Reactions Simonini

Ester formation when silver carboxylate is treated with iodine. Alternatively, when silver carboxylate is treated with bromine, the product is alkyl bromide, R-Br (Hunsdiecker reaction, page 202). 

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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. 

The first step is not a free-radical process, and its actual mechanism is not known.451 25 is an acyl hypohalite and is presumed to be an intermediate, though it has never been isolated from the reaction mixture. Among the evidence for the mechanism is that optical activity at R is lost (except when a neighboring bromine atom is present, see p. 682) if R is neopentyl, there is no rearrangement, which would certainly happen with a carbocation and the side products, notably RR, are consistent with a free-radical mechanism. There is evidence that the Simonini reaction involves the same mechanism as the Hunsdiecker reaction but that the alkyl halide formed then reacts with excess RCOOAg (0-24) to give the ester.452 See also 9-13. 

The Simonini Reaction differs by the ratio of I2. The products are significantly different, this reaction produces esters ... 

Silver(I) carboxylates have been obtained by the addition of equivalent amounts of freshly prepared silver oxide to aqueous solutions of the appropriate acid.247 Their degradation by halogens provides a convenient method for the preparation of alkyl halides (Hunsdiecker reaction) or esters (Simonini reaction).248 Equations (14)-(18) have been proposed to account for the products obtained and were the result of extensive studies. 

The reaction proceeds like the Hunsdiecker reaction to yield the R-Br, which then reacts with the silver salt to give the ester. This version of the Hunsdiecker reaction is called the Simonini reaction. 

Simonini reaction A 2 1 mixture of the silver salt of a carboxylic acid, RCOOAg, reacting with iodine gives the ester RCOOR. A 1 1 mixture gives the iodo product, RI, which is similar to the Hunsdiecker reaction. 

Simonini reaction. The preparation of aliphatic esters by the reaction of two moles of the silver salt of a carboxylic acid and one mole of iodine. 

The Hunsdiecker reaction is closely related to the Simonini reaction.5 As a matter of fact, the first half of the Simonini reaction is the Hunsdiecker reaction. Therefore, treatment of one equivalent of silver carboxylate 1 with iodine gives alkyl iodide 3. In the presence of another equivalent of silver carboxylate 1, an S 2 displacement reaction takes place, affording ester 4. Since there are so many practical ways to make esters, the Simonini reaction is no longer widely used. 

One particular radical decarboxylation reaction, which is used in the synthesis of alkyl or aryl bromide (Hunsdiecker reaction), involves reaction of the silver salt of a carboxylic acid with bromine, and results overall in loss of CO2 to form the corresponding alkyl or aryl bromide (Scheme 4.47). When silver carboxylate is treated with I2 ester formation occurs (Simonini reaction). 

This reaction is related to the Simonini Reaction and Hunsdiecker Reaction. 

Other references related to the Birnbaum-Simonini reaction are cited in the literature. ... 

By the same token, acyloxyhalides RCOOX are extremely labile by virtue of the hard (RCOO )-soft (X ) combination. They exist as transient intermediates in the Hunsdiecker and Simonini reactions (3). 

The Simonini reaction is now considered to be a variant of the Huns-diecker reaction if a sufficiently large excess of halogen is not present, the course of the Hunsdiecker is deflected to give coupled ester as Simonini product (Scheme 10). The synthetic limitations of the Hunsdiecker reaction are discussed. 

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