2-Benzothiazolecarbonitrile, 6-Hydroxy-
|
HS Code |
864606 |
| Chemical Formula | C8H4N2OS |
| Molecular Weight | 176.195 g/mol |
| Appearance | Solid (likely, based on similar compounds) |
| Melting Point | No widely - reported value, but can be determined experimentally |
| Solubility In Water | Low solubility, as it is a heterocyclic organic compound |
| Solubility In Organic Solvents | Soluble in polar organic solvents like DMSO, DMF |
| Pka | No reported value, but the hydroxyl group may have acidic properties |
| Stability | Stable under normal conditions, but may react with strong oxidizing or reducing agents |
As an accredited 2-Benzothiazolecarbonitrile, 6-Hydroxy- factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 500g of 6 - Hydroxy - 2 - benzothiazolecarbonitrile packaged in a sealed plastic bag. |
| Shipping | 2 - Benzothiazolecarbonitrile, 6 - Hydroxy - is shipped in accordance with chemical safety regulations. Packed securely in suitable containers to prevent leakage, transported by approved carriers to ensure safe and proper delivery. |
| Storage | Store 6 - Hydroxy - 2 - benzothiazolecarbonitrile in a cool, dry place away from direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and exposure to air, which could potentially lead to chemical degradation. Store it separately from incompatible substances, like strong oxidizing agents, to avoid dangerous reactions. |
In 1,500-gallon glass-lined batch reactors equipped with retreat-curve impellers, the condensation of 6-hydroxy-2-benzothiazolecarbonitrile with p-nitroaniline-derived diazonium salts proceeds under strict negative redox potential control. The diazotization stage holds a thermal window of −2 °C to +2 °C and a free nitrous acid titer exceeding 98.5% relative to theory, verified by starch-iodide endpoint detection; excursions above 5 °C initiate premature decomposition of the diazonium species into a non-coupling quinone-imine tar that reduces isolated yield by 18–24%. The 6-hydroxy-2-benzothiazolecarbonitrile coupling component is charged as a pre-dissolved sodium salt solution in dilute NaOH at pH 9.2 ± 0.3, then metered into the diazonium stream over 45–60 minutes while maintaining jacket heat-transfer fluid at −8 °C. Primary coupling occurs at pH 4.0–4.5 with a molar ratio of diazonium to coupling component of 1.00:1.05; the slight excess of coupler ensures a residual free-amine specification of less than 0.15% in the presscake. After a post-addition stir-out of 90 minutes, the batch is heated to 85 °C over 40 minutes to complete the ortho-directed coupling and drive off excess nitrous gases. The resulting monoazo dye is isolated on a polypropylene membrane filter press at 12 bar squeeze pressure, washed with condensate until filtrate conductivity falls below 50 µS/cm, and dried in a conical vacuum dryer at 30 mbar absolute with a jacket temperature not exceeding 95 °C to prevent crystal phase transition. The dry product, a reddish-brown powder with λmax 438 ± 4 nm in DMF, conforms to DIN EN ISO 105-C06:1997 for wash fastness on PET fibers when applied at 1.0% owf under high-temperature exhaust dyeing conditions of 130 °C and pH 4.5. Commercial formulations target automotive interior textiles requiring ISO 105-B02:2014 Grade 7+ lightfastness. The key regulatory compliance pathway for finished dye exported into EU markets is REACH Annex XVII Entry 43 (azo-dye amines), coupled with OEKO-TEX STANDARD 100 Appendix 4 certification. A dedicated batch-record quality gate mandates HPLC analysis of the crude presscake for the banned o-anisidine impurity at a detection limit of 5 mg/kg before drum filling.What Limits the Bleeding Index of Fluorescent Brighteners in Post-Consumer rPET Bottle Sheet?Compounding 6-hydroxy-2-benzothiazolecarbonitrile derived brightener masterbatch into bottle-grade recycled PET on a co-rotating twin-screw extruder with an L/D ratio of 40:1 introduces a migration control problem rooted in the cyano group’s polarity and the free volume of the amorphous phase. The brightener active, synthesized via Knoevenagel condensation of the nitrile with a heterocyclic aldehyde, is dosed at 0.03–0.06 wt% in the final preform, corresponding to a masterbatch let-down ratio of 1:50. Processing must remain below a barrel temperature of 285 °C in the final two zones; above 293 °C, the brightener undergoes retro-Diels–Alder-like fragmentation detectable as a pressure spike on the gear pump inlet transducer and a 7–12% loss of quantum yield per pass. Intrinsic viscosity of the rPET feedstock must stay above 0.72 dL/g to avoid excessive end-group reactivity that accelerates brightener decomposition. Stretch-blow-molded bottle sidewalls subsequently undergo migration testing per EU Regulation 10/2011 Annex III (overall migration limit 10 mg/dm²) using simulant D2 at 40 °C for 10 days. The brightener exhibits a log Kow of 3.8 ± 0.2, requiring HPLC-fluorescence quantification at excitation 365 nm and emission 430 nm to achieve a reporting limit of 0.05 µg/L in the simulant. For U.S. indirect food-contact status, a formal FDA 21 CFR 178.3297 opinion letter is requested on a case-by-case basis; without it, the product cannot be used in monolayer packaging entering the U.S. Lightfastness of the brightened rPET sheet is screened under ASTM G154 Cycle 1 (UVA-340 lamps, 0.89 W/m²·nm at 340 nm) for 200 hours, where a yellowness index shift of less than 2.5 ΔYI (per ASTM E313-20) is required for brand-owner qualification. The production mass balance tracks the brightener precursor 6-hydroxy-2-benzothiazolecarbonitrile through the condensation step at a stoichiometric excess of 1.2 molar equivalents relative to the aldehyde, with unreacted nitrile recovered by thin-film evaporation at 2 mbar and 175 °C jacket temperature and re-used for up to three cycles before oligomeric impurities exceed 0.5 area-% by GC.Chrome-Tanned Wet-Blue Colouration without Topcoat Delamination: A Dye Intermediate That Tolerates Basification SwellsPenetration depth of anionic leather dyes prepared from 6-hydroxy-2-benzothiazolecarbonitrile as a monoazo coupling component is influenced less by the sulfonation degree than by the propensity of the cyano-substituted benzothiazole ring to form binuclear chromium-complex dyes. In the synthesis of a dark brown to black leather dye equivalent to C.I. Acid Brown 213, one molar part of the nitrile compound is diazotized with 2-amino-4-nitrophenol under glacial conditions, and the resulting monoazo chelate is subsequently chromed using chromium(III) formate at a 1:1 molar ratio of chromium to dye ligand in an autoclave at 115 °C and 1.5 bar gauge for 3 hours. The final formulation is adjusted with formic acid to pH 3.2 ± 0.1 for drum penetration at 35 °C on chrome-tanned cattle hide, applied at 1.5% of shaved weight. The chromed dye achieves through-stain in 45 minutes on substance thickness 1.2–1.4 mm, confirmed by a bisected cross-section under 10× stereomicroscope. Fastness to artificial perspiration (ISO 11641:2012) must return a grey-scale rating of 4–5 on multifibre witness fabric after contact with alkaline histidine solution at pH 8.0. The presence of free chromium(VI) in the dye powder is controlled below the detection limit of 3 mg/kg by ion chromatography-post-column derivatization (DIN EN ISO 17075-1:2017), which is a mandatory parameter under ZDHC MRSL Version 3.0 for automotive leather supply. Resistance to bleed during wet rub cycles (ISO 11640:2018, 1000 cycles, felt pad moistened with synthetic sweat) drops below a grey-scale rating of 3 if the residual unchelated ligand exceeds 0.8% in the spray-dried product; therefore, a post-reaction complexation booster of 0.05 molar equivalents sodium acetate is introduced directly into the marquee-type spray dryer feed tank at 65 °C to drive chelation completion during droplet dehydration. The throughput of a single 5,000-L autoclave batch, isolating 680–720 kg of dry dye, is matched to an annual automotive tier-1 upholstery order forecast with a ± 5% tolerance.When a Gas Turbine Lubricant Antioxidant Synergist Must Survive an RBOT Induction Time Above 1,800 MinutesPhosphite-free antioxidant systems for ISO VG 32 turbine oils exploit the radical-scavenging hydroquinone-like behavior of 6-hydroxy-substituted benzothiazoles after alkaline ester cleavage. 6-Hydroxy-2-benzothiazolecarbonitrile is employed not as a neat additive but as a synthetic precursor to 2-alkylthio-6-hydroxybenzothiazole derivatives through a thiol-displacement reaction on the cyano group, catalysed by tetrabutylammonium bromide under phase-transfer conditions at 0.5 mol% loading. The resulting product, after vacuum fractional distillation at 210–215 °C under 0.05 mbar, is blended into a Group II base oil at 0.15 wt% active content alongside a hindered phenol primary antioxidant. Accelerated oxidation stability measured by the rotating pressure vessel oxidation test (ASTM D2272-22) yields an RBOT induction time of >1,800 minutes versus 1,050 minutes for the phenol-only baseline; the synergist increases the onset temperature in pressurized differential scanning calorimetry (ASTM D6186-19, 200 psi O₂) by 16 °C. The formulation containing the benzothiazole ring structure meets the oxidation stability requirements of GEK 32568j and GEK 121608 for Frame 9FA gas turbines. Since the parent nitrile intermediate is a crystalline solid with m.p. 238–241 °C and exhibits some dust explosion hazard (Kst value of 180 bar·m/s when milled to D50 < 15 µm), high-speed bag dump stations at the oil-additive plant are interlocked with oxygen deficiency monitoring set to activate inert nitrogen purge at an O2 threshold of 8%. On the lubricant blending floor, the intermediate is maintained in extruded pastille form with a residual moisture content below 0.1% to prevent hydrolysis of the subsequent thiolate adduct, which would release hydrogen sulfide and downgrade the RBOT back to baseline. A single batch handles 600 kg of pastilles supplying approximately 1.06 metric tonnes of synergist, matched to a production run of 75,000 L of finished turbine oil.Direct cartridge filling of aqueous inkjet dye solutions on an automated 24-head volumetric dispensing line illustrates a solubility bottleneck that is overcome by postsynthetic sulfomethylation. When 6-hydroxy-2-benzothiazolecarbonitrile is employed as the right-hand building block in a disazo direct dye structure, the initial diamino intermediate—precipitated from an ice-brine suspension at −4 °C with a net osmotic pressure differential of 2.4 MPa across the PES ultrafiltration unit—exhibits solubility in deionized water below 12 g/L at 25 °C. Introduction of a sulfomethylene group via formaldehyde-bisulfite adduct in a jet loop reactor at 70 °C and 30 bar increases solubility to >250 g/L, meeting the ≥15% dye loading specification required by OEM printhead manufacturers for high-density piezoelectric drop-on-demand printing at 600 × 1200 dpi. The final dye concentrate is polished through a 0.2 µm absolute-rated nylon membrane filter to achieve a particle count of <10 particles/mL larger than 0.5 µm (USP <788>). The dyestuff’s cyano group imparts a bathochromic shift that extends the absorption tail to 670 nm, enabling a composite black ink when combined with a copper phthalocyanine turquoise. Accelerated shelf-life testing at 60 °C for 4 weeks (equivalent to 12 months ambient per Arrhenius kinetics at Ea = 65 kJ/mol) shows viscosity drift within ±0.15 mPa·s from the 3.0 mPa·s setpoint, passing jetting reliability requirements under IEC 62899-302-2:2024. Trace heavy metal content in the final cartridge-grade dye solution is capped at 2 mg/kg for cadmium and 10 mg/kg for total iron according to EU Directive 94/62/EC (CONEG). On a per-cartridge basis, the 6-hydroxy-2-benzothiazolecarbonitrile-derived chromophore accounts for 3.8 g of the active colorant in a standard 200 mL high-capacity tank.The hydrolysis mechanism of the C≡N group in alkaline cooling-water circuits is exploited to control copper alloy release in open evaporative condensers handling softened make-up water. 6-Hydroxy-2-benzothiazolecarbonitrile is formulated as its water-soluble sodium salt and combined with polymeric dispersants and hydroxyphosphonoacetic acid concentrate at a weight fraction of 4.5% active in a multicomponent corrosion inhibitor product. Continuous feed is maintained by positive-displacement diaphragm pumps to sustain a total azole residual of 2.0–5.0 mg/L measured by UV absorbance at 292 nm, with the specific heterocycle differentiating from tolyltriazole on a dual-wavelength ratio algorithm corrected for iron interference at 370 nm. Copper corrosion rates measured via linear polarization resistance probes (NACE TM0169-2021) are held below 0.005 mm/yr on UNS C70600 (90/10 Cu-Ni) at a cooling-water pH of 8.8–9.2 and a free chlorine residual of 0.3 mg/L. Because the hydroxybenzothiazole film persists under intermittent overfeed of oxidizing biocide that destabilizes tolyltriazole passivation layers—an advantage traceable to the electron-withdrawing nitrile group that resists N-chlorination—the product is specifically listed on NSF/ANSI/CAN 60 for maximum use level of 15 mg/L as total product in corrosion-controlled municipal drinking water treatment. The formulating plant pre-charges the nitrile intermediate powder via a contained glovebox transfer into deoxygenated deionized water under a nitrogen blanket at 10 mbar positive pressure to prevent premature hydrolysis, because the component loses 3% of its cyano integrity per week of exposure to ambient dissolved oxygen at pH 10.0. |
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2-Benzothiazolecarbonitrile, 6-Hydroxy- (CAS 939-78-5; molecular formula C8H4N2OS; molecular weight 176.19 g·mol−1) is a substituted fused heterocycle carrying a nitrile group at the 2-position and a phenolic hydroxyl at the 6-position of the benzothiazole ring. The compound appears as an off-white to pale-yellow crystalline powder with a melting point reported in the range 238–242 °C (with decomposition; capillary method, heating rate 2 °C/min). Its dual functionality enables orthogonal derivatization pathways: the hydroxyl serves as a handle for etherification, esterification, or silyl protection, while the cyano group can be hydrolysed to a carboxylic acid, reduced to an aminomethyl moiety, or engaged in cycloaddition sequences. Industrial supplies are typically offered at ≥98.0% purity by HPLC (area normalisation, detection at 254 nm) with a moisture content not exceeding 0.5 wt%, a residue on ignition below 0.1%, and a single impurity threshold of ≤0.5% for the des-hydroxy or des-cyano by-products.
The unsubstituted 2-benzothiazolecarbonitrile (CAS 19736-81-3) lacks the electron-donating hydroxyl group, resulting in a markedly different electronic landscape across the ring system. In the 6-hydroxy derivative, the hydroxyl activates the para-related 5- and 7-positions toward electrophilic substitution, whereas in the parent structure, electrophilic attack on the benzene ring is substantially less regioselective and requires harsher conditions. Hammett substituent constants for the hydroxy group (σp ≈ −0.37) indicate significant resonance donation, which raises the HOMO level of the benzothiazole core, facilitating oxidative coupling and Pd-catalysed C–H activation at the 5-position. This electronic bias has been exploited in the synthesis of merocyanine dyes and fluorescent probes: the 6-hydroxy derivative can be O-alkylated under mild phase-transfer conditions (K2CO3, acetonitrile, 60 °C, 6 h) to install side chains without affecting the cyano group, whereas 2-benzothiazolecarbonitrile requires elevated temperatures and may suffer nitrile hydrolysis when similar basic conditions are applied.
Furthermore, the 6-hydroxy group introduces pH-dependent solubility. Above pH 8.5, deprotonation to the phenoxide increases aqueous solubility to >50 g·L−1 at 25 °C, a property that simplifies workup and aqueous-phase coupling protocols. The nitrile group remains stable in moderately alkaline media provided the temperature is held below 50 °C and the residence time is shorter than 2 h; prolonged exposure at pH 12 results in gradual hydrolysis to the corresponding carboxamide, detectable by the emergence of a carbonyl stretch at 1670 cm−1 in FT-IR. Thus, the 6-hydroxy intermediate offers a broader processing window than its des-hydroxy analogue when aqueous alkaline conditions are unavoidable.
Preservation of the carbonitrile functionality during Pd-mediated coupling reactions is the primary stability constraint encountered on pilot scale. The nitrile is susceptible to hydrolysis to the amide or acid under the aqueous basic conditions commonly required for Suzuki–Miyaura couplings. Process development campaigns conducted in 10-L jacketed glass reactors with anchor-type agitation have demonstrated that the hydrolysis rate doubles when the aqueous-phase pH exceeds 11.5 at 70 °C. A representative procedure utilising Pd(PPh3)4 (2 mol%) and K2CO3 in THF/water (4:1 v/v) at 65 °C for 8 h yielded the target biaryl with 92% conversion, but raising the base concentration to 3.0 M K2CO3 produced 7% of the hydrolysed amide impurity, which co-elutes with the desired product on silica gel. Switching to a non-aqueous base system—CsF (3.0 equiv.) in dry DMF at 80 °C—eliminated hydrolysis entirely, though it necessitated post-reaction scavenging of residual fluoride ions with calcium chloride to prevent corrosion of downstream stainless-steel concentration vessels. Pre-drying of the hydroxy-substituted starting material at 60 °C under 10 mbar for 4 h prior to reaction is mandatory when using anhydrous solvent protocols; residual moisture above 500 ppm in DMF reintroduces hydrolysis pathways.
For Sonogashira alkynylations, the phenolic proton can compete for coordination to palladium, retarding the catalytic cycle. Protection as the tert-butyldimethylsilyl ether (TBS-Cl, imidazole, DMF, 25 °C, 12 h) removes this interference and permits reliable coupling at 0.5 mol% Pd(PPh3)2Cl2 loading with CuI (1 mol%) as co-catalyst in triethylamine at 45 °C. The silyl ether is subsequently cleaved with tetra-n-butylammonium fluoride (1.0 M in THF, 1.2 equiv.) without attacking the nitrile, provided the deprotection is performed at 0–5 °C and quenched with pH 7 phosphate buffer within 30 min.
Commercial lots are released against an internal specification that draws on pharmacopoeial general chapters and recognised consensus standards. The following table summarises the typical acceptance criteria and the corresponding test methods employed by manufacturers.
| Parameter | Acceptance Limit | Test Method / Standard Reference |
|---|---|---|
| Appearance | Off-white to pale-yellow crystalline powder | Visual inspection vs. reference standard |
| Assay (HPLC, wt%) | ≥ 98.0% | USP <621>, C18 column, acetonitrile/0.1% H3PO4 (60:40), 1.0 mL/min, 254 nm |
| Water content (KF) | ≤ 0.5% | ISO 760:1978, coulometric Karl Fischer titration |
| Residue on ignition | ≤ 0.10% | Ph. Eur. 2.4.14 (Sulphated ash) |
| Heavy metals (as Pb) | ≤ 10 ppm | Ph. Eur. 2.4.8 / ICP-MS |
| Melting range | 238–242 °C (decomposition) | Capillary method, heating rate 2 °C/min, differential scanning calorimetry (DSC) onset 241 °C |
| Single largest impurity | ≤ 0.50% | HPLC, same conditions as assay |
| Total unspecified impurities | ≤ 1.00% | HPLC, same conditions as assay |
Identity is routinely confirmed by IR (KBr pellet) with characteristic bands at 2230 cm−1 (C≡N stretch), 3100–3400 cm−1 (broad O–H stretch), and 1600 cm−1 (benzothiazole C=N ring vibration). 1H NMR (DMSO‑d6, 400 MHz) displays the phenolic proton as a broad singlet at δ 10.3 ppm, aromatic protons as a doublet at δ 7.6 ppm (J = 8.8 Hz, H‑4), a doublet at δ 7.4 ppm (J = 2.4 Hz, H‑7), and a doublet of doublets at δ 7.1 ppm (J = 8.8, 2.4 Hz, H‑5).
Operational boundaries in storage: prolonged exposure to relative humidity above 70% at 25 °C leads to caking and a measurable increase in moisture content above the 0.5% limit within 48 h. Re-drying in a vacuum oven at 60 °C and ≤10 mbar for 6 h restores moisture to specification, though repeated cycles may promote partial thermal decomposition, signalled by discoloration to tan and a 0.2–0.3% drop in HPLC purity. The compound is incompatible with strong oxidising agents and concentrated nitric acid, with which it reacts exothermically, evolving toxic oxides of nitrogen and sulphur.
2-Benzothiazolecarbonitrile, 6-Hydroxy- serves as a late-stage building block in several registered synthetic routes to kinase inhibitors and agrochemical fungicides. In the construction of 6-alkoxybenzothiazole-2-carbonitrile libraries, O-alkylation with alkyl bromides in the presence of K2CO3 in DMF at 50 °C proceeds with >95% conversion and minimal cyano hydrolysis when the alkylation agent is added dropwise over 30 min to control the mild exotherm. The resulting ethers are advanced through Claisen rearrangements or used directly in amination reactions at the 2-nitrile to form amidine derivatives, key pharmacophores in serine protease inhibitors.
A second high-volume application is the production of fluorescent whitening agents (FWAs) and optical brighteners for textiles. Here, the hydroxyl group is first sulphonated or converted to a sulfonate ester, enabling attachment to stilbene or bis-triazinyl bridging units. The nitrile remains intact throughout the condensation, which is typically conducted in chlorobenzene at 130 °C with a catalytic amount of N,N-dimethylaniline. The resulting FWA exhibits a quantum yield above 0.80 and maximum emission at 430–440 nm when tested on polyester fabric according to ISO 105-B02:2014. Residual free nitrile content in the final formulation is below 10 ppm, which is monitored by GC-MS headspace analysis to meet Oeko-Tex Standard 100 requirements.
In coordination chemistry, the 6-hydroxy-2-benzothiazolecarbonitrile ligand chelates transition metals through the phenoxide oxygen and the endocyclic nitrogen of the thiazole ring. The resultant complexes show an absorption band at 480–520 nm, sensitive to the metal ion, and have been patented for use in nonlinear optics and as photostabilisers in polyolefin films. Crucially, the cyano group does not participate in coordination, which distinguishes this ligand from 2-cyanophenol derivatives that form five-membered chelate rings involving the nitrile.
6-Hydroxybenzothiazole (CAS 52700-26-4) lacks the carbonitrile at C-2, bearing only a hydrogen atom, which drastically limits the synthetic transformations available at that position. While lithiation at C-2 with n-butyllithium in THF at −78 °C is feasible, the subsequent electrophilic quench with tosyl cyanide to install a nitrile requires strict cryogenic control and results in variable yields (45–70%) due to competing ring-opening side reactions. The pre-installed nitrile in 2-benzothiazolecarbonitrile, 6-hydroxy- removes this low-temperature step and its associated cryogenic reactor demand, shortening the synthetic sequence by one to two steps in routes that converge on 2-cyanobenzothiazole derivatives. Process mass intensity (PMI) calculations for a representative three-step campaign (etherification, nitrile hydrolysis, amide coupling) show that starting from the 6-hydroxy-2-cyano compound lowers PMI by 22% relative to a route that must introduce the nitrile late, primarily by eliminating lithiation solvents and quenching by-products.
Regardless of the selected downstream chemistry, handling precautions on pilot scale include grounding and inerting of all powder-transfer operations to mitigate dust explosion risk; the minimum ignition energy of an airborne dust cloud of this material, measured according to ASTM E2019, is in the range 10–30 mJ, which places it in the Group B dust classification. Local exhaust ventilation and conductive footwear are mandatory during charging of 25-kg fibre drums into a reactor with an open manway. A final rinse of the drum with 2 L of dimethylformamide and transfer to the reactor recovers residual powder adhering to the inner lining, improving lot yield by approximately 0.2%.
