Halogen ketones

Thus a second method was envisaged, the reaction of a nitrile, hydrogen selenide, and an a-halogenated ketone in the presence of a condensation catalyst, which can be POCl, or POCI3 with a Lewis acid such as PCI3 or anhydrous ZnCl. The use of fresh AICI3 leads to the formation of tarry side-products. 

The synthesis of a-aminoketones can be achieved using a-halogenated ketones as starting material. These latter are converted into the hexamethylene tetraminium salts by the method of Mannich and Hahn (42). This reaction proceeds in two steps ... 

Acyl halides may also be added to ethylene ia the presence of aluminum chloride to form halogenated ketones. At low temperatures, ethylene reacts with halogens to yield dihaloethanes. At high temperatures, trichloroethylene and perchloroethylene are formed. The most profitable route for chloroethylene is via ethylene dichloride (see Chlorocarbonsandchlorohydrocarbons). 

Differences in solubility of the reactants may for example be utilized as follows. Sodium iodide is much more soluble in acetone than are sodium chloride or sodium bromide. Upon treatment of an alkyl chloride or bromide with sodium iodide in acetone, the newly formed sodium chloride or bromide precipitates from the solution and is thus removed from equilibrium. Alkyl iodides can be conveniently prepared in good yields by this route. Alkyl bromides are more reactive as the corresponding chlorides. Of high reactivity are a-halogen ketones, a-halogen carboxylic acids and their derivatives, as well as allyl and benzyl halides. 

Halogen-ketone werden i.a. selektiv zu Halogen-alkoholen reduziert z.B. ... 

Griinkreuz 3 (Green Cross 3) Phenylcarbylamine Chloride and Halogenated Ketones Mixture ... 

Halogenated ketones, 10 598 Halogenated organic compounds, bioremediation, 3 772-776... 

Favorskii rearrangement org chem A reaction In which a-halogenated ketones undergo rearrangement in the presence of bases, with loss of the halogen and formation of carboxylic acids or their derivatives with the same number of carbon atoms. fa vor-ske, re-3 ran -m3nt)... 

Levulinic acid is fairly easily converted into thiazole derivatives by the intermediate formation of an a-halogenated ketone such as the /3-bromo derivative (XL) or /3-chloro derivative, which reacts with thiourea to form 2-amino-4-methyl-5-thiazoleacetic acid (XLI) or with thioformamide to give 4-methyl-5-thiazoleacetic acid (XLII). The aminothiazole (XLI) and its ethyl ester (XLIII) have been converted into their corresponding sulfanilamide derivatives, (XLIV) and (XLV). These sulfanilamides, particularly the acid XLIV, have considerable chemotherapeutic activity moreover the acid possesses distinct solubility advantages over sulfathiazole itself. 

The most effective synthesis for thietanones is the eliminative cyclization of halogenated ketones with hydrogen sulfide ions in the presence of bases (Eq. lOb). The reaction of 1,3-dibromoketone derivatives with sodium hydrogen sulfide produced 3-thietanones in association with a five-membered cyclic disulfide (Eq. 10c). 

Statt der a-Halogen-ketone konnen auch a-Halogen-0,0-acetale eingesetzt werden. So erhalt man aus 2-Brom-l,l-dimethoxy-ethan mit Formamid unter Durchleiten von Ammoniak-Gas Imidazol in 50% Ausbeute51 ... 

All the experimental enthalpies of the Grignard reaction appear in Table 5 along with the enthalpies of formation calculated using the same method as illustrated above. Unfortunately there are no liquid enthalpy of formation data for the halogenated ketones, nor are... 

Table 3 lists some of the exchange reactions carried out for replacing halogens with fluorine in halogenated ketones. 

Figure 5 (a)-(c) shows the absorption spectra of some halogenated ketones in the near ultraviolet. In the case of acetone itself the absorption may be attributed to an n - tt transition associated with the carbonyl group. The substitution of halogen atoms leads to an increase in the molecular extinction coefficient and a shift of the absorption maximum toward the red. The ketones containing both chlorine and fluorine atoms show absorption curves with some fine structure but it is not possible to find any correlation between the structure and the shape of the absorption curve. 

Fig. 5(a). Adsorption spectra of halogenated ketones. 1 = CH3COCH3 2 = CFuCOCHa 3 = CF3COCF3. 

These considerations apply equally to the photolysis of halogenated ketones because the absorption maxima are not shifted by the introduction of halogen atoms sufficiently to involve any additional emission lines. 

The experimental results of a number of groups of workers, obtained with a variety of halogenated ketones, are reviewed below. It is interest-... 

The mechanism which has been proposed to explain the fluorescence and photolysis behavior of hexafluoroacetone,68 which may well be applicable to all halogenated ketones, involves an initial transition to a vibrationally excited singlet state (Am1). 

Related methods. The replacement of 3-chloro-2-butanone (or of similar a-halogenated ketones) by ethyl a-chloroacetoacetate [Graffenried and Kostanecki, 1910) gives aryloxyacetoacetates (77)]. Cyclodehydration of esters (77) (with H2S04) gives good yields (60-70%) of coumarilic esters (78),232 which are sometimes difficult to synthesize by other methods. 

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