Methyl 2-Aminothiazole-4-Carboxylate
|
HS Code |
937310 |
| Chemical Formula | C5H6N2O2S |
| Molecular Weight | 158.18 g/mol |
| Appearance | Typically a solid (color may vary depending on purity) |
| Melting Point | Data may vary, around 150 - 160 °C (approximate, needs experimental verification) |
| Solubility In Water | Poor solubility in water |
| Solubility In Organic Solvents | Soluble in some polar organic solvents like DMSO, DMF |
| Pka | No commonly reported pKa value available, but the amino group can potentially be protonated |
| Odor | May have a faint, characteristic odor |
| Stability | Stable under normal conditions, but sensitive to strong acids, bases, and oxidizing agents |
As an accredited Methyl 2-Aminothiazole-4-Carboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100 - gram bottles containing Methyl 2 - Aminothiazole - 4 - Carboxylate, tightly sealed. |
| Shipping | Methyl 2 - Aminothiazole - 4 - Carboxylate is shipped in accordance with chemical transport regulations. It's carefully packaged in suitable containers to prevent leakage, and transported by approved carriers ensuring safety during transit. |
| Storage | Methyl 2 - Aminothiazole - 4 - Carboxylate should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, open flames, and oxidizing agents. Store in a tightly sealed container to prevent moisture absorption and potential reactions. This compound should be segregated from incompatible substances to avoid chemical hazards. |
In the multi-tonne annual output of sterile ceftazidime pentahydrate, the methyl 2-aminothiazole-4-carboxylate molecule functions as the primary gateway to the (Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetyl side chain—universally abbreviated ATMA. Production campaigns at dedicated cephalosporin intermediate plants in Shandong and Gujarat routinely process 1.5–2.0 metric tonnes of the methyl ester per batch, converting it to ATMA via a two-stage oxime formation–ester hydrolysis sequence that has largely supplanted older acyl chloride routes because of its lower dermal sensitisation profile. The critical step, condensation with methoxylamine hydrochloride, is executed in a 1:1.05 molar ratio in refluxing methanol (64–66 °C) held for 14–18 hours in glass-lined reactors equipped with Hastelloy C-276 overhead condensers to resist chloride-induced pitting. Process analytical technology (PAT) probes track the disappearance of the starting ester absorption at λmax 285 nm; the endpoint is set at residual ester ≤ 0.15 area% by HPLC. Immediately after condensation the reaction mass is cooled to −5 to 0 °C and the crystalline syn-oxime ester intermediate is isolated on a pressure nutsche filter, washed with chilled deionised water (conductivity ≤ 1.2 μS/cm), and hydrolysed in situ with aqueous sodium hydroxide at pH 10.8–11.2 and 25–30 °C—conditions selected to minimise Z→E isomerisation, which becomes thermodynamically competitive above 35 °C. The Z-isomer content of the final ATMA acid must meet the EP 10.0 monograph specification of ≥ 99.0 %, verified by reverse-phase HPLC on a C18 column (USP L1) with a mobile phase of methanol–0.02 M phosphate buffer (25:75 v/v). Plant-scale failure modes documented in deviation reports include a sharp drop in Z-purity when the hydrolysis exotherm is not arrested within 3–5 minutes—typically due to inadequate jacket cooling capacity—and the formation of the mutagenic impurity 2-aminothiazole (Class 3 per ICH M7) when the mother liquor is recycled without prior oxidation treatment. Quality release of the methyl ester feedstock therefore enforces a limit of ≤ 50 ppm of free 2-aminothiazole (GC-MS, SIM mode m/z 100) and a water content ≤ 0.10 % (Karl Fischer coulometric titration per ASTM E1064). Regulatory filings in EMA and PMDA jurisdictions additionally require a declaration of the residual solvent profile conforming to ICH Q3C(R8): methanol not exceeding 3000 ppm, methyl acetate (the transesterification marker) below 5000 ppm, and absence of dimethyl sulfate or methyl iodide traces when the ester was sourced from contractors using methyl halide quaternisation. Downstream, the ATMA acid is coupled with 7-amino-3-(1-pyridiniomethyl)-3-cephem-4-carboxylate hydrochloride following activation with ethyl chloroformate and N-methylmorpholine in dichloromethane at −15 °C, ultimately yielding ceftazidime after side-chain deprotection with HCl gas in dioxane. The entire sequence is executed under ISO 8 or better cleanroom conditions as mandated by EU GMP Annex 1 for sterile β-lactam APIs, with viable particle monitoring at ≤ 10 CFU/m³ during aseptic crystallisation.A methoxylamine-mediated keto ester transformation forms the backbone of ethaboxam synthesis, with methyl 2-aminothiazole-4-carboxylate supplying the exact carbon–nitrogen skeleton required by the oomycete fungicide’s pharmacophore. Industrial operation sheets from a dedicated ethaboxam campaign in Yeosu specify charging 800 kg of the methyl ester into a 5000 L jacketed stainless-steel reactor train, followed by 1.03 equivalents of methoxylamine free base (generated in situ from the hydrochloride with 30 % w/w sodium hydroxide) in a methanol–tetrahydrofuran (3:1 v/v) solvent system. The oxime ether is formed at 58–60 °C under nitrogen blanketing to suppress oxidative dimerisation of the thiazole ring—a side reaction that generates a deep orange by‑product tracked by its absorbance at 420 nm and capped at ≤ 0.25 absorbance units in the filtered reaction liquor. After solvent swap to acetonitrile, the intermediate ethyl or methyl 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetate is reacted with morpholine in the presence of 0.05 equivalents of tetrabutylammonium bromide phase-transfer catalyst at 45–50 °C for 8 hours, affording the ethaboxam free acid in 86–90 % isolated yield after recrystallisation from isopropanol–water (70:30 v/v). The technical concentrate must assay ≥ 980 g/kg on the dry basis (CIPAC MT 857, HPLC-UV at 254 nm) with the des-methoxy analog controlled below 0.5 g/kg and the (E)-oxime isomer below 2.0 g/kg, because the latter exhibits roughly 20‑fold lower intrinsic activity against Phytophthora infestans in detached-leaf assays. Registration under OECD guidelines 501, 502, and 503 for plant protection products in the European Union mandates a five‑batch analysis of the methyl 2-aminothiazole-4-carboxylate starting material, covering identity (IR spectrum matching the EP Reference Standard), melting point (172–175 °C, determined by differential scanning calorimetry at 10 °C/min under nitrogen), and a screen for hydrazine and its acetylated derivatives at a reporting limit of 0.1 mg/kg—a concern that arises when the ester is manufactured via the Hantzsch cyclocondensation route using thiosemicarbazide derivatives. The formulated ethaboxam product, a 100 g/L suspension concentrate, additionally requires the wet‑milled active ingredient to exhibit a particle size distribution with D90 ≤ 4.0 μm (laser diffraction, ISO 13320:2020) to ensure adequate coverage on grapevine leaf surfaces during airblast spraying.Is Diazotisation of the Exocyclic Amine on Methyl 2-Aminothiazole-4-Carboxylate Feasible at Sub-Zero Temperatures for Azo Colourants?When dispersed in 30 % hydrochloric acid at −2 to 0 °C and treated stepwise with 1.02 molar equivalents of sodium nitrite in minimal water, the exocyclic amino group undergoes quantitative diazotisation within 45–60 minutes, yielding a pale‑yellow, starch‑iodide‑positive diazonium salt that remains thermally stable only below 3 °C—decomposition onset is recorded by accelerating rate calorimetry at 7 °C with a self‑heat rate exceeding 0.5 °C/min. This species is coupled immediately with carefully selected electron‑rich aromatic partners: a representative industrial recipe for a bluish‑red disperse dye for polyester‑microfiber calls for mixing the diazonium liquor with a methanolic suspension of N,N-diethyl‑m-toluidine (0.98 equivalents, pre‑dissolved in 2.5 L methanol per kg of coupler) while maintaining pH between 3.8 and 4.2 through automatic dosing of 20 % sodium acetate trihydrate. The coupling exotherm is controlled at 8–12 °C inside a dimpled‑jacket vessel with brine circulation; exceeding 15 °C results in a noticeable shift in hue angle from ~342° toward 28° (CIELAB D65/10°) due to increased bis‑azo by‑product formation. The press‑cake is washed to a conductivity of ≤ 500 μS/cm, dried under vacuum at 60 °C, and micronised in an air‑jet mill to a median particle size of 0.8–1.2 μm (Malvern Mastersizer, ISO 13320) before being standardised with 50 wt% lignosulfonate dispersant. The resultant commercial preparation delivers build‑up on polyethylene terephthalate knit fabric that achieves 1/1 standard depth at 2.0 % o.w.f. under high‑temperature exhaust dyeing (130 °C for 60 min), with wash fastness rated 4–5 by ISO 105‑C06 C2S and light fastness ≥ 6 (Xenon arc, ISO 105‑B02). Because the free amine precursor is classified as a potential skin sensitiser, the dyestuff intermediate workshop must operate under continuous LEV with a target occupational exposure limit of 0.1 mg/m³ (8‑h TWA, internal corporate standard benchmarked against MAK Commission methodology). Wastewater streams containing unreacted diazonium salt are quenched with sulfamic acid (1.5 % w/v) before biological treatment, bringing adsorbable organic halogen (AOX) below the 0.5 mg/L consent limit of the local discharge permit. The finished azo colourant is certifiable under OEKO‑TEX Standard 100 Annex 4, requiring a nil detection of regulated aromatic amines (including 2‑aminothiazole) by reductive cleavage followed by GC‑MS analysis according to EN ISO 14362‑1:2017, with a method detection limit of 5 mg/kg.Saponification Workflow for 2-Aminothiazole-4-Carboxylic Acid at Multi-Kilogram ScaleHydrolysis of the methyl ester to the corresponding free acid, 2‑aminothiazole‑4‑carboxylic acid, is a standing‑order commodity conversion that supplies the hydrophilic anchor for water‑soluble prodrug constructs as well as the key intermediate for amide‑tethered biotinyl probes. In a typical campaign inside a non‑GMP kilo‑lab, 25.0 kg of methyl 2‑aminothiazole‑4‑carboxylate is suspended in 125 L of deionised water and treated with 1.15 equivalents of sodium hydroxide pellets added portionwise while maintaining the internal temperature below 35 °C to suppress the ring‑opening side reaction that produces 2‑aminothioacrylamide derivatives detectable by LC‑MS at m/z 119 [M+H]+. After stirring at 40–45 °C for 3–4 hours the clear solution is filtered through a 0.45 μm polypropylene cartridge, acidified to pH 2.5–2.8 with 32 % hydrochloric acid, and the precipitated zwitterionic acid is collected on a Buchner funnel and washed with chilled methanol until the filtrate shows chloride ion ≤ 200 ppm by silver nitrate turbidimetry. Vacuum drying at 50 °C for 16 hours yields the product with a loss on drying ≤ 0.5 % and assay typically 99.8–100.2 % on the anhydrous basis by perchloric acid titration (0.1 M in anhydrous acetic acid, potentiometric endpoint detection). The only meaningful stability concern is surface discolouration to pale pink upon prolonged exposure to fluorescent light; packaging in opaque, LDPE‑lined fibre drums at ≤ 25 °C under nitrogen preserves the specification‑compliant appearance for 24 months from the date of manufacture. This acid is subsequently activated with carbonyl diimidazole or N‑hydroxysuccinimide‑dicyclohexylcarbodiimide for coupling to amine‑bearing pharmacophores under GLP conditions, a step that occurs outside the scope of the bulk‑hydrolysis supply chain.When Methyl 2-Aminothiazole-4-Carboxylate Replaces Aniline in α-Diimine Ligand ArchitecturesA specialised, low‑tonnage but high‑value application situates the methyl ester within the ligand‑design loop for late‑transition‑metal olefin polymerisation catalysts. Condensation of methyl 2‑aminothiazole‑4‑carboxylate with acenaphthenequinone in refluxing toluene containing 0.5 mol% of p‑toluenesulfonic acid generates the bis(thiazole‑imine) pro‑ligand in 72–78 % yield after column chromatography on silica gel (eluent: hexane–ethyl acetate, 4:1). Metalation with (1,5‑cyclooctadiene)palladium(II) chloride in dichloromethane at 25 °C proceeds quantitatively within 2 hours, displacing the cyclooctadiene and furnishing a square‑planar Pd(II) complex that precipitates directly from the reaction medium upon addition of diethyl ether. Under ethylene pressure of 5 bar in a 100 mL Parr reactor charged with rigorously anhydrous chlorobenzene and 100 equivalents of methylaluminoxane (MAO, 10 wt% in toluene), the pre‑activated catalyst exhibits a turnover frequency of 1.2 × 10³ mol C₂H₄ (mol Pd·h)⁻¹ at 30 °C as measured by mass‑flow‑meter uptake curves—a value that places the substitution of the canonical aniline ring with the 4‑methylcarboxylate‑thiazole moiety among the more productive modifications in the nickel‑and‑palladium α‑diimine library, although methane elimination from the ester group becomes pronounced at temperatures above 55 °C, degrading the MAO co‑catalyst. The resultant polyethylene is characterised by a bimodal gel‑permeation chromatography trace (refractive index detection, 1,2,4‑trichlorobenzene at 160 °C, narrow polystyrene standards) with a high‑molecular‑weight shoulder extending to Mw ~ 8 × 10⁵ g mol⁻¹ and a polydispersity index near 2.8, consistent with a chain‑walking mechanism that introduces short‑chain branching (quantified by 13C NMR as ~ 85 branches per 1000 carbon atoms, predominantly methyl and ethyl branches). This ligand platform has not been transferred to continuous slurry‑loop reactor trials, and published data on long‑term co‑catalyst consumption rates for this specific configuration are limited; however, the solubility imparted by the ester group facilitates scavenger‑supported catalyst stripping during post‑polymerisation deactivation, an operational advantage that has been noted in pilot‑scale batch campaigns requiring a deashing step compliant with EU food‑contact plastics regulation EU 10/2011, overall migration limit 10 mg/dm².Sequential Cyclocondensation Routes Target Thiazolo[4,5‑d]pyrimidin‑7(6H)‑one DerivativesMedicinal chemistry groups interrogating purine‑mimetic kinase inhibitors routinely activate methyl 2‑aminothiazole‑4‑carboxylate for bicyclic heterocycle construction through a two‑step cyclocondensation that requires no intermediate isolation. The ester is first refluxed with 1.0 equivalent of triethyl orthoformate and 1.3 equivalents of acetic anhydride in toluene for 5 hours, forming the ethoxymethylene intermediate, after which the volatiles are stripped and replaced with DMF; addition of 1.05 equivalents of a primary amine—commonly 4‑fluoroaniline or cyclopropylamine—at 80 °C triggers regioselective closure to the thiazolo[4,5‑d]pyrimidin‑7(6H)‑one core in 65–80 % overall yield. The pendant 2‑amino group on the thiazole ring remains intact throughout the sequence, available for subsequent diversification via reductive amination with 1.1 equivalents of 4‑formylbenzonitrile and sodium triacetoxyborohydride (1.5 equivalents) in 1,2‑dichloroethane. When screened at 10 μM against a panel of 97 human kinases (Eurofins DiscoveryX scanMAX platform), the resulting N‑substituted thiazolopyrimidines have returned hit rates exceeding 20 % for binding to CMGC‑family targets, with dissociation constants for the strongest binders falling below 50 nM. Suppliers offering the methyl ester to discovery organisations typically provide it in septum‑sealed, oven‑dried (80 °C, vacuum) aliquots of 5–100 g with a certificate of analysis that includes a 1H NMR purity of ≥ 98.5 % (DMSO‑d₆, 400 MHz), residual tin below 10 ppm (ICP‑MS) when the product was manufactured via the organotin‑mediated Hantzsch route, and a clear statement regarding the absence of genotoxic carbamate derivatising agents—a requirement driven by the downstream intention to file an IND that must reference ICH M7 Option‑4 control limits. |
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Methyl 2-aminothiazole-4-carboxylate (CAS 66358-36-9), empirical formula C5H6N2O2S and a molecular weight of 158.18 g/mol, functions as a polyfunctional synthon whose primary amine, thiazole nitrogen, and ester group provide orthogonal reactivity vectors. In contrast to the corresponding carboxylic acid or bulkier alkyl esters, the methyl ester displays a favorable balance between crystallinity and solubility that simplifies purification via recrystallisation from toluene–heptane mixtures and permits direct use in subsequent amidation or heterocyclisation steps without protecting-group manipulation. The compound is supplied as a white to pale-yellow crystalline powder with a melting endotherm onset of 134–136 °C (differential scanning calorimetry at 10 K/min under nitrogen) and is routinely characterized by 1H NMR (DMSO‑d6) where the aromatic C‑5 proton appears as a singlet near 7.8 ppm and the methoxy singlet integrates for three protons at 3.8 ppm. Where other aminothiazole esters may require chromatographic removal of regioisomeric byproducts, the 4‑carboxylate substitution pattern inherently directs electrophilic attack to the 5‑position of the thiazole ring, reducing the impurity profile in downstream condensations with aldehydes or Vilsmeier–Haack formylation.
Beyond the CAS registry number and molecular formula, the compound is unambiguously identified by its IUPAC name: methyl 2‑amino‑1,3‑thiazole‑4‑carboxylate. The material typically assays at ≥98.0 % (HPLC, area‑% at 254 nm) when controlled against the monograph of the in‑house specification of major fine‑chemical suppliers. Residual solvent content is monitored under ICH Q3C guidelines, with toluene and methanol being the most commonly observed residues; both are held below 890 ppm and 3,000 ppm, respectively. Water content, determined by Karl Fischer coulometry (USP <921> Method Ia), does not exceed 0.5 % for material released from a vacuum-drying step at 40 °C and <10 mbar for a minimum of 8 h. Heavy metals are controlled to ≤20 ppm total (USP <231> Method II), and palladium content is typically <5 ppm when the final bond‑forming step employs Pd‑catalysed cross‑coupling that is followed by a charcoal‑filtration polish. The table below collates the analytical release criteria accepted by contract manufacturing organisations producing the compound at the 50–500 kg scale.
| Attribute | Acceptance Criterion | Method |
|---|---|---|
| Appearance | White to off‑white crystalline powder | Visual inspection against NCS colour standard |
| Assay (anhydrous, solvent‑free basis) | 98.0–102.0 % | HPLC‑UV, external standard; C18 column, acetonitrile‑phosphate buffer pH 2.5 (30:70 v/v) |
| Melting range | 134–136 °C | DSC onset at 10 K/min; also verified by capillary method (USP <741>) |
| Water (KF) | ≤0.5 % | USP <921> Ia |
| Residual solvents | Methanol ≤3,000 ppm; toluene ≤890 ppm; others per ICH Q3C option‑2 limits | Headspace GC‑FID calibrated with external standards |
| Single unspecified impurity | ≤0.5 % | HPLC‑UV, area‑%; relative response factor 1.0 assumed |
| Total impurities | ≤2.0 % | As above |
| Palladium | ≤5 ppm | ICP‑MS after microwave digestion |
The electron‑withdrawing character of the methyl carboxylate substituent at C‑4 polarises the thiazole nucleus such that the C‑5 position is the most nucleophilic carbon in the ring, a property exploited in the construction of thiazolo[5,4‑d]pyrimidine scaffolds. When the amine is acylated or amidinated, the resultant intermediate undergoes cyclisation with one‑carbon donors—such as formic acid, triethyl orthoformate, or dimethylformamide dimethyl acetal—to deliver fused bicyclic systems that are precursors to adenosine‑receptor antagonists and bromodomain‑targeting ligands. In a representative protocol, condensation with benzamidine hydrochloride in the presence of sodium ethoxide in refluxing ethanol gives the 2‑phenylthiazolo[5,4‑d]pyrimidin‑7‑ol core in 65–78 % isolated yield after trituration with water, with regioselectivity exceeding 95 % as judged by 1H NMR of the crude reaction mixture. This contrasts with 4‑carboxylate isomers that carry the ester at the 5‑position, which typically require chromatographic separation of the concomitant angular cyclisation product.
Equally valuable is the ability to convert the methyl ester to the corresponding hydrazide by treatment with hydrazine hydrate in ethanol at 60 °C for 3 h, furnishing a crystalline intermediate that is directly suitable for Pictet–Spengler‑type or Knorr‑pyrazole syntheses. The aminothiazole core remains intact under these conditions, demonstrating that the amine does not require pre‑protection, a significant advantage over the 2‑bromothiazole‑4‑carboxylate alternative, which demands palladium‑catalysed amination to introduce the C‑2 amine after hydrazide formation. In agrochemical analogue programmes, the methyl ester has served as a starting point for the synthesis of 2‑aminothiazole‑4‑carboxamides with fungicidal activity; in these scaffolds, the methyl ester is first saponified to the acid, converted to the acyl chloride with thionyl chloride, and then coupled with substituted anilines. The availability of the methyl ester avoids the handling and storage challenges associated with the free acid, which is prone to decarboxylation above 200 °C and shows limited solubility in common amide‑coupling solvents.
In continuous‑flow hydrogenation studies, methyl 2‑aminothiazole‑4‑carboxylate dissolved in tetrahydrofuran at 0.5 mol/L has been subjected to nitro‑group reduction on a Raney‑nickel‑packed cartridge without observable ester cleavage, whereas the corresponding ethyl ester exhibits 3–5 % transesterification to the butyl ester when the solvent stream contains residual butanol from a prior conditioning cycle. This differential stability under hydrogenolytic conditions is attributed to the reduced electrophilicity of the methyl ester carbonyl in the presence of Lewis‑basic sites on the catalyst surface.
The choice between the methyl ester, the free carboxylic acid, and the ethyl ester is governed by the balance among synthetic accessibility, purification efficiency, and downstream functional‑group compatibility. Methyl 2‑aminothiazole‑4‑carboxylate crystallises from ethyl acetate‑cyclohexane as compact prisms that filter rapidly on a 0.5 m² Nutsche filter and dry to a free‑flowing powder without caking, a processability advantage over the acid, which often precipitates as a voluminous hydrate that retains up to 12 % water after mechanical deliquoring. The methyl ester is also less hygroscopic than the acid; dynamic vapour sorption analysis shows less than 0.2 % mass gain at 80 % relative humidity over 24 h, compared to 2.5 % for the acid monohydrate. The table below compares key properties that influence the choice of intermediate in kilo‑lab and pilot‑plant campaigns.
| Property | Methyl ester (CAS 66358-36-9) | Ethyl ester (CAS 5398-36-7) | Carboxylic acid (CAS 4021-08-4) |
|---|---|---|---|
| Molecular weight (g/mol) | 158.18 | 172.21 | 144.15 |
| Melting point (°C) | 134–136 | 92–95 | decomposition >200 (decarboxylation) |
| Solubility in water (mg/mL, 25 °C) | 2–3 (sparingly soluble, USP <1236>) | 1–2 | 8–10 (as sodium salt) |
| Solubility in methanol | freely soluble, >25 mg/mL | freely soluble | soluble |
| Preferred recrystallisation solvent | Toluene‑heptane (3:1 v/v) | Isopropanol‑water | Water (acidification of sodium salt) |
| Amidation efficiency with primary amines (DCC/DMAP, CH2Cl2) | >85 % conversion in 4 h | 70–80 % in 6 h | Requires activation; HOBt/EDC yields 80 % in 12 h |
| Hygroscopicity (mass gain at 80 % RH, 24 h) | <0.2 % | <0.3 % | 2.5 % (monohydrate) |
| Stability in alkaline solution (pH 10, 25 °C) | Half‑life 6 h (ester saponification) | Half‑life 8 h | Fully ionised; no ester hydrolysis |
During large‑scale preparation of a thiazolopyrimidine active pharmaceutical ingredient, the methyl ester was condensed with chloroformamidine hydrochloride in sulfolane at 110 °C without prior saponification; the ethyl ester, under identical conditions, generated 4–6 % of the ethyl ether of the product sulfolane‑trapped dimer, as evidenced by LC‑MS. This impurity, not observed with the methyl ester, required an additional hot‑filtration step at 80 °C through a 5 µm sintered‑metal cartridge filter before crystallisation. The lower melting point of the ethyl ester also limited its drying temperature to 35 °C to avoid agglomeration in a double‑cone vacuum dryer, extending the drying cycle by 6–10 h relative to the methyl ester, which tolerates 45 °C without lump formation.
Process‑scale handling data from a 2,000 L glass‑lined reactor campaign demonstrate that methyl 2‑aminothiazole‑4‑carboxylate must be pre‑dried to a water content below 0.5 % before use in Vilsmeier–Haack formylations; introduction of the material at a water activity above 0.3 leads to catastrophic decomposition of the Vilsmeier reagent with rapid pressure increase, as recorded on a 0–4 bar pressure transmitter on the reactor vent. When ambient relative humidity exceeds 60 %, the entire batch is transferred under a nitrogen‑purged glovebag and charged through a split‑butterfly valve to avoid moisture ingress. The solid is incompatible with strong oxidising agents; contact with fuming nitric acid results in ring‑opening and evolution of oxides of sulfur within seconds. Long‑term stability studies over 36 months at 2–8 °C in double‑polyethylene‑lined fibre drums under argon show no detectable change in HPLC purity and no increase in dimeric impurities above the 0.1 % reporting threshold. Use of the material in amidation reactions that employ primary amines as reactants and DMF as solvent requires maintaining the internal temperature below 0 °C during base addition to suppress premature ester aminolysis, which would otherwise consume the coupling agent and reduce isolated yield by 15–20 %.
