Silver salt-bromine reaction

Precaution Incompat. with alkalis and their carbonates, lead and silver salts explosive reaction with potassium chlorate or bromine trifluoride violent reaction with bromine pentafluoride, NH4, NO3, IF7... 

Toxicotogy ACGIH TLV/TWA10 mg/m STEL 20 mg/m LD50 (oral, rat) 1650 mg/ kg, (IP, mouse) 1439 mg/kg LDLo (IV, rabbit) 78 mg/kg poison by subcutaneous, IV and intramuscular routes severe eye irritant mutation data TSCA listed Precaution Incompat. with alkalis and their carbonates, lead and silver salts explosive reaction with potassium chlorate or bromine trifluoride violent reaction with bromine pentafluoride, NH4, NO3, IFj... 

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... 

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

Other anomeric-oxygen exchange reactions have been recently investigated quite extensively. Closely related to the Koenigs-Knorr method is the introduction offluorine as the leaving group (Scheme 1, path B) (6,9-13). Because of the difference in halophilicity of this element as compared with bromine and chlorine, additional promoter systems besides silver salts were found useful as activators for glycosylation reactions (14-16). However,... 

Mercury(II) oxide together with a halogen is an early development of the classic Hunsdiecker reaction (bromodecarboxylation of a carboxylic acid silver salt, see below) which is still in use.20 22 A double Hunsdiecker reaction of cyclobutane-1,1-dicarboxylic acid with red mer-cury(ll) oxide in the presence of bromine gave 1,1-dibromocyclobutane (2) in 46% yield.21 However, a similar reaction performed on spiro[3.3]heptane-2-carboxylic acid afforded 2-bro-mospiro[3.3]heptane (3) in only 16% yield.22... 

The mercuration of thiophene, which presumably goes by way of a coordination compound, gives an initial attack in the 2 position as expected from the reactions of thiophene itself (67). The bromination (or chlorination) of indazole or its silver salt also leads to the same products (82). 

Reaction of a silver salt of a carboxylic acid with bromine is called the Hunsdiecker reaction438 and is a way of decreasing the length of a carbon chain by one unit.439 The reaction is of... 

Decarboxylation of the silver salts of carboxylic acids in the presence of bromine or chlorine, the Hunsdiecker reaction, often is useful for the synthesis of alkyl halides ... 

In a Hunsdiecker reaction, the silver salt of an aromatic carboxylic acid is converted by bromine treatment to an acyl halide. 

Of lesser relevance to this discussion are halogenation methods involving the modification of the carbon skeleton (synthesis and degradation). The Hunsdiecker reaction, as applied to certain heterocyclic acids, has had limited application for the synthesis of halogen derivatives. The preparation of 3-bromo-4,6-dimethyl-2-pyridone from the silver salt of the respective 3-carboxylic acid by treatment with bromine in carbon tetrachloride is a rare example of success.13 The interaction of carbenes with heterocycles also has been employed infrequently, but recent advances in carbene generation may reactivate this approach.14 The Ciamician-Dennstedt ring expansion of pyrrole to / -halopyridines is a case in point18 [Eq. (4)] ... 

Peracetylated glucose, brominated in the 1-position, was reacted with V-methylimi-dazole to yield the corresponding carbohydrate functionalised imidazolium salt [114], Reaction with silver(l) oxide and subsequently with [Cp lrCyj yields the silver(I) and iridium(lll) NHC complexes, respectively (see Figure 6.47). The structural parameters of the Cp lr(NHC) complex are similar to those of analogous Cp lr(NHC) complexes featuring nonfunctionalised carbenes [115,116]. 

The classical Hunsdiecker reaction (equation 18), involving the reaction of silver caiboxylates widi halogens, and the various associated side reactions, has been reviewed several tunes. Optimum yields are obtain widi bromine, followed by chlorine. Iodine gives acceptable yields provid diat the correct stoichiometry of 1 1 is used. The reaction is most frequently carried out in tetrachloromediane at reflux. From a practical pmnt of view, one drawback is the difficulty encountered in the preparation of dry silver caiboxylates the reaction of silver oxide on the acyl chloride in tetrachloromediane at reflux has been employed to circumvent diis problem. Evidendy the use of molecular bromine limits die range of functional groups compatible widi die reaction the different reaction pathways followed by the silver salts of electron poor (equation 19) and electron rich (equation 20) aryl carboxyl s illustrate this point well. 

The Hunstliecker reaction, in which the silver salt of a benzoic acid is thermally decarboxylated in the presence of bromine, gives moderate yields of aryl bromides. The mechanism is uncertain, but may involve the generation of aryl radicals (Scheme 9.5). 

Fragmentation with loss of CO2 also occurs in the Hunsdiecker reaction, in which a silver salt of a carboxylic acid reacts with bromine to produce an alkyl halide. The reaction results in shortening of the carbon chain by one carbon. The overall reaction is as follows ... 

The conversion of 5a-cholestan-6/5-ol into the 6yS, 19-epoxide, by reaction with bromine and silver oxide, has been improved by the use of certain silver salts with bromine in pentane, in the dark. Silver acetate, carbonate, and... 

Surprisingly, the Hunsdiecker reaction using the silver salts of exo- and endo-7-chlorobicyclo[4.1.0]heptanecarboxylic acids and bromine at 0°C did not result in the same ratio of products but instead showed a high retention to inversion ratio of 88 12 for the exo acid and 88 12 for the endo acid". This anomalous result may be a reflection of the bromine radical s ability to trap the cyclopropyl radical but this is unlikely. Altman and Baldwin as well as Ando and coworkers found that the reduction of each of the isomers of 7-bromo-7-chlorobicyclo[4.1.0]heptane, 30 and 31, respectively, by the excellent radical scavenger triphenyltin hydride resulted in an identical mixture (21 79) of exo-(32) and en io-7-chlorobicyclo[4.1.0]heptane (33). This ratio of products is, within experimental error, identical with that found in the thermal decomposition of exo- and endo-t-buiy 7-chlorobicyclo[4.1.0]heptane-7-percarboxylate in cumene. 

Hunsdiecker reaction of the silver salts of both cis-(56) and trans-2-methylcyclopropanecarboxylic acid (57) yielded the same mixture of cis- (58) and trans-1-bromo-2-methylcyclopropane (59), thus demonstrating that the 2-methylcyclopropyl radical was incapable of maintaining its configuration . Brominative decarboxylation of the silver salts of exo- (60) and em/o-norcarane-7-carboxylic acid (61) produced the same mixture (16 84) of exo- (62) and entio-7-bromonorcarane (63)". Similarly, cis- and trans-silver 1,2-cyclopropanedicarboxylate gave rise to the same isomer ratio (24 76) of cis- and fraws-1,2-dibromocyclopropane. Consistent with these results is the report that the Hunsdiecker reaction with the silver salt of trans-2,2,3-d3-cyclopropanecarboxylic acid (64) gives an equimolar mixture of cis- (65) and rrans-2,2,3-d3-cyclopropane (66) . 

Norula, J. L. Mechanism of the reaction of bromine with the silver salt of a carboxylic acid. Chemical Era 1975,11, 40-42. 

This is a good method of synthesising symmetrical alkanes. The Kolbe reaction is usually performed using the potassium or sodium salt of the carboxylic acid. If the silver salt is reacted with bromine, then decarboxylation occurs again, but this time the alkyl bromide is formed. This reaction is called the Hunsdiecker reaction. The first step involves the formation of an acyl hypohalite, RC02X. 

Bromine-Silver oxide. The reaction of bromine in the presence of a silver salt, usually the oxide, with a tertiary alcohol gives in good yield a product of the insertion of oxygen. Thus 1,3,3-trimethylcyclohexanol (1) is transformed into the bicyclic ether (4) in 75% irield. It is suggested that the reaction proceeds through the hypo-bromite (2), the decomposition of which is catalyzed by silver ions. 

Hunsdiecker reaction. In the original Hunsdiecker reaction, the silver salt of an acid is prepared in one step and treated with bromine in another. Cristol found that isolation of a metal salt can be dispensed with addition of bromine to a refluxing snspension of red mercuric oxide in a solution of the acid in carbon tetrachloride affords the corresponding alkyl halide in good yield ... 

The Hunsdiecker reaction, a bromodecarboxylation classically involving treatment of the silver salt of a carboxylic acid with molecular bromine, results in the transient generation of an acyl hypobromite, followed by O-Br homolysis. It works with protected silver aldonates, as shown in Scheme 7.5. 

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