Halogen-aldehydes

The O-S exchange method in presence of a-halogenated carbonyl compound is a very good one for thiazole compounds. The thioamide is prepared in situ by the action of amide upon phosphorus pentasulphide with solvent. The a-halogenated aldehyde reacts directly. But the O-Se exchange cannot be performed with a-halogenated carbonyl compounds because of the apparition of phosphoric acid. (Scheme 3), The C-Se bond is very sensitive to add pH. 

Haloalkane,. see Alkyl halide Haloform reaction, 854-855 Halogen, inductive effect of, 562 resonance effect of, 563 Halogenation, aldehydes and, 846-848... 

Like aldehydes and ketones, the a-hydrogens of acid and acid derivatives are acidic and can be abstracted with base to generate the carban-ions, which can then react with various electrophiles such as halogens, aldehydes, ketones, unsaturated carbonyl compounds, and imines, to give the corresponding products. Many of these reactions can be performed in aqueous conditions. These have been covered in related chapters. 

More recently, a novel type of halogenating enzyme, named hydroperoxide halolyase, which generates halogenated aldehydes, has been described in the marine diatom Stephanopyxis turris (Wichard and Pohnert 2006). In other microalgae, halogenation of organic compounds was shown to mainly involve methyl halide transferases (Moore et al. 1996 Manley 2002), and no vHPO has yet been identified on genomic data obtained from diatoms (Scala et al. 2002 Armbrust et al. 2004). Clearly, these emissions are not directly associated with an oxidative burst. 

Unavailable because experimental methods for estimation of this parameter for halogenated aldehydes are lacking in the documented literature. However, its miscibility in water suggests its adsorption to soil will be nominal (Lyman et ah, 1982). 

Unavailable because experimental methods for estimation of this parameter for halogenated aldehydes are lacking in the documented literature... 

The possibility of hydrogenating halogenated aldehydes and ketones by means of phytochemical reduction was tested as early as 1913 the successful results in this field clearly demonstrate the importance of this method. Lintner and Ltters found that chloral hydrate can be converted to trichloroethyl alcohol. This transformation takes place so easily that, according to Willstatter and Duisberg, it can be used under favorable experimental conditions as a convenient method for the preparation of the halogenated alcohol. The tribromoethyl alcohol may be prepared in an analogous manner. 

As seen in Table 13.7, oxidation of HCFCs by OH generates a variety of halogenated aldehydes and ketones as well as phosgene (COCl2), its fluorine analog (COF2), C1C(0)F and HC(0)F, and the alcohol CF3OH. The ultimate atmospheric fate of these products depends on their structures, of course, which determines their absorption cross sections as well as reactivity with OH, and their solubility in aqueous solutions such as clouds, rainwater, and the oceans. 

Scollard, D. J., J. J. Treacy, H. W. Sidebottom, C. Balestra-Garcia, G. Laverdet, G. Le Bras, H. MacLeod, and S. Teton, Rate Constants for the Reactions of Flydroxyl Radicals and Chlorine Atoms with Halogenated Aldehydes, J. Phys. Chem., 97, 4683-4688 (1993). 

The facile reaction of CAA and BAA with nucleosides and nucleotides is one example of many of the applications of the bifunctional reactivity of halogenated aldehydes and ketones in modification of biomolecules. In an early example of the extensive use of halogenated ketones as protease substrate analogues, l-V-tosylamido-2-phenylethyl chloro-methyl ketone (TPCK) 30 was synthesized as a chymotrypsin substrate analogue. Stoichiometric inhibition was accompanied by loss of one histidine residue as a result of alkylation by the chloromethyl moiety68. A host of similar analogues were subsequently prepared and used as selective enzyme inhibitors, in particular for the identification of amino acid residues located at enzyme active sites69. 

The synthesis of furans from /3-ketoesters and a-halogenated aldehydes or ketones under basic conditions is known as the Feist-Benary furan synthesis (Equation 28). In most of the cases, the reaction is initiated by an aldol reaction. If the first step is alkylation, reversed regioselectivity is observed. 

C. SUBSTITUTED ALDEHYDES AND KETONES I. HALOGEN ALDEHYDES Tri-chlor Aldehyde CCI3—CHO Chloral... 

The halogen acids, of course, bear the same relation to the halogen aldehydes and the halogen alcohols (halogen hydrines) that unsubstituted acids do to the unsubstituled aldehydes and alcohols. That is, they are the direct oxidation products. 

Passerini, M. The isonitriies. III. Reaction with halogen aldehyde hydrates. Gazz. Chim. Itai. 1922, 52, 432-435. 

Toxicological data in experimental animals and humans for the haloketones and haloacetaldehydes are extremely limited. Slight liver and CNS effects were observed. Hepatocellular carcinomas in mice were reported, probably due to mutagenic effect. There is a potential carcinogenic hazard associated with halogenated aldehydes. 

Asymmetric ene Reaction In 1988 Yamamoto and coworkers provided the first indication that asymmetry in ene-reactions could be induced by catalytic amounts of chiral Lewis acids in the presence of 4-A molecular sieves (Scheme 6.64) [88]. They described the first example of asymmetric ene-reaction between prochiral, halogenated aldehydes and alkenes catalyzed by chiral binaphthol-derived aluminum complexes. The hindered 3,3-silyl substituents in the chiral catalyst are essential to achieve good enantioselectivity and high yield. In fact, the use of a catalyst derived from MesAl and 3,3 -biphenylbinaphthol led to the racemic product in a low yield. 

Perkow, W., Krockow. E.W., and Knoevenagel. K.. Reairangements with alkyl phosphites. Part 2. The reaction with a-halogenated aldehydes, Chem. Ber. 88. 662, 1955. 

Hohere a-Halogen-aldehyde liefern analog 2,5-disubstituierte 1,3-Thiazole (Tab. 7, S. 27). Mit a-Brom-aldehyden liegen die Ausbeuten zumeist hoher als bei Verwendung von a-Chlor-aldchyden ... 

---