taylor, Michael J.; Steele, Derek (1993). "Crystal Structure Determination of C3Cl3+AlCl4- and ab initio Studies of the Structure and Vibrational Spectrum of the Trichlorocyclopropenium Cation". Journal of the Chemical Society, Faraday Transactions 89 (19): 3597. doi:10.1039/ft9938903597.
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