Free Radicals in Alkaloidal Color Identification Tests

Abstract

A number of color tests for alkaloids, some appearing in the U.S.P. and N.F., have been studied by electron paramagnetic resonance (e.p.r.) spectroscopy with the ultimate aim of ascertaining the chemical species responsible for the colors. In the case of the Marquis test for opium alkaloids, in which an intense purple is produced at once with morphine and quickly changes to deep blue-violet, it is shown that a different free-radical spectrum appears concurrently with each of these colors. Data are presented on the e.p.r. spectra of radicals thus formed from various alkaloids and several synthetic compounds. These conditions also produced free radicals from phenol and benzene; therefore, it is suggested that the site of radical formation in the alkaloids studied is the aromatic group. No proposal for a chemical mechanism is made, but it is suggested that a common mechanism is involved when aromatic compounds are treated with the Marquis reagent. Free radicals have also been observed in other color tests for alkaloids, such as the Mecke test for morphine. Like the Marquis test, the latter also uses concentrated sulfuric acid as solvent.