Isopurpuric acid

Iso-polysaure,/. isopoly acid, -purpurinskure, /. isopurpuric acid. -saccharinsaure, /. isosaccharinic acid, isosmotisch, a. isosmotic. iso-therm, -thermisch, a. isothermal. Iso-therme, /. isotherm, -thlocyanat, -thio-cyanid, n. isothiocyanate, -thiocyansaure, f. isothiocyanic acid, -tonie, /. isotonicity. 

Moisture—when purchased dry - max 0.20 percent when purchased wet - max 22.0 percent Ash - Max 0.1 percent Insoluble matter — Max 0.1 percent Acidity - total sulfuric acid - max 0.1 percent nitric acid - none Lead - max 0.004 percent Analytical A qualitative test for PA depends on its reaction with aq KCN to form a red colored salt, the so-called isopurpuric acid . The reactions involved in this test are still in doubt (see Ref 35, p 492). PA is one of the few tri-nitroaromatics that does not produce a reddish coloration with strong alkalis (Ref 46). It has... 

The salts of isopurpuric acid are easier to prepare, are more stable and some are explosive, for example ... 

For the qualitative determination of picric acid a characteristic reaction with potassium cyanide may be utilized. When an aqueous solution of the two compounds is boiled a red-coloured potassium salt of isopurpuric acid is formed. Formula I was assigned to this compound by Nietzki and Petri [54], while Borsche and Bocker [55] suggested the formulae Ha or lib. 

However, Lobry de Bruyn [56] demonstrated that isopurpuric acid is a mixture of compounds in which one of the nitro groups has been reduced to an azoxy-, azo-, or nitroso group, while the cyano groups have entered the ring, replacing a hydrogen atom or a nitro group. 

The liberation of hydrocyanic acid due to complete hydrolysis of cyano-genic glycosides can be determined by a simple colour test using sodium picrate paper (yellow), which turns red (sodium isopurpurate) in contact with HCN. 

Guignard s Sodium Picrate PaperSodium picrate paper on exposure to gaseous hydrocyanic acid assumes a blood-red colour by the formation of sodium isopurpurate. ... 

A spectrophotometric method has been used for the determination of free cyanide in Prussian blue [30]. Trace amoimts of free cyanide in Prussian blue are hydrolyzed into hydrocyanic acid. The latter is captured by a lithium picrate solution contained in a test tube, which is placed in the reaction vessel. The color change due to the resulting lithium isopurpurate is measured spectrophotometrically at 500 nm. This method can detect cyanide down to a level of 2.5 pg in 100 mg of Prussian blue. 

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