Thymol blue

Other Names PhenoL 4,4 -(3H-2,l-benzoxathiol-3-ylidene)fcj5 [5-methyl-2-(l-mefliylethyl)-, 5,5-dioxide ThymoL 6,6 -(3H-2,l-benzoxathiol-3-ylidene)di-, 5,5-dioxide Thymolsulfonephthalein 3H-2,l-Benzoxathiole, phenol derivative NSC 11238 Thymol blue Thymolsulfophthalein CA Index Name HienoL 4,4 -(l,l-dioxido-3H-2,l-benzoxalhiol-3-ylidene) [5-methyl-2-(l-methyl-ethyl)- 

CAS R istry Number 76-61-9 Merck Index Number 9400 Chemical Structure 

Chemical/Dye Class Sulfonephthalein Molecular Formula C27H30O5S Molecular Weight 466.59 pH Range 1.2-2.8  

Physical Form Dark bluish-green to brownish powder Solubility Insoluble in water soluble in ethanol, methanol UV-Visible (XmaJ 594 ran, 376 ran, 544 ran, 430 ran Melting Point 223 C (decompose) 

Boiling Point (Calcd.) 580.5 50.0°C Pressure 760 Torr Synthesis Synthetic methods -  

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Thymol blue, thymol-sulfonphthalein (indicator) dissolve 0.1 g in 10.75 mL 0.02ANaOH and dilute with water to 250 mL or dissolve 0.1 g in 20 mL warm alcohol and dilute with water to 100 mL pH range (acid) red 1.2-2.8 yellow, and (alkaline) yellow 8.0-9.6 blue. 

The results of the complexation study of Cu(II), Pb(II), Zn(II), Fe(III), Hg(II), Cd(II), Sn(IV), Zr(IV), Ti(IV) with arsenazo III, sulfonazo III, SPADNS, Eriochrome T, Acid Chrome Dai k Blue, Xylenol Orange, Methyl Thymol Blue, Pyrocatechol Violet, Chrome Azurol S, Eriochrome Cyanin R, Basic Blue K, Methyl Violet, Brilliant Green, Rhodamine C and Astraphoxin in solid phase. The obtained data ai e used for the working out of a new method of metal determination. 

Starting material for synthesis is Thymol Blue. Purified as for Xylenol Orange on p. 387 in Chapter 4. 

The pFL-dependent partitioning of the ionizable, cationic dye thymol blue has also been investigated [6]. In its neutral, zwitterionic, and monoanionic forms, the dye preferentially partitions into the IL phase (from acidic solution), the partition coefficient to the IL increasing with increasing IL hydrophobicity. Under basic conditions, the dye is in the dianionic form and partitions into water (Figure 3.3-9). 

Thymol blue (base) Thymolsulphonphthalein 8.0-9.6 Yellow Blue 8.9... 

Sulphonphthaleins. These indicators are usually supplied in the acid form. They are rendered water-soluble by adding sufficient sodium hydroxide to neutralise the sulphonic acid group. One gram of the indicator is triturated in a clean glass mortar with the appropriate quantity of 0.1 M sodium hydroxide solution, and then diluted with water to 1 L. The following volumes of 0.1 M sodium hydroxide are required for 1 g of the indicators bromophenol blue, 15.0 mL bromocresol green, 14.4 mL bromocresol purple, 18.6 mL chlorophenol red, 23.6 mL bromothymol blue, 16.0 mL phenol red, 28.4 mL thymol blue, 21.5 mL cresol red, 26.2 mL metacresol purple, 26.2 mL. 

In general,it may be stated that weak acids(Kfl > 5 x 10-6) should be titrated with phenolphthalein, thymolphthalein, or thymol blue as indicators. 

The equivalence point for the primary stage of ionisation of carbonic acid is at pH = ( pK + pK2) = 8.3, and we have seen (Section 10.14) that thymol blue and, less satisfactorily, phenolphthalein, or a mixed indicator (Section 10.9) may be employed to detect the end point. 

The pH range for acids with Ka > 10-5 is 7-10.5 for weaker acids (Ka > 10-6) the range is reduced (8-10). The pH range 8-10.5 will cover most of the examples likely to be encountered this permits the use of thymol blue, thymolphthalein, or phenolphthalein. 

Thymol blue is used extensively as an indicator for titrations of substances acting as acids in dimethylformamide solution. It is used as a 0.2 per cent w/v solution in methanol with a sharp colour change from yellow to blue at the end point. 

Procedure B. The experimental details for the preparation of the initial solution are similar to those given under Procedure A. Titrate 25 or 50 mL of the cold solution with standard 0.1M hydrochloric acid and methyl orange, methyl orange-indigo carmine, or bromophenol blue as indicator. Titrate another 25 or 50 mL of the cold solution, diluted with an equal volume of water, slowly with the standard acid using phenolphthalein or, better, the thymol-blue cresol red mixed indicator in the latter case, the colour at the end point is rose. Calculate the result as described in the Discussion above. 

A slight excess of 10 per cent barium chloride solution is added to the hot solution to precipitate the carbonate as barium carbonate, and the excess of sodium hydroxide solution immediately determined, without filtering off the precipitate, by titration with the same standard acid phenolphthalein or thymol blue is used as indicator. If the volume of excess of sodium hydroxide solution added corresponds to timL of 1M sodium hydroxide and u mL 1M acid corresponds to the excess of the latter, then v — v = hydrogencarbonate, and V— v — v ) = carbonate. 

In the second procedure a portion of the cold solution is slowly titrated with standard 0.1M hydrochloric acid, using phenolphthalein, or better, the thymol blue-cresol red mixed indicator. This (say, YmL) corresponds to half the carbonate (compare Section 10.32) ... 

Mixed indicator solution. Mix two volumes of 0.1 per cent phenolphthalein solution and three volumes of 0.1 per cent thymol blue solution (both in ethanol). 

Mixed indicator. This should be prepared from 1 part of 0.1 per cent neutralised aqueous cresol red and 3 parts of 0.1 per cent neutralised thymol blue. 

Pipette 25 mL barium ion solution (ca 0.01 M) into a 250 mL conical flask and dilute to about 100 mL with de-ionised water. Adjust the pH of the solution to 12 by the addition of 3-6 mL of 1M sodium hydroxide solution the pH must be checked with a pH meter as it must lie between 11.5 and 12.7. Add 50 mg of methyl thymol blue/potassium nitrate mixture [see Section 10.50(C)] and titrate with standard (0.01 M) EDTA solution until the colour changes from blue to grey. 

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