On the chemistry of Raby tests for codeine and esculin

Professor L. Rabi devised a test for codeine and another for esculin, in both using chlorine water and sulphuric acid, but in different order. With codeine, the alkaloid is dissolved in ordinary sodium hypochlorite solution and sulphuric acid is added. A splendid sky-blue colour is developed. With the heteroside esculin, sulphuric acid is added first for hydrolysis, giving glucose and esculetin, the aglycone, which is 6,7-dihydroxy-coumarin. The reactive part of this molecule is the catechol moiety. Then is gradually added sodium hypochlorite solution. The liquid takes on an intense violet colour. The produced compounds in these tests are 2-chlorocodeine and the addition product of hypochlorous acid to the allyl alcohol in codeine. The mono-hypochlorite in esculetin and the remaining phenol group interact to give the violet ortho-quinone.