Phenol sulfonephthalein

Fia. 1. The structure of some phthalein dyes. (A) Phenol tetrachlorophthalein (B) tetraiodophenolphthalein (C) phenol tetrabromophthalein disulfonate (BSP) (D) phenol 3,6-dibromophthalein disulfonate (E) phenol sulfonephthalein (phenol red) (F) tetraiodotetrachlorofluorescein (rose bengal). 

We have found that bromophenol blue is chemically unaltered by passage through the liver into bile whereas phenolphthalein is excreted as glucuronide (C32) and phenol sulfonephthalein is not conjugated (D6). 

Sulfonephthaleins, such as phenol-sulfonephthalein, thymolsulfone-phthalein, dibromothjTnolsulfone-phthalein, o-cresolsulfonephthalien etc. 

In the following table are recorded the colors of the various sulfonephthaleins in strongly acid solution as observed by Kolt-HOFF.i The change in color of phenol red (P.R.) and of its dichloro- derivative should be observed in reflected light. 

Fortunately we are able to replace bromphenol blue and brom-cresol purple with other sulfonephthaleins which do not show dichromatism. W. C. Harden and N. L. Drake have prepared tetrabromophenoltetrabromosulfonephthalein (tetrabrom-phenol blue) which may be used in place of bromphenol blue. Both indicators have the same transformation range (pH 3.0-4.6) with a color change from pure yellow to pure blue. Chlor-phenol red, with a color change from yellow to red, is a good substitute for bromcresol purple. 

Preparation, purity, and properties of the sulfonephthaleins. The preparation of the various sulfonephthaleins from o-sulfobenzoic acid, molten zinc chloride, and a phenol (which may be halogen substituted) has been described by Clark and Lubs. A. Cohen has reported his method of obtaining xylenolsulfone-phthalein, while a number of other valuable sulfonephthaleins have become available through the work of Barnett Cohen. ... 

I. M. Kolthoff and T. Kameda have preferred to examine the purity by titrating the indicator solution conductometrically. The sulfonic acid group in sulfonephthaleins behaves as a strong acid and in a titration with alkali, the conductivity diminishes just as in the case of a strong acid. A break occurs in the titration curve when the sulfonic acid group is neutralized, and thereafter the conductivity increases until the phenol group is neutralized. A second break occurs at this point and from there on the conductivity increase is due to the free alkali added. Thus two breaks are obtained and for pure preparations the quantity of alkali required to reach the first point should equal the quantity used up between the first and second. Relatively few of the samples investigated by the author fulfilled this requirement. 

Dr. Klotz has found furthermore that the unbrominated sulfonephthaleins such as phenol red, cresol purple, thymol blue, etc., possess a marked tendency to form molecular compounds with their corresponding phenols. Apparently the stability of the indicator solutions depends upon this phenol content. 

In the last column of the following table, A represents the difference between the indicator constant in alcohol and in water (pAoiss. Aio. — pAdus. Water). We See from the table that, in changing from the yellow to the acid color, the dissociation constants of the sulfonephthaleins in alcohol are 10 -10 times smaller than in water. This is of the same order of magnitude as the difference exhibited by benzoic acid, salicylic acid, and phenol. 

The sulfonephthaleins are characterized by pronounced color changes and by the stability of both forms. Bromphenol blue and bromcresol purple are less satisfactory for pH determinations since they show a marked dichromatism during transformation. Fortunately these indicators may be replaced by tetrabromo-phenoltetrabromosulfonephthalein, bromcresol green, and chlor-phenol red. 

According to the previously cited reference (Hof nan, (1991), Appendix A), some dyelike materials show up as inhibitors of glutaminolysis. Thus, the agents listed as bromcresol (or bromocresol) green and bromcresol purple are dyes derived from sulfonephthalein, starting with the compound called mcto-cresol. Cresols in turn are related to phenol or carbolic acid, and to the coal-tar mixture called creosote. Phenolic-type compounds are also known to occur in chaparral or creosote bush (genus Larrea), hence its alternate common name. 

The most common acid-base indicators are either azo dyes for example, methyl orange and methyl red nitrophenols phthaleins such as phenol-phthalein or thymolphthalein or sulfonephthaleins like bromophenol blue or bromocresol green. Acid-base indicators are available that cover visual transitions usually expressed in intervals of 2 pH units ranging from pH 0.0 to 2.0 in small increments up to pH 12.0-14.0. 

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