Thymolphthalexone is a chemical compound from the group of
iminodiacetic acid derivatives of
thymolphthalein
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
In chemistry, the molar absorption c ...
. Its chemical formula is .
This is a metallochromic indicator widely used in complexometric titrations, particularly for the determination of
transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. The lanthanide and actinid ...
s. The compound features a thymolphthalein-derived core linked to
aminopolycarboxylic acid left, 120px, a metal complex with the EDTA anion
120px, Aspartic acid is an aminodicarboxylic acid and precursor to other ligands.
An aminopolycarboxylic acid (sometimes abbreviated APCA) is a chemical compound containing one or more nitrogen at ...
functional groups. This hybrid architecture grants the compound the ability to preferentially bind specific metal ions through coordinated interactions.
Synthesis
Thymolphthalexone can be obtained by
Mannich condensation of
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...
and iminodiacetic acid with thymolphthalein.
Physical properties
Thymolphthalexone forms a white crystalline powder soluble in water and organic solvents.
Uses
Thymolphthalexone and its sodium salt are used as an indicator or photometric reagent for alkaline metal ions, such as those of calcium, strontium, barium, and others.
[{{cite journal , last1=Babaei , first1=Ali , last2=Babazadeh , first2=Mitra , last3=Shams , first3=Esmaeil , title=Simultaneous Determination of Iron, Copper, and Cadmium by Adsorptive Stripping Voltammetry in the Presence of Thymolphthalexone , journal=Electroanalysis , date=2007 , volume=19 , issue=9 , pages=978–985 , doi=10.1002/elan.200603812 , url=https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/elan.200603812 , access-date=17 April 2025 , language=en , issn=1521-4109, url-access=subscription ]
See also
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Bromothymol blue
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Litmus
Litmus is a water-soluble mixture of different dyes extracted from lichens. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity. In an acidic medium, blue litmus paper ...
*
Methyl orange
Methyl orange is a pH indicator frequently used in titration because of its clear and distinct color variance at different pH values. Methyl orange shows red color in acidic medium and yellow color in basic medium. Because it changes color at the p ...
*
Phenolphthalein
Phenolphthalein ( ) is a chemical compound with the chemical formula, formula carbon, C20hydrogen, H14oxygen, O4 and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in ...
*
pH indicator
A pH indicator is a halochromism, halochromic chemical compound added in small amounts to a Solution (chemistry), solution so the pH (acidity or Base (chemistry), basicity) of the solution can be determined visually or spectroscopically by chang ...
*
Universal indicator
References
PH indicators
Triarylmethane dyes
Phthalides
Phenols
Isopropyl compounds
Tetracarboxylic acids
Tertiary amines