脱塩素、脱塩素反応

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/08/15 17:33:02」(JST)

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Reductive dechlorination is degradation of chlorinated organic compounds by chemical reduction with release of inorganic chloride ions.

Biological

In a biological context chlorine behaves similarly to other atoms in the halogen chemical series, and thus reductive dechlorination can be considered to fall within a somewhat broader class of biological reactions known as reductive dehalogenation reactions, in which the removal of a halogen substituent from an organic molecule occurs with a simultaneous addition of electrons to the molecule. This can be further subdivided into two types of reaction processes, the first of which, hydrogenolysis, is the replacement of the halogen atom with a hydrogen atom. The second, vicinal reduction (sometimes called, dihaloelimination), involves the removal of two halogen atoms that are adjacent on the same alkane or alkene molecule, leading to the formation of an additional carbon-carbon bond.^[1]

Biological reductive dechlorination is often catalyzed by certain species of bacteria. Sometimes the bacterial species are highly specialized for organochlorine respiration and even a particular electron donor, as in the case of Dehalococcoides and Dehalobacter. In other examples, such as Anaeromyxobacter, bacteria have been isolated that are capable of using a variety of electron donors and acceptors, with a subset of possible electron acceptors being organochlorines.^[2]

In many instances, microbiological reductive dechlorination of chlorinated organic molecules is important for bioremediation of polluted groundwater. One particularly important example for public health^[3] is the organochloride respiration of the dry-cleaning solvent, tetrachloroethylene (PCE), and the engine degreasing solvent trichloroethylene (TCE) by naturally occurring anaerobic bacteria, often members of the candidate genera Dehalococcoides. Bioremediation of these chloroethenes can occur when other microorganisms at the contaminated site provide H₂ as a natural byproduct of various fermentation reactions. The dechlorinating bacteria use this H₂ as their electron donor, ultimately replacing chlorine atoms in the chloroethenes with hydrogen atoms via hydrogenolytic reductive dechlorination. If the soil and groundwater contain enough organic electron donor and the appropriate strains of Dehalococcoides, this process can proceed until all of the chlorine atoms are removed, and TCE is dechlorinated completely via dichloroethene (DCE) and vinyl chloride (VC) to ethene, a harmless end-product.^[4]

Electrochemical

The electrochemical reduction of chlorinated chemicals such as chlorinated hydrocarbons and chlorofluorocarbons (CFCs) can be carried out by electrolysis in appropriate solvents, such as mixtures of water and alcohol. The cathode transfers electrons to the molecule, which decomposes to produce the corresponding hydrocarbon (hydrogen atoms substitute the original chlorine atoms) and free chloride ions. For instance, the reductive dechlorination of CFCs is complete and produces several HFCs plus chloride.^[5]

Radiation

It is known that by gamma irradiation of PCBs that they can be converted into biphenyl and inorganic chloride, this is formally a reduction of the organic compound as hydrogen is added. See the Polychlorinated biphenyl page for more details of this destruction method. This reductive destruction method works for many organochlorine compounds, for instance carbon tetrachloride when irradiated tends to form chloroform and chloride anions.

References

^ Mohn and Tiedje. Microbial reductive dehalogenation. Microbiol Rev (1992) vol. 56 (3) pp. 482-507 PMID 1406492
^ Smidt and de Vos. Anaerobic microbial dehalogenation. Annu Rev Microbiol (2004) vol. 58 pp. 43-73 PMID 15487929
^ Kielhorn et al. Vinyl chloride: still a cause for concern. Environ Health Perspect (2000) vol. 108 (7) pp. 579-88 PMID 10905993
^ McCarty. Breathing with chlorinated solvents. Science (1997) vol. 276 (5318) pp. 1521-2 PMID 9190688
^ P. L Cabot, M. Centelles, and L. Segarra and Juan Casado Palladium-Assisted Electrodehalogenation of 1,1,2-Trichloro-1,2,2-trifluoroethane on Lead Cathodes Combined with Hydrogen Diffusion Anodes J. Electrochem. Soc., Volume 144, Issue 11, p. 3749 (1997)

English Journal

Electron efficiency of nZVI does not change with variation of environmental parameters.

Schöftner P1, Waldner G2, Lottermoser W3, Stöger-Pollach M4, Freitag P5, Reichenauer TG6.
The Science of the total environment.Sci Total Environ.2015 Dec 1;535:69-78. doi: 10.1016/j.scitotenv.2015.05.033. Epub 2015 May 23.
Nanoscale zero-valent iron particles (nZVI) are already applied for in-situ dechlorination of halogenated organic contaminants in the field. We performed batch experiments whereby trichloroethene (TCE) was dehalogenated by nZVI under different environmental conditions that are relevant in practice.
PMID 26006053

Bioelectrochemically-assisted reductive dechlorination of 1,2-dichloroethane by a Dehalococcoides-enriched microbial culture.

Leitão P1, Rossetti S2, Nouws HP3, Danko AS4, Majone M5, Aulenta F6.
Bioresource technology.Bioresour Technol.2015 Nov;195:78-82. doi: 10.1016/j.biortech.2015.06.027. Epub 2015 Jun 11.
The aim of this study was to verify the possibility to use a polarized graphite electrode as an electron donor for the reductive dechlorination of 1,2-dichloroethane, an ubiquitous groundwater contaminant. The rate of 1,2-DCA dechlorination almost linearly increased by decreasing the set cathode pot
PMID 26099437

Evaluation of PCB dechlorination pathways in anaerobic sediment microcosms using an anaerobic dechlorination model.

Demirtepe H1, Kjellerup B2, Sowers KR3, Imamoglu I4.
Journal of hazardous materials.J Hazard Mater.2015 Oct 15;296:120-7. doi: 10.1016/j.jhazmat.2015.04.033. Epub 2015 Apr 14.
A detailed quantitative analysis of anaerobic dechlorination (AD) pathways of polychlorinated biphenyls (PCBs) in sediment microcosms was performed by applying an anaerobic dechlorination model (ADM). The purpose of ADM is to systematically analyze changes in a contaminant profile that result from m
PMID 25913678

Japanese Journal

2,2',3,4,4',5'-六塩素化ビフェニル（CB138）のモルモットにおけるin vivo代謝

太田千穂,原口浩一,加藤善久,遠藤哲也,古賀信幸,Ohta Chiho,Haraguchi Koichi,Kato Yoshihisa,Endo Tetsuya,Koga. Nobuyuki,オオタチホ,ハラグチコウイチカトウヨシヒサ,エンドウテツヤ,コガノブユキ
福岡医学雑誌 102, 167-174, 2011-04-25
… hand, the exact chemical structures of M-1 and M-2 were determined to be 6'-OH-2, 3, 3',4,4'-pentaCB and 4'-OH-2, 2',3,4,5'-pentaCB, respectively, by comparison of the retention time and mass fragmentation of the synthetic authentic amples in GC-MS. From these results, it is suggested that the metabolism of CB138 in guinea pigs may proceed by three pathways, a direct hydroxylation at 3'-position, and also the formation of 2',3'- or 3', 4'-epoxide and subsequent dechlorination and that three metabolites show the different mode of distribution and …
NAID 120003075310

Reductive dechlorination of chlorophenols in estuarine sediment of Lake Shinji and characterization of microbial community structure(Protection of Water Quality,Poster,2) Environmental Fate and Safety Assessment)