Halonitro compounds

In contrast to aromatic halonitro compounds, selective removal of halogen in aliphatic halonitro compounds presents little problem. The reaction can be done by hydrogenation over palladium-on-carbon in the presence of a hydrohalide acceptor 46,73). 

The one-pot conversions of oximes to gem-halonitro compounds have been achieved by using A(/V,/V.-trihalo-l,3,5-triazines,131 chloroperoxidase in the presence of hydrogen peroxide and potassium chloride,132 or commercial OXONE and sodium chloride.133 Of these methods, the case of OXONE may be the most convenient (Eq. 2.65). 

Reaction of Alkyl Phosphites with a-Halonitroso and a-Halonitro Compounds." Edited by... 

The presence of halonitro compounds, which are incapable of producing carbanion (such as 2-chloro-2-nitropropane and trichloronitromethane), considerably increases the rate of chain... 

In the second, >100 DBFs were identified in indoor chlorinated and brominated pools, including many nitrogenous DBFs (haloamides, halonitriles, haloanilines, haloamines, haloanisoles, and halonitro-compounds), likely due to the nitrogen-containing precursors from swimmers (urine, sweat, etc.) [143]. Trichloramine and THMs were also measured in the pool air [143]. Nitrosamines have been measured in chlorinated pools and hot tubs, up to a maximum of429 ng/L... 

The halonitro compounds and the methanol used were of purum or pract. quality from Fluka. The amidine derivatives (in the form of their salts) were purchased from Fluka or Aldrich (purum or pract.). The N,N-dialkyl-formamidine acetates were prepared by analogy to a published procedure (ref. 8) from cyanamide and used as isolated (containing ca. 10% ammonium acetate). 

Schematic representation of typical curves for hydrogen uptake and catalyst potential for the hydrogenation of aromatic halonitro compounds.

Amidine derivatives are effective dehalogenation inhibitors for the chemoselective hydrogenation of aromatic halonitro compounds with Raney nickel catalysts. The best modifiers are unsubstituted or N-alkyl substituted formamidine acetates and dicyandiamide which are able to prevent dehalogenation even of very sensitive substrates. Our results indicate that the dehalogenation occurs after the nitro group has been completely reduced i.e. as a consecutive reaction from the halogenated aniline. A possible explanation for these observations is the competitive adsorption between haloaniline, nitro compound, reaction intermediates and/or modifier. The measurement of the catalyst potential can be used to determine the endpoint of the desired nitro reduction very accurately. 

Zaks A, Yabannavar AV, Dodds DR, Evans CA, Das PR, Malchow R (1996) A Novel Application of Chloroperoxidase Preparation of gem-Halonitro Compounds. J Org Chem 61 8692... 

The presence of halonitro compounds, which are incapable of producing carbanion, such as 2-chloro-2-nitropropane and trichloronitromethane, considerably increases the rate of chain origin in an alkaline medium, pH > 8.0. These compounds accept electrons instead of nonionized 1-chloro-l-nitroethane, the concentration of which is small at a high alkalinity. 

TCC, without initiator, to give the corresponding chloromethyl compounds (Scheme 79) <87CB649>. Triazine derivatives l-sodio-3,5-dichloro-l,3,5-triazine- and l,3-dibromo-l,3,5-triazine-2,4,6 (l/7,3/7,5//)-trione are useful combination halogenation xidation reagents. Oximes are converted into ew-halonitro compounds (e.g. (237)). The three triazine derivatives may also be used in conjunction with ozone to accomplish the transformation in a stepwise manner (Scheme 79) <91JOC316>. 

Silyl nitronates 156, generated from a-halonitro compounds 155, undergo cycloaddition with a variety of olefins 157 such as styrene, acrylate, nor-bornene, cyclopentene etc to afford isoxazoline W-oxides 159 in good to high... 

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