A new color test for differentiating neoarsphenamine from sulfarsphenamine.

Abstract

Although sulfarsphenamine, which was first introduced clinically in France as Sulfarsenol, is closely related to neoarsphenamine, a distinct chemical difference exists between the two drugs, the former being a derivative of sulfurous acid while the latter is a derivative of the hypothetical sulfoxylic acid.

Publications of Macallum, 1 deMyttenaere 2 and others indicate that more or less uncertainty exists not only in the nomenclature of these drugs but also as to their chemical characteristics. It has also been found by various investigators that the trypanocidal and curative properties to which these drugs owe their practical importance, vary with these differences in chemical structure. It is therefore of great importance to be able to definitely distinguish between these two drugs.

Voegtlin and Johnson 3 in 1922 suggested a color test for differentiating between neoarsphenamine and sulfarsphenamine. This test is based on Reinking, Dehnel and Labhardt's 4 observations that compounds containing the group −CO-SO.Na reduced indigo carmine, while the compounds containing the group −CO-SO₂.Na did not reduce the dye. Voegtlin and Johnson 3 found that an aqueous solution of neoarsphenamine will decolorize indigo carmine in a few minutes, if gently heated, yielding a yellow solution. Under the same conditions they found that sulfarsphenamine did not decolorize the dye.

A test, such as that described above, which requires heating is objectionable because of the ease with which compounds of the arseno type undergo decomposition at higher temperatures. We have also observed that some sulfarsphenamines, under the conditions described, will decolorize indigo carmine, especially when the solutions are acidified or made strongly alkaline.

We have found that by using methylene blue in place of indigo carmine, we have a reagent which gives a more specific test for differentiation of neo and sulfarsphenamine. This test, which has the added advantage of king workable at room temperatures, is carried out by adding a few drops of a l/4 per cent aqueous solution of medicinal methylene blue to a 1 per cent or stronger solution of the drug. With neoarsphenamine, the blue color of the dye is reduced in a few seconds to the colorless leuco base, whereas sulfarsphenamine fails to decolorize the dye.