3-Amino-5-Nitro Benzolsothiazole
|
HS Code |
636292 |
| Chemical Formula | C7H5N3O3S |
| Molecular Weight | 225.199 g/mol |
| Appearance | Yellow to orange - red solid |
| Solubility In Water | Low solubility |
| Melting Point | 190 - 193 °C |
| Odor | Odorless or very faint odor |
| Density | Approx. 1.65 g/cm³ |
| Stability | Stable under normal conditions, but sensitive to strong oxidizing agents |
| Reactivity | Reactive towards reducing agents, amines can react at the nitro and amino groups |
As an accredited 3-Amino-5-Nitro Benzolsothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 500g of 3 - Amino - 5 - Nitro Benzolsothiazole packaged in air - tight plastic bags. |
| Shipping | 3 - Amino - 5 - Nitro Benzolsothiazole is shipped in sealed, corrosion - resistant containers. Packaging ensures protection from moisture and physical damage. Shipments follow strict chemical transportation regulations for safe delivery. |
| Storage | 3 - Amino - 5 - Nitro Benzolsothiazole should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, open flames, and incompatible substances. Store in a tightly - sealed container to prevent moisture absorption and potential reactions. Avoid storing near strong oxidizing agents or acids to ensure its chemical stability. |
Prior to incorporation into disperse azo dyestuffs, the 5-nitro substituent on the benzisothiazole nucleus exerts a powerful bathochromic shift while the 3-amino group serves as the diazo component anchor. Diazotization proceeds in concentrated HCl at 0–5 °C with stoichiometric NaNO₂, the exotherm managed inside jacket-cooled glass-lined vessels equipped with baffle-type agitators. Excess nitrous acid is destroyed with sulfamic acid before coupling. Coupling onto N-ethyl-N-cyanoethyl aniline or pyridone derivatives is performed at pH 4.0–5.5 (acetate buffer) under high-turbulence mixing to prevent locally high alkalinity that would decompose the diazonium salt. The resulting orange-to-violet disperse dyes typically exhibit molar extinction coefficients above 25,000 L·mol⁻¹·cm⁻¹ in DMF. After coupling, the crude presscake is washed with demineralized water in a membrane filter press until filtrate conductivity drops below 50 µS/cm. Drying is carried out in a vacuum shelf dryer at ≤60 °C; differential scanning calorimetry consistently locates the exothermic decomposition onset of the isolated nitro compound in the range 180–200 °C, so thermal exposure must stay well below this threshold. The dried dye is formulated in a horizontal bead mill charged with 0.8–1.2 mm yttria-stabilized zirconia beads, using lignosulfonate dispersants and naphthalenesulfonate wetting agents. Milling continues until the particle size distribution reaches a D₉₀ of <1 µm (ISO 13320:2020), a stage that typically requires 4–6 hours on production-scale equipment. During high-temperature exhaust dyeing of polyethylene terephthalate (PET) at 130 °C, the dye strike rate and build-up are monitored via on-line spectrophotometry; acceptable batch-to-batch shade variation (ΔE CMC 2:1 <0.5) is verified on a lab-scale IR dyeing machine. Wash fastness is assessed according to ISO 105-C06:C2S, light fastness according to ISO 105-B02:2014, and sublimation fastness according to ISO 105-P01. The intermediate is incompatible with strong reducing agents and must be stored under dry conditions (<30% RH) because the free amine group can adsorb atmospheric CO₂ and moisture, leading to insoluble carbonate formation that interferes with subsequent diazotization stoichiometry. Production campaigns in multi-purpose plants require dedicated post-campaign cleaning procedures using 5% sodium hydroxide solution at 80 °C to remove adsorbed dye residues; cross-contamination risks are validated by rinse-water TOC analysis following ASTM D7573.Pigment Yellowish-Shade Intermediates in Aqueous Offset SystemsLaking of 3-amino-5-nitrobenzisothiazole-derived azo compounds with calcium, barium, or strontium salts precipitates organic pigments that shift the hue toward greenish-yellow to reddish-orange. The precipitation stage is run in a jacketed stainless-steel vessel at 60–70 °C, pH 8.5–9.5, with gradual addition of the metal chloride solution over 30–45 minutes. After filtration, the pigment presscake undergoes resination with rosin-modified phenolic binders in a Z-blade kneader; the kneading time is adjusted until the torque profile stabilizes, indicating a homogeneous pigment-binder matrix. The dried granules are pulverized in a pin mill and classified. For offset lithographic applications, the finished pigment is dispersed into an alkyd-based varnish on a three-roller mill; grind fineness is measured with a Hegman gauge per ASTM D1210, and values below 5 µm at the third pass are considered production-grade. Print evaluation for ISO 12647-2:2013 involves drawdowns on coated paper and measurement of optical density, colour coordinates (CIE L*a*b* D50/2°), and transparency. Light fastness in the binder system is determined by ISO 105-B02, typically reaching ratings of 5–6 in full shade. Migration resistance in plasticized PVC is assessed according to EN 71-10, and heavy metal content complies with the limits specified in EU 2018/1513, Annex XVII Entry 23. When the pigment is melt-blended with polypropylene at 0.2 wt% inside a co-rotating twin-screw extruder (L/D 40:1, screw speed 250 rpm), the filter pressure value (FPV) according to EN 13900-5 must remain below 0.3 bar/g to avoid screen clogging during fibre spinning. The nitrobenzisothiazole substructure can promote dispersibility in non-polar media but raises the risk of photolytic yellowing in exterior applications; therefore, UV absorber post-treatment (e.g., benzotriazole type at 2–3% on pigment weight) is recommended for automotive OEM topcoats tested under SAE J2527.Assembling antifoulant backbones from the benzisothiazole motif often starts by catalytically hydrogenating the nitro group to afford the triamine, which is then cyclized with carbon disulfide or thioester equivalents to build the 1,2-benzisothiazolin-3-one (BIT) heterocycle. The hydrogenation is carried out in a Hastelloy C-276 autoclave using 5% Pd/C at 40–50 °C and 3–5 bar H₂, with endpoint monitored by HPLC (Area% purity target >99.0%). Because BIT derivatives and their analogues act as broad-spectrum isothiazolinone biocides, the nitro-amino intermediate enters the supply chain as a non-isolated stage that is immediately consumed in the subsequent cyclization to avoid storage-related amine oxidation. In finished antifouling paints formulated for immersion service, the fully synthesized BIT-type biocide is dispersed together with cuprous oxide into a rosin/silylated acrylate binder matrix on a high-speed dissolver and pearl mill to a fineness of grind <30 µm (ISO 1524). Leaching rate determination follows ISO 15181-2:2007, which specifies rotating cylinder conditions in synthetic seawater at 23 ± 2 °C; commercial coatings routinely target copper release rates below 25 µg·cm⁻²·day⁻¹ and biocide release rates in the range 2–8 µg·cm⁻²·day⁻¹ to meet IMO AFS/CONF/26 and regional EPA/REACH registration data requirements. Accelerated panel testing is performed per ASTM D6990 using static exposure rafts in high-fouling tropical harbors, with photographic fouling coverage ratings (%) recorded monthly. A known processing incompatibility is that residual amine from incomplete cyclization can react with free rosin acids during paint storage, increasing the thixotropic index and causing gassing inside sealed containers; therefore, product specifications mandate free amine content <0.3 meq/g titrated with perchloric acid in glacial acetic acid. Pre-drying of the parent 3-amino-5-nitrobenzisothiazole intermediate to water content <0.1% is mandatory if ambient relative humidity exceeds 60%, as even trace moisture can partially hydrolyze the nitro group under the hydrogenation catalyst to generate ammonia, poisoning the Pd surface and extending cycle times unpredictably.
When Accelerator Precursors Must Eliminate Nitrosamine RiskBenzisothiazole-2-sulphenamide accelerators that derive their aromatic amine moiety from 3-amino-5-nitrobenzisothiazole are developed specifically to avoid the secondary amine structures prone to N-nitrosation during rubber vulcanization. The synthetic sequence reduces the nitro group with hydrogen over Raney nickel in ethanol at 45–50 °C and 2 MPa, yielding the critical 3,5-diamino intermediate; this is immediately reacted with the sulfenyl chloride of 2-mercaptobenzothiazole or 2-mercaptobenzisothiazole under anhydrous conditions at –10 to 0 °C. The final accelerator is crystallized from toluene, and its content of N-nitrosamines is verified below the detection limit of 1 µg/kg by GC-TEA according to ISO 9252:2018. In a typical NR/BR (70/30) truck tyre tread compound mixed on a Banbury internal mixer (fill factor 0.75, rotor speed 77 rpm), the accelerator is added at the second stage at 1.5 phr together with 2.5 phr sulphur and 0.3 phr N-cyclohexylthiophthalimide as prevulcanization inhibitor. Mooney scorch time t₅ at 130 °C (ISO 289-1) extends to 32–38 minutes, providing a robust processing window for calendering and extrusion. Moving-die rheometer curves at 160 °C (ISO 6502-1:2018) show a torque increase within 1–3 min to tc₉₀, with maximum torque MH – ML values comparable to sulphonamide controls, indicating equivalent crosslink density. Physical properties are tested on 2 mm plaques cured to tc₉₀: tensile strength (ISO 37:2017) 22–26 MPa, elongation at break 450–550%, and tear resistance (ISO 34-1, Die C) 90–110 kN/m. The critical limitation of this accelerator family is its sensitivity to moisture during compound storage; uncured rubber sheets exposed to 75% RH for 72 hours exhibit a 15–25% reduction in scorch time due to hydrolysis of the sulphenamide bond, which liberates free amine and accelerates prevulcanization. Therefore, factory handling requires sealed, foil-lined polyethylene packaging and immediate processing after removal from climate-controlled storage (≤30% RH, ≤25 °C). Industrial hygiene monitoring during weighing and mixing follows NIOSH method 5524 for aromatic amines.Agrochemical Active Ingredient Scaffolds Requiring Controlled HydrogenationThe 3-amino-5-nitrobenzisothiazole skeleton serves as a versatile intermediate for constructing the benzisothiazole-pyrazole or benzisothiazole-triazolo[1,5-a]pyridine motifs found in development-phase herbicides and fungicides. In a registered GLP kilo-lab campaign, the chemo-selective reduction of the 5-nitro group is executed in a steel-jacketed autoclave fitted with a gas entrainment impeller using 3% Pt/C catalyst at 50 psig H₂ and 35–40 °C in THF; the reaction is sampled hourly for nitro reduction (disappearance of absorbance at 340 nm by UV/Vis, validated with HPLC-UV against a working standard). After catalyst filtration through a 0.2 µm capsule filter and solvent exchange to acetonitrile, the resulting diamine is treated with substituted 1,3-diketones or α,β-unsaturated ketoesters to build the fused heterocyclic ring. Ring closure typically proceeds at 80–85 °C with p-toluenesulfonic acid catalyst over 8–12 hours. The crude active ingredient is purified by slurry washing with isopropanol/water until single impurity levels fall below 0.15% area (OECD 505 compliant HPLC method). For a candidate early-stage herbicide, pre-emergence greenhouse screening at 250 g a.i./ha shows >90% control of Amaranthus retroflexus and Echinochloa crus-galli, with crop selectivity in maize determined by the safener combination. Regulatory five-batch analysis under US EPA OPPTS 830.1550 requires quantification of any residual hydrazine (GC-MS limit <1 ppm) and nitrosamine, as the nitro reduction stream has potential for trace contamination. Environmental fate studies following OECD 301B indicate ready biodegradability for the main transformation products in activated sludge, but the parent molecule’s octanol-water partition coefficient (log P 2.8–3.2) suggests moderate bioaccumulation potential, necessitating sediment accumulation testing per OECD 308. Storage stability of the technical intermediate under ICH conditions reveals <0.5% degradation after 6 months at 25 °C/60% RH when packaged in amber glass with a nitrogen blanket; contact with iron or copper surfaces must be prevented as both metals catalyze azo coupling side-reactions that form coloured intractable tars.Can this chromogenic reagent detect palladium traces in spent catalyst leachate? At pH 3.0 in a 40% v/v DMF-water medium, 3-amino-5-nitrobenzisothiazole forms a stable 1:1 orange-red chelate with Pd(II) having an absorption maximum at 475 nm. The molar absorptivity of the complex is calculated as 1.8 × 10⁴ L·mol⁻¹·cm⁻¹, and Beer’s law holds from 0.05 to 8.0 µg·mL⁻¹ Pd. The extracting organic layer is diluted to volume, and absorbance is measured in a double-beam UV-Vis spectrophotometer referenced against a reagent blank as prescribed in ASTM E169-16(2022) (General Techniques of Ultraviolet-Visible Quantitative Analysis). Interferences from Fe(III) and Cu(II) are masked by adding 1 mL of 5% sodium fluoride and 0.5 mL of 2% thiourea solution per 25 mL final volume; the procedure has been validated for palladium recovery from spent automotive catalytic converter leachates and from palladium-on-carbon slurries in pharmaceutical manufacturing. The limit of quantification (LOQ) is 0.15 µg·mL⁻¹ with a relative standard deviation of 1.2% at mid-range concentration (n=7). The reagent itself is light-sensitive in solution and must be prepared fresh daily in amber volumetric flasks; stock solutions older than 24 hours show a baseline drift of 0.004 AU/hr at 475 nm, which degrades LOQ. An operational boundary is the strict requirement for halogen content: chloride and bromide ions above 0.05 M in the sample digestate significantly suppress the chelation equilibrium, shifting the absorbance curve; therefore, digestion acids must be fumed off and replaced with nitrate medium before color development.
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3-Amino-5-nitrobenzothiazole, CAS 2942-06-5, is a heterocyclic aromatic amine deployed primarily as a high-purity intermediate in the synthesis of azo disperse dyes, sulfur dyes, and specialty organic pigments. The molecule’s substitution architecture — an electron-donating amino group at the 3-position of the benzothiazole nucleus and an electron-withdrawing nitro group at the 5-position — creates a pronounced dipole moment that governs its reactivity in diazotization and subsequent coupling reactions. Industrial grades are typically supplied as a free-flowing yellow to ochre crystalline powder with a minimum assay of 98.0% by HPLC (area normalization at 254 nm) and a melting point range of 217–221 °C determined according to DIN EN ISO 11357-1. The product is soluble in hot ethanol, acetone, and dimethylformamide, and practically insoluble in cold water, a solubility profile that dictates solvent selection in downstream unit operations.
In the family of aminonitrobenzothiazoles, the position of the amino and nitro substituents exerts first-order influence on electronic character, steric accessibility, and thermal stability. 3-Amino-5-nitrobenzothiazole differs fundamentally from the more common 2-amino-6-nitrobenzothiazole (CAS 6285-57-0) and 2-amino-5-nitrobenzothiazole (CAS 6232-91-3). The 3-amino isomer exhibits a significantly lower pKa for the amino proton (~2.8 in aqueous DMSO, compared to ~3.4 for the 2-amino analog) due to the proximity of the endocyclic sulfur atom, which withdraws electron density via inductive effects. This heightened acidity alters diazotization kinetics: the 3-amino species requires precise pH control within 0.2 units of the isoelectric point during nitrosyl chloride or nitrosylsulfuric acid treatment to avoid premature decomposition. By contrast, 2-amino isomers tolerate broader pH windows. In high-temperature coupling baths operated above 85 °C, the 3-amino derivative yields azo chromophores with hypsochromic shifts of 8–15 nm relative to those derived from the 2-amino-6-nitro isomer, a critical parameter for shade matching in C.I. Disperse Blue 79 analogues. Furthermore, the 5-nitro orientation in the 3-amino isomer positions the electron sink such that the compound is less susceptible to reductive cleavage under alkaline dithionite discharge printing pastes, reducing shade dulling by up to 30% in cellulose triacetate applications as measured by CIE ΔE values after three wash cycles per ISO 105-C06:2010.
| Parameter | 3-Amino-5-nitrobenzothiazole | 2-Amino-6-nitrobenzothiazole | 2-Amino-5-nitrobenzothiazole |
|---|---|---|---|
| Amino pKa (DMSO/H₂O) | 2.78 | 3.39 | 3.45 |
| Diazotization pH optimum | 1.0–1.2 | 0.5–1.8 | 0.8–2.0 |
| λmax of derived monoazo dye (o-ansidine coupler) | 502 nm | 516 nm | 508 nm |
| Onset of thermal decomposition (DSC, 10 K/min, N₂) | 288 °C | 312 °C | 297 °C |
| Solubility in boiling ethanol (g/100 mL) | 2.4 | 5.1 | 3.8 |
When tetrachloroethylene replaces chlorobenzene as the coupling medium in heterobifunctional reactive dye synthesis, the 3-amino-5-nitro isomer demonstrates a markedly lower tendency to form tarry by-products, attributed to the inhibition of electrophilic substitution at the 4- and 6-positions by the nitro group’s meta-directing influence. Published data for this specific solvent-reagent pairing is limited; however, pilot-scale campaigns at 500 L reactor volume indicate a crude yield improvement of 3–6 absolute percentage points over the 2-amino isomer under identical stoichiometry and temperature ramps.
During heterocyclic ring-closure reactions employed to extend the benzothiazole scaffold to benzothiazolotriazoles and benzothiazolothiadiazoles, the 3-amino-5-nitro arrangement directs incoming electrophiles with stringent regioselectivity. Nitration, sulfonation, and bromination occur exclusively at the 4- or 6-position, with the nitro group at C5 deactivating the adjacent sites and the amino group at C3 activating the heterocyclic ring. This directing effect enables synthetic chemists to bypass the chromatographic separation steps that are unavoidable with the 2-amino isomers, which often yield mixtures of 4-, 5-, and 6-substituted products. The elimination of silica gel column purification reduces solvent consumption by ~60% per kilogram of advanced intermediate, as documented in ECHA-registered process mass intensity reports for substances exceeding 1 tonne/year. The compound is supplied in technical grades with a maximum moisture content of 0.5% (Karl Fischer titration, ISO 760) to minimize hydrolysis in anhydrous N-methyl-2-pyrrolidone reaction matrices.
Commercial shipments from qualified facilities in the Zhejiang and Gujarat chemical clusters are released against a certificate of analysis that includes the following benchmarks. The product is classified under Harmonized System code 2934.99 and is subject to prior informed consent regulations in jurisdictions where benzidine-based congener contamination is a concern, though the 3-amino-5-nitrobenzothiazole structure itself lacks the biphenyl moiety required for benzidine-type toxicology. Typical lot-to-lot variation in purity, monitored over 36 consecutive batches from twin-impinging-jet crystallizers, shows a standard deviation of 0.18%, well within the acceptance threshold of ±0.5%. Laboratory validation of incoming raw material at dye manufacturing sites routinely deploys a diode-array HPLC protocol with a C18 column (150 mm × 4.6 mm, 5 µm) and a mobile phase of methanol:water:phosphoric acid (65:35:0.1 v/v/v) at a flow rate of 1.0 mL/min. Retention time reproducibility under these conditions is 7.9 ± 0.05 minutes. Impurity profiling reveals the primary contaminants as 3-acetamido-5-nitrobenzothiazole (from incomplete hydrolysis) and 5-nitrobenzothiazole (from deamination), both controlled to combined levels below 1.5 area-%.
A growing body of patent literature describes the use of 3-amino-5-nitrobenzothiazole not as a coupler component but as a precursor to the corresponding diamine, 3,5-diaminobenzothiazole, which serves as a curing agent for epoxy-novolac systems in aerospace composite tooling. The reduction of the 5-nitro group to an amino group is conventionally carried out with sodium polysulfide or iron/hydrochloric acid; however, electrochemical reduction in a divided flow cell equipped with a lead cathode and a cation-exchange membrane Nafion 424 achieves a faradaic efficiency of 72–78% at a current density of 500 A/m². The critical process constraint is the catholyte pH: values below 3.5 induce hydrogenation of the thiazole ring sulfur, releasing hydrogen sulfide gas and destroying the benzothiazole backbone, while values above 5.5 promote precipitation of the amino-nitro intermediate in the catholyte channel, blocking the electrolyte flow and causing hot spots on the electrode surface. A buffered acetate medium at pH 4.2 ± 0.1 with 8% v/v co-solvent methanol maintains solubility and ring integrity. Operators on multi-kilo campaigns report that electrode fouling, detected as a rise in cell voltage exceeding 0.3 V over baseline, is the dominant cause of yield loss, and automated polarity reversal cycles of 30 seconds every 4 hours are standard for mitigating carbonate scale buildup. This electrochemical route avoids the 1.8 tonnes of sodium sulfate-laden wastewater generated per tonne of isolated diamine by the conventional Bechamp reduction, aligning with ZDHC wastewater guidelines for dye intermediate manufacturing units.
In solid-state applications, 3-amino-5-nitrobenzothiazole is investigated as a building block for metal-organic frameworks (MOFs) with selective CO₂ adsorption capacity. The bent coordination geometry imposed by the 1,3-substitution pattern around the benzothiazole core creates pore apertures of approximately 5.2 Å, which discriminate between N₂ (kinetic diameter 3.64 Å) and CO₂ (3.30 Å) based on quadrupole moment interaction rather than size sieving alone. The nitro group participates in hydrogen bonding with guest molecules, enhancing the isosteric heat of adsorption to 32–35 kJ/mol, a range that allows for low-energy regeneration with a temperature swing of only 40 °C. Such frameworks remain at the laboratory-gram scale; scaled synthesis requires careful management of crystal polymorphism, as the orthorhombic phase, which grows in unbuffered solvothermal conditions at 120 °C, collapses upon activation, while the monoclinic phase, seeded with 0.1 wt% PEG-4000 in DMF, retains 95% of its BET surface area after guest removal.
Derivatives of 3-amino-5-nitrobenzothiazole are explored as delayed-action sulfenamide accelerators in natural rubber compounds. The parent compound itself exhibits insufficient scorch safety — Mooney scorch times at 121 °C are below 8 minutes even at 0.5 phr — but conversion to the N-cyclohexylsulfenamide via oxidative coupling with cyclohexyl mercaptan yields a product with a scorch time exceeding 28 minutes under ASTM D1646-19a. This derivative must be stored below 25 °C and at relative humidity <40%; prolonged exposure to moisture initiates hydrolysis of the sulfenamide bond, regenerating the free amine and mercaptan, the latter of which forms disulfide bridges that accelerate bin storage hardening of rubber masterbatches. In compounding trials on a 1.5 L intermeshing Banbury mixer, addition of 1.0 phr of this derivative to a carbon-black-filled NR/BR truck tread compound lowered the cure reversion at 160 °C by 22% compared to an equivalent molar loading of N-cyclohexyl-2-benzothiazolesulfenamide (CBS), measured as the torque decay 15 minutes past t90 on an MDR 2000 rheometer according to ISO 6502-3:2018. The incompatible substance list includes primary aliphatic amines, which displace the sulfenamide moiety and form strongly basic admixtures that prematurely cleave polysulfidic crosslinks during the vulcanization plateau, leading to a drop in tensile strength of up to 2.5 MPa in tire sidewall formulations.
| Storage Condition | Assay after 30 days (%) | Free Amine Content (%) | Scorch Time t5 at 121 °C (min) |
|---|---|---|---|
| 20 °C, 30% RH, sealed foil | 99.1 | 0.2 | 29.3 |
| 30 °C, 65% RH, permeable sack | 94.8 | 2.1 | 18.7 |
| 40 °C, 85% RH, open container | 86.3 | 5.7 | 9.2 |
Pharmaceutical intermediate applications demand a heavy-metal profile below 20 ppm lead, 10 ppm arsenic, and 5 ppm cadmium, aligned with ICH Q3D guidelines for drug substances. The nitro group can be catalytically hydrogenated in a trickle-bed reactor over Raney-nickel at 3 bar H₂ and 60 °C to yield 3,5-diaminobenzothiazole, a key scaffold in kinase inhibitors targeting BRAF V600E mutations. Residual solvent levels of ethanol and DMF must be controlled below 500 ppm as per USP <467> Option 1 to avoid ICH Class 2 impurity failures in the final active pharmaceutical ingredient.
Avoid combining 3-amino-5-nitrobenzothiazole with strong oxidizing agents such as perchloric acid or permanganate in solution, as exothermic nitro group oxidation can escalate to deflagration at temperatures above 190 °C in confined vessels. Dry mechanical blending with aluminum powder or zinc dust is proscribed owing to thermite-like reactivity initiated by localized shear heating during micronization. Bulk containers are purged with nitrogen to <5% oxygen to suppress dust explosion hazard, as the material exhibits a KSt value of 135 bar·m/s and a minimum ignition energy below 10 mJ, placing it in St1 dust explosion class with an ignition sensitivity rating requiring conductive grounding per NFPA 77.
