Cobalt Color Reaction of Barbiturates.

Abstract

Of the numerous analytical methods employed for the determination of barbiturates, those making use of specific color reactions have been most extensively studied. Handorf employed the mur-exide reaction for the detection of veronal, and Zwikker, Bodendorf, Herwick and Koppanyi, et al.,, have developed modifications of a color reaction with cobalt salts in conjunction with various bases. Kozelka and Tatum attributed this color formation to a specific reaction with substances containing one or 2 imide groups. In an investigation of amytal (isoamylethyl barbituric acid) excretion by dogs, using a modification of the reaction designed by Koppanyi et al., employing cobalt acetate and isopropylamine made up in absolute methanol solutions, it was observed in this laboratory, that of the more probable breakdown products of amytal only isoamyl-ethyl acetic acid gave the characteristic color reaction. Since this compound contains no imide grouping, it was apparent in this case that color formation was not due to such a group. This finding led to an examination of various classes of compounds a number of which have not been reported upon by other investigators. A partial listing is given in Table 1. Since the acids tested gave a color apparently identical with that obtained with amytal, a number of these test solutions were submitted to spectrophotometric analysis. The spectrophotometric curves given herewith were made with a Bausch and Lomb medium quartz spectrograph and sector photometer. The length of the absorption cells was 5 cm. To cobalt acetate and isopropylamine mixtures were added respectively, solutions of amytal, isoamyl ethyl acetic acid (RRC2H2O2) and stearic acid in amounts sufficient to give an intensity of color suitable for measurement.