Features of Phenolsulfonphthalein and Phenolphthalein Substituted at All Ortho-Positions of Phenols with Bromine
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The influence of bromination at all the ortho-positions of phenols on the features of phenolsulfonphtalein and phenolphtalein was investigated. The absorption spectra of Bromphenol Blue (H2BPS) in phosphate buffers demonstrated the complete opening of the lactone ring to form yellow HBPS- at pH 1 where pK2=3.8. The reaction of hydroxide ion with blue BPS2- was found to produce colorless BPS(OH)3- required heating where pK3=9. On the contrary, the spectra of 3′,3″,5′,5″-tetrabromophenolphtalein (H2BPP) demonstrated that the lactone ring was very stable. More than 99.5% of BPP2- species consisted of a colorless lactone possessing two isolated phenol groups where pK1′=6.0 and pK2′=6.8; the reaction of hydroxide ion with BPP2- to produce BPP(OH)3- was slow where pK3=10.3. These results indicate the increased acidity of phenols and the greater tendency of the central carbon atom to act as an electron acceptor.
- Analytical Sciences
Analytical Sciences 15(4), 339-342, 1999-04
The Japan Society for Analytical Chemistry