Fluorene-2,7-disulfonic acid

Guo, X., Fang, J., Watari, T., Tanaka, K., Kita, H. and Okamoto, K. 2002. Novel sulfonated polyimides as polyelectrolytes for fuel cell application. 2. Synthesis and proton conductivity, of polyimides from 9,9-bis(4-aminophenyl)fluorene-2, 7-disulfonic acid. Macromolecules 35 6706-6713. 

Most main-chain sulfonated diamines are synthesized by direct sulfonation of a non-sulfonated precursor (Pig. 6) or its dinitro analogue [69]. 4,4 -Diaminodiphenyl ether-2,2 -disulfonic acid (ODADS), 4,4 -bis(4-aminophen-oxy)biphenyl-3,3 -disulfonic acid (BAPBDS) [71,72], 2,2 -bis[4-(4-amino-phenoxy)hexafluoroisopropane disulfonic acid (BAHFDS) [73,74], 9,9-bis (4-aminophenyl)fluorene-2,7-disulfonic acid (BAPFDS) [35], and 2,2 -bis(4-aminophenoxy)biphenyl-5,5 -disulfonic acid (o-BAPBDS) [75] were synthesized accordingly. Because of the electrophihc nature of the sulfonation reaction, the sulfonic acid groups are usually introduced in the ortho/para position to the electron-donating substituents. Polymer-grade monomers are obtained with excellent yields (83, 85, and 90%, respectively, for BAPFDS, ODADS, and p-BAPBDS), except in some cases (o-BAPBDS, 48%). 

Fluorene. This is an example of a bridged biphenyl hydrocarbon. The action of chlorosulfonic acid and sulfuric acid on fluorene 39 results in substitution mainly at the 2- and 7-positions thus the action of chlorosulfonic acid (one equivalent) gives the 2-sulfonic acid while excess of the reagent affords 2,7-disulfonic acid. ... 

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