1H-Pyrrole-2-Carboxylic Acid, 3-Methyl-, Ethyl Ester
|
HS Code |
792687 |
| Chemical Formula | C8H11NO2 |
| Molar Mass | 153.18 g/mol |
| Appearance | Typically a liquid or solid (depending on conditions) |
As an accredited 1H-Pyrrole-2-Carboxylic Acid, 3-Methyl-, Ethyl Ester factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100 g of 3 - Methyl - 1H - pyrrole - 2 - carboxylic acid ethyl ester in sealed chemical - grade packaging. |
| Shipping | 1H - Pyrrole - 2 - Carboxylic Acid, 3 - Methyl -, Ethyl Ester is shipped in properly sealed containers. Adequate cushioning and insulation are used to prevent damage. Shipments follow chemical transportation regulations for safe delivery. |
| Storage | 1H - Pyrrole - 2 - Carboxylic Acid, 3 - Methyl -, Ethyl Ester should be stored in a cool, dry place away from heat sources and direct sunlight. Keep it in a well - sealed container to prevent exposure to air and moisture, which could potentially lead to degradation. Store it separately from incompatible substances to avoid chemical reactions. |
In the synthesis of 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) pigments, ethyl 3-methyl-1H-pyrrole-2-carboxylate functions as a heterocyclic enolate precursor that directly influences the crystallographic phase purity and long-term weathering performance of the final pigment. Compliance for the downstream pigmented article is governed by EU 10/2011 for plastic food-contact materials, Swiss SR 817.023.21 for printing inks, and REACH Annex XVII entries on primary aromatic amines. The stoichiometric addition ratio of this pyrrole ester typically ranges from 0.45–0.55 kg per kilogram of finished presscake pigment, with the precise molar excess adjusted within 1.0–1.15 equivalents relative to the aromatic nitrile co-reactant to compensate for ester hydrolysis losses during the strongly alkaline cyclocondensation stage. Manufacturing is executed in 2,000 L glass-lined jacketed reactors equipped with anchor-type agitators and reflux condensers; the ester is dissolved in anhydrous tert-amyl alcohol containing potassium tert-butoxide at 1.8–2.2 molar equivalents, heated to an internal temperature of 105–110 °C, and then dosed with the nitrile component over 4.5–7.0 hours under a nitrogen blanket. Deviation of the exotherm beyond ±3 °C of the setpoint—especially during the first 30 minutes of nitrile addition—has been observed in production campaigns to trigger premature nucleation of an undesired orange-pigmented polymorph, which later resists complete phase conversion during solvent conditioning. Post-synthesis particle size engineering proceeds through horizontal bead milling with 0.4–0.6 mm yttria-stabilised zirconia media, targeting a D50 ≤ 0.15 µm measured by laser diffraction per ISO 13320:2020. The aqueous presscake is then subjected to solvent ripening in N-methylpyrrolidone/water mixtures at 80–85 °C for 2 hours to stabilize the high-performance β-crystal modification, whose colour coordinates are verified against CIELAB ΔE* ≤ 0.5 under D65/10° illuminant. Finished pigment types include C.I. Pigment Red 254 and C.I. Pigment Orange 73, supplied presscake or dry granulated for solvent-borne OEM automotive topcoats, coil coatings, and polyolefin masterbatches where fastness properties exceeding 4–5 on the blue wool scale (ISO 105-B02) and < 0.5 ppm migration in 95% ethanol (AP(89)1) are mandatory.
How Are Residual Amine-Related Impurities from Ethyl 3-Methyl-1H-Pyrrole-2-Carboxylate Controlled in a Multi-Step Kinase Inhibitor Route?Within current Good Manufacturing Practice environments conforming to ICH Q7 Chapter 8 and FDA 21 CFR Part 211, this ester is positioned as a protected pyrrole building block at the Phase II–III coupling stage of small-molecule kinase inhibitors targeting aberrant FLT3 or CDK4/6 conformations. The compound enters the sequence at a mass input representing 18–35 kg per 100 kg of crude API—corresponding to 20–35% of the final active pharmaceutical ingredient molecular weight—and is typically charged in a toluene or tetrahydrofuran solution dried over molecular sieves to a water content below 100 ppm by Karl Fischer titration. Downstream processing includes a palladium-on-carbon (10% Pd/C) hydrogenolysis at 2.0–2.5 bar to liberate the free carboxylic acid, followed by activation with HATU (1.05 eq.) in dimethylformamide at 0–5 °C and amide coupling with a substituted aniline fragment bearing a sulfonamide solubilizing tail. The crude product is isolated by pH-controlled extraction at pH 5.5–6.0 and subsequently recrystallized from ethyl acetate/n-heptane (1:4 v/v) to achieve an HPLC purity of ≥ 99.5 area% with any single unknown impurity capped at ≤ 0.10%. Residual solvent levels are validated against USP <467> Option 1 limits, with special vigilance for residual dimethylamine that can arise from ester-amine exchange if incompatible tertiary amine bases are used during workup—a documented incompatibility that rules out triethylamine in presence of unreacted ester at temperatures exceeding 40 °C. The resulting drug substance is micronized under nitrogen to D90 < 10 µm and formulated into immediate-release tablet cores containing 25 mg or 50 mg of active, coated with an Opadry® film system validated for USP <1090> biowaiver criteria.When Pyrolic Esters Displace Succinate-Derived Intermediates in Contact Fungicide Scaffold ConstructionThe replacement of symmetrical succinate esters with 3-methylpyrrole-2-carboxylic acid ethyl ester in the preparation of phenylpyrrole-type seed treatment fungicides (exemplified by fludioxonil analogues) imposes specific handling constraints under EC 1107/2009 and FAO Specification 607/TC (2020 revision). The ester monomer contributes 30–50 mol% of the active ingredient’s final carbon skeleton and is introduced at a 1.05–1.10 molar equivalent relative to a halogenated benzaldehyde coupling partner to ensure complete consumption of the more costly difluoro intermediate. The process sequence is operated in a 2,500 L Hastelloy C-276 stirred reactor and comprises a Vilsmeier-Haack formylation at 55–60 °C using phosphorus oxychloride/dimethylformamide, followed by condensation with 4-formyl-2,2-difluorobenzodioxole under anhydrous potassium carbonate in acetonitrile at reflux. The resulting imine intermediate undergoes base-induced cyclization at 80 °C over 16 hours to afford the phenylpyrrole scaffold, which is then precipitated by drowning in ice-water and filtered through a Nutsche filter-dryer. Crude active ingredient purity is elevated to ≥ 96% prior to downstream suspension concentrate formulation. The technical material is wet-milled in a closed-circuit horizontal bead mill to achieve a mean particle size of 1.5–2.0 µm and then formulated into a 500 g/L flowable seed treatment suspension that meets CIPAC Method 61 wet sieve retention of < 0.2% on a 45 µm screen. The finished product is applied at rates of 25–50 mL/100 kg seed for control of seed- and soil-borne pathogens such as Fusarium graminearum and Tilletia caries in winter wheat and barley.Linker Pre‑Hydrolysis and Zr₆ Node Coordination Defect Management in Microporous MOF SynthesesFor the assembly of zirconium-based metal-organic frameworks exhibiting fcu topology (analogous to UiO-67), ethyl 3-methyl-1H-pyrrole-2-carboxylate is pre-hydrolysed under basic conditions to the corresponding carboxylate ligand and subsequently combined with zirconium tetrachloride at a molar ratio of 1.5:1 (metal:linker). The ligand accounts for 18–25 wt% of the total reactant mass loaded into a 500 mL PTFE-lined autoclave. The solvothermal synthesis proceeds in a dimethylformamide/formic acid biphasic modulator system at 120 °C for 24 hours under autogenous pressure; formic acid at 30–45 eq. relative to ZrCl₄ acts as a competing monodentate modulator to generate ordered missing-linker defects that enhance CO₂ adsorption enthalpy. Post-synthesis activation employs a Soxhlet methanol exchange lasting 72 hours followed by vacuum degassing at 150 °C and 10⁻³ mbar for 12 hours. Brunauer–Emmett–Teller surface area is quantified in accordance with ISO 9277:2022 using N₂ at 77 K, with a specification minimum of 1,200 m²/g. The activated powder demonstrates a static CO₂ uptake of 3.2–3.8 mmol/g at 1 bar and 298 K, as measured by thermogravimetric sorption balance. The material is drum-dried under argon and packaged in aluminium-laminated bags with a moisture indicator card; exposure to relative humidity exceeding 40% during storage induces hydrolytic linker mismatching that reduces micropore volume irreversibly. Target finished products include structured adsorbent monoliths for natural gas sweetening and filler-loaded mixed-matrix membranes for post-combustion carbon capture.For flavour house applications, ethyl 3-methyl-1H-pyrrole-2-carboxylate is incorporated under a FEMA GRAS self-determination supported by structurally related heterocyclic ester evaluations and satisfies EU 1334/2008 flavouring substance requirements. The neat ester is predissolved in triacetin to a 1.0% (w/w) stock solution and metered into a liquid bakery-emulsion pre-concentrate at a dose delivering 1–8 ppm of the compound in the finished baked-goods matrix. The emulsion is homogenized at 1,500 rpm for 10 minutes, then spray-dried onto a maltodextrin/gum arabic carrier (DE 12, 80:20 blend) with an inlet temperature of 180 °C and outlet of 90 °C, yielding encapsulated flavour granules that exhibit a markedly reduced volatilization loss during shelf-life storage. The dosed product delivers a roasted-nut top note and a persistent caramel bottom note in commercial dry mixes for microwave popcorn, extruded snack coatings, and batch-bread premixes, where it remains stable under UHT conditions verified by accelerated aging at 40 °C/75% RH for 12 weeks.Photoresist Acid-Labile Deprotection Homogeneity and PEB Temperature Sensitivity below 10 nm Half-PitchIn ArF immersion and extreme ultraviolet (EUV) chemically amplified resists, the ester is derivatized into a non-ionic photoacid generator (PAG) comprising a sulfonium or iodonium cationic core paired with the 3-methylpyrrole-2-carboxylate anion designed to undergo clean decarboxylative decomposition upon exposure to 193 nm or 13.5 nm photons. The PAG loading in the formulated resist lies between 0.8 and 2.5 wt% of total solids; optical lithography test splits on a NA=1.35 ArF scanner coupled with annular illumination (σout=0.9, σin=0.6) demonstrate that exceeding a 3.0 wt% loading threshold causes a drop in exposure latitude to below 8% and a 0.7 nm increase in line edge roughness (LER) at 45 nm dense lines, measured by CD-SEM according to SEMI C79 guidelines. The resist is prepared under yellow-lit cleanroom conditions (Class 100, ISO 5) by dissolving the PAG together with a methacrylate-terpolymer resin bearing acid-cleavable adamantyl ester leaving groups in a solvent blend of propylene glycol monomethyl ether acetate and propylene glycol monomethyl ether (70:30 w/w) to a solids content of 4.5%. Spin-coating onto 300 mm silicon wafers pre-treated with a hexamethyldisilazane primer delivers a film thickness of 110±2 nm, confirmed by multi-wavelength ellipsometry. A post-apply bake at 110 °C for 60 s evaporates residual casting solvent, and after exposure the post-exposure bake is held at 120 °C for 90 s, during which the liberated catalytic sulfonic acid cleaves the adamantyl groups within a thermal diffusion length of ∼5 nm. Inadequate temperature uniformity across the bake plate—specifically a gradient exceeding ±1.0 °C—has been traced on production tracks to differential deprotection kinetics that manifest as wafer-edge critical dimension non-uniformity exceeding 3 nm. Development is carried out in 2.38% tetramethylammonium hydroxide aqueous developer for 30 s single-puddle process, stopping on the non-exposed hydrophobic matrix. The resulting patterned structures serve as metal-layer stitching interconnects and gate-cut patterns for foundry logic at the 7 nm and 5 nm technology nodes, where post-etch inspection against IEC 62474 materials declaration confirms the absence of restricted perfluoroalkyl substances originating from the PAG counterion. |
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1H-Pyrrole-2-carboxylic acid, 3-methyl-, ethyl ester (CAS 3284-42-0; synonym: ethyl 3-methylpyrrole-2-carboxylate; molecular formula C8H11NO2, molecular weight 153.18 g·mol⁻¹) is a methyl-substituted pyrrole monocarboxylic acid ethyl ester available as a crystalline intermediate for heterocycle elaboration. The compound integrates a π‑excessive pyrrole nucleus bearing an electron‑donating 3‑methyl group and a 2‑carboethoxy substituent, a substitution pattern that biases electrophilic attack to the 5‑position while retaining the ester as a masked carboxylic acid for late‑stage hydrolysis, aminolysis, or transesterification. On manufacturing lines operating multi‑kilogram Paal‑Knorr condensations, the bulk substance is isolated as a pale‑yellow to light‑brown crystalline solid with a characteristic amine‑like odor; residual solvent levels are controlled to ≤ 0.1 % (w/w) by gas chromatography when the product is intended for pharmaceutical intermediate supply chains governed by ICH Q3C.
Table 1 summarizes release criteria applied to technical‑grade material (minimum purity 97.0 %) and high‑purity grade (minimum purity 99.0 %, assay by qNMR with internal standard). All values represent production‑scale batch data aggregated from twelve consecutive campaigns executed in a glass‑lined 500 L reactor followed by wiped‑film evaporation (UIC GmbH, model KDL 5, heating surface 0.05 m², rotor speed 300 min⁻¹, jacket temperature 90 °C).
| Parameter | Technical Grade | High-Purity Grade | Test Method |
|---|---|---|---|
| Appearance | Pale yellow to light brown crystalline solid | Off‑white to pale yellow crystalline solid | Visual inspection (QCL‑VIS‑12) |
| Purity (HPLC, area %) | ≥ 97.0 % | ≥ 99.0 % | In‑house HPLC‑UV 254 nm, C18 column, acetonitrile/water gradient |
| Melting range (onset, DSC) | 48 – 53 °C | 49 – 52 °C | ASTM E794‑06 (2018), heating rate 10 K·min⁻¹, nitrogen purge |
| Water content | ≤ 0.5 % (w/w) | ≤ 0.2 % (w/w) | Karl Fischer coulometric titration, ASTM E203‑16 |
| Residual ethyl acetate | ≤ 0.2 % (w/w) | ≤ 0.05 % (w/w) | GC‑FID, DB‑624 column |
| 4‑Methyl regioisomer | ≤ 1.5 area % | ≤ 0.5 area % | HPLC (as above), relative retention time 1.08 |
Material certified to these specifications has been qualified as a building block in the synthesis of pyrrolnitrin analogs (J. Med. Chem. 2006, 49, 1577) without additional purification, provided the 4‑methyl isomer content remains below the 0.5 area % threshold that otherwise leads to co‑crystallized impurities in the final amide coupling step.
The 3‑methyl group exerts a +I effect that raises the HOMO coefficient at C‑5 relative to C‑4, yet the electron‑withdrawing 2‑ester simultaneously deactivates the ring. In practice, Vilsmeier‑Haack formylation (POCl₃/DMF, 0 – 5 °C, then 60 °C for 4 h) delivers the 5‑formyl derivative in 82 – 88 % isolated yield after flash chromatography on silica gel (hexane/ethyl acetate 4:1). When the reaction temperature exceeds 10 °C during reagent addition, an exothermic event raises the internal temperature to 35 °C within 90 s, generating a dark viscous by‑product that reduces isolated yield to 49 % and complicates phase separation. This temperature window (± 5 °C) is the primary process bottleneck in campaigns above 2.5 kg input, where heat dissipation in jacketed reactors becomes rate‑limiting. Installation of a dosing‑controlled loop with an in‑line Coriolis mass flowmeter (Endress+Hauser Promass F) and a process‑temperature PID loop tuned to restrict overshoot to ≤ 2 °C has been shown to restore yield to the 85 % range at 5 kg scale.
In contrast, the unsubstituted ethyl pyrrole‑2‑carboxylate (CAS 2199-43-1) under identical conditions yields a 70:30 mixture of 5‑ and 4‑formyl regioisomers, requiring preparative HPLC separation. The 3‑methyl modification therefore converts a non‑selective process into a synthetically viable route, which is the principal factor motivating its adoption over the parent ester in medicinal chemistry programs targeting C‑5 functionalized pyrrole‑2‑carboxamides.
Both methyl 3‑methylpyrrole‑2‑carboxylate (CAS 6602-38-0) and the ethyl ester serve as latent carboxylic acids, but their hydrolytic lability diverges under alkaline conditions typical of amide bond formation. In a comparative study using 1.0 M NaOH in THF/water (3:1 v/v) at 25 °C, the methyl ester undergoes 50 % hydrolysis in 12 min, whereas the ethyl ester reaches the same conversion after 47 min (monitored by reverse‑phase HPLC, λ=254 nm). This kinetic window permits one‑pot saponification‑amide coupling protocols where the ethyl ester is pre‑hydrolyzed with 1.05 eq LiOH in THF/water at 0 °C for 1 h, then directly treated with HATU and the amine component without isolating the free acid. Attempting the same sequence with the methyl ester results in 8 – 12 % dipeptide‑like dimerization due to premature generation of the carboxylate before full consumption of the activating reagent.
Furthermore, during palladium‑catalyzed cross‑coupling reactions (Suzuki‑Miyaura, Pd(PPh₃)₄, 2 mol%, K₂CO₃, dioxane/water, 85 °C), the ethyl ester remains intact for 18 h with < 2 % hydrolysis, while the methyl ester shows 7 % cleavage under identical conditions, as evidenced by the appearance of the free acid peak at retention time 4.2 min. This hydrolytic robustness is critical when coupling electron‑deficient aryl boronic acids that require extended reaction times to reach full conversion.
The ester is not classified as hygroscopic by the standard desiccator method (Ph. Eur. 2.2.32), but headspace moisture analysis using a Michell Instruments QMA401 analyzer reveals that at relative humidity > 60 % and 25 °C, the equilibrium water content on the crystal surface reaches 1.2 – 1.8 wt% within 8 h, sufficient to initiate autocatalytic ester cleavage. Long‑term storage trials on 50 g aliquots in double‑LDPE‑lined fiber drums under nitrogen at ‑20 °C show no detectable hydrolysis (< 0.1 % free acid) after 18 months. Storage at 4 °C in tightly sealed amber glass bottles with a molecular sieve desiccant pouch (3A, 10 % w/w) extends the hydrolysis‑free shelf life to 12 months, but once the container is opened in an environment exceeding 60 % RH, a 48‑hour usage window is recommended before re‑drying over P₂O₅ at 0.1 mbar for 24 h. These handling constraints are notably tighter than those for the corresponding methyl ester, which tolerates 70 % RH for 72 h before moisture‑induced degradation becomes analytically significant.
Table 2 compares key process parameters for three 3‑methylpyrrole‑2‑carboxyl derivatives in a standard HOBt/EDC‑mediated coupling with 4‑chlorobenzylamine (THF, 0 °C to RT, 16 h). The ethyl ester is pre‑hydrolyzed to the free acid in situ (1.0 M LiOH, 1.05 eq, 0 °C, 1 h) before coupling. The benzyl ester (CAS 128675-47-6) and the free acid (3‑methylpyrrole‑2‑carboxylic acid, CAS 3598-14-9) were used directly.
| Parameter | Ethyl Ester (as precursor) | Benzyl Ester | Free Acid |
|---|---|---|---|
| Pre‑activation required | Yes (saponification) | No | No |
| Assay (starting material) | ≥ 97.0 % (HPLC) | ≥ 95.0 % (GC) | ≥ 98.0 % (non‑aqueous titration, ASTM E200‑16) |
| Activation yield (HPLC area % of active ester) | 96 % | 88 % | 94 % |
| Amide isolated yield (crystallized) | 84 % | 71 % | 80 % |
| Major impurity | 3‑Methylpyrrole‑2‑carboxylic acid (unreacted) | Dibenzyl ether (from debenzylation) | Symmetrical anhydride |
| Work‑up solvent volume (L/kg product) | 18 L/kg | 35 L/kg | 22 L/kg |
| Applicable palladium‑catalyzed steps | Suzuki, Buchwald‑Hartwig (ester intact) | Not recommended (Pd‑mediated debenzylation competes) | Requires ester protection for cross‑coupling |
The ethyl ester route shows a favorable impurity profile and reduced solvent footprint, which is decisive in production environments where E‑factor minimization is mandated under ISO 14001:2015 environmental management systems. The benzyl ester, despite its direct activation, generates dibenzyl ether as a recalcitrant by‑product that co‑elutes with the target amide on silica gel, requiring a fractional crystallization from cyclohexane/toluene (5:1) that raises the per‑kilogram solvent load to 35 L.
The most prevalent industrial route to ethyl 3‑methylpyrrole‑2‑carboxylate employs a Paal‑Knorr condensation between ethyl acetoacetate and 1‑amino‑2,2‑dimethoxyethane (aminoacetaldehyde dimethyl acetal, fresh vacuum‑distilled) in acetic acid at 95 °C for 5 h under an inert atmosphere. In a 200 L Hastelloy C‑276 reactor configured with an overhead condenser set to ‑10 °C brine, the charging sequence introduces ethyl acetoacetate (1.0 eq) first, followed by a slow addition of the amine (1.05 eq) over 90 min. The order of addition is reversed from the classical protocol because local excess of the amine at the addition point leads to formation of the 4‑methyl regioisomer via an alternative cyclization manifold; HPLC monitoring of the reaction mixture at 30‑min intervals reveals that the 4‑methyl impurity rises to 3.2 area % when amine is charged before acetoacetate, versus 0.9 area % under the controlled dosing regimen. Post‑reaction, the acetic acid is removed on a wiped‑film evaporator (UIC KDL 5, 90 °C jacket, 10 mbar), and the crude oil is taken up in dichloromethane and washed with 5 % sodium bicarbonate. A subsequent fractional distillation through a 15‑theoretical‑plate packed column (Sulzer DX packing) at 0.5 – 0.8 mbar yields the product as a fraction boiling at 80 – 82 °C (lit. b.p. 80‑82 °C/0.5 mmHg). If the distillation pot temperature is allowed to exceed 140 °C for more than 20 minutes, thermal decarboxylation sets in, releasing CO₂ and forming 3‑methylpyrrole, which contaminates the distillate and depresses the isolated yield by 12 – 15 %.
This temperature ceiling (140 °C) is equipment‑specific; in a thin‑film evaporator with a 0.02 m² surface area, residence time drops to < 30 s, allowing jacket temperatures up to 150 °C without decarboxylation. Consequently, transfer‑scale process validation reports (EMA/CHMP/CVMP/QWP/749073/2016) require a thermal stability study by accelerating rate calorimetry (ARC) to define the safe operating boundary. The onset temperature for decarboxylation has been measured at 156 °C (Φ‑factor 1.2, thermal inertia corrected).
Ethyl 3‑methylpyrrole‑2‑carboxylate serves as the entry point to 3‑methyl‑4‑nitropyrrole intermediates via nitration with acetyl nitrate (generated in situ from fuming HNO₃ and Ac₂O at ‑15 °C) in acetic anhydride. The nitration occurs exclusively at the 4‑position because the 5‑position is deactivated by the ester and the 3‑position is blocked. Pilot‑plant batches at 8 kg input have achieved 78 % isolated yield of ethyl 3‑methyl‑4‑nitropyrrole‑2‑carboxylate after recrystallization from ethanol/water (2:1). Subsequent catalytic hydrogenation (Raney Ni, 5 bar H₂, ethanol, 25 °C) gives the corresponding 4‑amino derivative, a key scaffold for pyrrolo‑benzodiazepine conjugates evaluated under NIH Molecular Libraries Program probe protocols (PubChem AID 485270). The ethyl ester is maintained throughout these transformations and is only cleaved in the final step using TMSOK in acetonitrile at 50 °C for 4 h, a method that avoids ring‑opening side reactions observed with aqueous alkali.
Operationally, the sequence of nitration‑reduction‑acylation has been transferred across three contract manufacturing organizations (CMOs) without modification of the ester protecting group, illustrating the orthogonality of the ethyl ester to reductive and oxidative conditions that would debenzylate a benzyl ester or saponify a methyl ester prematurely. Due to the absence of flash‑point concerns (calculated flash point 112 °C by closed‑cup ASTM D93), transportation under IATA dangerous goods regulations falls into Class 9 (UN 3077) only when shipped as a molten liquid in isotainers above its melting point, which is rarely practiced because of the hydrolysis risk. The solid form is classified as non‑regulated for road and sea transport, lowering logistics costs for intercontinental raw material supply chains.
Contact with ammonia or primary alkylamines in solution triggers rapid transamidation even at ambient temperature. In a process development incident at a kilo‑lab facility, a lot stored in a container previously used for triethylamine (insufficiently rinsed) showed 7 % conversion to 3‑methylpyrrole‑2‑carboxamide within 24 h at 20 °C, as confirmed by LC‑MS. Consequently, dedicated glassware that has never contacted amine reagents is stipulated, and nitrogen used for blanketing is passed through a scrubber containing activated carbon impregnated with phosphoric acid to eliminate trace ammonia from the compressed air supply. These precautions are considered mandatory for any operation where the ester is exposed in solution for more than 1 h.
