Mechanism of the polarographic reduction of some sulphonphthaleins in aqueous and alcoholic buffers

✍ Scribed by M.M. Ghoneim; A.M. Khalil; Amira M. Hassanein

• Publisher: Elsevier Science
• Year: 1979
• Tongue: English
• Weight: 391 KB
• Volume: 24
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(79)87042-5

✦ Synopsis

AMract -The polarographic reduction of cresol red, thymol blue, bromocresol purple, bromophenol blue and bromocresol green are studied in buffered aqueous solutions and alcohol-water mixtures of pH 2-11.5. It w'aa found that in solutions of pH values Z 10 the five depolarizers are reduced along two one-electron waves of equal heights. In solutions of pH values ~7, bromo-cresol purple and bromophenol blue are reduced through a single two-electron wave. Whereas cresol red, thymol blue and bromo-cresol green are reduced in two one-electron steps. Medium and substitueot effects on il and E1,2 are discussed. INTRODUCTlON The polarographic reduction of phenol red and its dihalogen derivatives in buffer solutions of pH values 2-11.5 was reported to be reduced through two oneelectron steps[l]. Whereas the reduction of phenolphthalein[2,3]

and some of its derivatives occurred through a single two-electron wave at pH values c9; at higher pH values this wave splits into two oneelectron steps.

In the present work, the polarographic behaviour of some derivatives of phenolsulphonphthalein is investigated in buffered aqueous media or in presence of different proportions of monohydric alcohols. This is