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Eriochrome Black T is an organic compound with the molecular formula C20H12N3NaO7S, CAS 1787-61-7. It is a black powder, soluble in water, and is jujube red to oar red; Slightly soluble in alcohol and brownish magenta; Slightly soluble in acetone. Dark blue in concentrated sulfuric acid, light reddish brown after dilution; It is orange yellow in concentrated nitric acid. Its aqueous solution and concentrated hydrochloric acid have no significant change; Add concentrated sodium hydroxide solution to turn brown and magenta. The solubility in water (90 ℃) is 25g/l. When dyeing with copper and iron, the color light has a great impact. It is mainly used for dyeing and printing wool textiles, as well as silk, nylon and other textiles, and fur dyeing. The pure product can be used as an indicator. It is used as a metal indicator for the determination of ba2+, mg2+, mn2+, zn2+ and rare earth by EDTA complexometric titration. It is also used as a developer for photometric determination of metal ions such as co2+, mg2+, etc.
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Chemical Formula |
C20H13N3NaO7S |
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Exact Mass |
462 |
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Molecular Weight |
462 |
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m/z |
462 (100.0%), 463 (21.6%), 464 (4.5%), 464 |
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Elemental Analysis |
C, 51.95; H, 2.83; N, 9.09; Na, 4.97; O, 24.22; S, 6.93 |
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Density 1.109 g/ml at 25 ° C, Flash point 185 ° C, Storage condition room temp, Solubility 50g/l, Color index 14645, Acidity coefficient (PKA) pk1:6.3; pK2:11.55 (25°C), Form powder/solid, Color brown black to black, Specific gravity 1.109, Odor odorless, PH value 3.7 (10g/l, H2O, 20 ℃), Water solubility 50 g/l (20 º C), Merck 14,3667, BRN 4121162, Stable Incompatible with strong oxidizing agents, strong reducing agents.
Eriochrome Black T indicator, also known as mordant black 11, is also known as electroless chrome black T indicator, and its scientific name is 1- (1-hydroxy-2-naphthylazo) - 6-nitro-2-naphthol-4-sulfonic acid sodium salt. It is a comprehensive indicator for the determination of barium, cadmium, indium, magnesium, manganese, calcium, lead, scandium, strontium, zinc, zirconium, etc. Chrome black T indicator is also used as an indicator when determining the total hardness (total calcium and magnesium ions) of water samples. When preparing the chrome black T indicator according to the sanitary standard for drinking water 2001, we found that in 9.1.3.6, only 95% ethanol was used to dissolve the chrome black T indicator and dilute it to 100ml. The resulting indicator was verified by water sample and pure water. The solution was dark purple red, and there was no change in the color of the titration end point.
Synthetic chrome black T:
1. the product is prepared by coupling 6-nitro-1,2,4-oxy-acid (i.e. 6-nitro-2-hydroxy-1-diazo-naphthalene-4-sulfonic acid) with 1-naphthol, salting out, filtering, drying and other schistosis processes. The external air of the product is black brown uniform powder, the color light is similar to that of the standard (blue light grey → blue light black), the strength is 100 ± 3 (min) of the standard, the moisture content is ≤ 5%, the content of water-insoluble impurities is ≤ 1%, and the fineness (the content of residue passing 80 mesh sieve) ≤ 5%, The dyeing fastness on wool meets the standard (the sun fastness is grade 7, the brown fastness to soaping, water immersion, perspiration, boiling, carbonization, ironing, dry cleaning, etc. are all grade 4-5, and the dry rubbing fastness is grade 3-4). Raw material consumption (kg/t) 6-nitro-1,2,4-oxomethoate (100%) 500 methylnaphthol (100%) 255 caustic soda (100%) 255 soda (industrial) 215 hydrochloric acid (31%) 675 refined salt 450.
2. dissolve 1-amino-2-naphthol-4-sulfonic acid in water, control the pH value to 3, add saturated solution of crystalline copper sulfate and 31% sodium nitrite solution for diazotization, filter after the reaction, and add hydrochloric acid to the filtrate to separate out yellow diazonium salt:
The prepared diazonium salt is dissolved with concentrated sulfuric acid, and mixed acid is added for nitration. The temperature is controlled below 10 ℃:
After nitrification, pour the reaction solution into ice water, and wash the precipitate with saturated salt water after filtration until it is qualified. Then add the pre prepared 1-naphthol sodium solution to the nitrated product, stir for 5 ~ 6h, and let it stand for 20h, then directly inject steam to 90 ℃, and then add acetic acid for neutralization reaction:
After the reaction, the crystallization is cooled naturally, washed with distilled water and dried.
Eriochrome Black T (EBT), as a classic azo organic compound, plays an irreplaceable role in analytical chemistry, textile industry, environmental monitoring and other fields due to its unique chemical properties and wide applicability. Its molecular formula is C20H12N3NaO7S, with a molecular weight of 461.38. It appears as a brownish black powder, easily soluble in water and ethanol, and slightly soluble in acetone.
The most well-known use is as a metal indicator, especially in the ethylenediaminetetraacetic acid (EDTA) complexometric titration method, which indicates the titration endpoint through color changes and becomes a "precise ruler" for detecting various metal ions.
1. Determination of water quality hardness: the "water quality guardian" from drinking water to industrial circulating water
The hardness of water quality (total amount of calcium and magnesium ions) is an important indicator for measuring water quality. In a buffer solution with pH 8-10, it appears blue and forms a red complex with calcium and magnesium ions. When EDTA is titrated to the endpoint, the metal ions are completely complexed, and the solution changes from red to blue with a sharp color change, and the error can be controlled within ± 0.1%.
For example, in drinking water testing, a 0.1% chromium black T-20% NH ∝ - NH ₄ Cl polyethylene glycol system is used, and the linear regression equation for calcium determination at a wavelength of 510nm is A=0.0065c+0.0708 (correlation coefficient r=0.99945), which is applicable to the calcium concentration range of 0-10 μ g/mL.
The hardness monitoring of industrial circulating water also plays a key role. For example, the benchmark value for hardness management of circulating water in a certain chemical plant is 500mg/L. By preparing indicators containing EDTA (3.7-7.5%), borax (0.45-0.48%), and chrome black T (0.05-0.2%), 100mL of water sample can be taken and 10mL of indicator can be added to quickly determine whether it exceeds the standard. The operation is simple and the results are reliable.
2. Specific Metal Ion Detection: Targeted Analysis from Trace Elements to Heavy Metals
Not only suitable for detecting calcium and magnesium, but also for determining trace elements such as cobalt and nickel through spectrophotometry. For example, in the detection of trace nickel in beverages, stable complexes are formed with nickel ions, and the absorbance at 540nm wavelength shows a linear relationship with nickel concentration, with a detection limit as low as 0.01mg/L. For heavy metal ions such as cadmium, lead, and chromium black T, they also exhibit high sensitivity. Under pH 9-10 conditions, the molar absorptivity of the complex can reach the order of 10 ⁴ L/(mol · cm).
However, chrome black T is not a "master key". The complex formed between it and Fe ³ ⁺, Al ³ ⁺, Cu ² ⁺, Co ² ⁺, Ni ² ⁺ is too stable, causing EDTA to be unable to replace the indicator and resulting in a "blocking phenomenon". For example, in magnesium ion titration, if the sample contains Fe ³ ⁺ impurities, the endpoint color change will be delayed or blurred. Therefore, in practical applications, interference needs to be eliminated through preprocessing (such as adding masking agent potassium cyanide).
The azo structure of chrome black T endows it with excellent dyeing properties. In the dyeing of textiles such as wool, silk, and nylon, it is not only a "color wizard", but can also be functionalized through chemical modification.
1. Traditional dyeing process: "exclusive color card" for wool and nylon
Eriochrome Black T has high affinity for wool fibers and can generate dark colored complexes under acidic conditions (pH 4-6), with a color fastness of 4-5 levels (international standard). For example, in the dyeing of Australian Merino wool, chromium black T is combined with sodium sulfate and treated at 90 ℃ for 60 minutes to obtain a uniform black color. The color fastness to washing remains above 90% after 5 washes.
For nylon fibers, chrome black T needs to be used under alkaline conditions (pH 8-9) to achieve dyeing by binding with the amino groups on the fibers.
The "Eco Dye" process developed by Japanese company Toray utilizes a combination of chrome black T and citric acid for dyeing at 120 ℃. Not only does it achieve a color fastness of 3-4 levels, but it also reduces the COD value of wastewater by 40%, which meets environmental protection requirements.
2. Functional modification: "cutting-edge exploration" from antibacterial to intelligent response
In recent years, chrome black T has been used to prepare functional textiles. For example, by combining chrome black T with silver ions, antibacterial wool fabrics can be prepared. The experiment showed that wool fabric containing 0.5% chromium black T-silver had a 99% antibacterial rate against Escherichia coli, and remained above 90% after 50 washes. In addition, chrome black T can also be used for the preparation of photochromic materials. By copolymerizing with spiropyran compounds, intelligent textiles can be developed that change from blue to red under ultraviolet light, which can be used for anti-counterfeiting labels and fashion design.
The chemical stability and chelating ability of chromium black T make it uniquely valuable in materials science, especially in the fields of metal segregation detection and electrochemical sensors.
1. Segregation detection of copper magnesium alloys: the "golden eye" of industrial quality inspection
In the aerospace field, magnesium segregation in copper magnesium alloys can lead to uneven material properties. Traditional detection methods, such as spectral analysis, are costly and time-consuming, while chromium black T alkaline solution can achieve rapid visual detection. Specific operation: Soak the alkaline solution containing chromium black T in filter paper, wrap it around the surface of the alloy, and react with the indicator to form a purple red complex. The color depth of the segregation area is proportional to the magnesium content.
After applying this technology, a certain aviation enterprise reduced the detection time from 2 hours to 10 minutes and reduced costs by 70%.
2. Electrochemical sensors: sensitive antennae from nitrite to dopamine
The performance of electrochemical sensors can be improved by chemically modifying electrodes. For example, by combining chromium black T with polyethylene glycol and modifying it on the surface of a glassy carbon electrode, nitrite can be detected. In a 0.1M phosphate buffer solution (pH 7), the peak current of nitrite oxidation shows a linear relationship with concentration in the range of 0.1-10 μ M, with a detection limit as low as 0.03 μ M. In addition, it can also be used for dopamine detection. By compounding with chitosan, the response time of the modified electrode to dopamine is shortened to 5 seconds, and the selectivity is better than that of ascorbic acid and uric acid.
Its environmental friendliness and biocompatibility make it applicable in the fields of environmental monitoring and biochemistry, although attention should be paid to its aquatic toxicity (acute aquatic toxicity category 2).
1. Environmental water pollution warning: the "early sentinel" of heavy metals
Can be used for rapid screening of heavy metal pollution in water bodies. For example, in river sediment detection, the chromium black T-EDTA system is used to determine zinc ion concentration by colorimetric method, with a linear range of 0.1-10mg/L and a recovery rate of 95-102%. For nickel pollution, compounding with dimethylglyoxime can improve selectivity and avoid interference from copper and iron.
2. Biochemical analysis: an emerging tool for protein determination
Can be used as a resonance light scattering probe to determine proteins. In Britton Robinson buffer solution at pH 2.5, proteins form complexes with the substance through electrostatic interactions, resulting in a significant increase in light scattering intensity at 550nm and a detection limit as low as 0.05 μ g/mL. This method is easy to operate and suitable for biological samples such as serum and urine.
From titration analysis in the laboratory to dyeing processes in textile factories, from segregation detection in alloy workshops to water quality screening in environmental monitoring stations, it has become a "bridge" connecting basic research and industrial applications with its unique chemical properties and wide applicability. In the future, with the advancement of materials science and green chemistry, Eriochrome Black T will undoubtedly demonstrate its "versatile" charm in more fields and contribute to the sustainable development of human society.
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