Ammoniacal silver solutions

During preparation of an oxidising agent on a larger scale than described [1], addition of warm sodium hydroxide solution to warm ammoniacal silver nitrate with stirring caused immediate precipitation of black silver nitride which exploded [2], Similar incidents had been reported previously [3], including one where explosion appeared to be initiated by addition of Devarda s alloy (Al—Cu—Zn) [4], The explosive species separates at pH values above 12.9, only produced when alkali is added to ammoniacal silver solutions, or when silver oxide is dissolved with ammonia [5], The Sommer Market reagent mixture used to identify cellulose derivatives led to a severe explosion [6],... 

Experiments.—Being a primary hydrazide (of carbamic acid), semicarbazide reduces ammoniacal silver solutions and Fehling s solution. It reacts readily with aldehydes and ketones with the elimination of water and formation of semicarbazones, which, since they are more easily hydrolysed than are phenylhydrazones and oximes, are to be preferred to the latter for purposes of separation and purification of carbonyl compounds. Shake an aqueous solution of the hydrochloride (prepared as described above) with a few drops of benzaldehyde, isolate the semicarbazone and purify it by recrystallisation from alcohol. Melting point 214° decomp. Benzaldehyde semicarbazone is decomposed into its constituents by gentle warming with concentrated hydrochloric acid. 

The aldehydes are readily oxidised and therefore behave towards ammoniacal silver solution and towards Fehling s solution as reducing agents. 

Experiment 1.—Dilute a few drops of formaldehyde or acetaldehyde with a few c.c. of water, add a small amount of ammoniacal silver solution, and divide the mixture between two test tubes. Into one test tube run a few drops of sodium hydroxide solution an immediate separation of metallic silver takes place. From the other solution after standing for some time in the cold, or more quickly on warming, the silver separates. Thus the oxidising action of ammoniacal silver solution is very considerably increased by sodium hydroxide (Tollens). Also test the reducing action of the aldehydes on Fehling s solution. 

Test the behaviour of phenylhydrazine towards Fehling s solution and towards ammoniacal silver solution. 

The liquid is now neutralised with baryta, and barium nitrate is added, so long as a precipitate of barium sulphate is formed this is filtered off and washed. The filtrate is concentrated to 300 c.c. and treated with silver nitrate, as before, till a test drop gives a yellow colour with baryta when this occurs it is exactly neutralised with baryta, and from a burette small quantities of baryta are added till the silver salt of histidine is completely precipitated this is determined by taking out a drop when the precipitate has settled and testing with ammoniacal silver solution if a precipitate easily soluble in excess of ammonia be formed, when the two liquids come together, histidine is still present and more baryta water must be added, until it is completely thrown out, when it is filtered off, stirred up with water, again filtered off and washed out. 

Phenylacetamide has been obtained by a wide variety of reactions from benzyl cyanide with water at 250-260° 6 from benzyl cyanide with water and cadmium oxide at 240° 6 from benzyl cyanide with sulfuric acid 7 8 by saturation of an acetone solution of benzyl cyanide with potassium hydrosulfide 9 from benzyl cyanide with sodium peroxide 10 by electrolytic reduction of benzyl cyanide in sodium hydroxide 11 from ethyl phenyl-acetate with alcoholic 12 or aqueous 13 ammonia from phenyl-acetic acid with ammonium acetate 14 or urea 15 from diazoacetophenone with ammoniacal silver solution 16 from phenyl-acetic acid imino ether hydrochloride and water 17 from acetophenone with ammonium poly sulfide at 215° 18 from benzoic acid 19 and by heating the ammonium salt of phenyl-acetic acid.20... 

An accurate electrometric method applicable to soluble sulphides consists in precipitating as silver sulphide in alkaline solution by titration with standard ammoniacal silver solution.6 The change of E.M.F. at the end-point is considerable. The method is satisfactory in the presence of sulphite, sulphate, thiosulphate, polysulphide or chloride. 

Tungsten dioxide thus acts as a powerful reducer, and will convert mercuric and cui>ric salts to the mercurous and cuprous condition, and precipitate the metal from ammoniacal silver solutions. The amorphous variety is soluble in hydrochloric and sulphuric acids, yielding red solutions which on standing undergo partial oxidation with loss of colour the ciystalline dioxide is unacted upon, even by the hot concentrated acids.Nitric acid has a slow oxidising action. Concentrated alkali solutions dissolve the amorphous oxide, with formation of the tungstate and liberation of hydrogen, but have no action on the crystalline variety. ... 

This salt crystallizes in thick columns with four molecules of water. Its chief use is as a reducing agent. It reduces an ammoniacal silver solution and in this way is used in silvering glass. It is also used as a constituent of Fehling s solution, (p. 332), which is an alkaline copper solution reduced by certain sugars. It acts as a purgative in Seidlitz powders which consist of sodium-potassium tartrate, sodium acid carbonate and free tartaric acid. 

The detection of aldehyde groups with ammoniacal silver solution, as recommended in the literature, -is dangerous because the reagent can explode after standing for longer periods. 

In the diamine stains, the ammoniacal silver solution must be acidified, usually with citric acid, for image production to occur. The addition of citric acid lowers the concentration of free ammonium ions, thereby liberating silver ions to a level where their reduction by formaldehyde to metallic silver is possible. The optimal concentration of citric acid also results in a controlled rate of silver ion reduction, preventing a non-selactive deposition of si 1ver. 

The described procedure is the only one that gives a variety of colors which may help the identification of polypeptides separated. It has, however, to be noted that some colors are dependent on the protein concentration. Comparison of the results of different variations of the silver stain method [225,226] and other staining procedures [227,228] proved that the method of Oakley et al. [227] is simple and quickly performed. In the Sammons procedures [224] (see above) the washing steps are rather time consuming but offer superior results. The most complicated procedure is that of Switzer et al. [225]. It must also be noted that the methods of Oakley et al. [227] and Switzer et al. [225] require ammoniacal silver solution which is more difficult to handle than silver nitrate. Also the above described method is the only one that allows more than one gel to be stained at once in the same tray. 

Explosion old ammoniacal silver solutions can cause explosion. in case of fire keep tanks/drums cool by spraying with water. 

As pointed out early in Chapter 9, aldehydes are easily oxidized by aqueous ammoniacal silver solutions [i.e., Ag(NHs)2, ToUen s reagent] as well as Fehling s reagent (Cu" in aqueous sodium tartrate) and Benedict s reagent (Cu in aqueous... 

The amount of sulphides may ho estimated by titrating the hot soda solution, to which ammonia has been added, with an ammoniacal silver nitrate solution, I c.c. of which corresponds to 0 005 gramme Na. S. As the titration proceeds, the precipitate is filtered off, and the addition of ammoniacal silver solution to the filtrate continued until a drop produces only a slight opacity. The presence of chloride, sulphate, hydrate, or carbonate does not interfere with the accuracy of this method. The ammoniacal silver nitrate solution is prepared by dissolving 13 345 grammes of pure silver in pure nitric acid, adding 250 c.c. liquor ammoniie fortis, and diluting to 1 litre. 

It must be noted that ammoniacal silver solutions are slightly reduced to metaUic silver by filter paper. Consequently a blank test is essential for small amounts of manganese. 

By the reduction of ammoniacal silver solutions with SnCU, 1 y Ag can be detected. ... 

The most commonly known historical technique is based on the simultaneous addition of sodium azide and silver nitrate solutions to a vigorously stirred solution of sodium hydroxide. The product obtained, in the form of small granules made of very small crystals, had good sensitivity but low initiating ability. Larger crystals were obtained by substituting sodium hydroxide with ammonium hydroxide, which increased the solubility of SA but created two problems (a) low yield and (b) dangerous waste (ammoniacal silver solution). Simultaneous addition of nitric acid to provide a nearly neutral solution solved the two problems and yielded a... 

Brooks states that this substance reacts quantitatively with bisulphite solution, but that it cannot be recovered from the bisulphite compound. This renders it jM-obable that the group CH. CH. CO is present in this body. The fact that the substance is a ketone is proved by its behaviour towards ammoniacal silver solution and magenta solution. The phenyl-hydrazone melts at 161. The ketone does not react with acetanhydride,. and with acetyl chloride it resinifies. When heated with an excess of alcoholic potash solution it gives rise to neutral succinate of potassium. It would seem that the succinic acid occurs in the ketone-molecule in the form of a neutral ester. In order to identify the alcohols which were associated with the succinic acid, the ketone was saponified with aqueous solution of caustic soda, but only ethyl alcohol could be detected. It appears that one of the carboxyl groups of the succinic acid is esterified with ethyl alcohol and the other with an alcohol Ok ijOj. ... 

T. is a strong acid, which is soluble in water and alcohol and has a refreshing taste. By careful heating, it forms an anhydride. T. is able to form complexes with heavy metal ions, e.g., Fe, Cu and Pb. Ammoniacal silver solution is reduced with formation of a silver mirror. 

---