ABSTRACT
A. Synthesis and Characterization The most common synthetic method involves a multistep coupling reaction between a primary aromatic amine and a coupling component. The latter is usually an electron-rich aromatic compound, for example Naphthol AS (3-hydroxy-2naphthoic anilide). Figure 1 illustrates the coupling reaction. The synthetic procedure involves reaction of the amine with nitrous acid to produce a diazonium compound, which is subsequently reacted with the coupling component. The resulting azo compound can be structurally visualized in terms of the coupling and amine components (I and II in Fig. 1), which are linked by the azo functionality. Subsequent purification by washing, water followed by acetone for example, produces a pigment that can be used as a generation layer without further purification (Cort et al., 1983). Virtually all of the azo compounds utilized as generation layers are in the form of pigment dispersions. These materials do not exhibit the polymorphic variety of the phthalocyanines; hence their preparation is considerably more straightforward.
