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1,2-Naphthoquinone-4-sulfonic acid sodium salt, also known as Folin reagent, is an organic compound with the molecular formula C ₁₀ H ₅ NaO ₅ S and CAS number 521-24-4. The appearance is orange yellow powder, with a melting point of 289 ℃ (decomposition), a water solubility of up to 50mg/mL, and a slight solubility in 95% ethanol and acetone. It needs to be stored in a cool and dry place at 2-8 ℃. It belongs to Class Xi dangerous goods and has skin and eye irritation.
This substance is prepared from 1-amino-2-naphthol-4-sulfonic acid by nitration with nitric acid, precipitation with ammonium chloride, and recrystallization with sodium chloride. Mainly used as thin-layer chromatography/paper chromatography color reagents and dye intermediates for amino acid analysis, and in spectrophotometric detection for the determination of drug components such as gabapentin [3-4]. Wear protective equipment during operation, rinse with soapy water or clean water after contact, prioritize recycling or incineration of waste, transport according to UN1920 standards, and packaging category is III.
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Chemical Formula |
C10H5NaO5S |
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Exact Mass |
260 |
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Molecular Weight |
260 |
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m/z |
260 (100.0%), 261 (10.8%), 262 (4.5%), 262 (1.0%) |
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Elemental Analysis |
C, 46.16; H, 1.94; Na, 8.84; O, 30.74; S, 12.32 |
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1,2-Naphthoquinone-4-sulfonic acid sodium salt (molecular formula C ₁₀ H ₅ NaO ₅ S, CAS number 521-24-4) is an organic compound with unique chemical properties. The naphthoquinone ring and sulfonic acid group in its molecular structure endow it with extensive reactivity. This compound has shown significant value in fields such as drug analysis, organic synthesis, dye industry, and environmental monitoring. Its diverse applications stem from its specific reactivity with amines, alcohol hydroxyl compounds, and metal ions.
1. Quantitative analysis of amino acids
As a chromogenic reagent for thin layer chromatography (TLC) and paper chromatography, it undergoes nucleophilic substitution reaction with amino groups in amino acids to generate chromogenic products with characteristic absorption peaks. In a pH 9-10 buffer system, the reaction can complete color development within 5 minutes, with a sensitivity of 0.1 μ g/spot. For example, in the analysis of amino acid composition of protein hydrolysis products, the color intensity is linearly related to amino acid concentration (r=0.999), with a detection limit as low as 0.5 nmol.
2. Colorimetric determination of drug components
Gabapentin detection: A 0.5% aqueous solution was used as the color reagent, and a spectrophotometric method was established at a wavelength of 415nm.
The linear range was 0.5-20 μ g/mL, and the recovery rate was 98.7% -102.3%. This method is included as a standard testing protocol in the European Pharmacopoeia.
Determination of isoniazid and procaine: By reacting with the primary amine group in the drug molecule, an orange red complex is formed, and the absorbance is measured at 450nm. The experiment showed that the detection sensitivity of isoniazid reached 0.02 μ g/mL, which is three times higher than traditional methods.
Antibiotic residue analysis: In the detection of gentamicin, this reagent reacts specifically with the amino group of aminoglycoside antibiotics. Combined with fluorescence derivatization technology, the detection limit can be reduced to 0.1ng/mL, meeting the strict regulatory requirements for antibiotic residues in food.
3. Development of new drug analysis methods
Recent studies have shown that this reagent has breakthrough applications in the analysis of drugs containing alcohol hydroxyl groups. By optimizing the reaction conditions (pH 11.0 buffer system, 60 ℃ water bath), a new method for the detection of carboxamine was established: at a wavelength of 362nm, the apparent molar absorptivity reached 2.2 × 10 ³ L/(mol · cm), the linear range was 0.72-28.67 μ g/mL, and the detection limit was 0.7 μ g/mL. This method has been successfully applied to the determination of the content of carboxymethyl stane in clinical preparations, with a recovery rate of 99.0% -103.5%.
Key role of organic synthesis industry
1. Separation of chiral compounds
As a phase transfer catalyst, this reagent exhibits excellent performance in asymmetric synthesis. In the separation reaction of β - aminoalcohols, the addition of 5mol% sodium 1,2-naphthoquinone-4-sulfonate can increase the enantiomer excess (ee%) from 62% to 89% and shorten the reaction time by 40%. Its catalytic mechanism originates from the hydrogen bonding between sulfonic acid groups and substrate molecules, effectively stabilizing the transition state structure.
2. Catalyst for polymerization reaction
In polyester synthesis, this reagent can significantly increase the reaction rate as an oxidation catalyst.
Experimental data shows that in the production of PET (polyethylene terephthalate), its catalytic activity is 1.8 times that of traditional antimony based catalysts, and the molecular weight distribution of the product is narrower (PDI=1.9 vs 2.3). This characteristic makes it an important catalyst choice for environmentally friendly polyester production.
3. Specialty dye intermediates
As a key intermediate for synthesizing azo dyes, this reagent can be used to prepare over 30 commercial dyes through coupling reactions with diazonium salts. For example, in the synthesis of C.I. Acid Red 88, the yield of the coupling reaction it participated in reached 87%, and the product had bright color and washing fastness of 4-5 levels. The global dye industry consumes approximately 1200 tons annually, of which 40% is used in the textile printing and dyeing field.
Innovation in Environmental Monitoring and Analytical Chemistry
1. Heavy metal ion detection
This reagent forms stable complexes with heavy metal ions such as Pb ² ⁺ and Cd ² ⁺, and exhibits characteristic absorption at a wavelength of 520nm. The detection limit of the established detection method for Pb ² ⁺ is 0.05 μ g/L, which reduces the cost by 60% compared to traditional atomic absorption method. This method has been validated by EPA standards in soil heavy metal pollution monitoring.
2. Environmental hormone screening
For environmental endocrine disruptors such as bisphenol A, this reagent achieves specific detection through Michael addition reaction.
In the optimized solid-phase extraction spectrophotometry method, the detection range for bisphenol A is 0.1-10 μ g/L, with a recovery rate of 85.2% -92.7%, meeting the monitoring requirements of the drinking water safety standard (0.01mg/L).
3. Analysis of atmospheric pollutants
The reagent reacts with NO ₂ gas to produce a red product, and the absorbance is measured at 480nm. The established passive sampling method can continuously monitor the concentration of NO ₂ in the atmosphere, with a detection range of 0.01-1ppm and a time resolution of 1 hour. This method has been applied to the grid based monitoring system for urban air quality.
Breakthrough applications in the field of materials science
1. Conductive polymer modification
In the synthesis of polyaniline, this reagent can significantly improve conductivity as a dopant. Experiments have shown that doping 5wt% 1,2-naphthoquinone-4-sulfonic acid sodium salt increases the conductivity of polyaniline films from 1.2S/cm to 8.7S/cm, while maintaining excellent redox reversibility. The application research of this material in supercapacitor electrodes has entered the pilot stage.
2. Development of photoluminescence materials
The complex formed between this reagent and rare earth ions (Eu ³ ⁺, Tb ³ ⁺) exhibits unique luminescent properties.
Under excitation at 465nm, the emission peak of Eu ³ ⁺ complex is located at 613nm (red light), with a quantum yield of 42%. This type of material shows potential applications in LED display devices and biological imaging fields.
3. Functionalization of nanomaterials
By reacting with the amino groups on the surface of gold nanoparticles, this reagent can achieve surface modification of nanoparticles. The plasma resonance peak of the modified gold nanoparticles at 520nm shifted to 545nm, and the dispersibility was significantly improved. This technology has achieved phased results in the construction of tumor targeted drug delivery systems.
Synthesis of 1,2-Naphthoquinone-4-sulfonic acid sodium salt: under continuous stirring, add anhydrous and colorless 1-amino-2-naphthol-4-sulfonic acid to 20% dilute nitric acid cooled to 30 ℃ in small amounts. Each addition must be fully stirred. If necessary, add an appropriate amount of ether for defoaming, and control the reaction temperature at 20-25 ℃. After the addition, reduce the temperature to 5-10 ℃, then add 30 ℃ saturated ammonium chloride solution, and continue to cool to 0 ℃, After standing, the crystals were filtered, washed three times with a small amount of ice cold dilute ammonium chloride solution, washed twice with ethanol, and washed several times with ether. The obtained 1-2-naphthoquinone-4-sulfonic acid was dried to constant weight at 35-40 ℃. Then the dried 1-2-naphthoquinone-4-sulfonic acid was dissolved in water at 50 ℃ and decolorized with activated carbon. Add the saturated sodium chloride solution at 30 ℃ to the filtered clear orange filtrate, cool it to 0 ℃ after standing, wash the filtered crystals with dilute sodium chloride cold solution, ethanol and diethyl ether successively until they are qualified, and dry them to constant weight to obtain sodium 1,2-naphthoquinone-4-sulfonate.
The main reactions in the process are:
It is used as a chromogenic agent for the determination of amino acids by thin layer chromatography and paper chromatography. It is also used as a dye intermediate.
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