594-18-3Relevant academic research and scientific papers
Chemistry of the biosynthesis of halogenated methanes: C1-organohalogens as pre-industrial chemical stressors in the environment?
Urhahn, Thorsten,Ballschmiter, Karlheinz
, p. 1017 - 1032 (2007/10/03)
We have chemical evidence that in the biosynthesis of the halomethanes C1H(4-n),X(n) (n = 1-4) three different pathways of biogenic formation have to be distinguished. The formation of methyl chloride, methyl bromide, and methyl iodide, respectively, has to be considered as a methylation of the respective halide ions. The dihalo- and trihalomethanes are formed via the haloform and/or via the sulfo-haloform reaction. The possible formation of tetrahalomethanes may involve a radical mechanism. Methionine methyl sulfonium chloride used as substrate in the incubation together with chloroperoxidase (CPO) and H2O2 gave high yields of monohalomethanes only. We were able to show that next to the CPO/H2O2 driven haloform reaction of carbonyl activated methyl groups also methyl-sulphur compounds - e.g. dimethylsulfoxide, dimethylsulfone, and the sulphur amino acid methionine - can act as precursors for the biosynthesis of di- and trihalogenated methanes. Moreover, there is some but not yet very conclusive evidence for an enzymatic production of tetrahalogenated methanes. In our experiments with chloroperoxidase involving amino acids and complex natural peptide based substrates, dihalogenated acetonitriles and several other volatile halogenated but yet unidentified compounds were formed. On the basis of these experiments we like to suggest that biosynthesis of halogenated nitriles occurs in general and therefore a natural atmospheric background should exist for halogenated acetonitriles and halogenated acetaldehydes, respectively.
Facile halogen exchange reactions: Chloroform with bromoform and carbon tetrachloride with carbon tetrabromide
Orvik, Jon A.
, p. 4933 - 4936 (2007/10/03)
Both of the title systems undergo rapid halogen exchange (half-life ca. 1-2 min) in N-methylpyrolidinone with catalytic sodium hydroxide at room temperature. Yet they differ markedly in response to added p-dinitrobenzene. The rate of the haloform exchange is unaffected, whereas the rate of the carbon tetrahalide exchange is severely retarded. The known base-induced halogen exchange reaction between chloroform and bromoform is shown not to proceed through a reversible carbene intermediate as claimed in the literature. It appears to be best described in terms of the so-called RARP mechanism (radical anion-radical pair). The mechanism proposed for the rapid exchange between carbon tetrachloride and carbon tetrabromide is initial electron transfer, halide ion loss, and ensuing radical chain scrambling of halogen atoms. The acronym RARC, standing for radical anion-radical chain, is proposed.
Fluoride anion catalyzed halogen dance in polyhalomethanes
Sasson, Y.,Kitson, F.,Webster, O, W.
, p. 599 - 600 (2007/10/02)
Tetrabutylammonium fluoride catalyzes the exchange of halogens between tetrahalomethanes.The presence of small amounts of haloform is suspected to be a necessary co-catalyst.Key Words: tetrabutyl ammonium fluoride; tetrahalomethanes; halogen exchange in.
Nucleophilic attack on halogeno(phenyl)acetylenes by halide ions
Tanaka, Ryuichi,Zheng, Shi-Qin,Kawaguchi, Kenji,Tanaka, Takehide
, p. 1714 - 1720 (2007/10/02)
Nucleophilic reactions between halogeno(phenyl)acetylenes and halide ions, ArC≡CX + Y-, where Ar = C6H5 or p-ClC 6H4, X = Cl or Br, and Y = Cl or Br, have been examined. Halogen exchange of the Finkelstein type was observed for the first time in acetylene halides in anhydrous dimethyl sulphoxide when X = Br and Y = Cl. This exchange did not occur with other X-Y combinations. In the presence of up to 20% water in dimethyl sulphoxide, or under aqueous-organic phase-transfer catalytic conditions, nucleophilic addition (formally of HY) took place for all the X-Y combinations studied. In the additions, the nucleophile Y- invariably attacked the carbon to which the phenyl group was bound. The mode of HY addition was stereospecifically trans; accordingly, the resulting dihalogenostyrenes always had the (Z)-1,2-dihalogeno-configuration.
