Emerson reagent

The linear (psoralens) and angular (angelicins) fur-anocoumarins can be readily differentiated with the Emerson reagent. It is used, also, for detection of pyrano-coumarins (selinidin, pteryxin) on TLC chromatograms. 

Phenols 2% 4-Aminoantipyrene in 80% ethanol, then 4% potassium hexacyanoferrate(III) in ethanol-water (1 1) (Emerson reagent) Red zones on light yellow background... 

When oxidized by iron(III) ions 4-aminoantipyrine reacts with phenols to yield colored quinonoid derivatives (cf. 4-aminoantipyrine — potassium hexacyanoferrate(III) reagent in Volume 1 a). It is an oxidative coupling based on the Emerson reaction. 

The use of fort-butyl hypochlorite with olefine was disclosed first in tho patent literature,B0S and was subsequently reported also by Emerson,4 and by Hanby and Rydon.707 Hennion and co-workers too have examined this reagent, although they used alcohols as solvents rather than water, thereby obtaining chloro ethers instead of chJorohydrins.64 -800 Unfortunately fert-butyl hypochlorite can be disconcertingly temperamental.170 and its usage has therefore been relatively infrequent. 

Although cyclobutadiene itself is unknown, it can be liberated as an intermediate by oxidative degradation of the organometallic compound cyclobutadiene tricarbonyliron by ammonium hexanitratocerate(IV) (Watts et al., 1965 Paquette and Kelly, 1969). The transient intermediate can be trapped by a dienophile (scheme 57). When the oxidation is carried out in presence of a CAN solution saturated with lithium chloride, tran5 -3,4,-dichloro-cyclobutene is formed (Emerson et al., 1965). Because tricarbonyliron complexes are often used as reagents or intermediates in organic synthesis, the possibility to remove the Fe(CO)3 group by decomplexation... 

In these cases it is usually possible to explain why the color is formed. The reactions can be further classified, on the basis of the type of colored compound formed, into reactions leading to the formation of azo dyes, di- or triphenylmethane dyes, xanthene dyes, polymethine dyes, indophenols, etc. Azo dyes are formed, for example, in the reaction of diazonium salts and phenols (p. 192) or amines (p. 324), azomethines in the reaction of primary aromatic amines with aromatic aldehydes (p. 215), di- and triphenylmethane dyes in the reaction of aromatic aldehydes with aromatic hydrocarbons in concentrated sulfuric acid (p. 213), triphenylmethane dyes in the reaction of phenols with aromatic aldehydes or oxalic acid (p. 196), xanthene dyes in the reaction of anhydrides of dicarboxylic acids with resorcinol (p. 196), polymethine dyes are formed after the cleavage of the pyridine ring in the reaction of the glutaconaldehyde formed and barbituric acid (p. 378), indophenols on reaction of phenols with Gibbs reagent (p. 195), or 4-aminoantipyrine according to Emerson (p. 194), or on the Liebermann reaction (p. 195). 

Emerson, D.W. Polymer-bound Active Chlorine Disinfection of Water in a Flow System. Polymer Supported Reagents. 5. Ind. Eng. Chem. Res. 1990, 29,448. 

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