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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/10/03 23:18:30」(JST)

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"Fluorination" redirects here. For the addition of fluoride to drinking water, see water fluoridation.

Halogenation is a chemical reaction that involves the reaction of a compound, usually an organic compound, with a halogen. Dehalogenation is the reverse, the removal of a halogen from a molecule.^[1] The pathway and stoichiometry of halogenation depends on the structural features and functional groups of the organic substrate as well as the halogen. Inorganic compounds, for example. metals, also undergo halogenation.

Halogenation of organic compounds

There are several processes for the halogenation of organic compounds, including free radical halogenation, ketone halogenation, electrophilic halogenation, and halogen addition reaction. The determining factors are the functional groups. Saturated hydrocarbons typically do not add halogens but undergo free radical halogenation, involving substitution of hydrogen atoms by halogen. Unsaturated compounds, especially alkenes and alkyne]s, add halogens. Aromatic compounds are subject to electrophilic halogenation.^[2]

The facility of halogenation is influenced by the halogen. Fluorine and chlorine are more electronegative and are more aggressive halogenating agents. Bromine is a weaker halogenating agent than both fluorine and chlorine, while iodine is least reactive of them all. The facility of dehydrohalogenation follows the reverse trend: iodine is most easily removed from organic compounds and organofluorine compounds are highly stable. Bromination and iodination are more likely to substitute at the beta carbon.^[3]

Fluorination

Organic compounds, saturated and unsaturated alike, react readily, usually explosively, with fluorine. This process requires highly specialized conditions. In practice, organic compounds are fluorinated electrochemically. Reactions occur at an anode using hydrogen fluoride as the source of fluorine. The method is called electrochemical fluorination. Aside from F₂ and its electrochemically generated equivalent, a variety of fluorinating reagents are known such as xenon difluoride and cobalt(III) fluoride.

Chlorination

Chlorination is generally highly exothermic. Both saturated and unsaturated compounds react directly with chlorine, the former usually requiring UV light to initiate homolysis of chlorine. Chlorination is conducted on a large scale industrially, major process include routes to 1,2-dichloroethane (precursor to PVC) and various chlorinated ethanes as solvents. Competitive with direct chlorination (use of Cl₂) is oxychlorination which uses hydrogen chloride in combination with oxygen.^[4]

Bromination

Bromination is more selective than chlorination because the reaction is less exothermic. Most commonly bromination is conducted by the addition of Br₂ to alkenes. Bromination of saturated hydrocarbons and aromatic substrates is common in nature, giving rise to a host of organobromine compounds. The usual catalyst is the bromoperoxidase which utilizes bromide in combination with oxygen as an oxidant. An example of bromination can be found in the organic synthesis of the anesthetic halothane from trichloroethylene:^[5]

Iodination

Iodine is the least reactive halogen and is reluctant to react with most organic compounds. The addition of iodine to alkenes is the basis of the analytical method called the iodine number, a measure of the degree of unsaturation for fats. The iodoform reaction involves degradation of methyl ketones.

Reaction mechanisms

The addition of halogens to alkenes is usually thought to proceed via intermediate salts of halonium ions. In special cases, such intermediates have been isolated.^[6]

Structure of a bromonium ion

Alkanes react via free-radical routes, and the regiochemistry of these reactions is usually determined by the relative weakness of the available C-H bonds. The preference for reaction at tertiary and secondary positions results from greater stability of the corresponding free radicals and the transition state leading to them. The bond-dissociation enthalpy to form a free radical by a breaking a bond between a hydrogen atom and a carbon atom is greatest for a methyl carbon, and it decreases for a primary carbon, a secondary carbon, and a tertiary carbon. The more highly substituted the carbon, the less energy is required to form the free radical. .

Related reactions

Specific halogenation methods are the Hunsdiecker reaction (from carboxylic acids) and the Sandmeyer reaction (arylhalides).

Inorganic chemistry

All elements aside from argon, neon, and helium form fluorides by direct reaction with fluorine. Chlorine is slightly more selective, but still reacts with most metals and heavier nonmetals. Following the usual trend, bromine is less reactive and iodine least of all. Of the many reactions possible, illustrative is the formation of gold(III) chloride by the chlorination of gold. The chlorination of metals is usually not very important industrially since the chlorides are more easily made from the oxides and the hydrogen halide. Where chlorination of inorganic compounds is practiced on a relatively large scale is for the production of phosphorus trichloride and sulfur monochloride.^[7]

References

^ Yoel Sasson "Formation of Carbon–Halogen Bonds (Cl, Br, I)" in Patai's Chemistry of Functional Groups, 2009, Wiley-VCH, Weinheim. doi:10.1002/9780470682531.pat0011
^ Ilustrative procedure for chlorination of an aromatic compound: Edward R. Atkinson, Donald M. Murphy, and James E. Lufkin (1951), "dl-4,4',6,6'-Tetrachlorodiphenic Acid", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV4P0872 ; Coll. Vol. 4: 872
^ MiVk6UhtgX8C&pg=PA159&dq=fluorination+halogenation+organic+chemistry&hl =en&ei=VHgvTs7KHIuXtweek8CkCQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCwQ6AEwAA#v=onepage&q&f=false ISBN=0-12-393201-7
^ M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
^ Synthesis of essential drugs, Ruben Vardanyan, Victor Hruby; Elsevier 2005 ISBN 0-444-52166-6
^ T. Mori, R. Rathore (1998). "X-Ray structure of bridged 2,2'-bi(adamant-2-ylidene) chloronium cation and comparison of its reactivity with a singly bonded chloroarenium cation". Chem. Commun. (8): 927–928. doi:10.1039/a709063c.
^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 0080379419.

English Journal

Detection of dehalogenation impurities in organohalogenated pharmaceuticals by UHPLC-DAD-HRESIMS.

Regalado EL1, Dermenjian RK2, Joyce LA2, Welch CJ3.Author information 1Merck Research Laboratories, Rahway, NJ 07065, USA. Electronic address: erik.regalado@merck.com.2Merck Research Laboratories, Rahway, NJ 07065, USA.3Merck Research Laboratories, Rahway, NJ 07065, USA. Electronic address: christopher_welch@merck.com.AbstractThe presence of dehalogenated impurities is often observed in halogen-containing pharmaceuticals, and can present a difficult analytical challenge, as the chromatographic behavior of the halogenated drug and the hydrogen-containing analog can be quite similar. In this study we describe the chromatographic separation and unambiguous identification of dehalogenation impurities or associated isomers in organohalogenated pharmaceuticals using UHPLC with a pentafluorophenyl column coupled with diode-array and high resolution electrospray ionization mass spectrometry detection (UHPLC-DAD-HRESIMS).
Journal of pharmaceutical and biomedical analysis.J Pharm Biomed Anal.2014 Apr 15;92:1-5. doi: 10.1016/j.jpba.2013.12.043. Epub 2014 Jan 7.
The presence of dehalogenated impurities is often observed in halogen-containing pharmaceuticals, and can present a difficult analytical challenge, as the chromatographic behavior of the halogenated drug and the hydrogen-containing analog can be quite similar. In this study we describe the chromatog
PMID 24469094

Comparison of 1,2-dichloroethane, dichloroethene and vinyl chloride carbon stable isotope fractionation during dechlorination by two Dehalococcoides strains.

Schmidt M1, Lege S2, Nijenhuis I3.Author information 1Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstrasse 15, 04318 Leipzig, Germany. Electronic address: marie.schmidt@ufz.de.2Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstrasse 15, 04318 Leipzig, Germany.3Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstrasse 15, 04318 Leipzig, Germany. Electronic address: ivonne.nijenhuis@ufz.de.AbstractCarbon stable isotope fractionation during 1,2-dichloroethane (1,2-DCA), dichloroethene (DCE) and vinyl chloride (VC) dechlorination was analysed for two Dehalococcoides strains, Dehalococcoides mccartyi strain 195 (formerly Dehalococcoides ethenogenes strain 195) and D. mccartyi strain BTF08, and used to characterize the reaction. The isotope enrichment factors (εC) determined for 1,2-DCA were -30.8 ± 1.3‰ and -29.0 ± 3.0‰ for D. mccartyi strain BTF08 and D. mccartyi strain 195, respectively. Enrichment factors (εC) determined for chlorinated ethenes with strain BTF08 were -28.8 ± 1.5‰ (VC), -30.5 ± 1.5‰ (cis-DCE) and -12.4 ± 1.1‰ (1,1-DCE). Product, ethene, related enrichment factors (εC1,2-DCA-ethene) calculated for 1,2-DCA (-34.1 and -32.3‰ for strain BTF08 and strain 195, respectively) were similar to substrate based enrichment factors (εC1,2-DCA), supporting the hypothesis that ethene is the direct product of 1,2-DCA dichloroelimination but that VC was a side product as result of branching in the reaction.
Water research.Water Res.2014 Apr 1;52:146-54. doi: 10.1016/j.watres.2013.12.042. Epub 2014 Jan 8.
Carbon stable isotope fractionation during 1,2-dichloroethane (1,2-DCA), dichloroethene (DCE) and vinyl chloride (VC) dechlorination was analysed for two Dehalococcoides strains, Dehalococcoides mccartyi strain 195 (formerly Dehalococcoides ethenogenes strain 195) and D. mccartyi strain BTF08, and u
PMID 24468425

Reductive dechlorination of 1,2,3,7,8-pentachlorodibenzo-p-dioxin and Aroclor 1260, 1254 and 1242 by a mixed culture containing Dehalococcoides mccartyi strain 195.

Zhen H1, Du S1, Rodenburg LA1, Mainelis G1, Fennell DE2.Author information 1Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901, USA.2Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901, USA. Electronic address: fennell@envsci.rutgers.edu.AbstractA mixed culture containing Dehalococcoides mccartyi strain 195 dechlorinated 1,2,3,7,8-pentachlorodibenzo-p-dioxin (1,2,3,7,8-PeCDD) and selected polychlorinated biphenyl (PCB) congeners in Aroclors 1260, 1254 and 1242. 1,2,3,7,8-PeCDD was dechlorinated to 1,3,7-trichlorodibenzo-p-dioxin (1,3,7-TrCDD) and/or 1,3,8-TrCDD via 1,3,7,8-tetrachlorodibenzo-p-dioxin (1,3,7,8-TeCDD), a pathway that excludes the production of the toxic congener 2,3,7,8-TeCDD. Dechlorination rate and extent was greatly enhanced by the addition of 1,2,3,4-tetrachlorobenzene (1,2,3,4-TeCB) as an alternate halogenated substrate and/or incubation temperature increase from 25 °C to 35 °C. The most extensive dechlorination of PCBs occurred for Aroclor 1260 with 13 major congeners making up 44.1 mol% of the original PCBs dechlorinated by 42% over 250 days at 25 °C. When 1,2,3,4-TeCB was amended as co-substrate, the extent of dechlorination increased to 82%, over 250 days. The mixed culture primarily dechlorinated the doubly-flanked chlorines on 2,3,4-, 2,3,4,6-, and 2,3,4,5,6-substituted chlorophenyl rings, whereas it primarily removed the doubly-flanked para chlorine from the 2,3,4,5-substituted chlorophenyl ring. Experiments using a 20% dilution of culture with 31.8 μg/mL 1,2,3,4-TeCDD or 2,3,4,4',5-pentachlorobiphenyl (PCB 114) as sole halogenated substrate exhibited less than 0.1 mol% dechlorination over 120 days. Further, dechlorination of PCBs and PCDDs by the fully grown culture in the absence of 1,2,3,4-TeCB eventually stopped or greatly slowed over the incubation period. Since Dehalococcoides spp. only gain energy for growth from organohalide respiration, absence of reductive dechlorination upon transfer and dilution or cessation of dechlorination after long incubation times suggest that it is unlikely that strain 195 can grow using the PCDDs or PCBs utilized in this study.
Water research.Water Res.2014 Apr 1;52:51-62. doi: 10.1016/j.watres.2013.12.038. Epub 2014 Jan 8.
A mixed culture containing Dehalococcoides mccartyi strain 195 dechlorinated 1,2,3,7,8-pentachlorodibenzo-p-dioxin (1,2,3,7,8-PeCDD) and selected polychlorinated biphenyl (PCB) congeners in Aroclors 1260, 1254 and 1242. 1,2,3,7,8-PeCDD was dechlorinated to 1,3,7-trichlorodibenzo-p-dioxin (1,3,7-TrCD
PMID 24462927

Japanese Journal

Isolation and Functional Gene Analyses of Aromatic-Hydrocarbon-Degrading Bacteria from a Polychlorinated-Dioxin-Dechlorinating Process

KAIYA SHINICHI,UTSUNOMIYA SATI,SUZUKI SAORI,YOSHIDA NAOKO,FUTAMATA HIROYUKI,YAMADA TAKESHI,HIRAISHI AKIRA
Microbes and environments 27(2), 127-135, 2012-06-01
NAID 10030431725

Complete detoxification of tris(1,3-dichloro-2-propyl) phosphate by mixed two bacteria, Sphingobium sp. strain TCM1 and Arthrobacter sp. strain PY1(ENVIRONMENTAL BIOTECHNOLOGY)

Takahashi Shouji,Obana Yuki,Okada Shohei,Abe Katsumasa,Kera Yoshio
Journal of bioscience and bioengineering 113(1), 79-83, 2012-01
… Also, 1,3-DCP dehalogenation by strain PY1 resting cells was optimal at 35℃ and pH 9.5. …
NAID 110008897359

Isolation and Functional Gene Analyses of Aromatic-Hydrocarbon-Degrading Bacteria from a Polychlorinated-Dioxin-Dechlorinating Process

Kaiya Shinichi,Utsunomiya Sati,Suzuki Saori,Yoshida Naoko,Futamata Hiroyuki,Yamada Takeshi,Hiraishi Akira
Microbes and Environments 27(2), 127-135, 2012
Aerobic aromatic-hydrocarbon-degrading bacteria from a semi-anaerobic microbial microcosm that exhibited apparent complete dechlorination of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) w …
NAID 130001390782