Preparation halides

Many salt-like halides can be prepared by the action of the hydro-halic acid. HX, on the metal or its oxide, hydroxide or carbonate. The halides prepared by this method are often hydrated, particularly when a less electropositive metal is involved, for example zinc, iron. 

Practical experience enables us to emphasize the simplicity and the efficiency of the activation of aldehydes by their conversion into N- -haloalkyl)heteroarylium halides upon treatment with an azine and a thionyl halide. Preparation of these salts requires a minimum of precautions, and a wide variety of solvents can be used. Special glassware and/or the use of an inert gas is not necessary. Tire salts can be reacted under numerous experimental conditions and, in most cases, it is unnecessary to isolate them. Tire flexibility of the method represents an interesting feature for the study of the reactivity of A-(l-haloalkyl)heteroarylium halides and deserves further investigations in this held. Many elegant compromises can be found in a judicious choice of the precursors and of the experimental conditions, and it is possible to design readily a salt suitable for each individual purpose. 

Benzophenone (Coll. Vol. x, 89) In 57 per cent yield from benzoyl chloride and diphenylcadmium or phenylcadmium halides, prepared by adding cadmium chloride to 2 moles of phenylmagnesium bromide. Gilman and Nelson, Rec. trav. chim. 55i Sig (1936). 

Table 21-1. Halides prepared from alcohols via imidazole-V-carboxylates, -sulfonates and -sulfinates.

The development of the Grignard-type addition to carbonyl compounds mediated by transition metals would be of interest as the compatibility with a variety of functionality would be expected under the reaction conditions employed. One example has been reported on the addition of allyl halides to aldehydes in the presence of cobalt or nickel metal however, yields were low (up to 22%). Benzylic nickel halides prepared in situ by the oxidative addition of benzyl halides to metallic nickel were found to add to benzil and give the corresponding 3-hydroxyketones in high yields(46). The reaction appears to be quite general and will tolerate a wide range of functionality. 

Benzylmanganese halides, prepared by the insertion of Rieke s manganese into benzylic halides, undergo cross-coupling with aryl iodides in the presence of Pd(PPh3)4.175... 

A recent review has been published on this important topic Except for the method which consists of the alcoholysis in the presence of mercury salts of aldose dialkyldithioacetals, most of the available procedures have been referred to earlier in this Chapter. Glycofuranosyl halides prepared from y-lactones offer a potentially valuable route (p. 410). 

KCl, dissolution process, 39 416 Ketab, synthesis, 30 263 Ketenimine complexes with iron, 12 245 KetiminoberyIlium halides, preparation and properties of, 14 307-308 a-Keto acid, formation, 43 427-428... 

Conversion of alcohols by hydrogen halides preparation of alkyl halides... 

Chlorine was distilled from cylinders directly into a side arm of the reaction tubes for halide preparations, using a dry ice-acetone bath. After distillation the liquid was frozen in liquid nitrogen and outgassed under high vacuum. 

Reagent-grade bromine was dried over phosphorus (V) oxide and distilled into dry, evacuated flasks. Samples then were vacuum-distilled into reaction tubes for the halide preparations. 

Reagent-grade iodine was transferred directly to the reaction tubes for halide preparations and was outgassed thoroughly at room temperature under high vacuum. 

Special reagents introduced more recently allow significant improvements in hydrohalogenation of alkenes. HC1, HBr, and HI in aqueous-organic two-phase systems under phase-transfer conditions readily add to alkenes affording halides in nearly quantitative yields.123 Appropriately prepared silica and alumina have been found to mediate the addition of HC1, HBr, and HI to alkenes.124 The method is very convenient since it uses hydrogen halides prepared in situ 124 125... 

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