Sodium nitroprusside, preparation

Colour reagent Mix equal volumes of a 4 0 5 per cent aqueous solution of sodium nitroprusside (prepared not more than two weeks before use and stored in the dark) and 4N sodium hydroxide the reagent must be used within fifteen minutes. 

To 2 ml. of a freshly prepared dilute aqueous solution of sodium nitroprusside, add 2 drops of ethyl malonate and shake then add 2-3 drops of 10% aqueous sodium hydroxide solution and shake again. A red coloration at once appears, but fades in a few minutes to pale brown,... 

Sulphur. THE LASSAIGNE SODIUM TEST. The sodium fusion will have converted any sulphur present in the original compounds to sodium sulphide. Dissolve a few crystals of sodium nitroprusside, Na8[Fe(CN)5NO],zH20, in water, and add the solution to the third portion of the filtrate obtained from the sodium fusion. A brilliant purple coloration (resembling permanganate) indicates sulphur the coloration slowly fades on standing. Note, (i) Sodium nitroprusside is unstable in aqueous solution and therefore the solution should be freshly prepared on each occasion, (ii) This is a very delicate test for sulphides, and it is essential therefore that all apparatus, particularly test-tubes, should be quite clean. 

Nitroprusside reaction. Add 1 ml. of a freshly prepared solution of sodium nitroprusside to the aldehyde or its solution. Add dil. NaOH solution in excess a red coloration is produced. 

Sulphuric add test. Heat 0 5 g. of citric acid or a citrate with 1 ml. of H2SO4 CO and COg are evolved and the mixture turns yellow, but does not char. Acetone dicarboxylic acid, OC(CH2COOH)g, is also formed, and is tested for after heating the mixture for 1 minute cool, add a few ml. of water and make alkaline with NaOH solution. Add a few ml. of a freshly prepared solution of sodium nitroprusside and note the intense red coloration (see Test 4 a) for ketones, p. 346). 

Now add a few drops of a freshly prepared solution of sodium nitroprusside. A purple coloration is obtained (test for - SH Group),... 

Sodium nitroprusside (for sulfur detection) dissolve about 1 g of sodium nitroprusside in 10 mL of water as the solution deteriorates on standing, only freshly prepared solutions should be used. This compound is also called sodium nitroferricyanide and has the formula Na2pe(NO)(CN)5 2H2O. 

Sodium nitroprusside (SNP), which is also known as Nipruss or Nipride to medical practitioners, was the first iron nitrosyl complex, prepared as far back as 1850 by Playfair [40]. The hypotensive property of SNP was first demonstrated by Johnson [41] in 1929. It was shown that application of a moderate dose of SNP reduces the blood pressure of a severely hypertensive patient without any side effect [42]. Since that time considerable research has been carried out to understand the mode of action of nitroprusside and its metabolic fate. SNP is now regarded as a potent vasodilator that causes muscle relaxation by releasing NO which activates the cytosolic isozyme of guanylyl cyclase [43-46]. 

Testing for Sulphur.—The qualitative test for sulphur is carried out in the same way as that for nitrogen. Ignite the substance in a small tube with sodium, dissolve the product in water, and add to one half of the cooled solution a few drops of sodium nitroprusside solution freshly prepared by shaking a few particles of the solid salt with cold water. A violet colour indicates the presence of sulphur. Since the nitroprusside reaction is extremely sensitive and does not allow any estimate of the amount of sulphur to be made, filter the second half of the liquid, add lead acetate solution to the filtrate, and acidify with acetic acid. According as the amount of sulphur is small or large, a dark turbidity or a more or less heavy precipitate will form. 

We close with a plea to investigators to report shift data with respect to a standard absorber, either clean iron foil or sodium nitroprusside or both. The logic behind this request is obvious since anyone who has tried to intercompare results between different papers, knows how frustrating it can be when no common substances were studied. We also suggest that inherently narrow line sources be used—i.e., Cu, Pt, Pd, or Cr. Stainless steel sources are usually so broad that they can often mask important features of the spectrum. Of the host matrices mentioned we prefer Cu since it doesn t give rise to any interfering x-rays and when prepared properly doesn t show any broadening at low temperatures. 

For the nitroprusside-cyanide reagent two solutions are prepared. For solution I, sodium nitroferricyanide (sodium nitroprusside, 1.5 g) is dissolved in 2M H2S04 (5mL) to which MeOH (95 mL) and NH4OH (10 mL) is added. A precipitate forms that is discarded. The clear, red solution is refrigerated. For solution II, sodium cyanide (2g) is dissolved in H20 (5 mL) and diluted with MeOH (95 mL), this is filtered if necessary. CAUTION Sodium cyanide can be absorbed through the skin and is extremely toxic. Appropriate safety precautions and first aid procedures should be adopted when handling sodium cyanide. 

Sodium nitroprusside was first prepared and investigated in the middle of the nineteenth century, and a comprehensive summary of the earlier chemical investigations has been published (17). Up to 1910-1930, the addition reactions of bases to NP were explored, involving the characterization of colored intermediates (e.g., with SH-, SR-, and SO3 ), useful for analytical purposes. The hypotensive action of NP was first demonstrated in 1929, and a considerable research effort has attempted to establish the mode of action of NP and its metabolic fate. Questions still arise on the mechanism of NO release from NP in the biological fluids, and we refer to them below. New accounts dealing with modern structural and reactivity issues associated with the coordination of nitrosyl in NP and other complexes have appeared (18-20). From the bioinorganic and environmental viewpoint, nitrosyl iron complexes have been studied with... 

About 15 c.c. of the distillate are treated with 1 c.c. of aqueous 4 % phenylhydrazine hydrochloride solution, 3-4 drops of freshly prepared 0-5% sodium nitroprusside solution and sufficient concentrated caustic soda solution to render the liquid alkaline an intense blue coloration gradually, and especially on heating, changing to red, indicates formaldehyde. 

The zinc nitroprusside paste is prepared by precipitating sodium nitroprusside solution with an excess of zinc sulphate solution and boiling for a few minutes the precipitate is filtered and washed, and kept in a dark glass bottle or tube. 

The characteristic colours and solubilities of many metallic sulphides have already been discussed in connection with the reactions of the cations in Chapter III. The sulphides of iron, manganese, zinc, and the alkali metals are decomposed by dilute hydrochloric acid with the evolution of hydrogen sulphide those of lead, cadmium, nickel, cobalt, antimony, and tin(IV) require concentrated hydrochloric acid for decomposition others, such as mercury(II) sulphide, are insoluble in concentrated hydrochloric acid, but dissolve in aqua regia with the separation of sulphur. The presence of sulphide in insoluble sulphides may be detected by reduction with nascent hydrogen (derived from zinc or tin and hydrochloric acid) to the metal and hydrogen sulphide, the latter being identified with lead acetate paper (see reaction 1 below). An alternative method is to fuse the sulphide with anhydrous sodium carbonate, extract the mass with water, and to treat the filtered solution with freshly prepared sodium nitroprusside solution, when a purple colour will be obtained the sodium carbonate solution may also be treated with lead nitrate solution when black lead sulphide is precipitated. 

The reagent must be freshly prepared by dissolving a crystal (about the size of a pea) of pure sodium nitroprusside in a little distilled water. 

The test is usually carried out by adding the reagent to the solution acidified with dilute hydrochloric acid carbonates, sulphites, and phosphates are not precipitated under these conditions. Concentrated hydrochloric acid or concentrated nitric acid should not be used, as a precipitate of barium chloride or of barium nitrate may form these dissolve, however, upon dilution with water. The barium sulphate precipitate may be filtered from the hot solution and fused on charcoal with sodium carbonate, when sodium sulphide will be formed. The latter may be extracted with water, and the extract filtered into a freshly prepared solution of sodium nitroprusside, when a transient, purple colouration is obtained (see under Sulphides, Section IV.6, reaction 5). An alternative method is to add a few drops of very dilute hydrochloric acid to the fused mass, and to cover the latter with lead acetate paper a black stain of lead sulphide is produced on the paper. The so-called Hepar reaction, which is less sensitive than the above two tests, consists of placing the fusion product on a silver coin and moistening with a little water a brownish-black stain of silver sulphide results. 

Use may be made of the intermediate formation of acetone dicarboxylic acid and of the interaction of the latter with sodium nitroprusside solution to yield a red colouration as a test for citrates. When about 0-5 g of a citrate or of citric acid is treated with 1 ml concentrated sulphuric acid for 1 minute, the mixture cooled, cautiously diluted with water, rendered alkaline with sodium hydroxide solution and then a few millilitres of a freshly prepared solution of sodium nitroprusside added, an intense red colouration results. 

Sulphur compounds are reduced to sulphide by this treatment the residue may be moistened with water and placed in contact with a silver coin when a brown to black stain of silver sulphide is obtained (Hepar reaction), or it may be extracted with a little water and filtered into a freshly prepared sodium nitroprusside solution, when an unstable purple colouration will indicate the presence of sulphur (see Section IV.6, reaction 5) (Table V.5). 

Sodium nitroprusside reagent. Rub 0-5 g sodium nitroprusside dihydrate, Na2[Fe(CN)5N0].2H20, in 5 ml water. Use the freshly prepared solution. 

Dilute one drop of the alkaline solution with 1 mL of water and add a drop of sodium nitroprusside a purple coloration indicates the presence of sulfur. (2) Prepare a fresh solution of sodium plumbite by adding 10% sodium hydroxide solution to 0.2 mL of 0.1 M lead acetate solution until the precipitate just dissolves, and add 0.5 mL of the alkaline test solution. A black precipitate or a colloidal brown suspension indicates the presence of sulfur. 

The preparation of substituted pentacyanoferrate(II) ion complexes involves a series of ligand exchange reactions at the iron(II) metal center. Equations (4.1)-(4.3) outline the synthesis of amino acid (AA) metal complexes in aqueous solution. Starting from sodium nitroprusside ion, [Fe(CN)5(NO)]2, equation (4.1), the nitrosyl ligand, NO+, is replaced by an ammine moiety, NH3. The aquapentacyanoferrate(II) ion, [Fe(CN)5(H20)]3, is then generated in situ, equation (4.2), followed by reaction with an AA to yield the desired [Fe(CN)5(AA)](3+n) complex, equation (4.3). 

A freshly prepared solution of D-thiogalactonic acid phenylhydrazide gives no reaction either with sodium nitroprusside or with lead acetate, but, when allowed to stand for a considerable time, both reactions are positive, presumably in consequence of decomposition. Boiled for an hour in aqueous solution, D-thiogalactonic acid phenylhydrazide is transformed into D-galactonic phenylhydrazide. 

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