The Phenazinimines: a Possible Explanation of Anomalies associated with Neutral Red

Abstract

D. L. Vivian and Morris Belkin in 1956 reported¹ that they had synthesized a compound which from the ‘unambiguous’ method used² should be 2-amino-8-dimethylamino-3-methylphenazine : This is the accepted structure for the colour base of neutral red, and a compound having this configuration, when converted to its hydrochloride, should show the normal neutral red behaviour of acting as a vital stain, that is, should stain living cells without killing them. As stated by Vivian and Belkin, however, the compound actually obtained, although giving an analysis agreeing with I, when converted to its hydrochloride, did not show the characteristic vital staining behaviour of neutral red. It also differed from the colour base obtained by removing the hydrogen chloride from a sample of commercial neutral red through Chromatographic adsorption on basic alumina, in that it had a very different melting point, as well as in giving a brown colour with concentrated sulphuric acid, instead of the deep green colour which the commercial base forms. Still another point of difference is that the free base from the commercial neutral red fluoresces very slightly if at all in ether solution, while the more soluble synthetic fluoresces a very strong green under ultra-violet illumination.