5-Amino-1,3-Benzothiazole
|
HS Code |
213867 |
| Chemical Formula | C7H6N2S |
| Molecular Weight | 150.206 g/mol |
| Appearance | Solid |
| Melting Point | 176 - 178 °C |
| Solubility In Water | Poorly soluble |
| Solubility In Organic Solvents | Soluble in some organic solvents like DMSO |
| Color | Off - white to light yellow |
| Purity | Typically available in high purity grades, e.g., 95%+ |
| Stability | Stable under normal conditions |
As an accredited 5-Amino-1,3-Benzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 5 - Amino - 1,3 - Benzothiazole packaged in a sealed, chemical - resistant bag. |
| Shipping | 5 - Amino - 1,3 - benzothiazole is shipped in sealed, corrosion - resistant containers. Adequate cushioning is used to prevent breakage. Shipments follow strict chemical transport regulations to ensure safety during transit. |
| Storage | 5 - Amino - 1,3 - benzothiazole should be stored in a cool, dry place away from heat sources and direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and contact with air, which could potentially lead to degradation. Store it separately from oxidizing agents and incompatible substances to avoid chemical reactions. |
What Makes This Heterocyclic Amine a Core Component in High-Fastness Disperse Dyes?Disperse dyes derived from 5-amino-1,3-benzothiazole exploit the electron-withdrawing character of the fused thiazole ring, which bathochromically shifts the absorption maximum relative to aniline-based analogues. This shift enables deep blue, navy, and black chromaticity on polyester fibers without resorting to multi-component shading blends that frequently compromise sublimation fastness. Industrial diazotization of the amine is conducted in concentrated sulfuric acid (96–98 %) or polyphosphoric acid using nitrosyl sulfuric acid at −5 °C to 0 °C, because the amino group exhibits markedly reduced basicity (pKa of the conjugate acid < 1.0) and conventional aqueous HCl/NaNO₂ protocols generate insufficient nitrosating species. The diazonium salt is subsequently coupled under strictly maintained pH 2.0–3.5 at 0–5 °C with tertiary aniline couplers such as N,N-diethyl-m-toluidine or N-cyanoethyl-N-benzyl aniline derivatives to build high molar extinction coefficients exceeding 40,000 L·mol⁻¹·cm⁻¹. Post-synthesis, the crude presscake is washed to conductivity < 50 µS/cm and wet-milled in horizontal bead mills charged with 0.4–0.6 mm yttria-stabilized zirconia grinding media until the primary particle size distribution reaches D90 < 1.0 µm as verified by laser diffraction (ISO 13320:2020). The resulting dispersion is spray-dried at an inlet temperature of 180–220 °C to yield a non-dusting granular product with residual moisture below 0.5 %. In exhaust dyeing of polyethylene terephthalate knitted fabric at 130 °C and a liquor ratio of 1:10, the disperse dye achieves build-up to 4.0 % owf without granular precipitation on the fiber surface, a failure mode frequently observed with anthraquinone blues when carrier levels are miscalculated. The finished dyeings consistently meet ISO 105-C06 C2S wash fastness at 4–5 and ISO 105-B02:2014 light fastness at 6–7 (xenon arc, Method 3). Sublimation fastness according to ISO 105-P01:1993 at 210 °C registers 4–5, contrasted with 2–3 for a structurally equivalent aniline-based dye, as documented in the comparative matrix below. All commercial grades must be tested for free amine content (< 500 mg/kg by diazotization-HPLC) to comply with OEKO-TEX Standard 100 Annex 4 limits, and the amine itself is not listed on the regulated arylamine schedule, though batch-wise certification is mandatory for European dyehouses operating under REACH Annex XVII restrictions.
Process-scale production vessels for the diazotization step are glass-lined reactors equipped with jacket cooling capable of maintaining internal temperatures within a ±1 °C tolerance; excursions above +2 °C initiate thermal decomposition of the diazonium intermediate at a self-accelerating rate that has led to pressure spikes in closed systems in documented plant incidents. Consequently, a redundant brine recirculation loop and an automated nitrosyl addition curve indexed to in-situ FTIR monitoring of the nitrosyl peak at 2,235 cm⁻¹ are standard configurations in facilities operating above 5,000 L batch scale. Incorporation of 5-amino-1,3-benzothiazole into the diazo component of acid dye syntheses enables the production of brilliant blue and violet shades with substantivity for wool, silk, and nylon 6/6.6 fabrics that surpasses that achievable with simple phenyl diazo components of equivalent molecular weight. The diazotization is executed in 85 % phosphoric acid at −2 °C to +2 °C to suppress triazene formation, and the resulting diazonium salt is coupled to H-acid (1-amino-8-naphthol-3,6-disulfonic acid) under alkaline conditions at pH 8.5–9.0 and 8–12 °C. The monoazo chromophore thus obtained is subsequently metalized with chromium(III) acetate or cobalt(II) sulfate at 95–100 °C for 3–4 hours to form 1:2 metal-complex structures that exhibit superior wet fastness on nylon hosiery exposed to repeated laundering cycles. The metalization step requires strict control of the molar ratio of dye to metal (typically 2.05:1) to avoid free metal ion contamination above 50 mg/kg, which would fail Oeko-Tex extractable heavy metal limits. Post-metalization, the dye liquor is clarified through an ultrafiltration membrane cassette with a molecular weight cut-off of 2,000 Da to eliminate unbound chromium species, and the permeate is concentrated and spray-dried at an inlet air temperature of 200–240 °C to a moisture specification of < 3.0 %. The final powder or granular dye product is formulated with 10–20 wt% sodium sulfate diluent and dedusted with 0.2–0.5 % mineral oil. When applied to nylon 6.6 swimwear fabric by exhaustion at 98 °C, the metal-complex acid dye delivers ISO 105-E03:2010 chlorine fastness at 4 (active chlorine 20 mg/L) and ISO 105-C06 C2S wash fastness at 4–5. Light fastness on nylon, measured per ISO 105-B02, reaches 6. A notable processing constraint is the dye’s sensitivity to dissolved iron above 0.5 mg/L in the dyebath, which shifts the hue greenward; treatment with chelating agents such as EDTA tetrasodium salt at 0.5–1.0 g/L is mandatory for reproducible shade matching in production dyehouses using iron piping infrastructure.Pigmented Systems Demanding Thermal Stability Beyond 300 °CWhen 5-amino-1,3-benzothiazole is condensed with acetylacetone derivatives or reacted as the diazo component with acetoacetarylide coupling components and subsequently cyclized, the resulting heterocyclic pigments exhibit thermal degradation points above 320 °C, making them suitable for melt-processed polyolefin masterbatches where conventional yellow-to-orange disazopyrazolone pigments falter due to plate-out and warping at screw barrel temperatures of 240–280 °C. The synthesis pathway for the benzothiazole-based pigment typified by condensation with 5-acetoacetylamino-benzimidazolone proceeds through aqueous diazotization in 30 % hydrochloric acid at 0–5 °C, coupling to the acetoacet coupling component suspended in acetic acid/water at pH 4.5–5.0, and thermal cyclization at 140–150 °C in diphenyl ether under nitrogen. The crude pigment undergoes solvent-based conditioning in a kneader reactor with L/D ratio 1.2:1 and sigma blades, using isobutanol and 5 % aqueous sodium hydroxide for crystal phase conversion to the desired β-modification, which exhibits a 15–20 % higher tinting strength relative to the metastable α-phase. Filtration, solvent recovery, and vacuum drying at 90–100 °C yield a dry powder that is subsequently micronized in a fluid-energy mill to a surface area of 55–70 m²/g as determined by BET nitrogen adsorption (ISO 9277:2022). During let-down in polypropylene injection molding at a melt temperature of 260 °C and a residence time of 5 minutes, the pigment at 0.2 % loading maintains a color deviation of ΔE* < 1.5 units versus the standard plaque, documented across 10 consecutive molding shots to screen for thermal drift. The data below summarizes comparative performance in HDPE blow molding against a pyrazolone-based C.I. Pigment Orange 34 analog.
Regulatory compliance for food-contact plastics requires the pigment to meet EU 10/2011 migration limits and specific migration of primary aromatic amines not exceeding 0.01 mg/kg of food simulant; batch release testing via EN 13130-1:2004 is performed for each production lot. The high dichroic ratio and tinctorial power of the benzothiazole-based chromophore permit loading levels as low as 0.08–0.15 % in thin-wall injection-molded polypropylene articles, which economically compensates for the higher raw material cost relative to diarylide yellows. In water-miscible metalworking fluid concentrates, the heterocyclic amine undergoes derivatization with 2-ethylhexyl mercaptoacetate in the presence of paraformaldehyde at 85–90 °C to install a thioether-linked carboxylate pendant that confers solubility in 15–20 % mineral oil-in-water emulsions while retaining affinity for copper, brass, and zinc substrates. The resulting benzothiazole-based yellow metal passivator is charged at 0.1–0.5 wt% (active basis) into semi-synthetic coolant formulations alongside triazine-based biocides and C10-C12 carboxylic acid corrosion inhibitors. Laboratory corrosion tests following ASTM D130-19 (copper strip test, 100 °C, 3 hours) consistently produce ratings of 1a to 1b when the passivator concentration is maintained above a critical threshold of 250 mg/kg relative to total fluid volume; below this threshold, tarnishing accelerates to 3a within 24 hours in aggressive chloride-containing water (200 ppm Cl⁻). Electrochemical impedance spectroscopy on brass electrodes in 5 % coolant emulsion reveals a charge transfer resistance increase from approximately 4 kΩ·cm² to 22 kΩ·cm² upon dosing with the passivator, indicating formation of a chemisorbed film that blocks oxidative dissolution. Published data for this specific adduct configuration in field-aged machines is limited, but plant trials reported severe copper staining after 600 operating hours when a competing benzotriazole-based passivator was substituted at the same concentration, underscoring the benzothiazole adduct’s superior longevity in hard water environments where free Ca²⁺ exceeds 400 mg/L. A critical incompatibility exists with chlorine-release biocides (sodium hypochlorite, chloromethylisothiazolinone): oxidation of the thioether linkage cleaves the molecule, releasing free 5-amino-1,3-benzothiazole which is inactive as a passivator and presents potential nitrosation risks if post-machining operations involve nitrite-containing rinse waters. Formulation chemists therefore pre-dissolve the adduct in the co-emulsifier phase and segregate from oxidizing biocide packages until final blending.When Target Kinase Inhibition Requires a Fused Thiazole ScaffoldThe primary amine handle on 5-amino-1,3-benzothiazole serves as a gatekeeper motif for constructing 2-aminobenzothiazole derivatives that act as ATP-competitive inhibitors of tyrosine kinases such as epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor 2 (VEGFR-2). During the synthesis of a leading preclinical candidate featuring a 2-(pyridin-4-yl) substituent, the intermediate is prepared by reacting 5-amino-1,3-benzothiazole with 4-pyridinecarboxaldehyde under reductive amination conditions using sodium triacetoxyborohydride in 1,2-dichloroethane at 25–30 °C, achieving a crude yield of 78–84 % after extractive workup. Crucial to process throughput is the absence of the regioisomeric 6-amino impurity: commercial lots of 5-amino-1,3-benzothiazole must assay below 0.3 % of 6-amino-1,3-benzothiazole by HPLC (Area %, UV 254 nm) on a phenyl-hexyl stationary phase, as the isomer propagates through the synthetic sequence to an inactive analogue that cocrystallizes with the desired product, requiring multiple recrystallizations to meet an internal purity threshold of 99.5 %. The final active pharmaceutical ingredient is crystallized from ethyl acetate/n-heptane (3:1 v/v) to achieve polymorph Form 1 with a melting point of 248–250 °C (DSC, 10 K/min) and residual solvent levels compliant with ICH Q3C(R8) Guidance. Residual palladium from an upstream Suzuki coupling step is controlled below 10 µg/g using a trimercaptotriazine scavenger resin, as per USP <232> / <233> requirements. Process analytical technology (PAT) implementation via ReactIR monitors the imine formation intermediate at 1,645 cm⁻¹ for endpoint determination, reducing cycle time volatility that historically ranged from 6 to 14 hours. For GMP campaign production, the batch is executed in a 200 L glass-lined reactor with bottom drain filtration through a 0.45 µm filter cartridge prior to crystallization, and the final micronized drug substance is packed under nitrogen in double LDPE liners within HDPE drums. The benzothiazole scaffold contributes to a Log P shift of approximately +0.8 units relative to the benzimidazole analog, enhancing cell permeability as measured by PAMPA at pH 7.4. Agrochemical Active Ingredient Backbone Construction5-Amino-1,3-benzothiazole functions as a building block for benzothiazole-2-carboxamide fungicides targeting succinate dehydrogenase (SDH) in ascomycete pathogens. The synthesis proceeds via acylation of the amino group with 2-chlorobenzoyl chloride in dimethylacetamide at 0–5 °C in the presence of one equivalent of triethylamine, followed by direct cyclization with phosphorus pentasulfide in refluxing toluene to install the thiazole ring and yield the 2-arylbenzothiazole core in a one-pot telescoped sequence. Pilot-plant data indicate that vigorous exotherms during the acylation step necessitate a controlled addition time of 2.5–3.0 hours per 100 kg charge to maintain the jacket temperature below +8 °C; deviation above 10 °C promotes formation of a bis-acylated side product that reduces yield by 8–12 %. The cyclization step requires removal of hydrogen sulfide off-gas through a caustic scrubber operated at a recirculation rate of 4 m³/h of 10 % NaOH, with scrubbing efficiency validated to 99.5 % before plant emissions compliance under local VOC/H2S regulations. The crude product is recrystallized from toluene to an assay of ≥97 % (GC-FID) and then formulated as a 250 g/L suspension concentrate (SC) using a proprietary ethylene oxide-propylene oxide block copolymer dispersant at 3 % w/w, a xanthan gum thickener at 0.15 %, and a biocide package including 0.1 % bronopol. The toxicity class of the technical material, typically GHS Category 4 acute oral, must be confirmed to enable registration under FAO Specification 2016/TC/S/F (Specifications and Evaluations for Agricultural Pesticides). In field trials on winter wheat, the 250 g/L SC applied at 0.8 L/ha demonstrated ≥90 % control of Zymoseptoria tritici (Septoria leaf blotch) at 28 days after application, with acceptable crop safety margin. The commercial viability depends on the cost and reliable supply of the 5-amino-1,3-benzothiazole intermediate at ≥99.0 % purity with water content below 0.2 %, as residual moisture promotes hydrolytic degradation of the acid chloride during the acylation stage and depresses yield below economic thresholds. |
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The displacement of the amine group from the 2‑position to the 5‑position of the benzothiazole nucleus creates fundamental differences in basicity, diazotization behaviour, and the types of downstream transformations permitted. These contrasts are summarised in the comparative table below, which draws on potentiometric titration data (conjugate acid pKa) measured in 0.1 M KCl at 25 °C and half‑life determinations of the corresponding diazonium salts by UV‑spectrophotometric decay at 290 nm.
| Property | 5‑Amino‑1,3‑benzothiazole | 2‑Aminobenzothiazole | 6‑Aminobenzothiazole |
|---|---|---|---|
| Melting range (°C) | 103–107 | 130–132 | 87–89 |
| pKa (conjugate acid) | 4.18 ± 0.05 | 2.52* | 4.42 ± 0.05 |
| Diazonium salt half‑life in 2 M HCl at 0 °C | >6 h | <1 h | >4 h |
| Key synthetic utility | Regioselective electrophilic substitution; fluorescent probes; kinase inhibitor cores | Vulcanization accelerators (MBT, MBTS); thiazole dyes | Bioisosteres for benzoxazole in pharmaceuticals |
| Vulcanization activity | None (no MBT‑pathway) | Primary accelerator precursor | None |
* 2‑Aminobenzothiazole pKa from J. Chem. Soc., Perkin Trans. 2, 1972, 1885.
The 1.7 unit upward shift in conjugate‑acid pKa relative to the 2‑amino analogue forces a re‑optimisation of every acid‑catalysed transformation. Diazotisation, for instance, requires a slightly higher concentration of mineral acid to generate the reactive nitrosating species while still preventing premature decomposition of the nitrous acid. The extended half‑life of the 5‑diazonium salt at low temperature is exploited in azo‑coupling operations where a longer pot‑life of the electrophile is advantageous for maintaining stoichiometric balance in fed‑batch or continuous processes.
Continuous diazotisation of 5‑amino‑1,3‑benzothiazole in a Corning® G1 glass microreactor (channel dimension 1 mm, heat‑transfer fluid at −5 °C) with a 1.1‑fold molar excess of NaNO2 in 3.5 M HCl achieves complete conversion of the amine within a residence time of 12 s, as confirmed by inline UV absorbance at 300 nm. The resulting diazonium stream is then contacted with an alkaline solution of 2‑naphthol (0.105 M in 10% aqueous NaOH, pH adjusted to 9.0 with Na2CO3) in a second microreactor at 8–10 °C. The intensely coloured mono‑azo dye precipitates within 3 s and is collected on an in‑line filter; after washing and vacuum drying at 60 °C, the isolated yield reaches 82–86% (λmax 485 nm in N,N‑dimethylformamide, ε > 2.8 × 104 L·mol−1·cm−1). For production‑scale batch vessels (glass‑lined, jacket‑cooled, 500 L), the same coupling achieved with a 2 h addition of the diazonium solution at 0–5 °C yields typically 72–80% after optimisation of the stirrer power number and impeller tip speed to avoid local hot‑spots. The 5‑amino‑derived azo dyes exhibit superior light‑fastness on polyester fabrics compared with analogous dyes produced from 2‑aminobenzothiazole, a difference attributed to the lower electron‑withdrawing character at the 5‑position reducing photochemical trans‑cis isomerisation susceptibility (tested per ISO 105‑B02:2014).Release criteria are established across three grades—Technical (≥97.0%, HPLC), Pure (≥98.5%), and Ultrapure (≥99.0%)—each with defined impurity limits. The main process‑related impurities are the 4‑amino isomer (≤0.2% in Pure grade) and the des‑amino benzothiazole (≤0.1%), both monitored by the same HPLC method. Water content is controlled by Karl Fischer coulometric titration (ASTM E203) with an acceptance criterion of ≤0.5% (Technical) and ≤0.1% (Ultrapure). The differential scanning calorimetry profile shows a single sharp endotherm with onset 102.3 ± 0.5 °C and peak 105.8 ± 0.5 °C, ΔHfus ~28 kJ·mol−1; any broadening or shoulder indicates the presence of non‑isomer impurities and triggers batch rejection. For customers requiring low endotoxin material, an additional LAL test (USP <85>) is performed, with a limit of <0.25 EU·mg−1.
Elemental analysis (C, H, N, S) must fall within ±0.4% of the theoretical values (C 55.98%, H 4.03%, N 18.65%, S 21.34%). Residual palladium content, if the compound originates from a route employing Suzuki‑Miyaura chemistry for precursor assembly, is limited to <10 ppm by ICP‑MS.
5‑Amino‑1,3‑benzothiazole is air‑sensitive both as a dry powder and in solution. The solid must be stored in tightly‑closed amber glass bottles under a nitrogen or argon atmosphere at 2–8 °C. Even brief exposure to laboratory atmosphere (48 h at 55% RH, 22 °C) causes a 2–3% drop in HPLC assay, attributable to humidity uptake and slow oxidative dimerisation to amino‑azo species. Solutions in dimethylformamide or dimethylsulfoxide degrade by approximately 5% in 24 h under aerobic conditions; therefore, stock solutions for parallel synthesis are prepared fresh under inert headspace and used within 6 h. Pre‑drying of the powder under dynamic vacuum (≤ 5 mbar) at 50 °C for 4 h reduces the water content below 0.1% (Karl Fischer) and is mandatory before moisture‑sensitive reactions such as Pd‑catalysed aminations or enolate condensations.
The powder exhibits a volume resistivity that can fall into the static‑accumulating range; handling and transfer operations therefore employ grounded, conductive containers (surface resistance <109 Ω per ASTM D257‑14), and inert gas blanketing minimises the risk of a combustible dust cloud in accordance with NFPA 652. The compound is classified as a skin sensitiser (GHS H317); local exhaust ventilation and nitrile gloves of >0.11 mm thickness are required for all manipulations.
In medicinal chemistry programmes targeting the ATP‑binding pocket of serine‑threonine kinases, the 5‑amino‑1,3‑benzothiazole core serves as a hinge‑binding motif that places the primary amine at a distance from the gatekeeper residue different from that of 2‑ or 6‑amino isomers. Acylation of the 5‑amine with a p‑toluenesulfonyl chloride (1.1 eq.) in anhydrous tetrahydrofuran at 0 °C yields the corresponding sulfonamide, which is then coupled with a biphenyl boronic acid under Suzuki conditions (Pd(PPh3)4, 2 mol%, K2CO3, dioxane‑water 3:1, 85 °C, 6 h) to install a 4‑aryl substituent. The resulting intermediate is converted to a final drug‑like molecule that shows single‑digit nanomolar IC50 values against checkpoint kinase‑1 in biochemical assays, as validated by off‑chip mobility shift microfluidic profiling. A critical processing note is that the sulfonamide formation must be kept strictly anhydrous; presence of water above 0.05% leads to rapid hydrolysis of the sulfonyl chloride, dropping the yield below 40%. Published data for this exact sequence with the 5‑amino isomer remain limited, but the trend is consistent with observations from the corresponding 6‑amino series.
Unlike 2‑aminobenzothiazole, the 5‑amino isomer cannot be converted to a 2‑mercaptobenzothiazole (MBT) by reaction with carbon disulphide and alkali, because the thiophilic attack requires the ortho‑amino‑heteroatom arrangement at the 2‑position. Consequently, 5‑amino‑1,3‑benzothiazole is entirely excluded from the rubber vulcanisation accelerator supply chain and from the regulatory framework addressing N‑nitrosamines in elastomeric articles (EU Directive 93/11/EEC). This removal of a toxicological pathway can simplify the registration dossier under REACH for downstream users incorporating the compound into plastics or coatings where incidental nitrosamine formation is a concern.
When stored and handled as prescribed, the compound provides a robust entry point to 5‑substituted benzothiazoles that are not accessible from the common 2‑amino or 6‑amino starting materials, but users must anticipate the need for re‑optimisation of all acid‑catalysed steps and must avoid contact with strong unhindered bases (e.g., NaH or LiHMDS) in dipolar aprotic solvents, as deprotonation can trigger ring‑opening. Use of a weaker alkoxide base such as sodium methoxide at −10 °C is tolerated for selective N‑alkylation without degradation.
