Abstract
Polyhalogenated benzenes, when reacted with hydrogen at atmospheric pressure or sodium hypophosphite and in the presence of Pd/C catalyst in a multi-phase system constituted by a hydrocarbon solvent, a strong alkaline aqueous solution and a quaternary onium salt, allow the rapid and progressive replacement of all the chlorine atoms. Thus, operating with hydrogen at 50°C, 1, 2, 4, 5-tetrachlorobenzene yields benzene after 50 min in 99% yield and using a Pd/Cl ratio of 1/120. The presence of an alkaline medium and a phase-transfer agent is synergic. The enhancement of the reaction rate, compared with the already known methods, has been attributed to the enhanced absorption of hydrogen by the catalyst surtace, to partition of halogenated compounds between the hydrocarbon solution and the liquid phase of the phase-transfer agent and to the rapid removal of HC1 absorbed on Pd/C by the alkaline medium. The reaction is effective also with deactivatedP-methoxyaryl halides.
Riassunto
Gli alogenuri aromatici sono facilmente ridotti ai corrispondenti sistemi non aiogenati per mezzo di palladio supportato su carbone, quando sono posti a reagire con idrogeno molecolare o ipofosfito di sodio in un sistema multifasico costituito da un idrocarburo alifatico, una soluzione acquosa di KOH e un sale di onio; quest’ultimo, essendo insolubile in entrambe le fasi, ricopre come un film liquido il catalizzatore supportato. In questo modo, operando con idrogeno a 50°C, il 1,2, 4, 5-tetraclorobenzene ridotto a benzene (99%) in 50 minuti e usando un rapporto Pd/Cl uguale a 1/120. La reazione è efficace anche con i disattivati para-metossi sostituiti. L’accrescimento della velocità di reazione, comparato ai metodi già noti, è attribuito all’aumentato assorbimento di idrogeno sulla superficie del catalizzatore, alia favorita ripartizione dell’aromatico alogenato fra la soluzione idrocarburica e il sale di onio quaternario e alla rapida rimozione dell’acido cloridrico dalla superficie del catalizzatore per mezzo della soluzione concentrata di idrossido di potassio.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Akagaii A., Polite J. C, Chanon M., 1985.Reactive Aluminium Powders for the Reduction of Haloarenes. Application of the «Planning of Experiments» Method for the Optimisation of Obtaining Reactive Metal Powder. Org. Prep. Proc. Int., 17: 219–223.
Anwer M. K., Spatola A. F., 1975.Applications of ammonium formate catalytic transfer hydrogenolysis. IV: a facile method for dehalogenation of aromatic chlorc carbons. Tetrahedron Letters, 26: 1381–1384.
Anwer M. K., Sherman D. B., Roney J. G., Spatola A., 1989.Applications of ammonium formate catalytic transfer hydrogénation. 6. Analysis of catalyst, donor quantity, and solvent effects upon the efficacy of dechlorination. J. Org. Chem., 54: 1284–1289.
Boyer S. K., 1986.Dehalogenation of Aryl and α-Araliphatic Halides. U. S. Pat., 4, 618, 686.
Boyer S. K., Bach J., Mckenna J., Jagdmann E., 1985.Mild Hydrogen-Transfer Reductions Using Sodium Hypophosphite. J. Org. Chem., 50: 3408–3411.
Coq B., Ferrat G., Figueraz F., 1986.Conversion of chlorobenzene over palladium and rhodium catalysis of widely varying dispersion. J. Catal., 101: 434–45.
de Koning A. J., 1975.Hydrogenolysis of aryl halides in the presence of Raney nickel in alkaline medium. Org. Prep. Proc. Int., 7: 31–34.
Dehmlow E. V., Dehmlow S. S., 1983.Phase-Transfer Catalysis. 2nd ed., Verlag Chemie, Weinheini.
DiNi P., Bart J. C. J., Giordano N., 1975.Properties of Poly amide-based catalysts. Part I. Hydrodehalogenation of Chlorobenzene. J. Chem. Soc. Perkin Trans., II 1479–1481.
Käsbauer J., Fiege H., Schmidt H., Wedemeyer K., 1988.Verfahren zur Herstellung von 1,2- Dichlorobenzol. Europ. Pat. 0 301 343.
Kiebon A. P. G., Van Rantwijk R., 1977.Hydrogenation and Hydrogenolysis in Synthetic Organic Chemistry. Delft University Press, Delft, The Netherlands.
Montanari F., Landini D., Rolla F., 1982.Phase-Transfer Catalyzed Reaction. Top. Curr. Chem., 101: 147–200.
Pandey P. N., Purkayastha M. L., 1982.Palladium-Catalyzed Hydrodehalogenation of Haloaromatic Compounds. Synthesis: 866–867.
Pearson R. G., Songstand J., 1967.Application of the principle of hard and soft acids and bases to organic chemistry. J. Am. Chem. Soc, 89: 1827.
Pinder A. R., 1980.The Hydrogenolysis of Organic Halides. Synthesis: 425–452.
Rylander P. N., 1973.Catalytic Hydrogenolysis in Organic Synthesis. Academic Press, New York: 235–248.
Starks C., Liotta C., 1978.Phase-Transfer Catalysis. Academic Press, New York.
Tundo P., 1991.Continuous Flows Methods in Organic Synthesis. Ellis Horwood, Chichcstcr, Chapt. 4.
Wiener H., Bllm H., Sasson Y., 1991.Transfer hydrogenolysis of aryl halides and other hydrogen acceptors by formate salts in the presence of Pd/C catalyst. J. Org. Chem., 56: 6145–6148.
Author information
Authors and Affiliations
Additional information
Nella seduta del 12 giugno 1992.
Rights and permissions
About this article
Cite this article
Tundo, P., Marques, C.A. & Selva, M. Hydrodehalogenation of polychlorinated aromatics with Pd/C catalyst under multiphase conditions.. Rend. Fis. Acc. Lincei 3, 283–294 (1992). https://doi.org/10.1007/BF03002936
Issue Date:
DOI: https://doi.org/10.1007/BF03002936