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Alizarin Red S
Alizarin Red S
Alizarin Red S
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Alizarin Red S
Chemical structure of Alizarin Red S
Names
IUPAC name
3,4-Dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2-sulfonic acid
Other names
  • Mordant Red 3
  • C.I 58005
  • Sodium alizarinesulfonate
  • Alizarine S
  • Alizarine sulfonate
  • Alizarin Red, water-soluble
  • Alizarin Carmine
  • Alizarin sodium monosulfonate
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.004.530 Edit this at Wikidata
EC Number
  • 204-981-8
UNII
  • InChI=1S/C14H8O7S.Na/c15-11-6-3-1-2-4-7(6)12(16)10-8(11)5-9(22(19,20)21)13(17)14(10)18;/h1-5,17-18H,(H,19,20,21);/q;+1/p-1
    Key: HFVAFDPGUJEFBQ-UHFFFAOYSA-M
  • [Na+].Oc1c(O)c2C(=O)c3ccccc3C(=O)c2cc1S([O-])(=O)=O
Properties
C14H7NaO7S
Molar mass 342.253 g/mol
Appearance yellow-orange powder
Soluble in water and ethanol
Hazards
Safety data sheet (SDS) [1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Alizarin Red S (also known as C.I. Mordant Red 3, Alizarin Carmine, and C.I 58005.[1]) is a water-soluble sodium salt of Alizarin sulfonic acid with a chemical formula of C
14H
7NaO
7S.[2][1] Alizarin Red S was discovered by Graebe and Liebermann in 1871.[2] In the field of histology alizarin Red S is used to stain calcium deposits in tissues,[3][4] and in geology to stain and differentiate carbonate minerals.[3]

Uses

[edit]
Alizarin Red S, as sold for use as a histologic stain.

Alizarin Red S is used in histology and histopathology to stain, or locate calcium deposits in tissues.[1][3][4] In the presence of calcium, Alizarin Red S, binds to the calcium to form a Lake pigment that is orange to red in color.[4] Whole specimens can be stained with Alizarin Red S to show the distribution of bone, especially in developing embryos.[4] In living corals alizarin Red S has been used to mark daily growth layers.[5]

In geology, Alizarin Red S is used on thin sections, and polished surfaces to help identify carbonate minerals which stain at different rates.[6]

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Alizarin Red S

View on Grokipedia
from Grokipedia
Alizarin Red S is a synthetic commonly employed as a histological for detecting calcium deposits in biological tissues and cell cultures. Chemically, it is the sodium salt of 1,2-dihydroxyanthraquinone-3-sulfonic , with the molecular C14H7NaO7S and a molecular weight of 342.26 g/mol. First synthesized in 1871 by German chemists Carl Graebe and Carl Liebermann as a water-soluble derivative of the natural —originally extracted from the roots of the madder plant ()—Alizarin Red S marked an early advancement in synthetic . Alizarin itself had been the first natural produced synthetically in 1868–1869, revolutionizing the , but the sulfonation in Alizarin Red S enhanced its and utility beyond . The compound appears as a dark red to brown powder, with a exceeding 250°C and in at approximately 1 mg/mL at . In biological and medical applications, Alizarin Red S binds selectively to calcium ions, forming an orange-red chelate complex that is visible under light microscopy, making it invaluable for assessing mineralization in , , and dental tissues. It is routinely used in protocols for osteogenic cell cultures, where fixed samples are immersed in a 40 mM solution at 4.1 for 20–30 minutes, followed by washing and optional quantification via at 405 nm after extraction in acetic acid. Beyond , it serves as a chromogenic agent in colorimetric assays for detecting trace metals and in environmental analyses for calcium quantification, though it also interacts with other divalent cations like magnesium and . Safety considerations include potential irritation to , eyes, and upon exposure, necessitating handling with protective equipment.

Chemistry

Structure and nomenclature

Alizarin Red S is the sodium salt form of alizarin sulfonic acid, possessing the molecular formula C₁₄H₇NaO₇S. Its systematic IUPAC name is sodium 3,4-dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate. The compound features an core—a system with a central ring fused to two rings, incorporating carbonyl groups at positions 9 and 10. This core bears two hydroxyl groups at adjacent positions 3 and 4 on one outer ring, along with a group (-SO₃⁻) at position 2, balanced by a sodium counterion (Na⁺). The structural numbering prioritizes the lowest locants for substituents in the IUPAC , placing the at position 2 and the hydroxyls at 3 and 4; in contrast, traditional numbering for the parent compound labels the hydroxyls at positions 1 and 2 with the at 3. A textual representation of the core structure highlights the key positions: the ring system with C=O at 9 and 10, OH at 3 and 4, and SO₃Na at 2, as captured in the canonical SMILES notation [Na⁺].OC1=C(O)C2=C(C=C1S([O⁻])(=O)=O)C(=O)C1=CC=CC=C1C2=O. In comparison to its parent compound (C₁₄H₈O₄), which shares the core and 1,2-dihydroxyl substitution but lacks the , Alizarin Red S gains the group to confer water solubility via the ionic sodium moiety.

Physical properties

Alizarin Red S is typically obtained as a dark red to orange-red crystalline powder. Its molar mass is 342.26 g/mol. The compound has a of approximately 1.54 g/cm³. It melts at around 280 °C but decomposes at this temperature. Alizarin Red S shows high in , reaching up to 68 g/L at 25 °C, due in part to the presence of the sulfonate group; it is also soluble in but insoluble in non-polar solvents such as . In aqueous solution, it displays an absorption maximum between 520 and 550 nm, which accounts for its characteristic red coloration.

Chemical properties

Alizarin Red S, or 1,2-dihydroxyanthraquinone-3-sulfonic acid sodium salt, displays pronounced acid-base properties arising from its sulfonate and phenolic functional groups. The sulfonate moiety imparts strong acidity with a pKa of approximately 1, ensuring high water solubility across a wide pH range, while the two phenolic hydroxyl groups deprotonate sequentially with pKa values of 5.82 and 10.78 at 25°C and ionic strength 0.1 M. These deprotonations result in distinct color changes: the neutral form (H₂ARS) appears yellow below pH 5.8, shifting to red for the monoanion (HARS⁻) between pH 5.8 and 10.8, and to violet for the dianion (ARS²⁻) above pH 10.8, making it useful as a pH indicator. In coordination chemistry, Alizarin Red S acts as a bidentate , forming insoluble red-orange chelates or lake pigments with divalent cations such as Ca²⁺ and Mg²⁺ through its deprotonated hydroxyl and adjacent carbonyl oxygen atoms. The stability constant for the 1:1 Ca²⁺ complex (log K ≈ 4.0) reflects moderate binding affinity, enabling selective in neutral to slightly alkaline media. These complexes exhibit characteristic absorption maxima around 520–550 nm, contributing to their vivid coloration. Alizarin Red S demonstrates good in neutral to alkaline aqueous solutions ( 6–10), where it remains intact for extended periods without significant . However, exposure to strong UV light leads to , primarily via cleavage of the ring and formation of reduction products such as anthrahydroquinone derivatives. Extreme conditions, either highly acidic ( < 2) or strongly basic ( > 12), accelerate of the group or phenolic moieties, resulting in loss of color and . The core of Alizarin Red S imparts reversible behavior, undergoing a two-electron, two-proton reduction to the corresponding form at potentials around -0.5 to -0.7 V vs. Ag/AgCl in aqueous media. This process is -dependent, with the shifting positively by approximately 60 mV per pH unit, and the semiquinone radical intermediate is stabilized in neutral conditions, enabling electrochemical applications.

History

Background on alizarin

Alizarin, chemically known as 1,2-dihydroxyanthraquinone, is the principal red pigment extracted from the roots of the madder plant (Rubia tinctorum). This natural dye has been employed since antiquity for coloring textiles and leather, with archaeological evidence indicating its use as early as 1500 BCE in ancient Egypt, where it appears on mummified wrappings and fabrics. Cultivation of madder spread across the Mediterranean, Asia Minor, and India, supporting extensive trade networks due to the dye's fastness and vibrant hue when mordanted with metals like aluminum or iron. In 1826, French chemists Jean-Jacques Colin and Pierre-Jean Robiquet achieved the first isolation of alizarin in pure form from madder root extracts, identifying it as the key coloring component responsible for the red shades. The molecular structure was elucidated in 1868 by German chemists Carl Graebe and Carl Liebermann, who established alizarin as 1,2-dihydroxyanthraquinone through degradative analysis and comparison with synthetic analogs. This determination marked a pivotal advancement in , revealing the compound's backbone and paving the way for targeted synthesis. The synthetic breakthrough occurred in 1869, when in and Graebe and Liebermann in independently developed methods to produce from , a byproduct of . These processes enabled cost-effective industrial production, supplanting natural extraction and causing synthetic to capture the market by the 1870s. Consequently, madder cultivation plummeted in major producing regions, including and the in and parts of , devastating local economies reliant on the crop. thus became the foundational compound for subsequent derivatives, such as sulfonated variants adapted for specialized applications.

Discovery of Alizarin Red S

Alizarin Red S, known chemically as the sodium salt of alizarin-3-sulfonic acid, was discovered in 1871 by German chemists Carl Graebe and Carl Liebermann during their research on derivatives. This innovation stemmed from their earlier efforts to synthesize itself in 1868, providing a foundation for exploring modified forms of the compound. The primary motivation behind the development was to address the limited of pure in , which hindered its practical application in industrial and analytical techniques. By sulfonating with , Graebe and Liebermann created a that dissolved readily in aqueous solutions while retaining the vibrant red coloring properties essential for textile processing. The discovery was detailed in their 1871 publication in Berichte der deutschen chemischen Gesellschaft, where the compound was characterized and confirmed as sodium alizarin-3-sulfonate, highlighting its potential as a versatile intermediate. (Note: This references related work; primary paper pages 571–574 in volume 4.) Following its introduction, Alizarin Red S saw rapid adoption in the for mordant dyeing in the , particularly on mordanted with to yield durable scarlet hues superior to those from unmodified . By the late , it found initial applications in for staining calcium deposits in and mineralized tissues, enabling early microscopic studies of skeletal development.

Synthesis

Early synthetic routes

The primary early synthetic route to Alizarin Red S, the sodium salt of sulfonic acid, involved sulfonation of (1,2-dihydroxyanthraquinone), a first reported by German chemists Carl Graebe and Carl Liebermann in 1871 as a means to enhance the solubility of the natural red for applications. This method employed fuming ( containing 10–20% SO₃) as the sulfonating agent, with heated in the reagent at 80–100 °C for 2–4 hours to introduce the group at the 3-position, forming alizarin-3-. The reaction can be represented as: C14H8O4+H2SO4→C14H8O7S(then neutralized with NaOH to C14H7NaO7S)\text{C}_{14}\text{H}_8\text{O}_4 + \text{H}_2\text{SO}_4 \rightarrow \text{C}_{14}\text{H}_8\text{O}_7\text{S} \quad (\text{then neutralized with NaOH to } \text{C}_{14}\text{H}_7\text{NaO}_7\text{S}) Early processes often resulted in a mixture of the desired 3-sulfonate isomer and minor sulfonated byproducts at other positions, leading to impurities that could diminish the dye's colorfastness and purity. Purification was achieved by neutralizing the reaction mixture with sodium hydroxide to form the soluble sodium salt, followed by salting out with sodium chloride to precipitate the product, and subsequent recrystallization from water to isolate the pure compound. These steps addressed solubility issues but highlighted challenges in selectivity, as the ortho-directing effects of the hydroxyl groups favored sulfonation at position 3 while producing trace isomers that required careful separation. By the 1880s, this sulfonation technique was scaled up industrially by German chemical firms, notably BASF, which adopted it around 1884 to produce Alizarin Red S for wool dyeing, marking a key advancement in synthetic dye manufacturing and contributing to the decline of natural madder-based alizarin.

Modern production methods

Contemporary industrial production of Alizarin Red S primarily involves the sulfonation of purified alizarin (1,2-dihydroxyanthraquinone) using oleum or fuming sulfuric acid in batch reactors, with optimizations focused on temperature control and waste reduction to achieve high regioselectivity for the 3-sulfonate isomer. In one efficient method, alizarin is reacted with oleum in a 1:2 to 1:3 molar ratio under an inert atmosphere at temperatures between 50°C and 130°C, followed by the addition of water (2-5 times the weight of initial sulfuric acid) and a bridging liquid such as dichloromethane to facilitate phase separation and solid recovery, yielding a high-purity product with minimal sulfate effluents. This approach improves upon traditional processes by operating at moderate temperatures (e.g., 50-70°C initially) and enhancing selectivity for the desired isomer, reducing the need for extensive downstream purification. Alternative synthetic routes begin with condensed with in the presence of aluminum chloride or to form , which is then isolated and subjected to sulfonation as described. For laboratory-scale production, direct sulfonation of in fuming (15-20% SO₃) at 42-110°C for 2-5 hours, followed by cooling, dilution with water, and with , provides the sodium salt in good yields after filtration and washing with or . Efforts toward greener production include processes that minimize acid waste through precise control of reaction conditions and recycling of phases, though enzymatic or ionic liquid-based sulfonation remains exploratory and not yet scaled for this compound. Purification for analytical-grade Alizarin Red S typically employs , multiple washes with solutions, and optional charcoal decolorization, ensuring compliance with dye standards such as Colour Index 58005. Global production is concentrated in and , mainly for and applications, with the market valued at around USD 50 million in 2023 and projected to grow modestly due to demand in biological and geological uses.

Applications

Histological and biological

is widely employed in histological and biological to visualize and quantify calcium deposits in tissues and cells due to its ability to form an insoluble red-orange calcium-alizarinate complex through at approximately 4.2. This mechanism selectively binds to calcium ions in calcified structures, such as , producing a birefringent that is observable under . The standard protocol involves fixing samples in 70% or formalin, followed by immersion in a 1–2% aqueous Alizarin Red S solution at pH 4.2 for 5–30 minutes, depending on the tissue type and desired intensity. After staining, samples are rinsed with distilled water and optionally destained with acetone or acetic acid to enhance contrast. For quantitative analysis in cell cultures, the bound dye is extracted with 10% , and absorbance is measured at 570 nm to assess mineralization levels. In histological applications, Alizarin Red S stains calcified elements in , , and dental tissues, providing clear differentiation of mineralized matrices in paraffin-embedded sections. It is particularly valuable in assays for mineralization, where it detects deposits formed during osteogenic differentiation. The dye's sensitivity allows detection of calcium at concentrations as low as 0.1–0.5 μg/mL in biological fluids or tissues. Specific uses include studies of embryonic bone development, where low concentrations (e.g., 0.01%) enable vital staining of skeletal elements in model organisms like without disrupting mineralization. In marine biology, it marks skeleton growth by immersion, creating visible lines for tracking rates over time. Advantages of Alizarin Red S include its simplicity, low cost, and compatibility with standard histological workflows, such as paraffin embedding and combination with Alcian blue for dual cartilage-bone staining. However, limitations arise from non-specific binding to divalent cations like magnesium, which can lead to background in samples with high magnesium content.

Geological and mineralogical uses

Alizarin Red S serves as a vital staining agent in geological and mineralogical applications, particularly for the identification and differentiation of carbonate minerals in thin sections of rocks. The typical protocol involves preparing a 0.2% solution of Alizarin Red S dissolved in cold 0.2% hydrochloric acid (HCl), which is applied directly to polished thin sections or rock surfaces. Upon application at room temperature, calcite and aragonite react rapidly to produce a bright red stain, while dolomite remains unstained or develops only a faint pink hue in mixtures, allowing for clear visual distinction under a petrographic microscope. This selective binding to calcium ions in CaCO₃ structures enables precise mineral mapping without altering the sample's overall integrity. In petrographic analysis of sedimentary rocks, Alizarin Red S is routinely used to differentiate from dolomite in sequences, facilitating the interpretation of depositional environments and diagenetic processes. Since the , it has been integral to oil exploration efforts, where it aids in evaluating core samples from reservoirs by highlighting cementation and distribution in and dolostone formations. The technique's sensitivity allows detection of minor phases, enhancing the accuracy of rock classification in complex lithologies. The adoption of Alizarin Red S extended to in the 1960s, where it proved effective for identifying fossil shell compositions in thin sections, such as distinguishing calcitic from dolomitic microstructures in ancient mollusks. Often combined with for additional color coding of iron-bearing carbonates, the stain supports detailed studies of biogenic minerals in sedimentary contexts.

Analytical and environmental applications

Alizarin Red S serves as a chromogenic in spectrophotometric methods for quantifying metal ions through the formation of stable, colored complexes. For aluminum (Al³⁺), it reacts in acidic media ( 3–4) to produce a lake with maximum at approximately 560 nm, enabling detection limits as low as 0.1 μg/mL in aqueous samples. Similarly, (Zr⁴⁺) forms a violet- complex measurable at 525 nm in buffer ( 4.75), with sensitivities suitable for trace-level in environmental and industrial waters. In (FIA), Alizarin Red S facilitates rapid determination of water hardness by complexing with calcium (Ca²⁺) and magnesium (Mg²⁺) ions, producing measurable color changes at 510–520 nm. This approach achieves detection limits of 0.01 ppm for total hardness, making it effective for real-time monitoring in quality assessments. As a , Alizarin Red S exhibits a color transition from (pH 4.0) to (pH 6.0), useful in acid-base titrations and complexometric analyses, such as EDTA titrations of (III) where the endpoint is marked by a sharp pink-to-green- shift at pH 2.1–2.5. In environmental applications, Alizarin Red S acts as a model azo-like for studying processes, particularly kinetics with natural adsorbents. For instance, Spirulina platensis algae biosorbs up to 69% of the at 6.5, following Langmuir isotherm models that describe adsorption with maximum capacities around 100 mg/g. With nanoparticle-based adsorbents like gold-loaded , ultrasound-assisted removal exceeds 90% efficiency at 3, fitting pseudo-second-order kinetics and Langmuir isotherms for optimized remediation of textile effluents. In , Alizarin Red S is coupled to quantum dots to enhance colorimetric sensing of and metal ions, providing water-soluble probes with dual functionality for . Recent advancements in the 2020s include photocatalytic degradation studies using TiO₂-based catalysts under UV irradiation, where Cu-doped TiO₂ achieves 87% removal of Alizarin Red S within 120 minutes by generating , demonstrating potential for scalable dye . Layered Zn-Al double hydroxides have also shown efficient UV-driven degradation, with kinetics following pseudo-first-order models and mineralization rates up to 80% in 60 minutes.

Safety and environmental impact

Toxicity and health effects

Alizarin Red S demonstrates low acute oral toxicity, with an LD50 exceeding 5,000 mg/kg in rats, indicating it is practically via this route under standard testing conditions. Limited data are available on the acute oral toxicity of Alizarin Red S; no reliable LD50 value has been established. It is classified as a irritant (GHS Category 2) and causes serious eye damage or (GHS Category 2), potentially leading to redness, , and upon direct contact. Inhalation of its dust or mist can result in , manifesting as coughing, , or throat discomfort. At the molecular level, Alizarin Red S exerts toxicity by binding to the active sites of enzymes such as catalase, thereby inhibiting their function and promoting oxidative stress through the accumulation of hydrogen peroxide and reactive oxygen species (ROS). Although anthraquinone structures like that in Alizarin Red S can undergo quinone reduction to generate ROS, potentially contributing to genotoxic effects, in vitro studies using comet and micronucleus assays have shown no evidence of genotoxicity or oxidative DNA damage at tested concentrations. Chronic exposure to Alizarin Red S has not been classified as carcinogenic by the International Agency for Research on Cancer (IARC Group 3 equivalent, unclassifiable due to lack of review), the National Toxicology Program, or OSHA. Occupational handling of related has been linked to in dye workers, characterized by eczematous reactions on exposed skin. Limited data exist on , with no established adverse effects reported in available toxicological profiles. No specific (PEL) has been established by OSHA for Alizarin Red S; exposures are managed under the general standard for respirable dust (particulates not otherwise regulated) at 5 mg/m³ over an 8-hour workday. Safe laboratory handling protocols recommend the use of nitrile gloves, goggles, and local exhaust ventilation to minimize dermal, ocular, and risks. Due to improved practices, documented cases of significant occupational exposure are rare, primarily limited to isolated incidents in laboratories prior to the when ventilation standards were less stringent.

Ecological concerns and remediation

Alizarin Red S (ARS), an anthraquinone-based synthetic , poses significant ecological risks primarily due to its release into aquatic environments from , histological, and industrial . As a persistent , ARS resists and conventional treatment processes, leading to long-term accumulation in water bodies. Its chemical stability, characterized by a fused aromatic structure, contributes to recalcitrance, exacerbating environmental especially in regions with inadequate . In aquatic ecosystems, ARS disrupts ecological balance by reducing light penetration, which inhibits in and aquatic plants, and exerts direct toxicity on organisms. It induces , membrane damage, and metabolic disruptions in and , with mutagenic and carcinogenic potential that may lead to through the . Studies on (Salmo trutta) demonstrate concentration- and life-stage-dependent toxicity following short-term immersion, with fry being most sensitive; after a 3-hour immersion at 150 mg/L, monitoring over 30 days showed 4–6% mortality, while over 267 days resulted in up to 69% mortality, varying by commercial brand due to impurities. assays on freshwater , such as Chlorella vulgaris (EC50 21.6 mg/L) and Spirulina platensis (EC50 38.4 mg/L), reveal growth inhibition at these concentrations. Remediation strategies for ARS focus on adsorption-based methods using low-cost, eco-friendly materials to remove it from contaminated water. waste, modified through or base treatment, serves as an effective biosorbent, achieving adsorption capacities up to 87.5 mg/g under optimal conditions ( 2.0, 45°C, 100 min contact time), with removal efficiencies reaching 86.5%. This approach leverages , minimizing secondary while following Langmuir isotherm and pseudo-second-order kinetics, highlighting its spontaneity and endothermic nature. Advanced , such as silica-supported nanoscale zero-valent iron (nZVI), offer high-efficiency removal, attaining 96.8% adsorption at 3.0 with chloride-modified variants, driven by electrostatic interactions and surface complexation. Clay-chitosan composites and from bovine have also demonstrated promising results, with removal rates exceeding 90% in batch studies, emphasizing sustainable alternatives to chemical treatments. These methods prioritize scalability and minimal environmental footprint, supporting broader efforts to mitigate in industrial effluents.

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