2.4- Dinitrophenylhydrazones thin layer chromatography

The dinitrophenylhydrazones were separated from the reaction mixture by thin-layer chromatography (silica gel G developed with benzene) and further purified by thin-layer chromatography on aluminum oxide G (petroleum ether-diethyl ether (96 to 4), silica gel G (chloroform), and silica gel G (diethyl ether)). In all cases, the specific activities of the dinitrophenylhydrazones remained constant over the course of the last two purifications. 

It also has been used as a spray reagent and for quantitation in paper and thin layer chromatography Section 6.5). It should be noted that A - 4-3-keto steroids react much less readily with isonicotinic acid hydrazide than do A4-3-keto steroidsThe 2,4-dinitrophenylhydrazone has also been described4. 

The milk and cream were centrifuged, and the fat fraction was removed. The fat was extracted with carbonyl free hexane, and the fat extract was immediately reacted with 2,4-dinitrophenylhydrazine. The carbonyl compounds formed respective 2,4-dinitrophenylhydrazones (2,4-DNPH). The hydrazones were separated into monocarbonyls and then further purified using thin layer chromatography (18). Alkanal 2,4-DNPH were analyzed by gas chromatography using a 1.83 m glass column (i.d. 4 mm) packed with 2% OV-1 on acid washed Chromosorb W ( 180-200 mesh) (18,19). ... 

Purpose. The experiment investigates the use of a polymer-bound chromium trioxide oxidizing agent in the oxidation of a secondary (2°) alcohol to a ketone. An alternative oxidizing agent, sodium hypochlorite, may be used instead. The progress of the reaction is monitored by thin-layer chromatography (TLC). The product ketone can be characterized by formation of its 2,4-dinitrophenylhydrazone (2,4-DNP) derivative. 

Thin-layer chromatography can also be used for the separation and identification of aldehydes and ketones in the form of their 2,4-dinitrophenylhydrazones (38 — 40). For simple aliphatic compounds silicagel G and the mobile phase cyclohexane-carbon tetrachloride- ethylacetate (10 75 15) can be used. 

The coloured p-nitro- and 2,4-dinitrophenylhydrazones are ideal derivatives for the separation and characterization of carbonyls by paper, thin-layer and column chromatography. The oximes can easily be revealed on the thin-layer plates by spraying with solutions of copper(Il) chloride or copper(II) acetate (alcoholic) or iron(III) chloride [21,22]. For the visualization of carbonyl compounds by means of fluorogenic labeling by Schiff base formation with reagents such as dansyl-hydrazine, we refer the reader to Chapter 9. 

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