Thymol blue

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Thymol blue
Thymolblau skeletal.png
Thymol Blue crystals.jpg
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
3D model (JSmol)
ECHA InfoCard 100.000.886
PubChem CID
Molar mass 466.59 g·mol−1
AppearanceBrownish-green crystal powder
Melting point 221–224 °C (430–435 °F; 494–497 K)
decomposes [1]
UV-vismax)594 nm (1st)
376 nm (2nd) [1]
Main hazards Harmful
Hazard X.svg Xn Hazard N.svg N
NFPA 704 (fire diamond)
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 codeThymol blue
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)
Infobox references

Thymol blue (thymolsulfonephthalein) 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 8.0above pH 9.6
Thymol blue(pH indicator)
below pH 1.2above pH 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]


Thymol blue has different structures at different pH.

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


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]


Related Research Articles

In physics, attenuation or, in some contexts, extinction is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates.

Ultraviolet–visible spectroscopy Range of spectroscopic analysis

Ultraviolet–visible spectroscopy or ultraviolet–visible spectrophotometry refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible spectral regions. This means it uses light in the visible and adjacent ranges. The absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved. In this region of the electromagnetic spectrum, atoms and molecules undergo electronic transitions. Absorption spectroscopy is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state.

Bromothymol blue chemical compound

Bromothymol blue is a pH indicator. It is mostly used in applications that require measuring substances that would have a relatively neutral pH. A common use is for measuring the presence of carbonic acid in a liquid. It is typically sold in solid form as the sodium salt of the acid indicator.

Spectrophotometry deals with visible light, near-ultraviolet, and near-infrared, but does not cover time-resolved spectroscopic techniques

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Isosbestic point specific wavelength, wavenumber or frequency at which the total absorbance of a sample does not change during a chemical reaction or a physical change of the sample

In spectroscopy, an isosbestic point is a specific wavelength, wavenumber or frequency at which the total absorbance of a sample does not change during a chemical reaction or a physical change of the sample. The word derives from two Greek words: "iso", meaning "equal", and "sbestos", meaning "extinguishable".

Fluorophore agents that emit light after excitation by light

A fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds.

Coomassie Brilliant Blue cbb r250

Coomassie Brilliant Blue is the name of two similar triphenylmethane dyes that were developed for use in the textile industry but are now commonly used for staining proteins in analytical biochemistry. Coomassie Brilliant Blue G-250 differs from Coomassie Brilliant Blue R-250 by the addition of two methyl groups. The name "Coomassie" is a registered trademark of Imperial Chemical Industries.

Bromophenol blue chemical compound

Bromophenol blue is used as a pH indicator, a electrophoretic color marker, and a dye. It can be prepared by slowly adding excess bromine to a hot solution of phenolsulfonphthalein in glacial acetic acid.

Thymol Chemical compound found in plants including thyme

Thymol (also known as 2-isopropyl-5-methylphenol, IPMP) is a natural monoterpenoid phenol derivative of cymene, C10H14O, isomeric with carvacrol, found in oil of thyme, and extracted from Thymus vulgaris (common thyme), Ajwain and various other kinds of plants as a white crystalline substance of a pleasant aromatic odor and strong antiseptic properties. Thymol also provides the distinctive, strong flavor of the culinary herb thyme, also produced from T. vulgaris.

Thymolphthalein chemical compound

Thymolphthalein is a phthalein dye used as an acid–base (pH) indicator. Its transition range is around pH 9.3–10.5. Below this pH, it is colorless; above, it is blue. The molar extinction coefficient for the blue thymolphthalein dianion is 38,000 M−1 cm−1 at 595 nm.

Universal indicator type of pH indicator

To judge how strong a given acid or base is, a universal indicator is used, which is a mixture of several indicators. A universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth colour changes over a wide range pH values to indicate the acidity or alkalinity of solutions. Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933. Details of this patent can be found in Chemical Abstracts. Experiments with Yamada's universal indicator are also described in the Journal of Chemical Education.

Phenol red chemical compound

Phenol red is a pH indicator frequently used in cell biology laboratories.

Chromophore the part of a molecule responsible for its color

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Cyanine is the non-systematic name of a synthetic dye family belonging to polymethine group. The word cyanin is from the English word "cyan", which conventionally means a shade of blue-green and is derived from the Greek κυάνεος/κυανοῦς kyaneos/kyanous which means a somewhat different color: "dark blue".

Dansyl chloride chemical compound

Dansyl chloride or 5-(DimethylAmino)Naphthalene-1-SulfonYL chloride is a reagent that reacts with primary amino groups in both aliphatic and aromatic amines to produce stable blue- or blue-green–fluorescent sulfonamide adducts. It can also be made to react with secondary amines. Dansyl chloride is widely used to modify amino acids; specifically, protein sequencing and amino acid analysis. Dansyl chloride may also be denoted DNSC. Likewise, a similar derivative, dansyl amide is known as DNSA.

Brookers merocyanine chemical compound

Brooker's merocyanine is an organic dye belonging to the class of merocyanines.

The near-infrared (NIR) window defines the range of wavelengths from 650 to 1350 nanometre (nm) where light has its maximum depth of penetration in tissue. Within the NIR window, scattering is the most dominant light-tissue interaction, and therefore the propagating light becomes diffused rapidly. Since scattering increases the distance travelled by photons within tissue, the probability of photon absorption also increases. Because scattering has weak dependence on wavelength, the NIR window is primarily limited by the light absorption of blood at short wavelengths and water at long wavelengths. The technique using this window is called NIRS. Medical imaging techniques such as fluorescence image-guided surgery often make use of the NIR window to detect deep structures.

Thiosulfate-citrate-bile salts-sucrose agar, or TCBS agar, is a type of selective agar culture plate that is used in microbiology laboratories to isolate Vibrio species. TCBS agar is highly selective for the isolation of V. cholerae and V. parahaemolyticus as well as other Vibrio species. TCBS agar contains high concentrations of sodium thiosulfate and sodium citrate to inhibit the growth of Enterobacteriaceae. Inhibition of Gram-positive bacteria is achieved by the incorporation of ox gall, which is a naturally occurring substance containing a mixture of bile salts and sodium cholate, a pure bile salt. Sodium thiosulfate also serves as a sulfur source and its presence, in combination with ferric citrate, allows for the easy detection of hydrogen sulfide production. Saccharose (sucrose) is included as a fermentable carbohydrate for metabolism by Vibrio species. The alkaline pH of the medium enhances the recovery of V. cholerae and inhibits the growth of others. Thymol blue and bromothymol blue are included as indicators of pH changes.

Distributed Bragg reflector laser

A distributed Bragg reflector laser (DBR) is a type of single frequency laser diode. Other practical types of single frequency laser diodes include DFB lasers and external cavity diode lasers. A fourth type, the cleaved-coupled-cavity laser has not proven to be commercially viable. VCSELs are also single frequency devices. The DBR laser structure is fabricated with surface features that define a monolithic, single mode ridge waveguide that runs the entire length of the device. A resonant cavity is defined by a highly reflective DBR mirror on one end, and a low reflectivity cleaved exit facet on the other end. Within the cavity is a gain ridge portion, where current is injected to produce a single spatial lasing mode. The DBR mirror is designed to reflect only a single longitudinal mode. As a result, the laser operates on a single spatial and longitudinal mode. The laser emits from the exit facet opposite the DBR end. The DBR is continuously tunable over approximately a 2 nm range by changing current or temperature. The temperature coefficient is approximately 0.07 nm/K, and the current coefficient is approximately 0.003 nm/mA. DBR lasers are stable, low noise optical sources. When operated with a low noise power supply at constant temperature, edge emitting DBR lasers have a linewidth of less than 10 MHz. Power levels typically can run up to several hundred milliwatts.

The molar attenuation coefficient is a measurement of how strongly a chemical species attenuates light at a given wavelength. It is an intrinsic property of the species. The SI unit of molar attenuation coefficient is the square metre per mole, but in practice, it is usually taken as the M−1⋅cm−1 or the L⋅mol−1⋅cm−1. In older literature, the cm2/mol is sometimes used with corresponding values 1,000 times larger. In practice these units are the same, with the difference being expression of volume in either cm3 or in L. The molar attenuation coefficient is also known as the molar extinction coefficient and molar absorptivity, but the use of these alternative terms has been discouraged by the IUPAC.


  1. 1 2 Thymol Blue
  2. "Product Specification: Thymol Blue- ACS reagent" (PDF). Sigma-Aldrich. 9 October 2017. p. 1.
  3. "Thymol blue". PubChem. Retrieved 2017-10-09.