Change of 2,4-Dinitrophenylhydrazones on alumina and silica gel chromatographic columns

Abstract

I n an investigation of the " cardboard " flavour in skim milk (Forss, Pont, and Stark 1955a, 1955b), the compounds responsible for this defect were found to be the C,-,, 2-enals and the 0,-,, 2,4-dienals. These unsaturated aldehydes were separated by passing their 2,4-dinitrophenylhydrazones through chromatographic columns. While these derivatives passed unchanged through alumina and silica gel columns when developed with ether and light petroleum, some of the 2,4-dinitrophenylhydraeones of the aliphatic saturated aldehydes and ketones which were also present were observed to change. Acetaldehyde 2,4-dinitrophenylhydrazone was the main product of these changes but formaldehyde and other 2,4-dinitrophenylhydrazones were also obtained. The proportion changed was greater when relatively small amounts of the 2,4-dinitrophenylhydrazone were applied to the column, and the effect was much more marked on silica gel than on alumina.Since alumina and silica gel columns have been widely used for the fractionation of 2,4-dinitrophenylhydreaones (Gordon et al. 1951) and since further work on mixtvres of aliphatic carbonyl compounds was contemplated in this laboratory, a study was made of the factors responsible for these changes.Use of ethanol in place of ether, use of other brands of silica gel, washing the gel with hydrochloric acid to remove iron, and extensive washing with water to remove hydrochloric acid, all failed to suppress the changes.It is poasible that 2,4-dinitrophenylhydrazones and carbonyl compounds present in the solvents enter into an exchange reaction, but then the use of carbonyl-free solvents should suppress the changes, but this was not so.There exists the possibility that carbonyl compounds are produced during the passage of the solvent through the column and, while the reason for this