Sulphonephthaleins

By condensing o sulphobenzoic anhydride with phenol in the presence of anhydrous zinc chloride, phenolsulphonephthalein (phenol red) is formed. Tetrabromination of the latter afibrds tetrabromophenolsulphonephthalein (bromophenol blue)  

Similarly o-sulphobeiizoic anhydride and o-cresol yields o-cresolsulphone-phthalein (o-cresol red) dibromination of the last-named gives dibromo-o-sulphonephthaleln (bromocresol purple)  

Phenolsulphonephthalein (phenol red). Mix 10 g. of o-sulpho-benzoic anhydride (Section VIII,9), 14 g. of pure phenol and 10 g. of freshly fused zinc chloride in a small conical flask. Place a glass rod in the flask and heat gently over a flame to melt the phenol. Then heat the flask containing the well-stirred mixture in an oil bath at 135-140° for 4 hours. Stir from time to time, but more frequently during the first hour if the mixture froths unduly, remove the flask from the bath, cool and then resume the heating. When the reaction is complete, add 50 ml. of water, allow the water to boil and stir to disintegrate the product. Filter the crude dye with suction and wash it well with hot water. Dissolve the residue in the minimum volume of warm (60°) 20 per cent, sodium hydroxide solution, filter, and just acidify the filtrate with warm dilute hydrochloric acid (1 1). Filter the warm solution, wash with water, and dry upon filter paper. The yield of phenol red (a brilliant red powder) is 11 g. 

Dibromo-o-cresolsulphonephthalein (bromocresol purple). Dissolve 6 g. of o-cresolsulphonephthalein in 50 ml. of glacial acetic acid, heat to boiling under reflux, add slowly a solution of 2 ml. of bromine in 

of glacial acetic acid, and boil gently for 1 hour. Allow to cool, filter off the bromocresol purple, wash with a little glacial acetic acid, followed by a little benzene, and dry. The yield is 4 g. 

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Table 5.1 summarizes the details of some useful acid-base indicators. Exact agreement with the pH range expressed by equation (5.5) is by no means always observed. This is because some colour changes are easier to see than others and so the general approximation made in deriving equation (5.5) is not uniformly close. Structurally, the indicators form three groups phthaleins (e g. phenolphthalein) sulphonephthaleins (e.g. phenol red) and azo compounds (e.g. methyl orange). 

Sulphones, 500, 1078 Sulphonephthaleins, 989, 990 Sulphonic acids, 548, 557, 1077 see also under Aromatic sulphonic acids alkyl esters of, 1079 ... 

S.S) is not unifonnly close. Structurally, the indicators form three groups phthaleins (e.g. phenolphthalein) sulphonephthaleins (e.g. phenol red) azo compounds (e.g. methyl orange). 

This method has been extensively exploited for the synthesis of a large group of 3H-2,1-benzoxathiole 1,1-dioxide derivatives known as sulphonephthaleins, many of which, such as phenol red, p-cresol red and bromothymol blue are well known acid-base indicators. There is excellent coverage of this subject in Breslow and Skolnik s monograph8 and equation 60 merely serves to illustrate two representative syntheses81,82. The sulphonephthaleins can also be prepared from 3ff-2,l-benzoxathiole-l-dioxide derivatives with reactive substituents (such as dichloro or carbonyl) at the 3-position (see Section III.D.3). 

Fenn, J. (1995). The cellulose nitrate time bomb using sulphonephthalein indicators to evaluate storage strategies. In Postprints Tate Gallery conference From Marble to Chocolate . The Conservation of Modem Sculpture London, 18—20 September 1995 (J. Heuman, ed.) pp. 87-92, Archetype Books. 

For dyes with structures similar to fluorescein and sulphonephathalein, two types of reactive sites are present tinoughout much of the pH range. They can exist as acids or their conjugate bases, the RO and RCOO (for the fluorescein) or RSO3 (for the sulphonephthalein dyes). Since they react similarly, only the fluorescein... 

The extracting solvent can be diethyl ether or carbon tetrachloride (tetrachloromethane). The former is advised in the method given here, because of its lower toxicity. ASTM Method D 4224-89 [3] is similar, but uses a 13.6% solution of the reagent, permits only carbon tetrachloride and directs that the initial extraction should be done by shaking for 10 min. It uses ortho-cresol red (o-cresol sulphonephthalein) as indicator, and adds the correction for extracted p-toluidine hydrochloride (step 10), which was not part of the original method. 

Measurement of the tubular secretory capacity by phenol-sulphonephthalein excretion. 

Certain substances are eliminated from the body by secretion from the renal tubules. The rate at which these substances are eliminated is a measure of the tubular secretory capacity. Phenol-sulphonephthalein (PSP) or p-aminohippuric acid at high levels can be used for this purpose. 

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