(untitled) - Reeves, P C; Mrowca, J J; Borecki, M M; Sheppard, W A (Org Synth, 1977)
Ferrocenecarboxylic acid (12) is commercially available but it can be conveniently prepared on large scale from ferrocene by Friedel-Crafts acylation with 2-ClC6H4COCl/AlCl3 followed by cleavage of the resulting ketone with KOH/t-BuOK, see: