Silver salt, drying

Formation and Decomposition Add 3 mL of the diluted silver amrronia complex solution to about 0.1 mL of 2-methyl-3-butyn-2-ol in a test tube, and note the formation of the silver acetylide salt. Collect the silver salt by vacuum filtration of the aqueous solution be careful not to let the silver salt dry, because the dry salt Is explosive. Transfer the wef silver salt to a clean test tube, and add a small amount of dilute hydrochloric acid. Observe what changes occur, especially in the color and form of the precipitate. 

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. 

From the silver salt. By refluxing the dry silver salt with an alkyl halide in anhydrous ether, benzene or absolute alcohol solution, for example ... 

Preparation of silver maleate. Dissolve 65 g. of pure maleic acid (Section 111,143) in the calculated quantity of carefully standardised 3-5N aqueous ammonia solution in a 1-htre beaker and add, whilst stirring mechanically, a solution of 204 g. of silver nitrate in 200 ml. of water. Filter oflf the precipitated silver maleate at the pump, wash it with distilled water, and press well with the back of a large flat glass stopper. Dry in an electric oven at 50-60° to constant weight. The yield of the dry silver salt is 150 g. Store in a vacuum desiccator in the dark. 

Sodium anthraquinone-p-sulphonate ( silver salt ). Place 60 g. of fuming sulphuric acid (40-50 per cent. SO3) in a 250 or 500 ml. round-bottomed flask and add 50 g. of dry, finely-powdered anthra-quinone (Section IV,145). Fit an air condenser to the flask and heat the mixture slowly in an oil bath, with occasional shaking, so that at the end of 1 hour the temperature has reached 160°. Allow to cool and pour the warm mixture carefully into a 2 litre beaker containing 500 g. of crushed ice. Boil for about 15 minutes and filter off the unchanged anthraquinone at the pump. Neutralise the hot filtrate with sodium hydroxide and allow to cool, when the greater part of the sodium anthra-quinone-p-sulphonate separates as silvery glistening plates ( silver salt ). Filter these with suction and dry upon filter paper or upon a porous plate. A second crop of crystals may be isolated by concentration of the trate to half the original volume. The yield is 40-45 g. 

Practically all pyridazine-carboxylic and -polycarboxylic acids undergo decarboxylation when heated above 200 °C. As the corresponding products are usually isolated in high yields, decarboxylation is frequently used as the best synthetic route for many pyridazine and pyridazinone derivatives. For example, pyridazine-3-carboxylic acid eliminates carbon dioxide when heated at reduced pressure to give pyridazine in almost quantitative yield, but pyridazine is obtained in poor yield from pyridazine-4-carboxylic acid. Decarboxylation is usually carried out in acid solution, or by heating dry silver salts, while organic bases such as aniline, dimethylaniline and quinoline are used as catalysts for monodecarboxylation of pyridazine-4,5-dicarboxylic acids. 

To a solution of 33 g. (O.S mole) of potassium hydroxide (Note 1) in 1.5 1. of distilled water in a 5-1. flask or other appropriate container fitted with a mechanical stirrer is added 80 g. (0.5 mole) of methyl hydrogen adipate (Note 2). With continuous stirring a solution of 85 g. (0.5 mole) of silver nitrate in 1 1. of distilled water is added rapidly (about IS minutes). The precipitated methyl silver adipate is collected on a Buchner funnel, washed with methanol, and dried in an oven at 50-60°. For the next step the dried silver salt is finely powdered and sieved through a 40-mesh screen. The combined yield from two such runs is, 213 g. (80%). 

Drying is carried out in the flask in which the final reaction is to be run in order to avoid a transfer. The success of this preparation depends upon the exclusion of moisture. The silver salt retains traces of water tenaciously. 

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... 

Methyl 2-deoxy-39496-tri-0-p-nitrobenzoyl-p-T>- yxo-hexoside. A solution of 370 mg. of 2-deoxy-3,4,6-tri-0-p-nitrobenzoyl- -D-Zyxo-hexosyl bromide (5) in 15 ml. of dry dichloromethane is added to a stirred suspension of 500 mg. of silver carbonate in 100 ml. of absolute methanol. The mixture is stirred for 20 hours and filtered the silver salts are washed several times with warm dichloromethane. The combined filtrate and washings are evaporated to dryness under diminished pressure, and the residue is recrystallized five times from ether-dichloromethane, giving 61% of pure product, having m.p. 173°-174°C. and [ ]D + 36° in chloroform. 

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 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. ... 

The precipitate is collected on filter paper (Note 7) in a Buchner funnel by vacuum filtration and is washed with 100 ml. of absolute ethanol. The solid is slurried in three 75-ml. portions of distilled water (Note 8), 100 ml. of absolute ethanol, two 100-ml. portions of reagent-grade acetone, and two 100-ml. portions of anhydrous ethyl ether. The filter cake is pressed dry in the funnel with suction by means of a piece of rubber dam, transferred to a tared, 500-ml., round-bottomed flask, and dried under reduced pressure (0.01 mm.) at room temperature for 24 hours (Note 9). The weight of the dry silver salt of succinimide is 51-54 g. (88-94%). 

A considerable amount of sodium nitrate is present in the precipitate. Although the presence of sodium nitrate did not hinder small-scale alkylation reactions (ca. 250 mg.), the submitters recommend that it be removed in larger runs to facilitate the isolation and drying of the silver salt. 

Silver salts may be unstable when heated. An explosion occurred while the silver salt of isatin was being dried under reduced pressure at ca. 100°. 

The silver salt may be handled moist, but when dry it explodes violently on touching with a glass rod. 

Polysilanes as reducing agents. In a paper on the formation of conductive circuits by UV patterning of polysilane films, the inherent reducing ability of polysilanes to effect the reduction of a silver salt to silver metal was described.307 PMPS, PPHS [(PhSiH) ], and PDFIS were separately spin-coated on glass or silicon wafer substrates, and after drying... 

A mixture of 2 g. of potassium chlorate, 30 g. of commercial sodium hydroxide, 10 g. of finely powdered sodium /3-anthraquinone-sulphonate ( silver salt ), and 40 c.c. of water is heated for twenty hours at 170° (oil bath) in an autoclave or in an iron tube with screwed-on cap. The cooled melt is repeatedly extracted with hot water and the extracts, after being combined and filtered, are acidified while hot with excess of hydrochloric acid, which precipitates the alizarin. When the mixture has cooled the precipitate is collected at the pump, washed successively with dilute hydrochloric acid and water, and dried. 

Most of the simplest formaldoximes are very labile at ambient temperature (often they are stable only at low temperatures) while their alkali and silver salts are stable in bulk due to kinetic stabilization. However, caution Although alkali and silver nitro-and nitrosomethanides are kinetically stable compounds, they are nonetheless energetic materials and appropriate safety precautions (e.g. a protection shield when dried substances are used, preparation of small quantities (<2 g), keeping these salts wet when stored) should be taken, especially when these compounds are prepared on a larger scale. 

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. 

Fluoroanions such as [BF4] , [PF6]-, and [AsF6] can be considered as potential sources of fluoride ions. The silver salts tend to be wet and abstraction reactions lead to hydrolysis3 (see the procedure in Section C) or yield either the aqua or fluoroanion complexes ([BF4] or [AsF6] , 4 Using dry reagents such as NO[PF6] can lead to the oxidative addition of fluoride (see the procedure in Section D).5... 

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