Fear of the Dark: Diazo Printing by Photochemical Decomposition of Aryldiazonium Tetrafluoroborates

The photochemical decomposition of aryldiazonium salts is the basis of the “diazo printing” technique, which has been the only means to reproduce technical drawings for many years. Several demonstrations of the procedure have been developed, but they all rely either on commercially available photosensitive paper, which is almost impossible to obtain now, or on the preparation of diazonium salts from toxic and carcinogenic aromatic amines. A variation of the procedure is reported, taking advantage of a recent synthetic method based on a one-pot deacylation–diazotization of acetanilides, which are noncarcinogenic, much less toxic than the corresponding amines, and insensitive to air oxidation. In the demonstration, p-ethoxybenzenediazonium tetrafluoroborate, easily synthesized from phenacetin, is combined with a coupling component, yielding photosensitive paper that can be printed by exposure to UV light through a suitable template (flat objects, drawings, etc.), and developed with ammonia. With the three couplers suggested, it is possible to obtain red, dark yellow, and purple prints.