6.75
[]. Shawn Blumberg, et al. -(Phenylazo)diphenylamine (PDA): a universal indicator for the colorimetric titration of strong bases, Lewis acids, and hydride reducing agents. Tetrahedron Letters. Volume 56, Issue 2, June 205, Pages 67-678.
H5-H9-H5
P26-P26-P27-P280-P02+P52-P0+P0-P62+P6-P05-P50