4′-Hydroxyazobenzene-2-carboxylic Acid (CAS: 1634-82-8) is a versatile aromatic azo compound, whose functions primarily derive from its azo chromophore (-N=N-), carboxyl (-COOH), and phenolic hydroxyl (-OH) groups. Below are its main applications:
1. Analytical Chemistry Reagent (Core Use)
It serves as a complexometric indicator and spectrophotometric detection reagent for metal ions, particularly known as the “Magnesium Reagent.”
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Specific Indicator for Magnesium Ions (Mg²⁺):
In alkaline solution (pH ≈ 10), it forms a claret-red or purplish-red complex with Mg²⁺. During EDTA titration, EDTA sequesters Mg²⁺, and the solution changes to the bright yellow color of the free indicator, precisely marking the titration endpoint.
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Detection of Other Metals: Also applicable for spectrophotometric analysis or as an indicator for ions such as aluminum, calcium, cobalt, copper, and manganese.
2. Dye and Pigment Intermediate
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It is itself a yellow-to-orange azo dye.
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The carboxyl and phenolic hydroxyl groups can be chemically modified through esterification, etherification, etc., to synthesize more complex azo dyes or pigments for use in textiles, inks, and coatings industries.
3. Functional Material Precursor
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Liquid Crystal Materials: As an azobenzene derivative, it can be used to construct photo-responsive liquid crystal materials for applications in optical data storage, optical switches, etc.
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Nonlinear Optical Materials: The conjugated azobenzene system exhibits potential nonlinear optical properties, making it suitable for research in optical devices.
4. Scientific Research Applications
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Photo-responsive Molecule: The azobenzene group undergoes trans-cis isomerization under UV/visible light irradiation, enabling its use as a “photoswitch” to modulate molecular functions or assembly behaviors.
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pH Indicator: Due to the presence of carboxyl and phenolic hydroxyl groups, its color changes with pH, allowing its use as a crude pH indicator.
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Coordination Chemistry: Acts as a multidentate ligand for synthesizing metal-organic complexes.
Summary
This compound is a classic analytical reagent and synthetic building block:
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Applied Chemistry: Primarily used as a metal ion analysis reagent (especially for magnesium ion indication).
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Industrial Chemistry: A key intermediate for dyes and functional materials.
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Scientific Research: Serves as a photo-responsive model molecule or ligand in fundamental studies.
Note: This product should be protected from strong light, stored in a cool, dry place, and handled with appropriate personal protective equipment.
