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| NIRE Annual Report | 
| 1998 |
Catalytic Dehalogenation of Organic Halides under Mild ConditionsCombustion Engineering DivisionThermal Energy and Combustion Engineering Department |
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Objectives
The development of effective procedures for dehalogenation of organic halides is a current issue in protecting ourselves from pollution by industrial halogen-containing organic wastes. In this study, we demonstrate that dehalogenation of organic halides can be completed in a 2-propanol solution of NaOH in the presence of noble metal catalyst under mild conditions.
Results
Catalytic dechlorination of 1,2,4-trichlorobenzene was carried out in an alcohol solution containing base compounds in the presence of Pd/C catalyst at 64ºC. Table 1 summarizes the conversion of 1,2,4-trichlorobenzene and the yield of mono-chlorobenzene (1-Cl), di-chlorobenzene (2-Cl) and benzene when various solvents and base compounds were used. It was found that NaOH and KOH are effective base compounds; the reaction was completed within 3 h by using 2-propanol as a solvent. In comparison, Na2CO3, Ca(OH)2 and (C2H5)3N were less active for the reaction, where Na2CO3 and Ca(OH)2 are insoluble to 2-propanol. When ethanol, 1-propanol and 2-butanol were used as a solvent, the conversion of 1,2,4-trichlorobenzene and the yield of benzene were very low. On the other hand, 2-propanol led to a high yield of benzene, indicating that 2-propanol is a suitable solvent for the dechlorination reaction. The following reaction scheme has been postulated including hydrogen-transfer from 2-propanol to aryl chlorides (Ar-Cl), where a hydrogen-transfer species is denoted as H*.
CH3CH(OH)CH3 CH3C(O)CH3 + 2H*
(1) Ar-Cl + 2H* (2) HCl + NaOH (3) (1) + (2) + (3) Ar-Cl + CH3CH(OH)CH3 + NaOH (4)
This catalytic system is expected to be effective for dehalogenation of a variety of toxic halogen-containing organic compounds.
Selected Publications
1) Catalytic Dechlorination of Polychlorinated Biphenyls with Carbon-supported Noble Metal Catalysts, Chemosphere, 33, 1523-1530 (1996). 2) Hydrogen-transfer Hydrodehalogenation of Aromatic Halides with Alcohols in the Presence of Noble Metal Catalysts, J. Mol. Catal. A: Chemical, 125, 135-142 (1997). 3) Catalytic Dehalogenation of Organic Halides in 2-Propanol with Pd/C Catalyst, Nippon Kagaku Kaishi, 369-371 (1998).
