Purpuric acid

Purpur-saure, /. purpuric acid, -scbwefel-saure, /. sulfopurpuric acid, purzeln, v.i. tumble. 

Purine derivatives (e. g. xanthine) are oxidized by chloramine T in the presence of hydrochloric acid and form purple-red anunonium salts of purpuric acid (murexide) with ammonia. Whether the murexide reaction is also the cause of the fluorescence is open to question. 

Purpuric acid lb 174 Pyrazolidine derivatives la 426 3,5-Pyrazolidindione derivatives lb 20 Pyrazolinone derivatives lb 277 Pyrazolin-5-one derivatives lb 327,329 Pyrazone lb 332 Pyrene lb 379 PyrethrinI lb 18 Pyrethrin II lb 18 Pyrethroids lb 86,87 Pyrethroid insecticides la 359 Pyridine alkaloids la 66 lb 279 Pyridine derivatives lb 119,244 Pyridinium carbinols lb 65 Pyridinium glycols lb 65 Pyridoxal la 157,158,253 Pyridoxamine la 253 Pyridoxine la 253... 

CgHgOgNg, /V-(4 -Hydroxy-2, 6 -dioxo-1, 3 -diazin-5 -yl)-5-imino(perhydro-l,3-diazine-2,4,6-trione) (purpuric acid) (murexide = L NH3), H3L... 

There were experiments prior to this working in the same area. In 1771 Woulfe treated indigo with nitric acid and discovered a yellow substance that dyed wool and silk. In 1779 Welter nitrated silk in another version of the same experiment. Both chemists had made picric acid, but without knowing it. In 1776 Scheele treated uric acid with nitric acid and evaporated the contents of the reaction. The reddish residue that appeared could dye skin. Scheele named it purpuric acid. In 1818 Proust prepared mureside from this. These experiments were not fully understood, but they were an unconscious groping towards the synthesizing of colour. 

Oxidation of xanthine or uric acid derivatives with chromic acid gives the appropriate alloxane and urea as primary products which undergo further oxidation to corresponding parabanic acids (imidazolidine-2,4,5-triones) and purpuric acids which, on addition of ammonia, constitute the murexide test. This is positive for all purines capable of oxidation to an alloxane derivative, For a review see ref 48. 

Murexide is the acid ammonram salt of purpuric acid, which does not exist in the free state. It is of historical interest, as besides picric acid it is the oldest artificial dyestuff used technically. Its application dates from the year 1853. 

Murexide dissolves in water with a fine purple-red colour, which is changed to blue-violet on addition of excess of alkali. Mineral acids set free purpuric acid, which immediately decomposes into uramil and alloxan, the solution being decolorised. 

Murexide, the ammonium salt of purpuric acid, was known for long to be a good indicator for Ca2+ in aqueous solution (74). The chemical composition of the dye is as follows ... 

This is ammonium salt of purpuric acid and its anion has the following structure. 

Ammonium purpurate Ammonium salt purpuric acid Ammonium 5-(2,4,6-trioxoperhydropyrimidin-5-ylidene-amino)barbiturate ... 

Ammonium salt purpuric acid 2587 Amoryl BR1244 1085... 

Carl Julius Fritzsche (Neustadt, nr. Stolpen, Saxony, 29 October 1808-Dresden, 20 June 1871), originally a pharmacist, then Dr. Phil. Berlin (1833) and assistant to Mitscherlich, became manager of Struve s mineral-water works in St. Petersburg, and member of the Academy of Sciences there (1838 adjunct, 1844 associate, 1852 full academician). He investigated pollen, purpuric acid, potassium bromate, crystalline ammonium sulphides, osmiridium, and vanadium compounds. He discovered compounds of hydrocarbons and picric acid, and grey tin. ... 

Ammonium salt of purpuric acid (the free acid cannot be isolated) formed by action of HNOjiAq. upon various purine derivs. Reddish... 

Well prepared purple solutions have a homogeneity scarcely less than that of the crystalloidal dyestuffs. The behavior toward mercury is another evidence of the correctness of the view upheld by Berzelius. Metallic mercury dissolves gold very easily, while the gold in purple is not attacked by mercury. The electrolysis of purple solutions resembles closely that of a complex, or that of a dyestuff dissolved by an electrolyte, such as Methyl Orange. Just as in the case of the last salt dimethylamidoazobenzolsulfonic acid is deposited on the anode in crystalline form, so is purpuric acid precipitated on the anode in form of a gel. 

Ruhemann S. Triketohydrmdene hydrate, Part V. The analogues of uramil and purpuric acid. J Chem Soc 1910 97 1486-92. 

Purpuric acid is a tetraacid that may be symbolized by H4ln. The acidities are due to the four imido groups its structure possesses or more probably to their tautomeric forms (lactime forms). Figure 29.1 shows the diagram log AT /pH for the complexation with Ca +. 

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