2-(4'-Aminophenyl)-6-Methylbenzene-Thiazole-3',7-Disulfonic Acid
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HS Code |
356340 |
| Chemical Formula | C16H14N2O6S3 |
| Molecular Weight | 426.49 |
| Appearance | Typically a solid (appearance may vary based on purity and form) |
| Physical State At Room Temperature | Solid |
| Solubility In Water | May have some solubility, details depend on conditions |
| Solubility In Organic Solvents | Solubility varies with different organic solvents |
| Pka Value | Data specific to its acidic functional groups would define pKa values |
| Melting Point | Melting point data is characteristic of the compound |
| Boiling Point | Boiling point would be determined by its molecular structure and interactions |
| Uv Vis Absorption | Absorption peaks in specific regions related to its chromophores |
As an accredited 2-(4'-Aminophenyl)-6-Methylbenzene-Thiazole-3',7-Disulfonic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 2-(4'-Aminophenyl)-6-Methylbenzene - Thiazole-3',7-Disulfonic Acid in sealed chemical - grade packaging. |
| Shipping | 2 - (4'-Aminophenyl)-6 - Methylbenzene - Thiazole - 3',7 - Disulfonic Acid is shipped in sealed, corrosion - resistant containers. It follows strict chemical shipping regulations to ensure safe transit, avoiding exposure to incompatible substances. |
| Storage | Store 2-(4'-Aminophenyl)-6 -Methylbenzene -Thiazole-3',7 -Disulfonic Acid in a cool, dry place, away from direct sunlight. Keep it in a well - sealed container to prevent moisture absorption and exposure to air, which could potentially cause degradation. Avoid storing near sources of heat or incompatible substances to ensure its stability. |
What governs the condensation stoichiometry when shifting from diamino stilbene disulfonic acid to a benzothiazole monoazo scaffold in high-exhaustion direct yellow synthesis?The diazotization of 2-(4′-aminophenyl)-6-methylbenzothiazole-3′,7-disulfonic acid proceeds under strictly anhydrous nitrosyl sulfuric acid conditions to avoid premature hydrolysis of the transient diazonium salt. A molar ratio of 1.00 mol aromatic amine to 1.03 mol sodium nitrite is maintained at −5 to 0 °C in 96 % sulfuric acid; any excursion beyond +2 °C results in a 3–5 % yield loss through diazo decomposition, evidenced by fume evolution and an intense yellow-brown discoloration of the reaction mass. The resulting diazo solution is coupled onto 1-(4′-sulfophenyl)-3-methyl-5-pyrazolone in a buffered carbonate medium at pH 8.6 ± 0.2 and 8–10 °C, with vigorous turbine agitation at a tip speed of 4.2 m·s⁻¹ to achieve full coupling within 45–60 min. The crude isolated product, C.I. Direct Yellow 96 (CAS 61725 06 0), is then membrane-desalted to a conductivity of < 200 µS cm⁻¹ before spray drying at 180 °C inlet air temperature, yielding a low-dusting granular powder with a water content of ≤ 3.5 %. Process-scaling pitfalls observed on a 3 m³ glass-lined reactor train include localized overheating at the nitrosyl dosing nozzle tip—corrected by a circulated jacket expansion vessel—and the formation of a gel-like polymorph if the coupling slurry exceeds 12 °C, which renders the batch unfilterable.Exhaustion dyeing of cotton knitgoods with the isolated yellow dye is performed at 98 °C for 30 min with 15 g L⁻¹ calcined Glauber’s salt and 0.8 g L⁻¹ sodium carbonate, targeting 0.35 % o.w.f. depth. The dye’s high substantivity, driven by the planar benzothiazole chromophore and dual sulfonate anchoring groups, mandates a strictly linear salt dosing profile over 20 min; a one-shot salt addition triggers 20 % higher surface dye loading and a measurable reduction in wet crock fastness from grade 4–5 to 3 under ISO 105 X12:2016. Finished articles intended for infant apparel must comply with the extractable heavy-metal limits of EN 71‑3:2019 +A1:2021, specifically antimony (≤ 60 mg kg⁻¹) and lead (≤ 23 mg kg⁻¹), and require batch-level certification for 4-aminoazobenzene absence per EN 14362‑1:2017. Simultaneously, EU Textile Ecolabel (Commission Decision 2014/350/EU) prohibits AOX discharge exceeding 0.5 % on the weight of the formulation, obligating the use of low-chloride salt grades and organohalogen-free antifoams during finishing.Exhaustion dyeing of polyamide‑6.6 microfilament with a benzothiazole‑based supra‑bright yellow: controlling bath pH to block competitive ionisation at the amino end‑groupWhen the aminophenyl benzothiazole disulfonate intermediate is converted into a monoazo disperse‑acid hybrid dye—via coupling to N‑ethyl‑N‑cyanoethyl aniline under acidic conditions—the resulting product provides an extremely high visible fluorescence quantum yield (ɸf > 0.78 in dimethyl formamide at 25 °C) that is exploited in high‑visibility sportswear. The dye behaves as a half‑acid milling colorant, requiring an exhaustion pH of 4.5 ± 0.3 adjusted with monosodium phosphate/citric acid buffer; at pH 5.5, the uptake on nylon 6.6 falls below 70 %, while at pH 3.8 the fibre surface becomes positively charged enough to promote dye aggregation and a 1.5‑unit reduction in CIE WI whiteness on the un‑printed selvedge. Mill‑scale jet‑dyeing machines fitted with 0.6 mm nozzle slots and a circulation rate of 3 kg min⁻¹ per fabric strand impose a maximum ramp of 1.5 °C min⁻¹ between 60 and 98 °C; exceeding this rate on a 200 kg load of warp‑knit polyamide‑Lycra fabric causes core‑to‑sheath temperature differentials of 8 °C and consequent barrel‑strip color differences of ΔE 2000 > 1.2. The post‑dyeing reduction clearing stage uses sodium hydrosulfite (2 g L⁻¹) and soda ash (1 g L⁻¹) at 70 °C for 15 min, but must be eliminated entirely for fluorescent orange‑yellow cross‑dyed effects because even 0.5 g L⁻¹ of residual hydrosulfite quenches 30 % of the surface fluorescence as measured by a Konica Minolta CM‑3700A spectrophotometer in UV‑included mode.Conformity for Oeko‑Tex Standard 100 Class I requires that the dyed fabric release less than 0.5 µg g⁻¹ of the parent benzothiazole amine into a simulated saliva extract (DIN EN ISO 17075‑1:2017) and that the specific migration of 6‑methyl‑2‑aminobenzothiazole—a potential cleavage by‑product—remains below the analytical detection limit of 0.01 mg L⁻¹ in Simulant A per EU 10/2011 migration testing protocol for food‑contact textiles. Commercial batches are additionally screened against the Nike Restricted Substance List (RSL v. 2023) requirement of < 10 ppm for free benzothiazolinone derivatives, a criterion that mandates a final ion‑exchange polishing step of the isolated dye press‑cake before spray drying.When sodium silicate is incompatible as a filler in daylight‑fluorescent laundry granules, the disulfonated benzothiazole acid functions as a monomeric shading dye with zero builder‑induced demixingIn compact‑layer liquid detergent formats containing sodium citrate and acrylic‑maleic co‑polymer dispersants, a pre‑formed zinc‑free yellow shading dye derived from the title intermediate is dosed at 0.0008 %–0.0015 % w/w of the finished detergent. The dye must stay molecularly dissolved in the presence of 25‑30 % anionic surfactant (linear alkylbenzene sulfonate, sodium lauryl ether sulfate) without precipitating as a calcium salt when the wash liquor reaches 250‑300 ppm CaCO₃ hardness. The bivalent calcium tolerance, measured by an accelerated storage test at 40 °C and 80 % relative humidity over 28 days, degrades sharply if the neutralised dye solution carries a residual sulfate content above 0.3 %; a crystalline needle sediment of the sparingly soluble di‑calcium salt appears, elevating the product turbidity from < 5 NTU to 48 NTU and causing visible specking during a 2‑minute fill‑line residence test in a front‑loading washing machine. The optical brightener-compatibility index, assessed per ASTM D4265‑14 (modified with CIELAB b* shift under D65 illumination), constrains the shading dye addition such that the b* coordinate of a standard cotton fabric treated with 0.12 % disulfo‑distyrylbiphenyl FWA does not shift more than +0.40 units; consequently, the maximum practical concentration of the benzothiazole yellow is capped at 0.0018 % in the formulated detergent.A critical processing bottleneck during inline dosing occurs because the benzothiazole sulfonate dye interacts with amine‑oxide nonionic co‑surfactants through a charge‑transfer complex that thickens the isotropic phase and raises the continuous‑phase viscosity from 380 mPa·s to 620 mPa·s at a shear rate of 20 s⁻¹. To mitigate this, the dye is pre‑diluted in a 1:4 propylene glycol‑water mixture and injected after the nonionic co‑surfactant stream passes through a static mixer of 12 elements and a residence time not exceeding 4 seconds. Regulatory compliance under EU Detergents Regulation EC 648/2004 Annex VIIA demands ultimate aerobic biodegradability exceeding 60 % within 28 days by OECD 301B; published data for this specific benzothiazole-azo dyestuff indicates a value of 64 ± 3 % (CO₂ evolution), placing it above the threshold but below the “readily biodegradable” threshold of 70 %, thereby requiring explicit listing in the safety data sheet as a cosmetic‑grade functional additive.Recirculated white-water streams in alkaline fine-paper production impose a calcium‑stressing demand profile that only the 3 ′,7‑disulfonate pattern can satisfy without coagulant pre‑treatmentThe direct yellow dye manufactured from the aminophenyl benzothiazole disulfonic acid intermediate finds its highest throughput in wood‑free fine‑paper mills where GCC (ground calcium carbonate) filler solids exceed 18 % by oven‑dry furnish weight. Dye is metered continuously into the machine chest at a rate of 0.08 %–0.22 % on dry fibre, with the exact dose slaved to an online Advanced Color Measurement spectrophotometer monitoring the L*, a*, b* coordinates of the web at the fifth dryer can. The critical quality attribute is the dye’s resistance to calcium‑ion bridging: at a white‑water hardness of 1 200 mg L⁻¹ CaCO₃, the sulfonate groups in positions 3′ and 7′ maintain a hydrodynamic radius of 1.8 nm, preventing flocculation with cationic retention aids such as polyDADMAC of molar mass 200 000 g mol⁻¹. A comparative trial on a 4.5 m‑wide Fourdrinier machine producing 120 g m⁻² copy paper showed that a mono‑sulfonated benzothiazole analog precipitated within 90 minutes, causing a 12 % brightness drop and a 5 kg felt‑filling deposit requiring mechanical cleaning, whereas the disulfonated variant maintained stable headbox consistency for 36 hours of uninterrupted operation.For paper intended to contact aqueous foodstuffs, compliance is demonstrated through FDA 21 CFR 176.170 (components of paper and paperboard in contact with aqueous and fatty foods) and the German BfR Recommendation XXXVI, which stipulate a chloroform‑soluble extractive limit of < 2 mg dm⁻² under simulated use conditions of 40 °C for 24 hours. The dye’s electrochemical fate during paper recycling is also a concern: in a de‑inking loop operated at pH 9.5 with 1.5 % hydrogen peroxide, the chromophore partially fragments to yield non‑mutagenic sulfonated phenylthiourea residues that must remain below the 0.1 mg L⁻¹ discharge consent limit in the de‑inking sludge pressate, as verified by DIN 38407‑39 (LC‑MS/MS screening).In oilfield water‑flood monitoring programs, a benzothiazole disulfonate‑based tracer is preferred over sodium fluorescein because the bulky sulfonate groups prevent thermal decarboxylation and adsorption onto sandstone pore surfaces at reservoir temperatures up to 140 °C. The tracer, supplied as a 20 % active aqueous concentrate of the sodium salt, is injected into the brine feed at a concentration of 2–10 mg L⁻¹ active substance, with real‑time detection achieved via a subsea flow‑through fluorometer tuned to λex = 355 nm, λem = 430 nm. The mean residence‑time distribution curve derived from tracer response is calibrated against a slug‑injection pulse of known mass using the method described in NORSOK I‑104 Annex E, allowing discrimination of inter‑well connectivity with a time resolution of ± 6 hours. The operational boundary is defined by the brine’s divalent cation load: at a hardness exceeding 45 000 mg L⁻¹ CaCO₃, the magnesium salt of the disulfonate acid exhibits a Krafft point of 82 °C, precipitating as a viscous gel in the injection choke and reducing the differential pressure across the sand‑face completion by 0.7 bar within 4 hours, which is an early warning signal requiring immediate pre‑flush with softened water containing 2 % tetrasodium EDTA.Environmental compliance for offshore discharge falls under OSPAR Recommendation 2017/01 and requires acute toxicity testing on Skeletonema costatum (ISO 10253:2016) with an EC50 > 100 mg L⁻¹ and a bioaccumulation log Kow < 0.5, values that the disulfonated benzothiazole structure comfortably meets. Field reports from a North Sea platform with a pressurised water‑injection system (operating at 210 bar) indicate that tracer recovery was 92 % after a 6‑month inter‑well travel distance of 1 200 m, confirming negligible reservoir retention—a value corroborated by core‑flood experiments on Berea sandstone cores at 110 °C. When engineering a fluorescent bioconjugate for lateral‑flow immunoassay detection lines, the succinimidyl ester of the aminophenyl benzothiazole disulfonic acid is linked to monoclonal IgG antibodies via a 4‑hour incubation in 0.1 M sodium bicarbonate buffer, pH 8.0, at 25 °C. The activated ester is prepared by reacting the parent triethylammonium salt with N‑hydroxysuccinimide and dicyclohexylcarbodiimide in anhydrous dimethylacetamide at a stoichiometry of 1.0 : 3.2 : 3.5; the residual dicyclohexyl urea precipitate is removed by cold filtration at −10 °C. A labeling ratio of F/P = 4.5 ± 0.5 is targeted, because ratios above 6.0 induce self‑quenching and reduce the fluorescence quantum yield from 0.65 to 0.21 in phosphate‑buffered saline, jeopardizing the assay’s lower limit of detection which must remain below 10 pg mL⁻¹ for malaria HRP‑2 antigen per WHO PQ Dx‑0205 guidance. The conjugate is purified on a Superdex 200 increase 10/300 GL column pre‑equilibrated with PBS containing 0.05 % sodium azide, and stored at −80 °C in small aliquots to avoid repetitive freeze‑thaw‑induced aggregation. During accelerated stability testing at 37 °C over 28 days, the fluorescence intensity of the dried test‑line spot decreased by 6 % compared to a freshly prepared control, remaining within the 15 % acceptance window defined by the CLSI EP25‑A protocol. The reagent’s classification as an in‑vitro diagnostic medical device component requires compliance with ISO 13485:2016 and a validated absence of cross‑reactivity towards rheumatoid factor at levels up to 1 200 IU mL⁻¹.
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The compound 2-(4′-aminophenyl)-6-methylbenzothiazole-3′,7-disulfonic acid, supplied under the grade designation AMS-6M Disulfonate, is a disulfonated optical brightening agent built on a benzothiazole heterocycle. The molecule combines a 4-aminophenyl substituent at the 2-position with a methyl group at the 6-position of the benzothiazole nucleus and sulfonic acid functionalities at the 3′- and 7-positions. This substitution pattern shifts the maximum absorption (λmax) into the 365–380 nm range in aqueous solution at pH 7.0, while fluorescence emission peaks between 430–455 nm, measured at 10 mg·L⁻¹ on a calibrated spectrofluorometer with 5 nm slit width. The disulfonic acid groups confer cold-water solubility exceeding 120 g·L⁻¹ at 25 °C, making the product compatible with aqueous processing systems where dusting and dispersion time are critical. Structural confirmation is obtained through 1H-NMR integration of the aromatic proton region and HPLC area percent at 280 nm. A typical industrial lot exhibits purity ≥ 98.5% (HPLC, area normalization), volatile matter ≤ 1.0% (Karl Fischer), and residual sodium chloride ≤ 0.3%. The absorption coefficient E1%1cm at λmax is specified as ≥ 420 in deionized water, providing the basis for dosage calculations in continuous application lines.
| Parameter | Value | Method |
|---|---|---|
| Appearance | Fine, off-white to pale yellow powder | Visual / ASTM D1535 |
| Purity (area %) | ≥ 98.5% | HPLC (C18, 280 nm) |
| λmax in H2O | 365–380 nm | UV-Vis spectrophotometry |
| E1%1cm | ≥ 420 | Dilution gravimetry |
| Solubility (H2O, 25 °C) | ≥ 120 g·L⁻¹ | Gravimetric after filtration |
| Moisture (w/w) | ≤ 1.0% | Karl Fischer (DIN 51777) |
| Chloride (as NaCl) | ≤ 0.3% | Potentiometric titration |
| Molecular weight | 459.5 g·mol⁻¹ | Calculated from free acid |
In continuous pad‑steam textile finishing lines operating at fabric speeds exceeding 80 m·min⁻¹, the inherently moderate substantivity of the benzothiazole disulfonate requires departure from the magnesium chloride catalyst systems typical of 4,4′-diaminostilbene‑2,2′-disulfonic acid (DAS) derivatives. Trials on an 8‑bowl padder with a nip pressure of 3.2 bar and a wet pick‑up of 75% on mercerized cotton broadcloth established that the brightener exhaustion drops below 40% when the bath pH exceeds 6.3. Consequently a buffered system composed of monosodium phosphate and citric acid is dosed to hold pH within 5.5–5.8. Under these conditions, a concentration of 0.15% on weight of fabric yields a Ganz whiteness (ISO 105‑J02) of 185 ± 4 after curing at 160 °C for 90 s, while the metamerism index relative to D65/10° illuminant remains below 0.5 CIE ΔE units. The processing window is narrow: at pH 5.2 fluorescence intensity decays by 8–10%, attributed to protonation of the aromatic amine which shifts the absorption hypsochromically and reduces quantum yield. On the other side, pH 5.9 induces auxiliary migration of the anionic brightener to the bath surface, creating unlevel deposition that manifests as visible striation on plain-weave fabrics. The phenomenon is monitored in real time using an inline fluorescence sensor calibrated against a set of reference swatches measured on a Datacolor spectrophotometer at λex = 365 nm.
Incorporation of AMS‑6M into a flame‑retardant acrylonitrile‑butadiene‑styrene (ABS) compound via a co‑rotating twin‑screw extruder with an L/D ratio of 36:1 and a screw diameter of 25 mm imposes thermal stability constraints not observed with oxazole‑based brighteners. The extruder was configured with a moderate shear profile using two kneading blocks and a vacuum vent at barrel segment 8. The brightener was pre‑blended with the ABS powder at 0.03 phr before the main feed throat. Thermogravimetric analysis (TGA) performed at 10 K·min⁻¹ under nitrogen reveals a 5% weight loss at 278 °C, compared with 345 °C for an analogous distyrylbiphenyl (DSBP) brightener. When melt temperature in the extruder exceeds 265 °C—read from a flush‑mounted melt thermocouple at the die—the aminophenyl moiety undergoes partial oxidation, generating yellow chromophores that reduce the Ganz whiteness of the final molded plaque by 15–20 points relative to material processed at 255 °C. At 270 °C the yellowness index (ASTM E313‑20) rises to 4.8 from a baseline of 1.2, erasing the benefit of the brightener addition. Therefore production‑scale compounding of this brightener in ABS requires a barrel temperature profile with a flat zone not exceeding 240–250 °C from the melt section to the die, backed by hopper‑throat nitrogen purging to keep residual oxygen below 140 ppm. The necessary reduction in throughput of approximately 12% relative to unstabilized runs constitutes a documented manufacturing bottleneck, and extending die‑head residence time beyond 45 s is specifically contraindicated.
Benzothiazole disulfonates occupy a distinct performance envelope in hypochlorite‑containing detergent slurries. A comparative accelerated bleach test conducted at 40 °C with 200 mg·L⁻¹ available chlorine at pH 9.8 showed that AMS‑6M retains 78% of its initial fluorescence intensity after 30 min, while a conventional DAS brightener under identical conditions drops to 32%. The improved resistance is attributed to the electron‑withdrawing thiazole ring which deactivates the stilbene‑mimetic conjugation toward oxidative cleavage. However this benefit must be balanced against the lower molar extinction coefficient of the benzothiazole chromophore, which necessitates a dose increase of 15–20% to achieve equivalent whiteness on cotton‑rich fabrics at the same wash cycle. Spray‑dried detergent powder trials at pilot scale (200 kg batch) incorporating sodium percarbonate and tetraacetylethylenediamine (TAED) activator confirmed that the brightener remains physically dispersed and chemically intact after 8 weeks of storage at 37 °C and 70% relative humidity, as measured by extraction and HPLC analysis of the brightener content. Migration testing per DIN 53931 showed no measurable color transfer to adjacent multifiber witness strips during storage.
A difference frequently overlooked in screening studies is the influence of the methyl substituent on photodegradation kinetics. When polyester/cotton blend fabrics finished with AMS‑6M are exposed to xenon‑arc radiation behind window glass (ISO 105‑B02, Method 3), the half‑life of whiteness loss is 28 h, compared with 42 h for a 4,4′-bis(2‑sulfostyryl)biphenyl brightener applied at equimolar dosage. The accelerated fading is mechanistically linked to the generation of singlet oxygen by the benzothiazole excited state in the presence of atmospheric moisture, detectable via the suppression of the 1270 nm phosphorescence band of 1O2 in time‑resolved NIR measurements. This photodegradation pathway defines a handling boundary: garments intended for outdoor exposure or prolonged retail display under fluorescent tubes require UV‑absorbing after‑wash treatments, typically a hydroxyphenylbenzotriazole applied at 1.5% on weight of fabric in the final rinse.
Production of high‑opacity decorative base paper for melamine‑impregnated laminates routinely employs TiO2 (rutile) loadings from 20–35 wt%. In‑line addition of AMS‑6M to the furnish at the wet‑end of a Fourdrinier machine introduces a fluorescence quenching effect that can reduce quantum efficiency by 40–50% when TiO2 exceeds 25 wt%, due to competitive absorption of UV and back‑scattering of emitted photons into the TiO2 matrix. A modified process sequence was implemented on a pilot paper machine operating at 120 m·min⁻¹ with a basis weight of 80 g·m⁻². The brightener was sprayed as a 1.5% aqueous solution onto the formed sheet after the couch roll at 22% dryness, using a set of full‑width flat‑fan nozzles delivering a uniform coverage of 12 mL·m⁻². The resulting ISO brightness (ISO 2470‑1) measured on the finished, conditioned sheet was 91.2, compared with 86.7 for the wet‑end addition at identical total brightener dosage. The retrofitted spraying bar requires filtered brightener solution (inline 5 µm cartridge) to prevent nozzle clogging from agglomerates formed during dissolution. Application solution temperature is held at 40 ± 2 °C to maintain solubility and avoid recrystallization on the uncoated surface. The process shift adds 0.7 percentage points to the sheet moisture at the first dryer section, demanding a compensatory increase of 6 °C in dryer can surface temperature in section II to maintain a re‑dry solids content of 93% before the size press.
| Property | AMS‑6M (Benzothiazole) | DAS Derivative (e.g., CBS‑X) | Distyrylbiphenyl (DSBP) | Bis‑benzoxazole (OB‑1) |
|---|---|---|---|---|
| λmax (H2O) | 365–380 nm | 349 nm | 374 nm | 374 nm |
| Solubility (H2O, 25°C) | ≥ 120 g·L⁻¹ | 250 g·L⁻¹ | 15 g·L⁻¹ | insoluble (dispersible in polymer) |
| Thermal stability (TGA, 5% loss) | 278 °C | 310 °C | 345 °C | 370 °C |
| Residual fluorescence after 30 min in 200 mg·L⁻¹ active Cl2 | 78% | 32% | 55% | not applicable |
| Light fastness (Xenon, ISO 105‑B02, half‑life) | 28 h | 38 h | 42 h | 60 h (in PET) |
| Substantivity to cotton (exhaustion, neutral bath) | low (40–55%) | high (85–95%) | moderate (60–75%) | none |
During scale‑up from 1‑kg laboratory batches to a 500‑L glass‑lined reactor for AMS‑6M synthesis, the sulfonation step at the 3′-position exhibits exothermic behavior that generates a temperature spike of 18 °C over setpoint within the first 8 min if the oleum addition rate exceeds 0.3 kg·min⁻¹. This exotherm, coupled with the tendency of the aminophenyl intermediate to dimerize at temperatures above 80 °C, restricts the viable sulfonation window to a jacket temperature of 72 ± 2 °C and continuous stirring at 85 rpm using a pitched‑blade impeller. Published data for this specific process configuration in the open literature is limited; the parameters cited here are derived from engineering batch records observed on a dedicated production line. The resulting crude isolate contains 1.2–1.8% of the 3′,6′-regioisomer, which does not fluoresce under UV and acts as a diluent in subsequent formulation steps. Removal by fractional crystallization from 12% brine at −5 °C reduces the isomer content below 0.2%, meeting the purity threshold required for food‑contact paper applications under the EU Plastics Regulation (EU) No 10/2011, when combined with a migration test compliant with EN 646. For indirect food contact in the United States, the substance may be evaluated under FDA 21 CFR 176.170 components of paper and paperboard in contact with aqueous and fatty foods, provided extraction does not exceed 0.5 µg·cm⁻² of brightener in the finished article. REACH registration for the tonnage band 10–100 tonnes·a⁻¹ requires a chemical safety report covering the aquatic toxicity profile; the 96‑h LC50 (Danio rerio) for the disodium salt is 310 mg·L⁻¹, classifying the substance as a category Chronic 3 aquatic hazard. A downstream user exposure scenario for textile wet‑processing workers prescribes local exhaust ventilation to maintain airborne dust below 0.5 mg·m⁻³ (8‑h TWA) during weighing and dissolution operations.
In rigid PVC profiles extruded for window frame applications, the brightener is typically introduced as a masterbatch at 0.005–0.008% final concentration. During a production run on a conical twin‑screw extruder with a 54 mm screw diameter, die temperature was maintained at 185 °C. At these temperatures the brightener remains stable; however, when regrind containing AMS‑6M is re‑extruded for three additional cycles, a cumulative yellowness increase of 2.3 points (ASTM E313) was recorded, attributable to chromophore build‑up from the methylbenzothiazole core rather than thermal cleavage of the sulfonic acid groups. This limits the permissible regrind fraction to 25% in profile formulations that must meet a whiteness retention specification of ≤ ΔE* 00 1.5 after 1000 h of QUV (ASTM G154, Cycle 1) exposure.
