| Abstrakt: |
Synthesis, purification, elemental analysis, and spectroscopic studies were undertaken to characterize the structure of the red adduct 2:1 thiobarbituric acid (TBA)-malonaldehyde involved in the evaluation of oxidative rancidity in fats and oils. Thin-layer chromatography, infrared and ultravioletvisible absorption, 1H (1H NMR) and 13C nuclear magnetic resonance (NMR) spectra were used. A yield of 93% was obtained in the synthesis. The results of elemental analysis agree with the formula for the chloro-monohydrated form, C11H11N4O5S2Cl. Three characteristic absorption maxima at 532, 310, and 245 nm, respectively, were shown in acid aqueous medium (pH 2.9). The characteristic vibrations assigned to the -NH, -OH, CαH (exocyclic) and -C=S groups were confirmed in the infrared spectra. There was no evidence of thioenolization. 1H NMR data at δ 5.10 (-CONH- group, H2O and HCl molecules); δ 11.54 (-OH group of keto-enol tautomer, -NH group); and δ 176.4 (-CONH- group) also were observed. The experimental results obtained were consistent with the existence of two spectral equivalent tautomeric structures. The colored adduct was compared with other TBA-aldehyde compounds. [ABSTRACT FROM AUTHOR] |
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