Green acidification

The nitrosophenol is precipitated from the cooled aqueous solution by acidification with dilute sulphuric acid and is extracted with ether in a separating funnel. After brief drying over calcium chloride the brownish-green solution is concentrated on the water bath. The sparingly soluble compound crystallises from the ether on cooling. Melting point 120°-130° (decomp.). Complete purification of nitrosophenol is difficult. 

The easiest way to 10 goes via the synthesis of KDNM (see Section n.C). Acidification of an aqueous solution of KDNM, which should be buffered with H3PO4 (pH = 6.5), followed by low-temperature extraction with diethyl ether, gives the monomeric emerald-green nitrosolic acid 10 dissolved in the ether phase. Slow removal of the solvent yields the yellowish dimeric form of 10. The acid (10) is only poorly characterized. It is known to slowly decompose into HCN and HNO2 in basic solution (decomposition of the anion DNM), while the free acid (10) rapidly decomposes to give fuhninic acid, HCNO and hyponitrous acid, HON=NOH. It should be noted that both the free acid and its metal DNM salts are highly explosive. 

The addition of base (OH-) shifts the equilibrium to the left while acidification of the solution shifts the equilibrium to the right in favor of Cr20 2. In other coIor/pH relations, red CrOs is acidic, green Cr20s is amphoteric and the black CrO is basic in nature. 

Thus, simple deproteinization of plasma with trichloroacetic acid, perchloric acid, phosphoric acid, or acetonitrile, followed by centrifugation and direct injection of the supernatants, yielded low recoveries of malachite green and leuco-malachite green, probably due to insufficient debinding of the analytes (495). Acidification or alkalinization of plasma and subsequent extraction with ethyl acetate also resulted in poor recoveries. In contrast, protein denaturation with a mixture of either acetonitrile or methanol and citric acid could substantially improve Ute recovery of the analytes, possibly due to the pairing-ion function of Ure citrate ions. 

The properties of 5-hydroxylamino-3-phenyl-l,2,4-thiadiazole (272) have been studied in some detail.170 The compound dissolves in alkalis, giving intensely green solutions (273), from which the red azo-1,2,4-thiadiazole 274 is precipitated upon acidification. Hydrogen sulfide reduces 274 to the colorless hydrazothiadiazole 275, which is reconverted, by air oxidation in alkaline solution, into 273 (i.e. 274 as base-adduct). 

But how can this acidification be effected without adding large amounts of strong acid (recall that permanganate is unstable in concentrated acid) Simple Dissolve the potassium manganate/potassium hydroxide mixture in water, throw in a few chunks of dry ice, and in the witches cauldron effect, watch the solution turn from green to deep purple ... 

After isolation of the microcrystalline precipitate which is the peroxo complex 25, there remains a reddish brown filtrate which contains further peroxo complex. Acidification of the latter with hydrochloric acid produces, after a few hours, the superoxo complex [(l)CO-02-Co(l)](Cl)5 (26) in the form of green microcrystals. As has already been mentioned, mononuclear chloro complex may finally be isolated from the red mother liquor of this preparation. If 25 is treated with a measured quantity of aqueous hydrochloric acid, the superoxo... 

The solution is green. This reaction is reversible on (slight) acidification and also on boiling chromium(III) hydroxide precipitates again. 

Redaction of (5) with alkali metal forms the green clnster anion Co6(CO)i5 , which can be further rednced to the red dianion Co6(CO)i4, and isolated as a potassinm salt. The latter clnster anion is an early example of the expanding family of highly rednced transition metal carbonyls, for example Na3Co(CO)3, where np to two CO gronps are replaced by two electrons each. Co6(CO)is is also the mainprodnct from valence disproportionation of Co2(CO)g in ethanol. Oxidation (or acidification) of the clnster anions gives Co6(CO)i6. 

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