Metal carboxylate salts, Hunsdiecker reactions

Hunsdiecker Reactions. The Hunsdiecker reaction is the de-carboxylative halogenation of metal carhoxylate salts. The reaction of a,/3-unsaturated carboxylic acids with NCS and catalytic lithium acetate in acetonitrile-water provides the corresponding /3-halostyrenes in moderate yields under mild conditions. The reaction proceeds with a good degree of stereospecificity. For example, the reaction of 3-(4-methoxy-phenyl)-acrylic acid with NCS with a catalytic amount of lithium acetate at room temperature provides l-(2-chloro-vinyl)-4-methoxybenzene in good yield (eq 23). 3... 

The procedure described here allows for a convenient and efficient preparation in very high yields of large quantities of bromides from carboxylic acids containing an olefinic functionality. The Hunsdiecker reaction is traditionally accomplished by treating anhydrous silver carboxylates with bromine or iodine.2 Heavy metal salts such as mercury,3 lead,4 and thallium5 have also been used successfully as well as tert-butyl hypoiodite.6 The major disadvantages associated with the above methods, such as use of heavy metal salts and non-tolerance towards olefins, has led to the development of a more versatile method using O-acyl thiohydroxamates.7 8 The O-... 

The Hunsdiecker reaction treats heavy-metal (e.g, Ag ) carboxylate salts with Br,. 

Decarboxylation of silver carboxylates is a well known thermal process and is involved in the Hunsdiecker76 or Kolbe77 reactions. The Hunsdiecker reaction is the thermal decarboxylation of silver salts of acids and is used for the formation of bromoalkanes and related compounds, while the Kolbe process involves electrolysis of carboxylates as a route to decarboxylated radicals that can dimerize. Silver carboxylates are also photochemically reactive and the irradiation has been described as a facile process for the formation of alkyl radicals, as illustrated in equation 678. Later experimentation has shown that the irradiation of silver trifluoroacetate can serve as a route to trifluoromethyl radicals. This development uses irradiation of silver trifluoroacetate in the presence of titanium dioxide as a photocatalyst. The reaction follows the usual path with the formation of metallic silver and the formation of radicals. However, in this instance the formation of metallic... 

Decarboxylation of an aliphatic acid to the hydrocarbon is best effected by the so-called salt degradation method. That method is to treat the silver or mercury salt of, preferably, an aliphatic or alicyclic carboxylic acid with bromine in an inert solvent a halogenated hydrocarbon is then formed, together with carbon dioxide and the metal bromide, usually in an exothermic reaction, and the bromine can then usually be readily removed either cata-lytically or by means of a Grignard reagent (the Hunsdiecker reaction) ... 

Hunsdiecker reaction conversion of a carboxylic acid into an alkyl halide by heating a heavy metal salt of the carboxyhc acid with bromine or iodine, hybrid orbital an orbital formed by mixing (hybridizing) orbitals. 

---