4,4'-DIAMINO-2,2'-STILBENEDISULFONIC ACID

4,4'-Diamino-2,2'-stilbenedisulfonic acid is an aromatic diamino stilbene compound and an important industrial intermediate for fluorescent whitening agents, optical brighteners, direct dyes, and other functional colorants.
The molecule combines a conjugated stilbene framework with two amino groups and two sulfonic acid groups, providing both a reactive aromatic amine functionality and the structural foundation used in many stilbene-derived brightening compounds.
4,4'-Diamino-2,2'-stilbenedisulfonic acid is particularly important in chemical manufacturing for paper, textile, detergent, and colorant value chains, where the parent material is normally converted into more highly substituted functional derivatives.

CHEMICAL IDENTITY AND COMMON NAMES

4,4'-Diamino-2,2'-stilbenedisulfonic acid consists of two aromatic rings connected through an ethene bridge, with amino groups at the 4- and 4'-positions and sulfonic acid groups at the 2- and 2'-positions.
The conjugated and highly symmetrical molecular framework is the defining structural feature behind its extensive use in optical-brightener and dye-intermediate chemistry.

The industrial material is frequently referred to as DSD acid, DASDA, or DASD.
Amsonic acid and Flavonic acid are also established alternative names for the same chemical identity.

The free acid should be distinguished from 4,4'-Diamino-2,2'-stilbenedisulfonic acid disodium salt.
The sodium salt has different formula weight, ionic form, aqueous processing characteristics, and registry identity even though both materials provide the same diaminostilbenedisulfonate structural core for downstream synthesis.

A stereochemically explicit trans or E-form can also appear separately in chemical registries.
The conventional CAS identity used broadly for 4,4'-Diamino-2,2'-stilbenedisulfonic acid is CAS Number 81-11-8.

Synonyms and Common Names: Diaminostilbenedisulfonic acid, 4,4'-Diaminostilbene-2,2'-disulfonic acid, 4,4'-Diaminostilbene-2,2'-disulphonic acid, 4,4'-Diamino-2,2'-stilbenedisulphonic acid, DSD acid, DASDA, DASD, Amsonic acid, Flavonic acid, p,p'-Diaminodiphenylethylene-o,o'-disulfonic acid, p,p'-Diaminodiphenylethylene-o,o'-disulphonic acid, 4,4'-Diamino-2,2'-stilbene disulfonic acid, 4,4'-Diamino-2,2'-stilbene disulphonic acid, 4,4'-Diaminostilbene disulfonic acid, 4,4'-Diaminostilbene disulphonic acid, Amsonsaeure, 5-amino-2-[(1E)-2-(4-amino-2-sulfophenyl)ethenyl]benzenesulfonic acid

TECHNICAL IDENTIFICATION

CAS Number: 81-11-8
EC / EINECS Number: 201-325-2
Molecular Formula: C14H14N2O6S2
Molar Mass: 370.40 g/mol
Chemical Class: Diaminostilbene disulfonic acid
Functional Groups: Primary aromatic amines, sulfonic acid groups, conjugated stilbene
Common Industrial Abbreviations: DSD acid, DASDA, DASD
Disodium Salt CAS Number: 7336-20-1
Stereochemically Explicit E-Form CAS Number: 28096-93-7

PHYSICAL AND CHEMICAL PROPERTIES

Appearance: Pale yellow to yellow crystalline powder or solid
Physical State: Solid
Molecular Formula: C14H14N2O6S2
Molar Mass: 370.40 g/mol
Chemical Character: Aromatic diamine and disulfonic acid
Structural Framework: Conjugated stilbene
Acid Functionality: Two sulfonic acid groups
Amine Functionality: Two primary aromatic amino groups
Water Behaviour: Free-acid form has limited aqueous processability compared with its alkali-metal salts
Alkali Behaviour: Forms water-compatible salts upon neutralization with suitable bases
Colour Characteristics: Pale yellow in purified commercial material
Thermal Behaviour: High-temperature treatment leads to decomposition rather than useful distillation
Volatility: Very low under normal handling conditions
Reactivity: Amino groups readily undergo diazotization and condensation reactions
Light Response: Stilbene conjugation provides strong ultraviolet absorption and forms the structural basis of many fluorescent whitening derivatives

The two sulfonic acid groups give 4,4'-Diamino-2,2'-stilbenedisulfonic acid strongly acidic functionality and allow formation of sodium and other water-compatible salts.
This property is especially important because many downstream brightener and dye syntheses are conducted in aqueous media under controlled pH conditions.

The two para-positioned amino groups provide symmetrical reactive sites on the stilbene framework.
These groups can be diazotized for azo-dye synthesis or reacted with electrophilic intermediates such as cyanuric chloride to construct bis-triazinyl stilbene optical brighteners.

The central carbon-carbon double bond maintains conjugation between the two aromatic rings.
This extended conjugated system contributes to ultraviolet absorption and provides the electronic framework from which fluorescent whitening derivatives are developed.

FUNCTIONAL CHARACTERISTICS

4,4'-Diamino-2,2'-stilbenedisulfonic acid functions primarily as a chemical building block rather than as the final optical brightener used in most paper, textile, or detergent formulations.
Its commercial importance arises from the combination of a conjugated stilbene core, two reactive amino groups, and two sulfonic acid groups within the same molecule.

The amino groups provide convenient reaction sites for symmetrical derivatization.
Reaction with cyanuric chloride can introduce triazine units that are subsequently substituted with amines, alcohol-containing amines, aromatic amines, or other nucleophilic components to produce application-specific fluorescent whitening agents.

The amino groups can also undergo diazotization.
The resulting diazonium functionality can be coupled with aromatic coupling components to form azo and disazo structures used in dye chemistry.

The sulfonic acid groups contribute ionic character and facilitate conversion into alkali-metal salts.
This allows many downstream intermediates and derivatives to be processed in aqueous systems and helps control solubility in finished optical-brightener and dye molecules.

The stilbene framework provides an extended π-electron system.
Appropriate substitution of this framework produces compounds that absorb ultraviolet radiation and emit visible blue fluorescence, which visually compensates for yellow coloration in white substrates.

PRODUCTION AND COMMERCIAL FORM

A major industrial route to 4,4'-Diamino-2,2'-stilbenedisulfonic acid begins with 4-nitrotoluene-2-sulfonic acid.
Oxidative coupling under alkaline conditions converts this precursor into 4,4'-dinitrostilbene-2,2'-disulfonic acid.

The dinitro intermediate is subsequently reduced to convert both nitro groups into primary amino groups.
Catalytic and other controlled reduction technologies can be used to produce 4,4'-Diamino-2,2'-stilbenedisulfonic acid from the corresponding dinitro compound.

Industrial reduction and isolation can be controlled by pH to obtain the free acid as a pale yellow crystalline material.
Filtration, washing, and drying provide the solid product, while neutralization can instead be used where an alkali-metal salt is required for downstream processing.

Commercial 4,4'-Diamino-2,2'-stilbenedisulfonic acid may therefore be encountered as free acid, sodium salt, aqueous process solution, wet cake, or another manufacturing form depending on the subsequent chemical operation.
The precise chemical form is commercially important because free acid content and sodium-salt content cannot be compared directly on an equal-weight basis.

Purity is particularly important in optical-brightener manufacture because residual nitro compounds, partially reduced intermediates, starting materials, inorganic salts, and coloured organic impurities can affect subsequent condensation reactions and final product colour.

APPLICATIONS AND INDUSTRIES

OPTICAL BRIGHTENER INTERMEDIATE

4,4'-Diamino-2,2'-stilbenedisulfonic acid is one of the most important structural intermediates used in the manufacture of stilbene-based fluorescent whitening agents.
The parent compound supplies the symmetrical diaminostilbene disulfonic acid nucleus found in numerous commercial optical-brightener chemistries.

The amino groups are commonly reacted with cyanuric chloride to introduce reactive triazine rings.
Subsequent substitution of the remaining chlorine atoms with selected amines, aromatic compounds, hydroxyalkylamines, or other nucleophiles allows solubility, affinity, fluorescence, shade, stability, and substrate compatibility to be adjusted.

This modular chemistry gives 4,4'-Diamino-2,2'-stilbenedisulfonic acid substantial importance as a platform intermediate.
A single parent structure can therefore lead to several brightener families designed for different paper, textile, detergent, and related applications.

PAPER AND PAPERBOARD OPTICAL BRIGHTENERS

4,4'-Diamino-2,2'-stilbenedisulfonic acid is a major precursor for fluorescent whitening agents used by the paper and paperboard industries.
These derivatives absorb ultraviolet radiation and emit blue-violet visible light, increasing the perceived whiteness and brightness of paper.

Stilbene-derived optical brighteners can be used in pulp, wet-end applications, surface sizing, coating formulations, or other stages of paper manufacture depending on the derivative selected.
The required affinity, solubility, electrolyte tolerance, and fluorescence performance are established through chemical substitution of the original 4,4'-Diamino-2,2'-stilbenedisulfonic acid structure.

Paper grades intended for high visual whiteness can benefit particularly from this chemistry.
Writing papers, printing papers, coated papers, board, and other white cellulosic materials are important downstream application areas for derivatives manufactured from 4,4'-Diamino-2,2'-stilbenedisulfonic acid.

4,4'-Diamino-2,2'-stilbenedisulfonic acid itself is therefore best understood as an upstream chemical intermediate for these brighteners rather than as a universal direct paper additive.

TEXTILE OPTICAL BRIGHTENERS

4,4'-Diamino-2,2'-stilbenedisulfonic acid is used to manufacture optical brighteners designed for cellulosic and other suitable textile substrates.
These derivatives increase apparent whiteness by converting invisible ultraviolet radiation into visible blue fluorescence.

Cotton and regenerated cellulose are major substrates associated with many stilbene-disulfonate brightener chemistries.
Derivative structure determines fiber affinity, exhaustion behaviour, application method, shade, washing behaviour, and compatibility with bleaching or finishing processes.

Brighteners based on 4,4'-Diamino-2,2'-stilbenedisulfonic acid can be engineered for use during textile washing, bleaching, finishing, or dedicated optical-whitening treatments.
The specific derivative is selected according to fiber type and process conditions.

The symmetrical molecular structure of 4,4'-Diamino-2,2'-stilbenedisulfonic acid is particularly useful because equivalent functional groups can be installed on both sides of the molecule.
This allows balanced and highly conjugated fluorescent structures to be produced efficiently.

DETERGENT OPTICAL BRIGHTENERS

4,4'-Diamino-2,2'-stilbenedisulfonic acid is an important precursor for fluorescent whitening agents incorporated into laundry detergents.
These derivatives deposit on suitable textile fibers during washing and increase the visual perception of whiteness after cleaning.

Detergent brighteners require more than fluorescence alone.
Useful derivatives must combine adequate water solubility, detergent compatibility, substrate affinity, chemical stability, and acceptable performance in the presence of surfactants, builders, electrolytes, and other formulation components.

Bis-triazinylamino stilbene derivatives prepared from 4,4'-Diamino-2,2'-stilbenedisulfonic acid represent an important class of detergent optical brighteners.
Chemical substitution around the triazine groups allows formulators to tailor solubility and textile affinity.

Powder detergents, detergent cakes, and other laundry compositions have historically used optical-brightener derivatives based on this chemistry.
The parent 4,4'-Diamino-2,2'-stilbenedisulfonic acid serves as the manufacturing intermediate from which the functional brightener molecule is constructed.

DYE INTERMEDIATE

4,4'-Diamino-2,2'-stilbenedisulfonic acid is an established intermediate in azo and direct dye chemistry.
Both amino groups can be converted into diazonium groups and subsequently coupled with suitable aromatic components.

This bis-diazotization capability enables preparation of symmetrical and unsymmetrical disazo structures.
Selection of the coupling components controls colour, substantivity, solubility, fiber affinity, and other properties of the resulting dye.

The sulfonic acid groups contribute water-compatible ionic functionality to downstream dye structures.
This is particularly important for direct and other water-applied dyes used with cellulosic materials.

4,4'-Diamino-2,2'-stilbenedisulfonic acid can therefore serve simultaneously as a chromophoric structural element and as a bifunctional aromatic amine intermediate.
Its use is especially valuable when the final dye requires a rigid conjugated central linker between two azo-containing regions.

DIRECT DYE MANUFACTURE

Direct dyes can be produced through tetrazotization of 4,4'-Diamino-2,2'-stilbenedisulfonic acid followed by coupling with appropriate aromatic components.
The resulting extended conjugated structures can provide yellow, orange, brown, and related shades depending on the selected coupling chemistry.

The sulfonate functionality of the finished dyes contributes aqueous solubility and suitability for application to cellulose.
The elongated planar aromatic structures can additionally promote affinity for cellulosic fibers through non-covalent interactions.

Process control during tetrazotization is important because both amino groups must be converted effectively while minimizing decomposition of the diazonium intermediates.
Temperature, acidity, nitrite addition, reaction time, and subsequent coupling conditions influence yield and product quality.

PAPER DYES

Derivatives of 4,4'-Diamino-2,2'-stilbenedisulfonic acid also contribute to the manufacture of water-compatible dyes used for paper coloration.
The stilbene disulfonic framework can be incorporated into azo chromophores possessing useful affinity for cellulose.

Paper-dye applications require control of colour strength, shade, solubility, electrolyte behaviour, bleed resistance, and interaction with papermaking additives.
These characteristics depend mainly on the completed dye structure rather than on the parent intermediate alone.

TEXTILE DYES

4,4'-Diamino-2,2'-stilbenedisulfonic acid can serve as a central intermediate for dyes intended for cotton and other textile materials.
Diazotization followed by coupling provides access to extended azo systems with both chromophoric and sulfonate functionality.

The chemical structure of the coupling component strongly affects the shade and fastness characteristics of the resulting dye.
The 4,4'-Diamino-2,2'-stilbenedisulfonic acid unit provides a rigid symmetrical backbone onto which these dye-forming groups can be constructed.

FLUORESCENT WHITENING AGENT CHEMISTRY

4,4'-Diamino-2,2'-stilbenedisulfonic acid is important not simply because it is fluorescently related, but because its molecular structure is particularly suitable for systematic derivatization.
Substitution at the amino groups extends conjugation while retaining the sulfonated stilbene core.

Derivatives can be engineered to produce intense blue fluorescence under ultraviolet illumination.
The emitted blue light reduces the visual effect of yellow tones in paper, textiles, and washed fabrics and creates a cleaner and brighter white appearance.

Differences between fluorescent whitening agents are achieved through the substituent groups added during downstream synthesis.
These structural changes influence fluorescence maximum, substrate affinity, solubility, acid or alkali behaviour, electrolyte resistance, and light stability.

CYANURIC CHLORIDE CONDENSATION CHEMISTRY

One of the most commercially important reactions of 4,4'-Diamino-2,2'-stilbenedisulfonic acid is condensation with cyanuric chloride.
The two amino groups react with the reactive triazine compound to produce bis-triazinyl intermediates.

The remaining chlorine atoms on the triazine rings can then be sequentially substituted.
Aniline, morpholine, alkanolamines, sulfonated aromatic amines, ammonia, and other nucleophiles can be selected according to the desired optical-brightener structure.

Reaction temperature and pH are particularly important because the three chlorine atoms on cyanuric chloride exhibit different substitution reactivity.
Stepwise control allows different groups to be introduced selectively and provides a practical route to complex optical-brightener molecules.

SPECIALTY COLORANT SYNTHESIS

4,4'-Diamino-2,2'-stilbenedisulfonic acid can also be used as an intermediate for specialised colorants in which the stilbene-disulfonic framework provides conjugation, ionic character, or a symmetrical molecular core.
Its bifunctional aromatic amine character enables numerous coupling and condensation sequences.

These applications are more specialised than its principal use in optical brightener manufacture.
They are most relevant when the desired molecular architecture specifically benefits from a sulfonated stilbene linker.

GRADE SELECTION AND PRODUCT SUITABILITY

Assay is one of the principal procurement parameters for 4,4'-Diamino-2,2'-stilbenedisulfonic acid.
Higher active content improves control of reaction stoichiometry during cyanuric-chloride condensation, diazotization, and other downstream chemical conversions.

Purity should be evaluated together with the identity of the impurities rather than only as a total assay value.
Residual 4,4'-dinitrostilbene-2,2'-disulfonic acid, partially reduced intermediates, starting-material residues, coloured organic compounds, and inorganic salts may have different effects on downstream processing.

Residual nitro compounds are especially relevant because they indicate incomplete reduction.
Such impurities do not provide the same amino functionality as 4,4'-Diamino-2,2'-stilbenedisulfonic acid and can therefore reduce effective reactive content.

Colour is an important practical parameter for applications leading to fluorescent whitening agents.
Excessive yellow, brown, or other coloration in the starting intermediate can increase purification requirements or influence the appearance of subsequent products.

Inorganic salt content can become important when 4,4'-Diamino-2,2'-stilbenedisulfonic acid is supplied from an aqueous reduction and neutralization process.
Sodium chloride, sodium sulfate, and other inorganic residues can affect active-content calculations, solubility, filtration, and downstream electrolyte concentration.

Water content is also relevant when comparing dry powder, wet cake, and solution forms.
Purchasing specifications should therefore distinguish material supplied on an as-is basis from assay calculated on a dry or active basis.

Free acid and disodium salt are technically distinct purchasing forms.
The free acid has a molar mass of 370.40 g/mol, while conversion to the disodium salt changes molecular weight and aqueous behaviour.

FORMULATION AND PROCESS CONSIDERATIONS

4,4'-Diamino-2,2'-stilbenedisulfonic acid is frequently neutralized before reactions conducted in aqueous media.
Formation of sodium or other compatible salts improves aqueous processability and facilitates controlled addition to subsequent reaction stages.

pH control is particularly important during cyanuric-chloride condensation.
Acid generated during substitution must be neutralized while maintaining conditions suitable for the desired reaction stage.

Low temperatures are commonly used during the first substitution of cyanuric chloride because this highly reactive reagent can undergo unwanted hydrolysis or additional substitution when conditions are not controlled.
Subsequent substitution stages can be conducted at progressively higher temperatures according to the nucleophile and desired final derivative.

Mixing efficiency is important when the free acid, sodium salt, or cyanuric chloride is present as a slurry.
Uniform suspension and efficient mass transfer support reproducible conversion and prevent localized concentration differences.

Diazotization requires controlled acidity and temperature.
The resulting tetrazonium intermediates are reactive and are normally generated as part of an integrated process leading directly to the coupling stage.

Light exposure should be controlled during storage and processing where product colour and stilbene configuration are important.
Conjugated stilbene compounds can undergo photochemical reactions under sufficiently energetic light.

QUALITY, SPECIFICATIONS AND DOCUMENTATION

Relevant quality parameters for 4,4'-Diamino-2,2'-stilbenedisulfonic acid can include assay, appearance, colour, water content, insoluble matter, inorganic salts, residual dinitro compound, partially reduced intermediates, and other process-related organic impurities.
The most important parameters depend on the downstream brightener or dye being manufactured.

Assay directly determines the amount of reactive diamino compound available for subsequent synthesis.
Accurate assay therefore supports control of cyanuric chloride ratios, diazotization requirements, coupling stoichiometry, yield, and batch reproducibility.

Residual dinitro content can provide useful information about reduction completeness.
Chromatographic methods can distinguish 4,4'-Diamino-2,2'-stilbenedisulfonic acid from precursor and partially reduced species.

Spectrophotometric and chromatographic methods are useful for monitoring coloured impurities and related aromatic compounds.
These parameters are particularly significant when the downstream product is a fluorescent whitening agent intended to produce a clean white visual effect.

Moisture or loss-on-drying measurements are important when comparing lots supplied as powder or wet material.
A significant difference in water content changes the actual amount of 4,4'-Diamino-2,2'-stilbenedisulfonic acid delivered per unit mass.

A Certificate of Analysis provides batch-specific results for the selected specification parameters.
A Technical Data Sheet provides relevant product and processing characteristics, while the Safety Data Sheet provides information for workplace handling, exposure control, storage, transport, and emergency procedures.

SAFETY AND REGULATORY CONSIDERATIONS

4,4'-Diamino-2,2'-stilbenedisulfonic acid should be handled using industrial hygiene practices appropriate for an aromatic amine-containing powder.
Operations should minimize formation and inhalation of airborne particulate matter.

Direct contact with eyes and prolonged or repeated skin contact should be avoided.
Protective gloves, protective clothing, safety eyewear, and suitable workplace ventilation are appropriate controls for routine industrial handling.

Dust generated during charging, sampling, weighing, grinding, or packaging should be collected effectively.
Local exhaust ventilation can substantially reduce worker exposure and prevent accumulation of powder on equipment and surrounding surfaces.

4,4'-Diamino-2,2'-stilbenedisulfonic acid should not be confused with its downstream dyes and fluorescent whitening agents when reviewing regulatory or toxicological information.
Chemical substitution substantially changes molecular size, composition, physicochemical properties, and regulatory identity.

The free acid should likewise be distinguished from 4,4'-Diamino-2,2'-stilbenedisulfonic acid disodium salt.
The two forms are closely related chemically but possess separate registry identities and different molecular weights.

Wastewater from manufacture can contain sulfonated aromatic compounds, residual salts, reduction by-products, and other process materials.
Industrial treatment should therefore be designed around the actual composition of the manufacturing stream rather than the parent compound alone.

FIRST AID

Inhalation: Move the exposed person to fresh air and keep at rest.
Obtain medical attention if coughing, respiratory irritation, breathing discomfort, or other symptoms persist.

Skin Contact: Remove contaminated clothing and wash the affected skin thoroughly with soap and water.
Obtain medical attention if persistent irritation or other symptoms develop.

Eye Contact: Rinse cautiously with plenty of clean water for several minutes while holding the eyelids open.
Remove contact lenses when easy to do and continue rinsing until particulate material has been removed.

Ingestion: Rinse the mouth and obtain medical advice following significant ingestion.
Do not induce vomiting unless directed by qualified medical personnel.

Note to Physicians: Treatment should be based on the route and degree of exposure and the observed clinical condition.

HANDLING AND STORAGE

Handling: Avoid generating 4,4'-Diamino-2,2'-stilbenedisulfonic acid dust and prevent unnecessary skin and eye contact.
Use controlled charging and transfer procedures during industrial processing.

Ventilation: Provide effective general ventilation and local exhaust ventilation at points where powder or dust can become airborne.

Storage: Store 4,4'-Diamino-2,2'-stilbenedisulfonic acid in tightly closed containers in a cool, dry, well-ventilated location.
Protect the product from moisture, contamination, excessive heat, and prolonged intense light exposure.

Incompatibilities: Keep separated from strong oxidizing agents and other highly reactive substances capable of attacking aromatic amines or the conjugated stilbene structure.

Packaging: Use clean, dry, chemically compatible packaging that prevents moisture uptake, contamination, and release of powder during transport and storage.

PACKAGING AND PROCUREMENT CONSIDERATIONS

4,4'-Diamino-2,2'-stilbenedisulfonic acid can be procured according to active-content requirement, physical form, impurity limits, packaging size, and intended downstream chemistry.
The most suitable specification differs between optical-brightener production, dye synthesis, research use, and specialised intermediate manufacture.

The chemical form should be stated clearly during purchasing.
CAS Number 81-11-8 identifies the conventional free-acid form, while the disodium salt has a separate registry identity and different formula weight.

Optical-brightener producers can place particular emphasis on assay, residual dinitro material, colour, inorganic salt content, and moisture.
These parameters directly influence reaction stoichiometry, condensation behaviour, purification, and final brightener appearance.

Dye manufacturers can additionally require close control of compounds that interfere with tetrazotization.
Consistent diamino functionality is important because incomplete reduction products do not diazotize in the same manner as fully reduced 4,4'-Diamino-2,2'-stilbenedisulfonic acid.

Powder, wet cake, and sodium-salt solution can each provide practical advantages depending on the receiving process.
Dry material provides high active-content density, while wet or neutralized forms can reduce dissolution or neutralization requirements in aqueous manufacturing.

Package size should be matched with batch consumption and solids-handling equipment.
Appropriate packaging helps maintain product cleanliness, prevent moisture changes, and minimize dust generation during charging.

Procurement specifications can include assay, basis of assay calculation, water content, inorganic salts, residual precursor limits, appearance, colour, physical form, packaging, and required analytical documentation.
Clear definition of the final optical brightener or dye process allows the most commercially meaningful parameters to be selected.

Ataman Kimya can support enquiries for 4,4'-Diamino-2,2'-stilbenedisulfonic acid concerning grade selection, assay, impurity requirements, free-acid or salt form, technical specifications, documentation, packaging, optical-brightener applications, dye-intermediate applications, and supply requirements.
For product and procurement information, contact Ataman Kimya at +90 216 577 10 10 or [info@atamankimya.com](mailto:info@atamankimya.com).