2.3.1. Tetrazotization of 4,40-diamino diphenylmethane-2-
sulfonic acid (FC-acid) and coupling with H-acid
FC-acid (2) (3.36 g, 0.01 mol) was suspended in H2O (80 ml).
Hydrochloric acid (15 ml) was added drop wise to this well
stirred suspension. The mixture was gradually heated up to