10287. Methylthymol Blue

Nomenclature

CAS number: 3778-22-1
N,N′-[(1,1-Dioxido-3H-2,1-benzoxathiol-3-ylidene)bis[[6-hydroxy-2-methyl-5-(1-methylethyl)-3,1-phenylene]methylene]]bis[N-(carboxymethyl)glycine]; 3,3′-bis[N,N-di(carboxymethyl)aminomethyl]thymolsulfonephthalein; thymolsulfonphthalein-3′,3″-bis(methyliminodiacetic acid).
C37H44N2O13S; mol wt 756.82.
C 58.72%, H 5.86%, N 3.70%, O 27.48%, S 4.24%.

Description and references

Multidentate cation chelant ligand; indicator that forms soluble, colored complexes with metal ions. Prepn from thymol blue, q.v.: J. Krbl, R. Pribil, Chem. Ind. (London) 1957, 233; J. Krbl, Collect. Czech. Chem. Commun. 22, 1789 (1957). Chromatographic purification: T. Yoshino et al., Talanta 16, 151 (1969) DOI; S. Nakada et al., Bull. Chem. Soc. Jpn. 53, 3365 (1980) DOI. Spectroscopy studies: S. Kiciak, M. A. Mehdi, Talanta 39, 265 (1992) DOI; idem et al., ibid. 42, 1245 (1995) DOI. Acid equilibrium and complex formation constants: T. Yoshino et al., ibid. 21, 211 (1974) DOI. Metal chelate studies: B. Karadakov et al., ibid. 15, 525 (1968) DOI; C. Bremer, E. Grell, Inorg. Chim. Acta 241, 13 (1996) DOI. Chelation ion chromatography applications: B. Paull et al., Anal. Commun. 35, 17 (1998); eidem, Anal. Chim. Acta 375, 117 (1998) DOI. Reviews of analytical uses: B. Budesinsky in Chelates in Analytical Chemistry, H. A. Flaschka, A. J. Barnard, Jr., Eds. (Marcel Dekker, Inc., 1967) pp 15-47; S. Rani et al., Chem. Era 13, 372-388 (1978).

Chemical structure

Properties

Solid, mp 252-256° (dec). Absorption max: 435 nm. pKa1 1.76; pKa2 1.11; pKa3 0.78; pKa4 1.13; pKa5 2.60; pKa6 3.24; pKa7 7.2; pKa8 11.1; pKa9 13.4. Color of aq soln transitions between yellow, blue, and violet; color is dependent upon protonation state.

Derivative

Tetrasodium salt.

Nomenclature

CAS number: 1945-77-3
C37H40N2Na4O13S; mol wt 844.74.
C 52.61%, H 4.77%, N 3.32%, Na 10.89%, O 24.62%, S 3.80%.

Properties

Crystalline black powder of dull metallic luster. Dec ≈300° with swelling. Sol in 2-3 parts cold water. Insol in organic solvents. Absorption (0.5M sulfuric acid): 455 nm (ε 18900); 485 nm (ε 11800); 545 nm (ε 4450).

Note

Not to be confused with methyl thymol blue, a mixed acid-base indicator composed of methyl red and thymol blue.

Use

Chromogenic indicator for complexometric and spectrophotometric determn of numerous metal ions, including iron, zinc, and magnesium. Also to detect sulfate, fluoride, oxalate, and polyphosphate ions. In chelation ion chromatography. As pH indicator.