Gaschromatographic determination of carbonyl compounds by pyrolysis of 2, 4-dinitrophenylhydrazones.

Abstract

C₂C₆ Carbonyl compounds were regenerated quantitatively from 2, 4-dinitrophenylhydrazones by heating with dicarbonic acids. The regeneration reaction was carried out in a glass tube attached to gaschromatography unit (see Fig. 1), and the liberated carbonyl compounds were carried directly into the column. Among dicarbonic acids studied, ο-phthalic acid, α-ketoglutaric acid, glutaric acid etc. had an excellent property in liberating carbonyl compounds on heating with 2, 4-dinitrophenylhydrazones.
However, α-ketoglutaric acid and glutaric acid produced volatile products on heating alone at 250°C, and disturbed base line (see Fig. 2). On the other hand, ο-phthalic acid produced no volatile material except water, which could be eliminated by fixing on calcium chloride, and regenerated carbonyl compounds in good yield from 2, 4-dinitrophenylhydrazones.
The ratio of ο-phthalic acid to the hydrazones should be more than 10 (see Fig. 3). Carbonyls were completly recovered in the case of n-butyraldehyde and methylethylketone. Formaldehyde was detected but not determined quantitatively. Aqueous solutions of carbonyl compounds (concentrations less than 1%) were analyzed quantitatively by this technique in good accuracy (see Table V).