An Infrared Study of the Reaction of Barbiturates with p-Nitrobenzyl Chloride

In alkaline media barbiturates of the general formula HNCONHCOCR'R“CO react with p-nitrobenzyl chloride to sive derivatives of the composition NCONCOCH 2 C 6 HNO 2 CR'R”COCH 2 -C 4 HNO 2 . It is postulated that the process of complex formation proceeds via the interaction of a negatively charged enolized barbituric acid ion with a positively charged p-nitrobenzyl ion. The infrared absorption spectra of the derivatives are in accord with this mechanism and suggest that in the complex the barbiturate is bonded to the p-nitrobenzyl moiety through the carbonyl oxygens in the 4 and 6 positions The compounds show unique features throughout the region studied, 4000–650 cm −1 , and hence the method affords a high degree of specificity for detecting and characterizing these sedative drugs