Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Thymol Blue (Thymolsulfonphthalein; 4,4′-(3H-2,1-Benzoxathiol-3-ylidene)bis-[5-methyl-2-(1methylethyl)phenol] S,S-Dioxide) Part 4, Monographs for Reagent Chemicals: General Descriptions, Specifications, and Tests eISBN: 9780841230460 Tom Tyner Chair, ACS Committee on Analytical Reagents James Francis Secretary, ACS Committee on Analytical Reagents
ABSTRACT This monograph for Thymol Blue provides, in addition to common physical constants, a general description including typical appearance, applications, and aqueous solubility. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Clarity of Solution, Visual Transition Interval (Acid Range), and Visual Transition Interval (Alkaline Range).
C27H30O5S
Formula Wt 466.59
CAS No. 76-61-9
Note: This specification applies to both the free acid form and the salt form of this indicator.
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . brownish-green solid Applications . . . . . . . . . . . . . . . . . . . . . . . . acid–base indicator Aqueous solubility . . . . . . . . . . . . . . . . . . . . insoluble
SPECIFICATIONS Clarity of solution . . . . . . . . . . . . . . . . . . . . Passes test
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4404 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Visual transition interval (acid range) . . . . . . . From pH 1.2 (pink) to pH 2.8 (yellow) Visual transition interval (alkaline range) . . . . . From pH 8.0 (yellow) to pH 9.2 (blue)
TESTS Clarity of Solution If the indicator is the acid form, dissolve 0.1 g in 100 mL of alcohol. If the indicator is a salt form, dissolve 0.1 g in 100 mL of water. Not more than a faint trace of turbidity or insoluble matter should remain. Reserve the solution for the tests for visual transition interval.
Visual Transition Interval (Acid Range) Dissolve 1 g of potassium chloride in 100 mL of water. Adjust the pH of the solution to 1.20 (using a pH meter) with 1 N hydrochloric acid volumetric solution. Add 0.1–0.3 mL of the 0.1% solution reserved from the test for clarity of solution. The color of the solution should be pink. Titrate the solution with 1 N sodium hydroxide volumetric solution until the pH is 2.2 (using the pH meter). The color of the solution should be orange. Continue the titration until the pH is 2.8. The color of the solution should be yellow.
Visual Transition Interval (Alkaline Range) Dissolve 1 g of potassium chloride in 100 mL of water. Adjust the pH of the solution to 8.0 (using a pH meter) by adding 0.01 N hydrochloric acid or sodium hydroxide. Add 0.1–0.3 mL of the 0.1% solution reserved from the test for clarity of solution. The color of the solution should be yellow. Titrate the solution with 0.01 N sodium hydroxide until the pH is 8.4 (using the pH meter). The color of the solution should be green. Continue the titration until the pH is 9.2. The color of the solution should be blue.
© 2017 American Chemical Society
B
DOI:10.1021/acsreagents.4404 ACS Reagent Chemicals, Part 4
