Thymol blue

Thymol blue
Names
IUPAC name
4-[9-(4-hydroxy-2-methyl-5-propan- 2-yl-phenyl)-7,7-dioxo-8-oxa- 7λ6-thiabicyclo[4.3.0]nona-1,3,5-trien-9-yl]- 5-methyl-2-propan-2-yl-phenol
Other names
α-hydroxy-α,α-bis(5-hydroxycarvacryl)- o-toluenesulfonic acid γ-sultone; thymolsulfonephthalein
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.000.886
Properties
C27H30O5S
Molar mass 466.59 g·mol−1
Appearance Brownish-green crystal powder
Melting point 221–224 °C (430–435 °F; 494–497 K)
decomposes[1]
Insoluble
UV-vis (λmax) 594 nm (1st)
376 nm (2nd)[1]
Hazards
Main hazards Harmful
Xn N
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oilHealth code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentineReactivity (yellow): no hazard codeSpecial hazards (white): no codeNFPA 704 four-colored diamond
1
1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Thymol blue (thymolsulphonephthalein) is a brownish-green or reddish-brown crystalline powder that is used as a pH indicator. It is insoluble in water but soluble in alcohol and dilute alkali solutions.

Thymol blue (pH indicator)
below pH 8.0 above pH 9.6
8.0 ⇌ 9.6
Thymol blue (pH indicator)
below pH 1.2 above pH 2.8
1.2 ⇌ 2.8

It transitions from red to yellow at pH 1.2–2.8 and from yellow to blue at pH 8.0–9.6. It is usually a component of Universal indicator.

At wavelength (378 - 382) nm, extinction coefficient > 8000 and at wavelength (298 - 302) nm , the extinction coefficient > 12000.[2]

Structures

Thymol blue has different structures at different pH.

thymol blue.
Color of thymol blue solution at different acid-base conditions: left: acidic, middle: neutral, right: alkaline

Safety

It may cause irritation. Its toxicological properties have not been fully investigated. Harmful if swallowed, Acute Toxicity. Only Hazardous when percent values are above 10%.[3]

Bibliography

  • Merck. "Thymol Blue." The Merck Index. 14th ed. 2006. Accessed via web on 2007-02-25.

References

  1. 1 2 Thymol Blue
  2. ↑ "Product Specification" (PDF). Thymol Blue- ACS reagent. 1: 1. 9 October 2017 – via Product Specification.
  3. ↑ Pubchem. "Thymol blue". pubchem.ncbi.nlm.nih.gov. Retrieved 2017-10-09.
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