Ethyl 4-Methyl-1H-Pyrrole-2-Carboxylate

Product Name Ethyl 4-Methyl-1H-Pyrrole-2-Carboxylate
Alias Ethyl 4-methyl-2-pyrrolecarboxylate
Einecs 629-622-6
Mininmum Order 1g
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
Price Inquiry sales9@bouling-chem.com
Manufacturer Bouling Chemical Co., Limited
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In terms of specification, Ethyl 4-Methyl-1H-Pyrrole-2-Carboxylate is supplied with ≥97% purity (HPLC) and ≤0.5% water content, making it suitable for use as a pharmaceutical intermediate.

Specifications

HS Code	871394
Chemical Formula	C8H11NO2
Molar Mass	153.18 g/mol
Appearance	Typically a liquid
Boiling Point	Around 230 - 235 °C
Solubility In Water	Insoluble
Solubility In Organic Solvents	Soluble in common organic solvents like ethanol, dichloromethane
Density	Approx. 1.04 g/cm³
Flash Point	Probably around 97 - 100 °C
Odor	Characteristic organic odor
Purity	Can be obtained in high purity (e.g., 95%+ in commercial products)

As an accredited Ethyl 4-Methyl-1H-Pyrrole-2-Carboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of Ethyl 4 - Methyl - 1H - Pyrrole - 2 - Carboxylate packaged in a sealed plastic bottle.
Shipping	Ethyl 4 - Methyl - 1H - Pyrrole - 2 - Carboxylate is shipped in sealed, corrosion - resistant containers. Packaging ensures protection from moisture and physical damage. Shipment follows strict chemical transportation regulations for safe delivery.
Storage	Ethyl 4 - Methyl - 1H - Pyrrole - 2 - Carboxylate should be stored in a cool, dry, and well - ventilated area. Keep it away from heat sources, flames, and oxidizing agents. Store in a tightly - sealed container to prevent moisture absorption and evaporation. Suitable storage containers are typically made of glass or corrosion - resistant plastics. Label the storage container clearly to avoid mix - ups.

Application of Ethyl 4-Methyl-1H-Pyrrole-2-Carboxylate

For drug discovery programmes targeting kinase-dependent malignancies, this pyrrole ester serves as a privileged scaffold for biorthogonal fragment elaboration. Synthesis of 5-aryl-4-methyl‑1H‑pyrrole‑2‑carboxylate libraries proceeds via microwave-assisted Suzuki–Miyaura cross-coupling using the corresponding 5‑bromo intermediate, which is generated by selective electrophilic bromination with N‑bromosuccinimide in anhydrous THF at ‑10 °C. A production‑scale procedure charges 1.05 eq of arylboronic acid, 2.0 mol% Pd(PPh₃)₄, and 2.5 eq of aqueous K₂CO₃ (2 M) into a nitrogen‑blanketed 50 L glass‑lined reactor. The biphasic dioxane/water mixture (4:1 v/v) is held at 82 °C with vigorous agitation for 8–12 h until IPC by HPLC confirms consumption of the bromide below 0.3 area%. Post‑reaction, the cooled crude is filtered through a 0.5 µm bag filter containing 3 wt% activated carbon and treated with 3‑mercaptopropyl‑functionalised silica gel under mechanical stirring for 4 h to scavenge residual palladium. After celite‑assisted polish filtration, the organic phase is concentrated under reduced pressure (≤45 °C jacket) and the product crystallised from n‑heptane/ethyl acetate 9:1 to yield off‑white needles with a chromatographic purity of ≥99.5% and residual Pd below 10 ppm as measured by ICP‑MS (USP 〈232〉). The isolated intermediate conforms to ICH Q3D elemental impurity limits and enters the next synthetic stage without additional polishing. Downstream, the ethyl ester is preserved through a reductive amination sequence to deliver tertiary amine‑substituted pyrrole‑2‑carboxylates that display low‑nanomolar IC₅₀ values against mutated forms of the tyrosine kinase domain in biochemical ADP‑Glo™ assays. Regulatory starting material designation under ICH Q7 is often assigned at this 5‑aryl‑pyrrole stage, with GMP batches routinely manufactured in 25–50 kg campaigns under ISO 8 cleanroom conditions. Supply‑chain deviations observed on twin‑screw extruder lines during hot‑melt extrusion of amorphous solid dispersions have been traced to residual ethyl acetate solvate levels exceeding 0.15 wt%; consequently, the final drying protocol mandates a 48‑h vacuum tray‑drying step at 40 °C and ≤5 mbar, reducing residual solvent to <40 ppm for ethyl acetate and <25 ppm for n‑heptane as verified by headspace GC against ICH Q3C Option 1 limits.When tetrachloroethane replaces methylene chloride in the Vilsmeier–Haack formylation of ethyl 4-methyl‑1H‑pyrrole‑2‑carboxylate, the resulting 5‑formyl derivative exhibits markedly different work‑up rheology that must be accommodated in pilot-plant piping design. Addition of phosphorus oxychloride (2.4 eq) to a chilled solution of the pyrrole ester in 1,1,2,2‑tetrachloroethane maintained at ‑5 to 0 °C under a nitrogen purge disperses the initially formed Vilsmeier adduct as a fine‑grained, thixotropic slurry. Delayed addition of dimethylformamide (2.2 eq) over 90 min with a peristaltic pump prevents runaway exotherms that have been documented to spike jacket temperatures to +28 °C within 45 s on a 100 L scale when DMF is charged in a single portion. The batch is subsequently warmed to 55 °C and agitated for 6 h until in‑process HPLC reveals <1.5% unreacted starting material. The quench into 15% sodium acetate solution is executed through a submerged dip tube to localise the exotherm, and the neutralised organic phase is washed with deionised water until conductivity falls below 50 µS/cm. Distillation under partial vacuum delivers the crude aldehyde as a viscous oil that crystallises upon seeding with 0.5 wt% authentic product; recrystallisation from hot cyclohexane provides pale‑yellow prisms of ≥98.7% purity by qNMR. This 5‑formyl synthon undergoes Hantzsch‑type cyclocondensation with ethyl acetoacetate and ammonium acetate in refluxing ethanol to construct a pyridopyrrole‑2‑carboxylate heterocycle, a core substructure found in several ATP‑competitive inhibitors undergoing preclinical profiling. Process safety assessments at the 200 L scale demand reaction calorimetry data showing a specific heat release of −185 kJ/mol for the formylation step, triggering a SIL 2 interlock on the jacket temperature control loop. The final active pharmaceutical ingredient intermediate is subjected to a panel of genotoxicity alerts under ICH M7; the 5‑formyl intermediate itself is flagged as a potential DNA‑reactive impurity and controlled to <15 ppm in the drug substance by a dedicated LC‑MS/MS method with an LLOQ of 0.8 ppm.

Comparative process performance of cross‑coupling methodologies for 5‑aryl‑4‑methyl‑1H‑pyrrole‑2‑carboxylate construction
Parameter	Suzuki–Miyaura (Br → Ar)	Negishi (Br → Ar)	Pd‑catalysed C–H arylation
Catalyst system	Pd(PPh₃)₄ 2.0 mol%	Pd₂(dba)₃ 1.5 mol% / SPhos 3.6 mol%	Pd(OAc)₂ 5 mol% / PCy₃·HBF₄ 10 mol%
Organometallic reagent	Aryl‑B(OH)₂ 1.05 eq	Aryl‑ZnBr 1.2 eq (freshly prepared)	Direct C–H activation; Ag₂CO₃ 2.0 eq as halide abstractor
Solvent/base system	1,4‑Dioxane/H₂O 4:1; K₂CO₃ 2.5 eq	THF; no additional base	DMF; Cs₂CO₃ 2.0 eq
Temperature / Time	82 °C, 8–12 h	60 °C, 3–5 h	120 °C (sealed tube), 24 h
Isolated yield	85–93%	78–88%	62–74%
Residual Pd in isolated product	<10 ppm after silica‑based scavenger	<20 ppm after activated‑carbon filtration	<50 ppm; requires recrystallisation
Scalability attention	Aqueous work‑up; good oxygen tolerance	Organozinc sensitive to moisture and O₂; requires glovebox preparation	Poor atom economy; heavy metal waste from silver salt; limited to 0.5 mol scale

Direct deprotonation at the 5‑position with lithium diisopropylamide eclipses traditional halogen–metal exchange for installations requiring electrophilic quenching in multi‑kilogram batches, largely because the post‑quench lithium bromide by‑product is avoided. A representative protocol charges ethyl 4‑methyl‑1H‑pyrrole‑2‑carboxylate into anhydrous THF (10 volumes) and cools the solution to ‑78 °C in a 300 L stainless‑steel cryogenic reactor. Freshly prepared LDA (2.0 M in THF/n‑hexane, 1.3 eq) is metered at a rate that maintains the internal temperature below ‑65 °C. After 60 min of ageing, the deep‑orange lithiated species is treated with the electrophile — most commonly trimethyl borate for in situ formation of the boronate ester, or methyl chloroformate when preparing the 2,5‑diester intermediate. The boronate route furnishes a pinacol ester after solvent swap into methanol and addition of pinacol (1.1 eq); this crystalline organoboron entity is isolated by filtration and dried to a water content below 0.1% before use in subsequent O‑arylation chemistry. Quality control specifications demand ≥99.0% HPLC purity and an unknown single impurity threshold of <0.10 area%. The direct‑lithiation process eliminates the bromide handling and heavy waste streams associated with bromination–magnesiation sequences, yet demands rigorous exclusion of moisture (<20 ppm H₂O in reactor atmosphere) and limits the choice of reactor alloys — Hastelloy C‑22 is preferred over SS316L to resist trace chloride‑induced pitting when the crude product solution is later acidified. On one contract manufacturing campaign, insufficient pre‑drying of the THF supply (KF titration read 320 ppm) caused a 22% yield reduction and triggered a deviation investigation per ICH Q7 § 2.5. The terminal products derived from this lithiation sequence include fused pyrrolopyrimidine‑2‑carboxylates encountered in clinical candidates for autoimmune indications, where the ethyl ester is retained until the final saponification step to improve membrane permeability during biological evaluation.Agrochemical discovery teams routinely exploit the carboxylic acid derivative of this building block to access pyridine‑fused biheterocycles with unknown modes of action. Hydrolysis of ethyl 4‑methyl‑1H‑pyrrole‑2‑carboxylate to the free acid is accomplished with 3.0 eq lithium hydroxide monohydrate in THF/water 2:1 at 45 °C over 16 h; after phase separation and acidification to pH 2.5 with 6 M HCl, the precipitated acid is isolated by centrifugation and dried to a loss‑on‑drying value below 0.5%. The acid is converted to the corresponding Weinreb amide using N,O‑dimethylhydroxylamine hydrochloride (1.2 eq), EDC·HCl (1.3 eq), and N‑methylmorpholine (2.0 eq) in dichloromethane at 20–25 °C. This Weinreb amide accepts 4‑pyridylmagnesium chloride (1.1 eq, freshly prepared in THF) at 0 °C to give a pyridyl ketone that cyclises to a pyrrolopyridine system upon treatment with ammonium acetate in acetic acid under Dean–Stark reflux. Such pyrrolopyridine‑2‑carboxylate analogues have been cited in structure–activity relationship tables of patent filings as showing broad‑spectrum herbicidal symptomology in greenhouse screens, though published field‑trial data for this specific scaffold remain sparse. Process‑development reports for a 30 kg campaign of the Weinreb amide highlight a recurring foaming problem during the aqueous quench of the EDC coupling mixture; installating a 200‑rpm pitched‑blade agitator with a foam‑breaking ring reduced batch‑cycle extension from 6 h to 45 min. The final pyrrolopyridine ester is purified by flash chromatography on a 20–40 µm silica stationary phase with an ethyl acetate/hexane gradient, yielding an agrochemical lead candidate of 97.3% purity that meets the 5‑kg demand for outdoor microplot evaluation.Catalytic decarboxylative transformation of ethyl 4‑methyl‑1H‑pyrrole‑2‑carboxylate yields 4‑methyl‑1H‑pyrrole, a volatile monomer that undergoes anodic polymerisation to form adherent poly(4‑methylpyrrole) films on indium tin oxide substrates. Decarboxylation is performed in sulfolane with 10 mol% Cu₂O and 20 mol% 1,10‑phenanthroline at 180 °C under a nitrogen sweep that carries the liberated CO₂ through a scrubber containing 1 M NaOH. The distilled 4‑methylpyrrole (bp 143–145 °C) is collected as a clear, air‑sensitive liquid and immediately dissolved in anhydrous acetonitrile containing 0.1 M tetrabutylammonium hexafluorophosphate as supporting electrolyte. Electropolymerisation on a 2 cm² ITO working electrode at a constant potential of +1.2 V vs. Ag/AgCl for 120 s deposits a 150–220 nm thick film, as measured by stylus profilometry. The resulting polymer in its doped state exhibits a conductivity of 0.8–2.4 S/cm (four‑point probe, ASTM D4496‑21) and undergoes a reversible colour switch from blue‑grey in the reduced state to pale yellow upon oxidation, a property exploited in prototype electrochromic smart‑window devices. Performance is heavily influenced by the water content of the acetonitrile bath: potentiostatic depositions conducted at ≥500 ppm H₂O produce films with pin‑hole densities exceeding 40/cm², undermining barrier‑coating integrity. Published pilot‑scale data for this specific electropolymerisation are limited; all thickness‑versus‑charge correlations above originate from 50 mL single‑compartment cells and their extrapolation to roll‑to‑roll manufacture remains unvalidated. In parallel, the monomer finds niche application as a co‑monomer in oxidative chemical polymerisation with pyrrole‑3‑carboxylic acid, generating carboxyl‑functionalised nanospheres that serve as dispersible primers for polyamide‑6 composites.

Cleavage of the ethyl ester: three industrially applicable routes to 4‑methyl‑1H‑pyrrole‑2‑carboxylic acid
Method	Conditions	Conversion / Selectivity	Process comment
Alkaline hydrolysis (LiOH)	3.0 eq LiOH·H₂O, THF/H₂O 2:1, 45 °C, 16 h	>99% conversion; 97% isolated yield	Minimal epimerisation risk; easy isolation by acidification; lithium salt copes with polar aprotic solvent carry‑over.
Enzymatic cleavage (lipase B from Candida antarctica)	Phosphate buffer pH 7.0, 30 °C, 24 h, 15 wt% enzyme loading	92% conversion; >99% selectivity	Mild, suited to heat‑sensitive downstream steps; requires ultrafiltration to recover enzyme; scale‑up limited by enzyme cost and substrate concentration <50 g/L.
Acid‑catalysed hydrolysis (H₂SO₄)	6 M H₂SO₄, reflux (105 °C), 6 h	>99% conversion; 93% isolated yield	Corrosive media necessitate glass‑lined equipment; decarboxylation side‑reaction (~1.5 area%) forms 4‑methylpyrrole; rigorous neutralisation before extraction mandatory.

What limits the hydrazide‑derived [¹⁸F]radiolabelling yield when applied to this pyrrole core? Preclinical positron emission tomography tracer programmes utilise ethyl 4‑methyl‑1H‑pyrrole‑2‑carboxylate as a pro‑auxiliary for installing the hydrazine‑trifunctional linker required for ¹⁸F‑AlF complexation. The neat ester reacts with hydrazine monohydrate (5.0 eq) in ethanol at reflux for 5 h to furnish the carbohydrazide as a white microcrystalline solid in 85% yield after filtration. This hydrazide is conjugated to a maleimide‑DOTA‑PEG₄‑NCS bifunctional chelator in DMF containing 1% v/v triethylamine at ambient temperature. The critical bottleneck arises during ¹⁸F‑AlF radiolabelling of the pyrrole‑chelator bioconjugate: the pyrrole ring’s inherent susceptibility to electrophilic attack under the acidic labelling conditions (pH 4.0, 100 °C, 15 min) triggers a 12–18% radiolytic decomposition pathway that generates free ¹⁸F⁻ detected by radio‑TLC. Process optimisation confines the AlCl₃·6H₂O concentration to 2 mM and introduces sodium ascorbate (10 mg/mL) as a radical scavenger, which suppresses decomposition to <5% and achieves a non‑decay‑corrected radiochemical yield of 34–41% at end‑of‑synthesis. The formulated tracer is purified by semi‑preparative reverse‑phase HPLC (C18, 5 µm, 250 × 10 mm) using a gradient from 0.1% TFA in water to acetonitrile, then sterile‑filtered through a 0.22 µm PVDF membrane. Quality release tests conform to USP 〈823〉 for PET drugs, including bacterial endotoxins (<2 EU/mL), residual ethanol (<500 ppm), and radiochemical purity >99% as determined by radio‑HPLC. The final injectable tracer targets tumour‑associated integrin receptors, with preclinical biodistribution data obtained on a Siemens Inveon microPET/CT scanner; attempts to substitute the pyrrole hydrazide with an aliphatic spacer resulted in a 6‑fold reduction in tumour‑to‑background ratio, underscoring the scaffold’s pharmacokinetic influence.

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Certification & Compliance

Ethyl 4-Methyl-1H-Pyrrole-2-Carboxylate is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales9@bouling-chem.com.

More Introduction

Chemical Identity and Baseline Specifications

Ethyl 4-methyl-1H-pyrrole-2-carboxylate (CAS 32811-42-6, molecular formula C₈H₁₁NO₂, molecular weight 167.21 g/mol) is a heterocyclic building block supplied as a crystalline, faintly beige solid with a characteristic pyrrolic odour. Typical commercial deliveries meet an assay specification of ≥ 98.0% (HPLC, area normalization at 230 nm), with the principal impurity being the regioisomeric ethyl 3-methyl-1H-pyrrole-2-carboxylate, typically controlled below 1.5%. The melting range, determined by differential scanning calorimetry at a ramp rate of 10 K/min under nitrogen, falls between 40°C and 44°C, while the boiling point is reported as 274°C at atmospheric pressure with gradual discolouration. Storage recommendations specify sealed, light-resistant containers under inert gas at 2–8°C; repeated melt–freeze cycling promotes ring oxidation and ester hydrolysis, reducing purity below the 97% threshold required for subsequent stoichiometric steps. A certificate of analysis typically accompanies each batch, reporting residual solvent levels (ethyl acetate or methanol, below 500 ppm) via headspace GC-FID and water content by Karl Fischer coulometric titration (target ≤ 0.3% w/w).

What Distinguishes the 4-Methyl Substitution Pattern from 3- and 5-Methyl Isomers?

Methyl group placement on the pyrrole ring determines the electron density distribution and steric profile at the reactive α- and β-positions. In the 4-methyl congener, the electron-donating methyl substituent enhances nucleophilicity at the unsubstituted 5-position without creating the peri-interaction that a 3-methyl group imposes on the ester carbonyl. This manifests in condensation kinetics: when reacting with aromatic aldehydes under standard Lindsey conditions (BF₃·OEt₂ at 0.1 M in CH₂Cl₂, 23°C), the 4-methyl derivative reaches 85% dipyrromethane conversion in 90 min, whereas the 3-methyl isomer requires 3.5 h to achieve comparable yields due to steric retardation of the carbocation intermediate. By contrast, ethyl 5-methyl-1H-pyrrole-2-carboxylate (CAS 61394-97-2) suffers from competing electrophilic attack at the 3-position, generating regioisomeric mixtures that complicate macrocycle purification. The 4-methyl isomer therefore occupies a design space where reactivity remains predictably directed while retaining sufficient stability for multi-step sequences—a balance that has led to its preferential selection in dipyrromethane and BODIPY precursor manufacturing. Published comparative Hammett substituent data remain sparse, though qualitative reactivity scales derived from Vilsmeier–Haack formylation half-lives consistently place 4-methyl substitution between the unsubstituted and 3,5-dimethylated extremes.

Dipyrromethane synthesis, a foundational step in porphyrinoid construction, illustrates the practical consequences of the 4-methyl substitution pattern on production-scale equipment. In a 20 L jacketed glass reactor equipped with a retreat-curve impeller operating at 120 rpm, a 0.20 M solution of ethyl 4-methyl-1H-pyrrole-2-carboxylate in dichloromethane is treated with 1.0 equivalent of benzaldehyde and 0.10 equivalent of trifluoroacetic acid. The exothermic condensation raises the internal temperature from 22°C to 28°C within 15 min; the jacket setpoint is maintained at 15°C to limit thermal broadening of the oligomer distribution. After 2 h, quenching with triethylamine (1.5 equivalents relative to acid) precipitates a crude solid that, upon recrystallization from ethanol/water (70:30 v/v), yields the meso-phenyl dipyrromethane diester in 72–78% isolated yield with HPLC purity ≥ 97.5%. The 4-methyl substituent suppresses the formation of tripyrrane byproducts—GPC analysis of the crude shows an oligomer dispersity (Đ) of 1.08 compared to 1.24 for the unsubstituted ethyl pyrrole-2-carboxylate—reducing the column chromatography burden at scale. Pre-drying of the starting ester is mandatory when ambient relative humidity exceeds 60%: water content above 0.5% w/w attenuates the catalytic activity of BF₃·OEt₂ and increases the fraction of unreactive aldehyde–water adducts, leading to batch failure marked by sub-50% conversion. In such cases, azeotropic drying with heptane in a rotary evaporator (40°C bath, 50 mbar) prior to dissolution routinely restores kinetic performance.

Process chemists working with this building block on pilot lines (glass-lined steel, 100–500 L capacity) observe that the 4-methyl ester exhibits a narrower thermal processing window than the parent pyrrole-2-carboxylate. Differential scanning calorimetry traces show an exothermic decomposition onset at 235°C (sealed pan, 10 K/min), approximately 15°C lower than the unsubstituted analogue, a shift attributed to radical-mediated methyl group oxidation initiating ring degradation. This imposes a maximum safe distillation or melt-handling temperature of 180°C, enforced by cascade-controlled oil bath heaters with over-temperature interlocks set to 190°C. Additionally, the methyl group slightly raises the pKa of the pyrrole N–H; the resultant weaker hydrogen-bond donation alters the supramolecular assembly of porphyrin precursors, a factor exploited in templated macrocyclization but undesirable when discrete dipyrromethane isolation is the sole objective.

When Condensation Reactions Require Controlled Reactivity at the α-Position

Aldehyde condensations at the 5-position of ethyl 4-methyl-1H-pyrrole-2-carboxylate proceed with measurable regioselectivity that distinguishes it from many commercially available pyrrole esters. The electron-donating methyl group accelerates electrophilic attack at the free α-carbon while simultaneously deactivating the β-position toward further substitution; kinetic isotope effect studies (using deuterated trifluoroacetic acid) indicate a primary KIE of 2.3 for 5-proton loss, confirming that C–C bond formation is partly rate-limited by rearomatization. This behavior aligns with the requirements of sterically congested aldehyde coupling partners, where the 4-methyl substituent reduces the propensity for rotameric scrambling of the incipient dipyrromethane framework. For example, condensation with 2,6-dichlorobenzaldehyde under Lindsey conditions gives a single regioisomeric adduct (HPLC retention time 14.2 min, C₁₈ column, acetonitrile/water 65:35) in 81% yield, while the 5-methyl isomer produces a 1:0.4 mixture of 5,5'- and 5,3'-linked dimers that co-elute poorly. Custom synthesis laboratories therefore select the 4-methyl variant when the downstream target demands unambiguous connectivity for pharmacological or photophysical purity.

Comparative physicochemical data for methyl-substituted pyrrole-2-carboxylate isomers
Parameter	Ethyl 4-methyl-1H-pyrrole-2-carboxylate	Ethyl 3-methyl-1H-pyrrole-2-carboxylate	Ethyl 5-methyl-1H-pyrrole-2-carboxylate
CAS RN	32811-42-6	170945-16-7	61394-97-2
Molecular weight (g/mol)	167.21	167.21	167.21
Melting range (°C)	40–44	72–75 (lit.)	Liquid at 23°C
Typical HPLC purity specification	≥ 98.0% (230 nm)	≥ 97.0% (230 nm)	≥ 95.0% (254 nm)
Dipyrromethane formation half-life (Lindsey conditions, min)	90	210	75 (with regioisomer formation)
Key synthetic advantage	Directed α-reactivity, low tripyrrane fraction	Chelation-capable ester orientation	Low melting point simplifies molten-phase handling

Stability and Handling Limits

Long-term stability studies conducted on sealed, amber-glass ampoules stored at 2–8°C and ≤ 30% relative humidity document a purity decline of less than 0.2% over 24 months when the headspace oxygen level is maintained below 50 ppm. In contrast, storage at 25°C in breathable polyethylene containers under ambient light induces a 4–6% purity loss within 90 days, characterized by the emergence of a brown discolouration and HPLC peaks consistent with pyrrole ring-opened lactam esters and oligomeric oxidation products. The compound is incompatible with strong mineral acids (concentrated HCl induces rapid decarboxylation, evolving CO₂ at ambient temperature) and with primary amines under dehydrating conditions, where slow aminolysis of the ethyl ester competes with Schiff-base formation at the pyrrole α-position, generating complex product mixtures that have frustrated direct amidation attempts in the absence of enzymatic catalysis. For moisture-sensitive applications, recommended pre-drying involves dissolution in dry tetrahydrofuran, addition of 10% w/w activated 4 Å molecular sieves, and gentle agitation for 12 h under argon; this reduces water content below 50 ppm as measured by Karl Fischer titration, enabling reproducible Grignard reagent consumption and anionic oligomerization stoichiometry.

A routine analytical quality control protocol pairs reversed-phase HPLC (Kinetex C₁₈ column, 150 mm × 4.6 mm, 5 µm; mobile phase A: 0.1% TFA in water, B: acetonitrile; gradient 20% B to 90% B over 15 min; flow rate 1.0 mL/min; detection at 230 nm) with gas chromatography–mass spectrometry. Under these conditions, the title ester elutes at 8.9 min, well resolved from the 3-methyl isomer (9.4 min) and the des-methyl analogue ethyl 1H-pyrrole-2-carboxylate (7.3 min). The mass spectrum displays a molecular ion at m/z 167.1, with characteristic fragments at m/z 121.1 (loss of ethanol) and m/z 94.1 (pyrrole methyl arene). Deviation from this fingerprint in excess of 5% relative ion abundance triggers a request for batch recrystallization or vacuum sublimation (0.1 mbar, 60°C oil bath) prior to release for synthetic use.