A dimolecular base formed by the gentle oxidation of morphine in alkaline soln. Refs: Broockmann, Polstorff, Ber. 13, 88 (1880); Bentley, Dyke, J. Chem. Soc. 1959, 2574. Review and bibliography: K. W. Bentley, The Chemistry of the Morphine Alkaloids (Oxford, 1954) p 54.