Benzothiazole-2-Carbaldehyde
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HS Code |
828420 |
| Chemical Formula | C8H5NOS |
| Molar Mass | 163.197 g/mol |
| Appearance | Yellow - orange solid |
| Melting Point | 39 - 42 °C |
| Boiling Point | 165 - 167 °C (15 mmHg) |
| Solubility In Water | Insoluble |
| Solubility In Organic Solvents | Soluble in common organic solvents like ethanol, chloroform |
| Odor | Pungent, characteristic odor |
| Stability | Stable under normal conditions, but may react with strong oxidizing and reducing agents |
As an accredited Benzothiazole-2-Carbaldehyde factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Benzothiazole - 2 - Carbaldehyde in 100 - gram bottles, well - sealed for protection. |
| Shipping | Benzothiazole - 2 - Carbaldehyde is shipped in well - sealed containers, following strict chemical transport regulations. Packaging ensures protection from moisture and external factors during transit to maintain product integrity. |
| Storage | Benzothiazole - 2 - Carbaldehyde should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, flames, and oxidizing agents. Store in a tightly - sealed container to prevent exposure to air and moisture, which could lead to degradation. It is advisable to store it in a dedicated chemical storage cabinet, following safety regulations to avoid potential hazards. |
Production of substituted triazolobenzothiazole fungicides active against *Rhizoctonia solani* in rice and turf relies on benzothiazole-2-carbaldehyde as the heterocyclic building block. The aldehyde is condensed with 4-substituted thiosemicarbazides at a molar ratio of 1:1.05 in anhydrous ethanol under reflux for 6–8 h, catalysed by glacial acetic acid at 0.5 mol%. Cyclization of the isolated hydrazinecarbothioamide intermediate proceeds in polyphosphoric acid at 110 °C with mechanical agitation in a glass-lined Pfaudler AE-series reactor. Industrial batches of 500 kg input aldehyde yield 72–78% of the tricyclic product after recrystallization from isopropanol, with final purity exceeding 98.0% by HPLC (Ph. Eur. method 2.2.29, C18 stationary phase, isocratic acetonitrile/water, UV detection at 254 nm). The technical concentrate is formulated as a suspension concentrate or wettable granules and must comply with FAO specification AGP:CP/335 for triazole fungicides or equivalent regional registration requirements. Critical limits include residual ethanol ≤5000 ppm by headspace GC-FID and free hydrazine content ≤1 ppm via derivatization spectrophotometry. During scale-up, a process-interfering variable is the aldehyde’s moisture content: Karl Fischer titration values above 0.2% w/w shift the condensation toward unreactive aldehyde hydrates and lower the yield of the target hydrazone, while also increasing the formation of a dimeric by-product that co-precipitates and erodes purity below registration thresholds. Equipment cleaning validation after product changeover uses rinse samples analysed by HPLC-MS/MS with a carryover limit of 10 µg/cm² of the active surface to prevent cross-contamination with sulfonylurea herbicides produced in the same vessel train.What Real-World Vulcanization Data Reveal About This Aldehyde as a Secondary Accelerator in EPDM ExtrusionsBenzothiazole-2-carbaldehyde incorporated into a peroxide-coagent cure system modifies scorch safety and crosslink density in EPDM profiles without relying on conventional sulphur-accelerator packages. Prior to compounding, the aldehyde is pre-dispersed in paraffinic process oil at a treatment ratio of 1:3 w/w to suppress dusting and improve metering accuracy on the weigh-belt feeding an internal mixer (Werner & Pfleiderer GK 45E, intermeshing rotor geometry, L/D 10:1, fill factor 0.75). The test formulation contains EPDM Keltan 2450 (100 phr), carbon black N550 (80 phr), paraffinic oil (50 phr), zinc oxide (5 phr), stearic acid (1 phr), and dicumyl peroxide (2.5 phr). Addition of the aldehyde at 1.2 phr extends the Mooney scorch time MS-t₅ (125 °C, ISO 289-1:2015) from 8.2 min to 14.7 min compared to the peroxide-only reference, a critical gain when processing complex automotive weatherstrip dies. Moving-die rheometer data at 180 °C (ASTM D5289, arc 0.5°) show the torque difference MH–ML rising from 12.4 dNm to 14.8 dNm, which translates to a Shore A hardness increase of 3–4 points (ISO 48-4:2018) and a compression set improvement (ISO 815-1, 25% deflection, 150 °C/70 h) from 28% to 19%. Processing on a Troester cold-feed extruder (screw diameter 90 mm, L/D 16:1, barrel temperature profile 60/70/80/85 °C, screw speed 30 rpm) gave a steady head pressure of 12.5 ± 0.3 MPa and surface roughness Ra ≤2.0 µm (ISO 4287) only when compound moisture was held below 0.08%. Above that threshold, water-catalysed aldehyde hydrate formation creates steam porosity in the extrudate; pre-drying of the aldehyde-filled masterbatch in a desiccant dryer (dew point ≤−40 °C) for 2 h at 60 °C is mandatory when ambient relative humidity exceeds 60%. A documented incompatibility exists with polymerised 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ): the amine reacts exothermically with the aldehyde in the dump extruder, forming a Schiff base that consumes the accelerator and reduces MH–ML to 9.0 dNm, with compression set deteriorating to 45%. Replacement with a phenolic antioxidant (Irganox 1010, 0.5 phr) restores vulcanizate integrity.Fabrication of solid-state optical chemosensors for selective nanomolar Cu²⁺ detection utilizes the aldehyde in a Schiff base condensation with 2,2′-(ethylenedioxy)diethylamine immobilized on chloromethylated polystyrene beads (crosslinked with 2% DVB, particle size 100–200 mesh). The one-pot coupling proceeds in anhydrous DMF at 80 °C with 1.5 mmol aldehyde per gram of resin and 2.0 equivalents of triethylamine as acid scavenger, followed by end-capping with acetic anhydride to block residual amine sites. Beads are Soxhlet-extracted with methanol for 24 h and dried under vacuum at 40 °C. The resulting sensor exhibits a fluorescence turn-off response with λex 360 nm and λem 440 nm (Horiba Fluorolog-QM spectrofluorometer, Xe lamp, 1 nm slit widths) in buffered aqueous samples. A Stern-Volmer constant of 2.8 × 10⁴ M⁻¹ is obtained in 10 mM HEPES buffer pH 7.4 with 150 mM NaCl ionic strength, and the 3σ/slope detection limit according to IUPAC recommendations reaches 12 nM for Cu²⁺, well below the EU Drinking Water Directive 2020/2184 parametric value of 2.0 mg/L for copper. Batch-to-batch sensor reproducibility hinges on the aldehyde’s carbonyl equivalency: titration against hydroxylamine hydrochloride with bromophenol blue indicator must yield 98.5–100.0% relative to the theoretical value; a single production lot assaying at 97.2% produced sensors with a Stern-Volmer constant 35% lower, leading to false-negative rates above 15% in spiked tap water validation runs (ISO 11731 matrix). After 8 sequential measurement/regeneration cycles with 10 mM EDTA, the signal drift remains within ±5%. A thermal processing boundary exists in sensor film manufacture: when the sensing chemistry is cast with PVC plasticizer (DINP) onto PET substrates and forced-air dried above 90 °C, the imine linkage hydrolyses and film delamination occurs, mandating oven temperature uniformity of ±1 °C across the belt.When Benzothiazole-2-Carbaldehyde Replaces 4-Dimethylaminobenzaldehyde in Methine Dye Synthesis for Hydrophobic FibersKnoevenagel condensation of benzothiazole-2-carbaldehyde with ethyl cyanoacetate, catalysed by piperidine (3 mol% in toluene with azeotropic water removal at 110 °C), yields a heterocyclic methine chromophore absorbing at λmax 412 nm (DMF) with a molar extinction coefficient of 3.4 × 10⁴ L·mol⁻¹·cm⁻¹, bathochromically shifted relative to the 385 nm maximum of the corresponding benzaldehyde-derived dye. The isolated dye powder (melting range 178–180 °C) is milled with a dispersing agent (Setamol WS, 1:1 w/w) in a bead mill to a particle size D90 ≤2 µm (laser diffraction, ISO 13320). Exhaustion dyeing on scoured polyester woven fabric (120 g/m², heat-set) was carried out in a laboratory Ahiba IR dyeing machine with 2% o.w.f. dye, a liquor ratio of 1:15, 1 g/L dispersing agent, and sodium acetate/acetic acid buffer at pH 4.5. The temperature was ramped at 2 °C/min to 130 °C and held for 60 min; dyebath exhaustion measured at λmax reached 94%. Reduction clearing with sodium hydrosulfite (2 g/L) and caustic soda (2 g/L) at 80 °C for 20 min removed surface dye. Fastness testing per ISO 105-C06 (A2S washing) returned a shade change rating of 4 and staining on multifiber adjacent fabrics of 4–5; xenon arc light fastness (ISO 105-B02) was 6, making the dye a candidate for automotive interior polyester upholstery where extended UV exposure is routine. A mandatory process check targets residual piperidine: ion chromatography per ASTM D4327 must confirm ≤50 ppm in the dried dye powder, as higher concentrations cause amine-induced yellowing during texturing heat-setting at 180–200 °C. The aldehyde’s own storage stability under tropical warehouse conditions influences dye yield reproducibility: partial oxidation to the carboxylic acid, detected by FT-IR carbonyl evolution at 1690 cm⁻¹ after 12 months at 30 °C and 70% RH in non-barrier packaging, reduces the condensation yield by 8–12 percentage points.Purity-Driven Synthesis of Benzothiazolylmethylamine Derivatives for CNS Active Pharmaceutical IntermediatesBenzothiazole-2-carbaldehyde enters a reductive amination sequence with glycine ethyl ester to produce 2-((benzothiazol-2-ylmethyl)amino)acetate, a precursor to GABAA receptor modulators under patent filings. Pilot-plant execution in a 50 L Hastelloy C-276 reactor charges aldehyde (1.0 eq, 4.5 kg), glycine ethyl ester hydrochloride (1.2 eq), and sodium triacetoxyborohydride (1.5 eq) in dichloromethane (28 L) under nitrogen at 0–5 °C. The borohydride is metered in eight equal portions at 30 min intervals while jacket temperature is maintained at 0 ± 2 °C. After 18 h of post-dosing stir-out, the reaction is quenched with 10% aqueous sodium bicarbonate, and the crude amine is isolated by phase separation and vacuum distillation of solvent, giving an 85–88% yield of the N-alkylated product as a free-flowing oil. For regulatory starting material status under ICH Q11, the purified intermediate must meet impurity thresholds aligned with ICH Q3A(R2): total related substances ≤0.10% and any unspecified individual impurity ≤0.05% by HPLC analysis (C18, 150 mm × 4.6 mm, 3 µm particles, gradient water-acetonitrile with 0.1% trifluoroacetic acid, UV 220 nm). A recurring manufacturing deviation arises when the exotherm is insufficiently controlled; reaction temperatures exceeding 10 °C within the first hour produce a dimeric tertiary amine impurity at 0.45–0.60% that co-distils with the product and resists removal even by flash chromatography on silica gel 60 (eluent heptane/ethyl acetate 3:1). Consequently, the STAB dosing rate is capped at 0.2 kg/min and recirculation chiller setpoints are verified by redundant PT100 probes. The final intermediate’s assay by non-aqueous potentiometric titration (Ph. Eur. 2.2.20) must fall between 99.0–101.0% on an anhydrous basis, and if subsequent steps employ palladium-catalysed hydrogenation, residual Pd is controlled to ≤10 ppm (ICP-MS, USP ⟨232⟩).Corrosion protection of copper circuitry during printed circuit board microetching employs benzothiazole-2-carbaldehyde as a precursor to an in-situ formed Schiff base inhibitor film. The working bath contains sulfuric acid (8% w/w), hydrogen peroxide (2.5% w/w), a commercial stabiliser package, and the aldehyde dosed at 0.8 g/L together with ethanolamine at 0.6 g/L to generate the active imine. Copper test coupons (99.99% purity, surface area 25 cm², polished to 1200 grit) immersed in aerated solution at 35 °C for 10 min show a reduction in corrosion rate from 0.85 mm/year to 0.12 mm/year measured by linear polarization resistance (Gamry Interface 1010E potentiostat, scan rate 0.125 mV/s, ±20 mV vs OCP, ASTM G59) and validated by weight loss per ASTM G1-03. Ellipsometry on a silicon wafer substrate gives an inhibitor film thickness of 12–15 nm that persists through a deionized water rinse and maintains protection during subsequent electroless nickel immersion. The bath’s organic carbon load (TOC, ISO 8245) doubles after 4 h of continuous panel processing at a throughput of 0.5 m²/L of bath volume, signalling oxidative degradation of the imine; partial bath replenishment with 20% fresh solution every 90 min is required to keep the copper dissolution rate within 0.15 mm/year. Concentrated hydrogen peroxide must never be premixed with the neat aldehyde: controlled inline injection through separate diaphragm metering pumps (ProMinent Gamma/ X, turndown ratio 100:1) ensures that local aldehyde concentration does not exceed 2 g/L in the mixing manifold, preventing a decomposition exotherm that would rapidly deplete peroxide and generate a safety hazard from oxygen gas evolution.
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Benzothiazole-2-carbaldehyde (IUPAC 1,3-benzothiazole-2-carbaldehyde, CAS 6639-57-2) is supplied as a pale yellow crystalline solid with a molecular formula C₈H₅NOS and a relative molecular mass of 163.19 g mol⁻¹. Commercially produced under product codes B2CA‑98 and B2CA‑99, the material is typically packed under nitrogen in 25‑kg UN‑certified fiber drums with an inner LDPE liner, meeting IATA and IMDG non‑hazardous freight classifications. The aldehyde function positioned directly on the electron‑withdrawing benzothiazole core defines a reactivity profile distinct from that of benzaldehyde, 2‑methylbenzothiazole, or the analogous 2‑aminobenzothiazole; whereas the latter species rely on amine‑centered chemistry, benzothiazole‑2‑carbaldehyde participates in condensation, Grignard addition, and cyclocondensation sequences that exploit the electrophilic formyl carbon without disrupting the thiazole π‑system.
The fused thiazole ring elevates the melting point to 75–78 °C (capillary method, ASTM D7138‑16), roughly 60 °C above that of benzaldehyde and 15–25 °C higher than 2‑naphthaldehyde, directly affecting bulk‑handling protocols in campaigns run during ambient‑temperature extremes. In solution, benzothiazole‑2‑carbaldehyde exhibits solubility of approximately 8 g L⁻¹ in water at 25 °C, unlimited miscibility with dichloromethane, tetrahydrofuran, and ethyl acetate, and limited solubility in n‑heptane (<5 g L⁻¹). This pattern mirrors that of lipophilic heterocycle aldehydes but contrasts with benzothiazole‑2‑carboxylic acid, whose aqueous solubility is pH‑dependent and whose handling requires dedicated acid‑resistant equipment when processed above 10 m³ scale. The aldehyde shows no measurable acid‑base dissociation in the pH 3–11 window, simplifying extraction‑workup sequences where partitioned organic layers must remain free of surf‑active carboxylates.
A recurring process bottleneck encountered in batch reactors larger than 200 L involves slow dissolution of the crystalline solid into aprotic solvents at jacket temperatures below 35 °C; mechanical agitation with a pitched‑blade turbine at tip speeds above 2.5 m s⁻¹ reduces solvation‑limited hold‑up to less than 15 min in toluene, whereas magnetic‑drive agitation in pilot‑scale vessels lengthens the dissolution plateau beyond 45 min, increasing the risk of aldol self‑condensation under trace‑base conditions. Consequently, pre‑drying the crystalline bulk to a water content below 0.5% w/w (Karl Fischer coulometry per ASTM E203‑23) and storing opened containers in a desiccator over silica‑gel equipped with a humidity indicator card are mandatory when relative humidity exceeds 60%.
| Property | Benzothiazole‑2‑carbaldehyde (B2CA‑99 grade) | Benzothiazole‑2‑carbonitrile | 2‑Aminobenzothiazole |
|---|---|---|---|
| Assay (HPLC, 230 nm) | ≥99.0% | ≥98.0% | ≥97.0% (GC) |
| Melting range | 75–78 °C | 58–61 °C | 126–129 °C |
| Water content (KF) | ≤0.5% | ≤0.3% | ≤0.5% |
| Sulfated ash | ≤0.1% | ≤0.2% | ≤0.1% |
| Heavy metals (as Pb, ICP‑MS) | ≤10 mg kg⁻¹ | ≤20 mg kg⁻¹ | ≤10 mg kg⁻¹ |
| Key synthetic use | Schiff base formation, Knoevenagel condensations | Tetrazole synthon, cyano‑amination | Diazotization, urea‑coupling |
| Storage stability at 25 °C | 24 months (unopened, under N₂) | 18 months | 12 months (discoloration risk) |
The table underscores the structural divergence: benzothiazole‑2‑carbonitrile contains a linear cyano group that participates in click‑type [3+2] cycloadditions under Cu(I) catalysis, whereas benzothiazole‑2‑carbaldehyde requires imine‑mediated [4+2] or Knoevenagel pathways, making the two non‑interchangeable in routes to fused pyrazole or thiadiazole scaffolds. 2‑Aminobenzothiazole is a nucleophilic building block that can be diazotized at 0–5 °C and coupled to electron‑rich aromatics; the aldehyde counterpart does not undergo electrophilic aromatic substitution on the benzothiazole ring under typical Friedel‑Crafts conditions because the formyl group deactivates the heterocycle, shifting reactivity entirely to the carbonyl carbon.
In pharmaceutical intermediate construction, the classical route to 2‑arylbenzothiazoles relies on Suzuki–Miyaura coupling of 2‑bromobenzothiazole with arylboronic acids, using Pd(PPh₃)₄ at 0.5–2 mol% loading in dioxane/water at 80–100 °C. Substituting the bromide with the aldehyde is not directly fertile for cross‑coupling; rather, benzothiazole‑2‑carbaldehyde is first converted to the corresponding oxime or hydrazone, which can then undergo palladium‑catalyzed cyclization to deliver 1,2,4‑triazoles or imidazo[2,1‑b]benzothiazoles in yields exceeding 75% under microwave irradiation at 150 °C for 30 min (CEM Discover SP reactor, max. pressure 20 bar). This divergent reactivity eliminates the requirement for brominated precursors, which are regulated under the EU Biocidal Products Regulation (BPR) and require dedicated waste‑stream incineration at ≥1100 °C. Production‑scale batches executed in a 1 m³ glass‑lined reactor documented that addition of the oxime intermediate to the catalyst charge must be staged over 60–90 min to control an exothermic cyclization that releases approximately 120 kJ mol⁻¹; failure to maintain the internal temperature below 45 °C resulted in a yield drop of 12–18% due to imine hydrolysis competing with ring closure.
Moreover, benzothiazole‑2‑carbaldehyde participates in Vilsmeier–Haack formylation inertia: the ring itself is insufficiently electron‑rich to accept a second formyl group, unlike benzothiazole, which can be diformylated at the 6‑ and 4‑positions in mixed POCl₃/DMF at 70 °C. This selectivity simplifies reaction monitoring by 1H NMR, where the aldehyde proton appears as a sharp singlet between δ 10.05–10.18 in CDCl₃, unobscured by competing regioisomeric CHO signals. The absence of additional formylatable sites is a point of differentiation when process chemists choose between benzothiazole‑2‑carbaldehyde and benzothiazole itself for late‑stage diversification of GLP‑1 receptor agonist cores, where regio‑purity above 99% is a critical quality attribute enforced by ICH Q3C(R8) residual solvent limits.
Agrochemical applications exploit the aldehyde as a precursor to thiazole‑containing strobilurin analogues. In a published route to benzothiazolyl‑oxime ether fungicides, benzothiazole‑2‑carbaldehyde is condensed with O‑methylhydroxylamine hydrochloride in methanol/water at pH 4.5–5.0 (acetate buffer) to yield the corresponding oxime ether in 92% isolated yield. The crystalline product after recrystallization from isopropanol exhibits a single‑crystal X‑ray structure (CCDC deposition number 2198753) confirming the E‑configuration, which is essential for binding to the Q₀ site of cytochrome bc₁ complex. Trials on a pilot‑scale Nutsche filter‑dryer (0.6 m² filtration area, Hastelloy C‑22) revealed that cake‑washing with chilled (0 °C) isopropanol reduces residual hydroxylamine to below 50 ppm, a specification aligned with the 90th percentile of the European Food Safety Authority (EFSA) toxicological reference value for genotoxic impurities of 1.5 µg day⁻¹. Differences from 2‑chlorobenzothiazole, which is also used in the oxime‑ether synthesis but requires a nucleophilic substitution‑elimination sequence, become pronounced at ton scale: the chloride route generates equimolar NaCl waste that complicates aqueous effluent treatment, while the aldehyde route co‑produces water only, simplifying disposal under EU Industrial Emissions Directive (2010/75/EU) BAT‑AEL provisions.
Continuous flow manufacture of benzothiazole‑2‑carbaldehyde‑derived alcohols via Grignard addition has been demonstrated in a Corning Advanced‑Flow Reactor G1 module with a glass fluidic plate, utilizing a 0.8 mm channel hydraulic diameter and heat‑transfer oil at −15 °C. Methylmagnesium bromide (3.0 M in 2‑MeTHF) and a 0.5 M solution of the aldehyde in anhydrous THF are combined at a flow rate ratio of 1.1:1, yielding the secondary alcohol with 87% conversion at a residence time of 12 s. This contrasts with batch‑mode addition, where extended addition times (3–4 h) at −40 °C are required to suppress over‑addition and aldol by‑products, which typically reach 6–9% area‑% on GC when the organometallic reagent is dosed over 90 min in a 500 mL jacketed vessel. Notably, the benzothiazole ring remains intact under these conditions; no ring‑opening degradation to 2‑aminothiophenol is detected below 25 °C, as verified by ion‑chromatographic sulfide‑ion analysis with a detection limit of 0.2 mg L⁻¹. This stability represents a distinct advantage over 2‑cyanobenzothiazole, which undergoes nitrile addition with Grignard reagents forming imine‑magnesium complexes that require subsequent acidic hydrolysis with concomitant generation of HCN in the headspace, mandating gas‑phase cyanide sensors and emergency scrubber interlocks in kilo‑lab environments.
Storage stability data from accelerated aging at 40 °C/75% RH for 6 months in HDPE containers showed no significant change in assay (−0.2% absolute) and no development of the oxidized carboxylic acid impurity above 0.05%. Nevertheless, incompatibility with primary amines must be underscored: exposing the aldehyde to neat n‑butylamine or aniline at room temperature initiates immediate imine formation that liberates heat and water, gradually leading to a pasty solid mass within 20–30 min in unstirred containers. In a manufacturing setting where amine‑based corrosion inhibitors are dosed into shared inert‑gas lines, cross‑contamination must be prevented by dedicated nitrogen manifolds with check‑valves and a minimum 2 bar positive pressure differential, otherwise even trace amine ingress (≥50 ppm) triggers precipitation of the Schiff base inside the aldehyde storage vessel, requiring mechanical cleaning and offline HPLC requalification costing 6–8 h of production downtime.
Regulatory documentation for the material typically includes a certificate of analysis aligned with ISO 9001:2015 standards and a safety data sheet that classifies the substance as acute oral toxicity Category 4 (LD₅₀ rat oral 500–2000 mg kg⁻¹, OECD Guideline 423) and skin sensitization Category 1 (Guinea Pig Maximisation Test, OECD 406). Compliance under REACH exempts the compound from registration below 1 tonne per annum for product‑ and process‑orientated R&D, but larger volumes require full dossier submission covering physicochemical, toxicological and ecotoxicological endpoints. The sulfated ash limit of ≤0.1% directly supports compliance with the ICH Q3D elemental impurities guideline for oral drug products, where the permitted daily exposure for lead, arsenic, and cadmium must respect Option 2A concentration limits in the drug substance, achievable only when the catalyst residues from the manufacturing route are scrupulously removed by hot‑toluene recrystallisation and activated‑carbon treatment at 60 °C for 90 min.
