Accordingly, FC-acid (2) was tetra azotized at low temperature
0–5 C in order to stabilize the azo compound. Coupling
of tetrazo of FC-acid with H-acid (3) was achieved to afford
(4) in alkaline medium to accomplish the coupling at position
ortho to the hydroxyl group of H-acid at 0–5 C and the coupling
was completed in 3 h