Uncovering John Holliday’s industrial dye synthesis patented in 1865

Holliday’s industrial dye synthesis of 1865 was repeated by heating aniline hydrochloride with nitrobenzene and the products were characterised by modern spectroscopic methods. A red dye was isolated in low yield and characterised by an X-ray single-crystal structure determination as 9-phenyl-3-anilinophenazone-2-anil. The structure was identical to that made 93 years later in 1958 by the oxidation of 2-aminodiphenylamine hydrochloride with FeCl3 followed by heating the two products with aniline. An X-ray single-crystal structure determination was obtained for an isomer of anilinoaposafranine. A proposal is made that 9-phenyl-3-anilinophenazone-2-anil, isolated from Holliday’s synthesis, arises via the oxidation and dimerisation of 2-aminodiphenylamine with hot nitrobenzene so there is a common intermediate in both syntheses.