Methylthymol blue

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Structural formula
Structural formula of methylthymol blue
Surname Methylthymol blue
other names


Molecular formula
  • C 37 H 44 N 2 O 13 S (free acid)
  • C 37 H 40 N 2 Na 4 O 13 S (sodium salt)
Brief description

beige solid with a faint odor (sodium salt)

External identifiers / databases
CAS number
PubChem 73038
ChemSpider 65835
Wikidata Q1925610
Molar mass
  • 756.82 g mol −1 (free acid)
  • 844.76 g mol −1 (sodium salt)
Physical state



good in water (460 g l −1 at 20 ° C, sodium salt)

safety instructions
GHS labeling of hazardous substances

Sodium salt

no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Methylthymol blue is a chemical compound from the group of triphenylmethane dyes . It is used as an indicator substance that changes its color depending on the pH value from red to yellow to blue. Methylthymol blue sodium salt , also known as water-soluble methylthymol blue , is a brownish- green solid that is used as an indicator for metal titration (e.g. for lead and uranium).


Methylthymol blue or methylthymol blue sodium salt solutions can be used for the determination of many metals ( titration to complex compounds ) and sulfate . The complexes formed by metals with methylthymol blue are generally blue in color. The barium salt of methylthymol blue is used to detect magnesium.

Individual evidence

  1. a b c d e data sheet methylthymol blue (PDF) from Merck , accessed on December 25, 2019.
  2. External identifiers or database links for methylthymol blue sodium salt : CAS number: 1945-77-3, EC number: 217-743-3, ECHA InfoCard: 100.016.131 , PubChem : 73037 , ChemSpider : 65834 , Wikidata : Q27258002 .
  3. ^ Daniel C. Harris: Textbook of Quantitative Analysis . 8th edition. Springer Spectrum, Berlin / Heidelberg 2014, ISBN 978-3-642-37788-4 , p. 289 .
  4. Angela Charlotte Pütz: Monitoring of seasonal, housing and domestication-related influences on the horn quality of the horse's hoof . Berlin 2007, DNB  1022446355 , p. 77 f ., urn : nbn: de: kobv: 188-fudissthesis000000002792-8 (dissertation, FU Berlin ).