Silver salts of acids

Although this is the classical method of anhydride formation it has been replaced to a large extent by the acylation of free carboxylic acids (method 341). The conditions employed and the solvents used in this reaction vary widely. Excellent directions are given for the preparations of nicotinic anhydride (89%) and acetic propionic anhydride (60%) from the respective potassium and sodium salts of the carboxylic acids. Silver salts of acids have also been used. The reaction has been extended to the preparation of mixed anhydrides of short- and long-chain fatty acidsbut has failed in the preparation of mixed anhydrides of substituted benzoic acids. ... 

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... 

RCOX, SF4, X2, HOX, or RX with alcohols, ethers, diazonium compounds, Grignard reagents, silver salts of acids, acids, amides, aromatic compounds, aldehydes, ketones, olefins, and amines. Many other organic compounds also undergo these reactions. 

In the former, it gives precipitates with halides (except the fluoride), cyanides, thiocyanates, chromates(VI), phosphate(V), and most ions of organic acids. The silver salts of organic acids are obtained as white precipitates on adding silver nitrate to a neutral solution of the acid. These silver salts on ignition leave silver. When this reaction is carried out quantitatively, it provides a means of determining the basicity of the acid... 

By the action of alkyl halides on the silver salt of the acid. 

The silver salts of most carboxylic acids are only sparingly soluble in cold water, and hence are readily prepared. Moreover they very rarely contain water of crystallisation, and therefore when dried can be analysed without further treatment. The analysis itself is simple, rapid and accurate, because gentle ignition of a weighed quantity of the silver salt in a crucible drives off the organic matter, leaving a residue of pure metallic silver. 

Since the silver salts of the carboxylic acids are usually soluble in dilute nitric acid, they must be prepared by treating an aqueous solution of a neutral salt of the acid (and not the free acid itself) with silver nitrate solution. It is not practicable to attempt to neutralise the acid with sodium or potassium hydroxide solution, because the least excess of alkali would subsequently cause the white silver salt to be contaminated with brown silver oxide. The general method used therefore to obtain a neutral solution j to dissolve the acid in a small excess of ammonia solution, and then to boil the solution until all free... 

Reaction with alcoholic silver nitrate. To carry out the test, treat 2 ml. of a 2 per cent, solution of silver nitrate in alcohol with 1 or 2 drops (or 0 05 g.) of the compound. If no appreciable precipitate appears at the laboratory temperature, heat on a boiling water bath for several minutes. Some organic acids give insoluble silver salts, hence it is advisable to add 1 drop of dilute (5 per cent.) nitric acid at the conclusion of the test most silver salts of organic acids are soluble in nitric acid. 

A better method involves the use of silver salts of arsonic acids ... 

Bromine reacts with the silver salts of carboxyhc acids to give an alkyl bromide containing one less carbon atom than the acid (24). 

Although no acyl hypochlorites [RCO2CI] have been isolated in pure form, they have been characterized in solution and employed as reactants via in situ generation from CI2O or HOCl and carboxyUc acids, or from CI2 and silver salts of carboxyUc acids (246,247). Perfluoroacyl hypochlorites have also been prepared (248). 

Although it is seldom used, esterification of pyrimidinecarboxylic acids proceeds normally. Conditions are illustrated by the conversion of pyrimidine-4-carboxylic acid (181 R = H) into its methyl ester (181 R = Me) by methanol/sulfuric acid (47%), methanol/hydrogen chloride (80%), or by diazomethane (ca. 100%) (60MI21300). The isomeric methyl pyrimidine-2-carboxylate is formed by treatment of the silver salt of the acid with methyl iodide. Higher esters, e.g. (182 R = Bu), are usually made by warming the acid (182 R = H) with the appropriate alcohol and sulfuric acid (60JOC1950). 

This method with some slight modihcations is applied in the synthesis of to-bromo esters from Cs to Cn. Methyl 5-bromovalerate has been prepared by treating the silver salt of methyl hydrogen adipate with bromine. The ethyl ester has been prepared from the acid by esterification or through the acid chloride. ... 

Ethoxy-2-cyclohexenone has been prepared by reaction of the silver salt of dihydroresorcinol with ethyl iodide and by the reaction of dihydroresorcinol with ethyl orthoformate, ethanol and sulfuric acid." The acid-catalyzed reaction of dihydroresorcinol with ethanol in benzene solution utilized in this preparation is patterned after the procedure of Frank and Hall. ... 

The latter, by a similar series of reactions, yields homoajsecincheninic acid ethyl ether the silver salt of this on heating loses carbon dioxide, giving a quinolylphenetole, which, on dealkylation with hydrobromic acid, yields a quinolylphenol, identical with 4-o-hydroxyphenylquinoline. 

Other methods for the preparation of esters are the action of alcohol on the acid chloride or anhydride (see Reactions, p. 75), or by boiling up the dry powdered silver salt of the acid with the alkyl iodide,... 

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... 

Kunlze finds that the precipitate of silver sulphide, which is formed hy both melhods under Ihc same conditions, is always contaminated wilh more or less silver salt of allyl-ihiocarbamiuic acid ester. 

By the interaction of the silver salt of the acid with the halogen derivatives of the alcohol, when the reaction is as follows —... 

If the dissociation constant of the acid HA is very small, the anion A- will be removed from the solution to form the undissociated acid HA. Consequently more of the salt will pass into solution to replace the anions removed in this way, and this process will continue until equilibrium is established (i.e. until [M + ] x [A-] has become equal to the solubility product of MA) or, if sufficient hydrochloric acid is present, until the sparingly soluble salt has dissolved completely. Similar reasoning may be applied to salts of acids, such as phosphoric(V) acid (K1 = 7.5 x 10-3 mol L-1 K2 = 6.2 x 10-8 mol L-1 K3 = 5 x 10 13 mol L-1), oxalic acid (Kx = 5.9 x 10-2 mol L-K2 = 6.4 x 10-5molL-1), and arsenic)V) acid. Thus the solubility of, say, silver phosphate)V) in dilute nitric acid is due to the removal of the PO ion as... 

Block or graft copolymem can be obtained by cationic polymerization of THF with macromolecular initiators. The recommended groups for the initiation are the dioxolenium cation, the acyl cation and the super acid ester, each of which can be introduced into the backbone polymer by reaction with silver salts of strong acids. Introduction of the dioxolenium group into polystyrene was carried out by the following route32 ... 

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. 

The production of fatty acid-capped silver nanoparticles by a heating method has been reported [115]. Heating of the silver salts of fatty acids (tetradecanoic, stearic, and oleic) under a nitrogen atmosphere at 250°C resulted in the formation of 5-20-nm-diameter silver particles. Monolayers of the capped particles were spread from toluene and transferred onto TEM grids. An ordered two-dimensional array of particles was observed. The oleic acid-capped particle arrays had some void regions not present for the other two fatty acids. 

In a subsequent reaction, n-BuSnClg was reacted with the silver salt of cyclohexane carboxylic acid in the presence of wet solvent. This reaction gave the ladder formulation, 3, identified above, Equation 2. 

Use of nitrous acid to liberate a free keto-acid from its semicarbazone caused formation of hydrogen azide which was co-extracted into ether with the product. Addition of silver nitrate to precipitate the silver salt of the acid also precipitated silver azide, which later exploded on scraping from a sintered disc. The possibility of formation of free hydrogen azide from interaction of nitrous acid and hydrazine or hydroxylamine derivatives is stressed. 

Methyl pyruvate has been prepared from the silver salt of pyruvic acid and methyl iodide,3 and from the free acid by the alcohol-vapor method without a catalyst.4 Pyruvic esters have also been prepared by the dehydrogenation of lactic acid esters.5... 

As noted in the Introduction sulfenic acids are generally unstable and reactive. A few, namely, anthraquinone-1-sulfenic acid [1], anthraquinone-l,4-di-sulfenic acid [2], and the sulfenic acid [3] (generated by thermolysis of sulfoxide [4]) have, however, been isolated as pure crystalline compounds (Bruice and Sayigh, 1959 Bruice and Markiw, 1957 Chou et al., 1974). Another sulfenic acid that appears to be of considerable stability is the pyrimidine derivative [5]. The silver salt of [5] was isolated by Pal et al. (1969) from the alkaline hydrolysis of the corresponding disulfide. The free sulfenic acid [5] was then liberated in solution by treating the silver salt with dilute aqueous hydrochloric acid and filtering off the silver chloride formed. Solutions... 

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