Separation of the Dinitrobenzoate Esters DNBs

Another way of characterising alcohols is through TLC after having treated them with 3,5-dinitrobenzoyl chloride (preparation, see Chapter TS, 3a). Dhont and Derooy [49] were the first to show that the dinitrobenzoate esters could be separated by using benzene-petrol ether (50 + 50) on silica gel G layers. Butter yellow (p-dimethylamino-azobenzene) was chosen as reference substance to determine the positions in the chromatogram. The following values, 

Beaxjn [20], Gbaf and Hoppe [79) and Mehlitz and co-workers [163] have used similarly non-polar solvent combinations. Menthol and isomenthol dinitrobenzoates can be separated with hgroiu (105—120° C)-isopropyl ether (95 + 5) on silica gel G laj -ers under normal conditions [79]. The dinitrobenzoates of other terpene and sesquiterpene alcohols could be clearly differentiated by double development on 500 xm-silica gel G layers using petrol ether-isopropyl ether (94 + 6). Solvent mixtures containing twice as much ether are more suitable for TLC of the dinitrobenzoates of lower alcohols. 

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