Silver carboxylates, reaction

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

The reaction is likely to proceed by a radical-chain mechanism, involving intermediate formation of carboxyl radicals, as in the related Kolbe electrolytic synthesis. Initially the bromine reacts with the silver carboxylate 1 to give an acyl hypobromite species 3 together with insoluble silver bromide, which precipitates from the reaction mixture. The unstable acyl hypobromite decomposes by homolytic cleavage of the O-Br bond, to give a bromo radical and the carboxyl radical 4. The latter decomposes further to carbon dioxide and the alkyl radical 5, which subsequently reacts with hypobromite 3 to yield the alkyl bromide 2 and the new carboxyl radical 4Z... 

The present procedure offers a convenient alternative to the Prevost reaction and the Woodward modification of the Prevost reaction in which silver carboxylates are used instead of thal-lium(I) carboxylates. Thallium(I) salts have the advantages of being generally stable crystalline solids that can be readily prepared in high yield by neutralization of the appropriate carboxylic acid with thallium(I) ethoxide. Silver salts, on the other hand, are frequently unstable and difficult to dry. Thallium and its compounds are, however, extremely toxic, and great care must therefore be taken in the use and disposal of thallium salts. ... 

When colloidal selenium was heated with mercuric trifluoroacetate or silver trifluoroacetate, bis(trifluoromethyl)diselenide was formed (43). Later work with selenium/silver carboxylate, RC02Ag (R = CF3, C2F5, or C3F7), mixtures at 280° C in a vacuum produced a mixture of the bis(perfluoroalkyl)selenide and the bis(perfluoroalkyl)diselenide (44). Formation of a polyselenium trifluoroacetate, which decarboxylates to produce the trifluoromethylselenides, was the proposed mechanism for R = CF3 (44). However, silver trifluoroacetate is a source of trifluoromethyl radicals when heated above 260° C (21), hence the trifluoromethylselenides may be formed by reaction of trifluoromethyl radicals with selenium, as in the reaction of CF3I with selenium [Eq. (34)] (45). 

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-... 

Hundsdieke reaction org chem Production of an alkyl halide by boiling a silver carboxylate with an equivalent weight of bromine in carbon tetrachloride. honz.dek-o re,ak-sh3n ... 

Hunsdiecker, H. Hunsdiecker, C. Ber. Dtsch. Chem. Ges. 1942, 75, 291. Clare Hunsdiecker was the only woman to give a name reaction in this book. 1 hope there will be many more in future editions. Clare Hunsdiecker was born in 1903 and educated in Cologne. She developed the bromination of silver carboxylate alongside her husband, Heinz. 

In the reaction of sulfenyl chlorides with silver carboxylates mixed anhydrides are formed they are known as sulfenyl carboxylates 90, 130) ... 

The Hunsdiecker reaction is a free-radical reaction for the synthesis of an alkyl halide. The starting material comes from the reaction of a silver carboxylate with a solution of a halogen in a solvent such as carbon tetrachloride (see Figure 12-44). The overall free-radical mechanism is shown in Figure 12-45. 

Both the reactions are essentially the additions of iodine carboxylate (formed in situ) to an alkene, i.e., the reaction of an alkene with iodine and silver salt. The Prevost procedure employs iodine and silver carboxylate under dry conditions. The initially formed transiodocarboxylate (b) from a cyclic iodonium ion (a) undergoes internal displacement to a common intermediate acylium ion (c). The formation of the diester (d) with retention of configuration provides an example of neighbouring group participation. The diester on subsequent hydrolysis gives a trans-glycol. 

The products of the reactions between silver(I) carboxylates and triphenylphosphine were colourless, diamagnetic solids, stable at room temperature to oxygen and not significantly light sensitive. Reaction with triphenylphosphine was also found useful as a method of solubilizing silver carboxylates. 

Reaction of [PdCl2(diene)] with silver carboxylates yields complexes [Pd2(/u -... 

Extensive C-C bond scission and rearrangements have been observed in systems other than thiophene-Ag. Table IV presents a number of such cases. The silver carboxylates (56) have already been mentioned briefly. A preponderance of CO -containing adducts suggests a gas phase analogue to the classical Hunsdiecker reaction (Equation 4). The behavior observed with methyl acetate... 

Silver nitrate test The compound to be tested is treated with a few drops of 1% alcoholic silver nitrate. A white precipitate indicates a positive reaction. This could be due to either silver chloride (reaction with a reactive alkyl halide), silver alkynide (reaction with a terminal alkyne), or the silver salt of a carboxylic acid (reaction with a carboxylic acid). 

Acyl hypohalites are usually prepared in situ by reaction of a metal salt of die carboxylic acid widi a halogen (equation 3). Classically the silver salt is used, but problems associated widi die preparation of dry silver carboxylates, as well as the more obvious economic factor, have led to the development of methods using mercury and thallium salts. Evidently, those functional groups which react readily widi halogens are not compatible with this approach. A major limitation of the acyl hypohalites is the readiness with which they transfer halogen atoms to alkyl radicals this property essend ly limits their use to decarboxylative halogenation reactions. 

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

IsoxazoIe-3-carboxylic acid, 5-phenyl-silver salt reactions, 6, 52 synthesis, 6, 85 IsoxazoIe-4-carboxyIic acid esters... 

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