Hunsdiecker

HUNSDIECKER - BORODIN - CRISTOL - FIRTH Decarix)xylation Bromination... 

Substitution of caiboxylic groups by halogen via Ag saHs (Hunsdiecker, Borodin) or Hg salts (Cnstol-Rrth)... 

In some cases we have combined similar reactions under one heading, for instance the Hunsdiecker-Borodin-Cristol-Firth decarboxy-iative bromination. It is not a simple task to decide whether credit is due to... 

The Hunsdieckers method for replacing a carboxyl group by a halogen has been applied to the preparation of simple fluoroalkyl iodides [44], fluoroiodoalkyl ethers [45], and fluorovinyl iodides [46] (equations 27 -29)... 

Sodium thenoate is bromodecarboxylated in low yield, slower than sodium anisate, but more rapidly than sodium benzoate. However, the Hunsdiecker reaction with silver salts has been used preparatively for the synthesis of 2,3-dibromo-4-nitrothiophene from 3-bromo-4-nitro-2-thiophenecarboxylic acid. ... 

Silver carboxylates 1 can be decarboxylated by treatment with bromine, to yield alkyl bromides 2 in the so-called Hunsdiecker reaction. ... 

Suitable substrates for the Hunsdiecker reaction are first of all aliphatic carboxylates. Aromatic carboxylates do not react uniformly. Silver benzoates with electron-withdrawing substituents react to the corresponding bromobenzenes, while electron-donating substituents can give rise to formation of products where an aromatic hydrogen is replaced by bromine. For example the silver /)-methoxybenzoate 6 is converted to 3-bromo-4-methoxybenzoic acid 7 in good yield ... 

In a modified procedure the free carboxylic acid is treated with a mixture of mercuric oxide and bromine in carbon tetrachloride the otherwise necessary purification of the silver salt is thereby avoided. This procedure has been used in the first synthesis of [1.1.1 ]propellane 10. Bicyclo[l.l.l]pentane-l,3-dicarboxylic acid 8 has been converted to the dibromide 9 by the modified Hunsdiecker reaction. Treatment of 9 with t-butyllithium then resulted in a debromination and formation of the central carbon-carbon bond thus generating the propellane 10." ... 

The Hunsdiecker reaction is the treatment of the dry silver salt of a carboxylic acid with bromine in carbon tetrachloride. Decarboxylation occurs, and the product isolated is the corresponding organic bromide 16). Since dry silver salts are tedious to prepare, a modification of the reaction discovered by Cristol and Firth (77) is now... 

Bromotrithiatriazepine 8 can also be obtained from the carboxylic acid 6 in 52 % yield by a modified Hunsdiecker reaction involving irradiation of a mixture of the acid, bromine, mer-cury(II) oxide and carbon tetrachloride. The iodo derivative is formed when iodine is employed418... 

The Hunsdiecker reaction has been used to convert indazole carboxylic acids into the bromo heterocycles [67HC(22)1],... 

Bromocyclopropane has been prepared by the Hunsdiecker reaction by adding silver cyclopropanecarboxylate to bromine in dichlorodifluoromethane at —29° (53% yield) or in tetrachloro-ethane at —20° to —25° (15-20% yield).3 Decomposition of the peroxide of cyclopropanecarboxylic acid in the presence of carbon tetrabromide gave bromocyclopropane in 43% yield.4 An attempt to prepare the bromide via the von Braun reaction was unsuccessful.3... 

The present procedure is substantially simpler and quicker than the best previous procedure,3 which requires 4 days instead of 4 hours. It is also safer, for no explosions have been encountered with the present procedure, even on a 1.2-mole scale,3 whereas care must be taken to prevent explosion of the intermediate hypobromite when the Hunsdiecker method is used,3 and one detonation has been reported. In comparison with the peroxide method,4 it is simpler and gives better yields. 

Reaction of a silver salt of a carboxylic acid with bromine is called the Hunsdiecker... 

When iodine is the reagent, the ratio between the reactants is very important and determines the products. A 1 1 ratio of salt to iodine gives the alkyl halide, as above. A 2 1 ratio, however, gives the ester RCOOR. This is called the Simonini reaction and is sometimes used to prepare carboxylic esters. The Simonini reaction can also be carried out with lead salts of acids." A more convenient way to perform the Hunsdiecker reaction is by use of a mixture of the acid and mercuric oxide instead of the salt, since the silver salt must be very pure and dry and such pure silver salts are often not easy to prepare. 

Reaction between diazonium salts and CuCl or CuBr (Sandmeyer) Decarboxylative halogenation (Hunsdiecker)... 

A related method for conversion of carboxylic acids to bromides with decarboxylation is the Hunsdiecker reaction.276 The usual method for carrying out this transformation involves heating the carboxylic acid with mercuric oxide and bromine. 

The decarboxylation of carboxylic acid in the presence of a nucleophile is a classical reaction known as the Hunsdiecker reaction. Such reactions can be carried out sometimes in aqueous conditions. Man-ganese(II) acetate catalyzed the reaction of a, 3-unsaturated aromatic carboxylic acids with NBS (1 and 2 equiv) in MeCN/water to afford haloalkenes and a-(dibromomethyl)benzenemethanols, respectively (Eq. 9.15).32 Decarboxylation of free carboxylic acids catalyzed by Pd/C under hydrothermal water (250° C/4 MPa) gave the corresponding hydrocarbons (Eq. 9.16).33 Under the hydrothermal conditions of deuterium oxide, decarbonylative deuteration was observed to give fully deuterated hydrocarbons from carboxylic acids or aldehydes. 

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