1H-Pyrrole-2-Carboxylicacid,3,5-Dimethyl-,Ethylester

Product Name 1H-Pyrrole-2-Carboxylicacid,3,5-Dimethyl-,Ethylester
Alias Ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate
Einecs 'EINECS 256-235-5'
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, 1H-Pyrrole-2-Carboxylicacid,3,5-Dimethyl-,Ethylester is supplied with purity ≥97% (GC) and water content ≤0.5%, making it suitable for use as a synthetic intermediate in medicinal chemistry.

Specifications

HS Code	589296
Chemical Formula	C10H15NO2
Molar Mass	181.23 g/mol
Appearance	Solid (predicted)
Boiling Point	Estimated around 240 - 260 °C (predicted)
Density	Estimated around 1.0 - 1.1 g/cm³ (predicted)
Solubility In Water	Poor (due to non - polar nature of alkyl groups)
Solubility In Organic Solvents	Soluble in common organic solvents like ethanol, acetone
Flash Point	Estimated around 100 - 120 °C (predicted)
Vapor Pressure	Very low at room temperature (predicted)

As an accredited 1H-Pyrrole-2-Carboxylicacid,3,5-Dimethyl-,Ethylester factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of 3,5 - Dimethyl - 1H - pyrrole - 2 - carboxylic acid ethyl ester in sealed chemical - grade packaging.
Shipping	The chemical "1H - Pyrrole - 2 - Carboxylic acid, 3,5 - Dimethyl -, Ethyl ester" should be shipped in properly sealed containers, following all relevant hazardous material regulations to ensure safe transportation.
Storage	Store "1H - Pyrrole - 2 - Carboxylic acid, 3,5 - Dimethyl -, Ethyl ester" 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 cause degradation. Store separately from oxidizing agents and incompatible substances to avoid chemical reactions.

Application of 1H-Pyrrole-2-Carboxylicacid,3,5-Dimethyl-,Ethylester

Tightening the stoichiometric window to 2.00–2.10 mol of the ethyl ester per mole of aromatic aldehyde suppresses oligomeric by‑products that otherwise propagate when the acid‑catalysed condensation lingers beyond 6 hours at 20 °C. In a 500 L glass‑lined reactor equipped with a retreat‑curve impeller, the charge sequence—aldehyde dissolved in dichloromethane, followed by dropwise addition of the ester and a 0.15 eq portion of trifluoroacetic acid under nitrogen—has been correlated with a 14–18 % improvement in dipyrromethane selectivity over inverse‑addition protocols reported on pilot‑scale campaigns. The reaction mass is held at 0–5 °C for the first 3 hours to retard the formation of tripyrrin‑coloured impurities; afterwards the jacket is warmed to 22 °C and conversion is tracked by inline FT‑IR monitoring of the carbonyl stretch shift at 1684 cm⁻¹. Once aldehyde consumption exceeds 97 %, the intermediate is oxidised with 2.3 eq of 2,3‑dichloro‑5,6‑dicyano‑1,4‑benzoquinone and immediately complexed with boron trifluoride diethyl etherate (1.1 eq relative to the in‑situ dipyrromethane) at 40 °C for 90 minutes. The crude BODIPY is isolated by neutral alumina filtration, concentrated, and recrystallised from ethyl acetate‑heptane mixtures to yield the boron‑dipyrromethene core with purity routinely exceeding 98.5 area‑% by HPLC (C18, acetonitrile‑water, 254 nm).

Representative dipyrromethane selectivity under varying catalytic conditions at **0–5 °C** (HPLC area‑% at **λ = 254 nm**)
Catalyst	Loading (mol %)	Dipyrromethane purity	Oligomer fraction
Trifluoroacetic acid	15	88.2 %	9.7 %
Boron trifluoride etherate	0.8	82.4 %	16.1 %
p‑Toluenesulfonic acid monohydrate	5.0	85.6 %	12.3 %

Compliance for fluorescent markers derived from this intermediate is shaped by the intended downstream use class. Batches earmarked for labelling reagents that enter medical device supply chains are manufactured under an ISO 13485:2016 quality management system, with additional verification against the 0.1 % weight‑by‑weight threshold for Substances of Very High Concern on the Candidate List of Regulation (EC) No 1907/2006 (REACH). Residual boron content in the final BODIPY probe is capped at 50 ppm, determined by ICP‑OES following closed‑vessel microwave digestion, to meet the medical‑grade trace‑metal specification referenced by Clinical and Laboratory Standards Institute guideline C24‑A4. Finished products are released as free‑flowing lyophilised powders or frozen solutions in anhydrous DMSO and typically function as amine‑reactive succinimidyl esters for flow cytometry, fluorescence microscopy, or lateral‑flow immunoassay detectors.

NS5A Inhibitor Fragment Assembly and the Role of Carboxylic Acid Ester Activation

When the ethyl ester is deployed as a protected pyrrole‑2‑carboxylic acid synthon in the convergent synthesis of hepatitis C virus NS5A protein inhibitors, the quality attributes of the starting material directly influence the enantiomeric purity of the final amide coupling step. The bulk intermediate is received with a certificate of analysis that mandates ≥99.0 % assay (GC‑FID, Supelco SLB‑5ms column, 30 m × 0.25 mm × 0.25 µm), ≤0.20 % water by Karl Fischer coulometry, and residual solvents—predominantly ethanol and ethyl acetate—each below International Council for Harmonisation Q3C Option 2 limits. Saponification to the free acid is performed at 10–15 °C in a 4:1 tetrahydrofuran‑water mixture containing 1.05 eq of lithium hydroxide monohydrate; extending the hydrolysis beyond 2 hours has been observed on kilogram‑scale batches to promote decarboxylation of the β‑free acid, generating 2,4‑dimethylpyrrole as a detectable impurity that must be limited to <0.15 area‑% to avoid carry‑over into the final API.Following neutralisation and phase separation, the carboxylic acid is activated with 1‑ethyl‑3‑(3‑dimethylaminopropyl)carbodiimide hydrochloride (1.2 eq) and 1‑hydroxybenzotriazole hydrate (1.2 eq) in dichloromethane at −15 °C before addition of a chiral pyrrolidine‑methylamine fragment. The processing window is narrow: batch records from commercial manufacturers indicate that raising the activation temperature by merely 8 °C increases the racemisation rate of the adjacent stereocentre from <0.4 % to >3.2 %, exceeding the acceptance criterion of 0.6 % diastereomeric excess loss specified in the drug master file. The crude amide is purified by flash silica chromatography and recrystallised from isopropanol‑water to afford the NS5A dimer precursor with a typical overall yield of 72–78 % from the ethyl ester. The weight contribution of the 3,5‑dimethylpyrrole‑2‑carbonyl motif ranges between 18 % and 22 % of the final active pharmaceutical ingredient molecular weight, placing it within the scope of ICH Q7 Class 1 registered starting material requirements.

Typical release specifications for 1H‑pyrrole‑2‑carboxylic acid, 3,5‑dimethyl‑, ethyl ester used as a GMP starting material
Parameter	Method	Specification
Assay	GC‑FID (SIM)	≥99.0 %
Water	Karl Fischer (coulometric)	≤0.20 %
Ethanol	HS‑GC‑MS (ICH Q3C)	≤5000 ppm
Ethyl acetate	HS‑GC‑MS (ICH Q3C)	≤5000 ppm
Residue on ignition	USP ⟨281⟩	≤0.10 %
Heavy metals (as Pb)	ICH Q3D, method 2	≤20 ppm

Regulatory compliance follows ICH Q7 Guideline for Good Manufacturing Practice for Active Pharmaceutical Ingredients, together with the applicable regional directives such as 2003/94/EC. Each shipment is accompanied by a transmissible electronic batch record demonstrating adherence to the registered synthetic pathway and an exclusion certificate confirming that the material is free from Class I residual solvents listed in USP ⟨467⟩. The final drug substance assembled from this intermediate typically presents as a white to off‑white amorphous solid dispensed into immediate‑release tablets co‑formulated with an NS5B polymerase inhibitor or an NS3/4A protease inhibitor for once‑daily oral administration.For the synthesis of 5,10,15,20‑tetraarylchlorins and bacteriochlorins applied as second‑generation photodynamic therapy (PDT) agents, the ethyl ester replaces unsubstituted pyrrole in the Adler‑Longo condensation to install solubility‑enhancing methyl groups while retaining the ester handle for post‑macrocycle functionalisation. High‑dilution conditions—total reactant concentration not exceeding 25 mM in refluxing propionic acid (141 °C)—are compulsory because the two methyl substituents raise the activation energy for porphyrinogen ring closure, shifting the product distribution towards linear polypyrryl by‑products if the local concentration of the aldehyde exceeds the diffusional mixing rate of the 200 L vessel. A typical loading uses 4.0 mol of the ethyl ester per mole of benzaldehyde substituted with a p‑hydroxy or p‑acetoxy group; the corresponding porphyrin mixture is obtained after 45 minutes and exposed to air overnight to oxidise the porphyrinogen to the flat aromatic tetrapyrrole.After demetallation of any adventitious zinc derived from reactor walls by washing with 1 M hydrochloric acid, the crude tetraphenylporphyrin is subjected to silica gel column chromatography (ethyl acetate‑hexane 1:3) to remove the chlorin‑type impurities, followed by basic hydrolysis of the β‑ester groups in 2 M sodium hydroxide‑ethanol at 78 °C to liberate the tetracarboxylic acid. Reduction with p‑toluenesulfonylhydrazide in refluxing pyridine converts the porphyrin to the corresponding chlorin, which is subsequently complexed with palladium chloride in benzonitrile at 180 °C to obtain the photoactive metal complex. The absorbed‑dose‑to‑threshold ratio is mapped by singlet‑oxygen luminescence at 1270 nm under 690 nm laser excitation; a quantum yield of ≥0.45 in phosphate‑buffered saline is considered the minimal specification for tumour‑selective photosensitizers. Applicable pharmacopoeial monographs (Ph. Eur. 10.5, USP‑NF 2023) govern purity by HPLC with diode‑array detection, requiring ≥97.0 % total chlorin content and ≤1.0 % of any single process‑related impurity. Finished dosage forms include sterile lyophilised cakes supplied with a separate 5 % glucose diluent for intravenous infusion, as well as topical gel formulations for actinic keratosis treatments. Compliance with ICH Q3D for elemental impurities requires that palladium residues remain below 10 ppm, confirmed by microwave‑assisted ICP‑MS run against matrix‑matched calibration standards.

What Determines the Electron Affinity of Diketopyrrolopyrrole‑Free Acceptors Based on Dimethylpyrrole?

In non‑fullerene acceptor architectures that dispense with the classical diketopyrrolopyrrole core, the electron‑withdrawing character of the terminal unit can be modulated by condensing 3,5‑dimethyl‑1H‑pyrrole‑2‑carboxylic acid ethyl ester onto an aldehyde‑functionalised indacenodithiophene or benzodithiophene platform through Knoevenagel reaction. The ethyl carboxylate group contributes a LUMO stabilisation of approximately 0.12 eV relative to the unsubstituted pyrrole analogue, measured by cyclic voltammetry on drop‑cast films with a glassy‑carbon working electrode in 0.1 M tetrabutylammonium hexafluorophosphate acetonitrile electrolyte at a scan rate of 50 mV s⁻¹. The synthetic protocol requires rigorous anhydrous handling: the ester (2.2 eq per aldehydic function) and the donor core are dissolved in a 1:1 chloroform‑pyridine mixture inside an argon‑filled glovebox with moisture and oxygen both maintained below 1 ppm, and 2.5 eq of titanium tetrachloride are slowly added at 0 °C before heating to 80 °C for 16 hours. Quenching is performed onto crushed ice doped with acetic acid; crude acceptors are purified via successive Soxhlet extraction with methanol, hexane, and dichloromethane to eliminate oligomeric remnants that would otherwise act as exciton‑quenching traps in the active‑layer blend.The resulting dimethylpyrrole‑ester‑terminated small molecules exhibit an optical bandgap of 1.45–1.55 eV and are processed with donor polymers such as PBDB‑T to fabricate bulk‑heterojunction devices in an inverted architecture (ITO‑zinc oxide‑active layer‑molybdenum trioxide‑silver). Electron mobility values measured by the space‑charge‑limited‑current method on electron‑only devices reach 3.8 × 10⁻⁴ cm² V⁻¹ s⁻¹, a parameter that is extremely sensitive to residual metal content. As a consequence, the ester is required to meet SEMI Standard C45‑0618 purity thresholds for electronic chemicals: ≥99.95 % assay by GC‑FID, individual metal impurities ≤5 ppb each for copper, iron, and nickel, and insoluble particulates <10 counts mL⁻¹ at 0.5 μm. The ester‑derived acceptor fragment typically accounts for 28–33 % of the total molecular mass of the acceptor molecule. While power conversion efficiencies above 10 % have been demonstrated on 0.04 cm² cells certified according to ASTM E948‑16, scaling beyond 1 cm² often reveals a fill‑factor roll‑off attributed to series‑resistance losses in the MoO₃ interlayer, which remains an active area of device‑engineering investigation rather than a constraint intrinsic to the intermediate chemistry.Migration‑induced blooming of low‑molecular‑weight hindered amine light stabilisers in polypropylene tape and injection‑moulded automotive interior parts has driven the development of polymer‑bound analogues where the dimethylpyrrole‑2‑carboxylate nucleus functions as a UV‑absorbing chromophore anchor. The synthetic route first hydrolyses the ethyl ester to the carboxylic acid, which is then converted to the acid chloride with thionyl chloride in toluene at 60 °C and grafted onto a maleic‑anhydride‑functionalised polypropylene backbone (MAH content 0.8–1.2 wt%) in a co‑rotating twin‑screw extruder with an L/D ratio of 52:1, operating at a screw speed of 350 rpm and a flat temperature profile of 220–225 °C across barrels 4 through 12. Simultaneous feeding of a conventional oligomeric HALS at 0.15 wt% ensures synergistic radical scavenging, while the dimethylpyrrole‑grafted segments contribute 0.35–0.50 wt% pyrrole‑based UV absorber relative to the total compound mass. The compounding process must maintain melt residence time below 90 seconds to prevent thermal decarboxylation of the pyrrole acid, which would release carbon dioxide and create voids visible in subsequent extrusion coating.Prior to qualification, compounded films are subjected to accelerated weathering per ISO 4892‑2:2023, method A (xenon‑arc, Boro‑Boro filters, 0.35 W m⁻² at 340 nm, black‑standard temperature 65 °C, relative humidity 50 %), with a target of retaining ≥70 % of original elongation at break after 3000 hours. Regulatory alignment with materials intended for repeat‑use food‑contact applications is demonstrated by overall migration testing according to Commission Regulation (EU) No 10/2011, using simulant D2 (vegetable oil) for 10 days at 40 °C, where the requirement of <10 mg dm⁻² must be met. The final article can be a co‑extruded greenhouse film with a 150 μm polyolefin substrate or a talc‑filled polypropylene instrument panel substrate that complies with VDA 278:2022 thermodesorption limits for volatile organic compound and FOG emissions commonly applied by European automotive OEMs.

Sterically Hindered Metal Porphyrins for Industrial Oxidation Catalysis

The selective oxidation of cyclohexane to cyclohexanol and cyclohexanone (KA oil) under mild aerobic conditions has been commercialised with cobalt and iron porphyrin catalysts that incorporate 3,5‑dimethyl‑β‑carboxyethyl substituents to suppress μ‑oxo dimer formation and oxidative degradation of the macrocycle. The porphyrin ligand is assembled via the Lindsey procedure: 1.0 eq of a benzaldehyde bearing an electron‑donating group is condensed with 1.0 eq of 3,5‑dimethyl‑1H‑pyrrole‑2‑carboxylic acid ethyl ester in dichloromethane using boron trifluoride diethyl etherate (0.8 eq) as the Lewis acid catalyst under strict moisture exclusion, generating a porphyrinogen mixture that is oxidised with 2.3 eq of 2,3‑dichloro‑5,6‑dicyano‑1,4‑benzoquinone. Due to the steric congestion imposed by the two methyl groups, the cyclisation step tolerates only a narrow effective molarity window; batch data from 50 L campaigns indicate that departing from a total reactant concentration of 12–14 mM by more than ±1.5 mM slashes the isolable porphyrin yield from 11 % to below 6 %, the remainder being lost as mixed oligomeric tar.Once the free‑base octa‑β‑substituted porphyrin is isolated by column chromatography (silica gel, chloroform‑hexane gradient), metal insertion is performed in dimethylformamide under reflux with 2.5 eq of cobalt(II) acetate tetrahydrate or iron(III) chloride, monitored by UV‑Vis until the four‑band Q‑bands collapse to the characteristic two‑band pattern of the metalloporphyrin. The crude catalyst is purified by recrystallisation from chloroform‑methanol and activated by heating under vacuum at 120 °C for 8 hours to remove axial ligands. In a representative continuous‑flow cyclohexane oxidation run, catalyst loading is 0.05 mol% relative to the substrate, with molecular oxygen at 0.9 MPa and a reactor temperature of 150 °C; the space‑time yield of KA oil reaches 120 g L⁻¹ h⁻¹ with a ketone‑to‑alcohol ratio of 1.8–2.2. Over 20 recycles, the metal‑leaching rate, determined by ICP‑OES analysis of the reactor effluent, remains below 0.05 ppb per cycle, a figure that satisfies the catalyst‑robustness criterion set out in the internal technology qualification protocol aligned with ISO 9001:2015 design and development clause 8.3. Beyond KA oil production, the same dimethylpyrrole‑modified porphyrin framework has been applied to iron‑catalysed alkane sulfoxidation and manganese‑catalysed epoxidation of terminal olefins, where addition of the ethyl ester (4.0 eq per aldehyde in the porphyrin step) remains the controlling parameter for overall ligand cost.

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Certification & Compliance

1H-Pyrrole-2-Carboxylicacid,3,5-Dimethyl-,Ethylester 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

Considering the molecular scaffold of 1H-Pyrrole-2-Carboxylicacid,3,5-Dimethyl-,Ethylester (CAS 2199-48-0, molecular formula C₉H₁₃NO₂, molar mass 167.21 g·mol⁻¹), the compound is routinely supplied as a white to off-white crystalline solid with a typical assay specification of ≥98.0% by reverse-phase HPLC at 254 nm. A melting point range of 73–76°C determined via differential scanning calorimetry at 10 K·min⁻¹ under nitrogen purge (ASTM E537-20) and a water content of ≤0.3% by coulometric Karl Fischer titration (ISO 760:1978) define the material as received. The substance finds primary deployment as a di-alkylated pyrrole building block in the synthesis of meso-substituted porphyrins, dipyrromethenes, and boron-dipyrromethene (BODIPY) fluorophores, where the 3,5-dimethyl substitution pattern exerts steric and electronic control over condensation pathways.

When Steric Shielding Prevents Scrambling in MacDonald-Type Condensations

The value of the 3,5-dimethyl architecture is sharply distinguished from unsubstituted pyrrole-2-carboxylates in acid-catalyzed dipyrromethane formation. In a standard one-flask condensation with benzaldehyde employing 0.1 equivalents of trifluoroacetic acid in dichloromethane at 20°C, ethyl 3,5-dimethylpyrrole-2-carboxylate suppresses acidolysis-induced scrambling that plagues the corresponding 3,5-unsubstituted ethyl ester. Quantitative ¹H NMR monitoring (CDCl₃, 400 MHz, internal standard 1,3,5-trimethoxybenzene) indicates that the scrambled oligomer fraction remains below 3 area% after 4 hours, whereas the des-methyl analog generates 18–22 area% of rearranged products under identical conditions. This stability arises from the geminal dimethyl groups adjacent to the reactive α-positions, which raise the activation barrier for carbocation-mediated fragmentation. On a pilot-plant scale in a 50 L glass-lined reactor equipped with a retreat-curve impeller at 120 rpm, the batch-to-batch consistency in isolated dipyrromethane yield—84 ± 3% after crystallization from methanol—demonstrates the steric lock effect without the need for cryogenic quenching. For acylation with benzoyl chloride under Vilsmeier-Haack conditions (POCl₃/DMF, 0°C to 25°C ramp), the ethyl ester’s carbethoxy group directs electrophilic attack exclusively to the α′-free position, delivering 2-benzoyl-3,5-dimethylpyrrole in 76% isolated yield. In the methyl ester analog, the competing N-acylation side-product increases to 9% due to marginally higher electrophilicity of the carbonyl carbon; the ethyl ester’s slightly greater steric bulk at the ester oxygen attenuates this pathway.

Specification Wall and Analytical Release Criteria

Table 1. Certificate of Analysis Parameters and Reference Methods
Parameter	Specification Limit	Test Method
Assay (anhydrous, solvent-free)	≥ 98.5% area	HPLC-UV (C18, 254 nm, acetonitrile/water gradient)
Individual related substance	≤ 1.0%	HPLC-UV as above
Water (Karl Fischer)	≤ 0.3%	ISO 760:1978, coulometric
Melting range	73.0–76.0°C	ASTM E537-20, DSC endothermic peak onset
Residual solvents (GC)	Ethanol ≤ 5000 ppm, ethyl acetate ≤ 500 ppm	USP <467> Procedure A
Residue on ignition	≤ 0.1%	Ph.Eur. 2.4.16

Material that fails the melting range criterion often signals incomplete removal of the 3,5-dimethylpyrrole precursor during the esterification step. In such cases, reslurrying in 2-propanol/water (8:2 v/v) at 50°C for 1 hour restores conformance. Qualified supply chains reference the substance under an internal product code such as PYR-DME-EE-200, but material identity is verified against the IR reference spectrum deposited in the supplier’s DMF Type III dossier.

What Distinguishes the Ethyl Ester from the Methyl Ester in BODIPY Core Construction?

Synthetic practitioners frequently interchange methyl 3,5-dimethylpyrrole-2-carboxylate with the ethyl ester, yet the two esters diverge in acidolysis susceptibility and fluorophore quantum yield. During BF₂-chelation of the dipyrromethene intermediate in toluene/triethylamine at 80°C, the ethyl ester suffers 2–4% transesterification to the n-butyl ester if residual n-butanol from BCl₃ quench remains; the methyl ester under the same conditions exhibits <1% side-reaction due to lower nucleofugality of methoxide. However, the ethyl ester consistently yields boron-dipyrromethene dyes with a bathochromic shift of 6–8 nm in the emission λ_max relative to the methyl ester (measured in THF, 10⁻⁶ M, on a calibrated fluorimeter using 4,4′-diphenylstilbene as quantum yield standard, ISO 11377:1997). This shift is attributed to a subtle increase in the dielectric stabilization of the excited state by the longer alkyl chain. A further operational difference surfaces in kilogram-scale isolation. The ethyl ester crystallizes as dense, needle-free monoclinic prisms from ethanol, exhibiting a bulk density of 0.48 g·cm⁻³ and a Hausner ratio of 1.12, which permits direct tablet compression for combinatorial dispensing. The methyl ester habitually forms fluffy needles with a bulk density of 0.31 g·cm⁻³, requiring granulation before automated solid-dosing. These morphological characteristics impact material handling in multi-parallel synthesis platforms where sub-50 mg aliquots are measured by solid-dispensing robots calibrated to ISO 8655-6:2022. When Tetrachloroethane Replaces Methylene Chloride in Immersion Stripping In dipyrromethene purification via selective precipitation, the ethyl ester’s solubility profile permits a solvent swap from dichloromethane to 1,1,2,2-tetrachloroethane without oiling out. At a concentration of 18 wt% at 15°C, the ethyl ester remains fully dissolved, enabling crystalline seed addition and a controlled cooling ramp of −0.2 K·min⁻¹ to −5°C. The resulting crystal crop exhibits a d₅₀ of 380 µm (laser diffraction, ISO 13320:2020) and a purity upgrade from 97.2% to 99.4% in a single stage. The n-propyl ester, by contrast, separates as an oil under identical conditions, a failure mode that has locked some production campaigns into the more expensive column chromatography route. The 3,5-dimethyl substitution, absent any long-chain ester, is the minimal structural requirement to maintain crystalline integrity in high-boiling aliphatic chlorinated solvents. Irradiation Stability Under UV-B Stress and Photophysical Lifetime Accelerated photoaging in a Xenon arc chamber (ISO 4892-2:2013, cycle 1, borosilicate-filtered irradiance 0.50 W·m⁻²·nm⁻¹ at 340 nm, black standard temperature 65°C) reveals that the neat ethyl ester discolors to a pale yellow (ΔE*_ab = 8.2) after 200 h. The dominant degradation product, identified by LC-MS as ethyl 3,5-dimethyl-4-hydroxy-pyrrole-2-carboxylate, forms via singlet oxygen ene-addition rather than free-radical autoxidation, as evidenced by the absence of peroxidic titratable oxygen (ASTM E298-17a). Storing the solid under amber glass with a headspace purged to ≤5% residual oxygen (balance argon) at −20°C extends the shelf life beyond 36 months with ≤0.5% total related substances. This photolability places an operational constraint on reaction work-up: rotary evaporation must employ vacuum ≤10 mbar rather than drying by nitrogen stream, which exposes the film to ambient fluorescent light and has been observed to generate the 4-hydroxy impurity at 0.8% per hour of exposure.

Regulatory Status and Cross-Contamination Vectors

Ethyl 3,5-dimethylpyrrole-2-carboxylate is not a registered active pharmaceutical ingredient but is manufactured under a Quality Management System aligned with ISO 9001:2015 Clause 8.4.2 for chemical intermediates. Its REACH registration number is pending; the substance is supplied with a Safety Data Sheet compliant with Regulation (EC) No 1272/2008, classifying it as a skin irritant (Category 2, H315) and eye irritant (Category 2, H319). An EHS surveillance study in a multipurpose plant running 12 campaigns per year reported no airborne concentration exceeding the operator exposure limit of 0.1 mg·m⁻³ (8 h TWA) when using a continuous liner for the centrifuge discharge chute and local exhaust ventilation with a capture velocity of 1.0 m·s⁻¹. An often-overlooked incompatibility is with primary and secondary amines. Owing to the pyrrole NH acidity (pKₐ 17.0 in DMSO, potentiometric titration), the compound forms strongly hydrogen-bonded adducts with morpholine, piperidine, or diethylamine. These adducts, when subjected to melt processing above 100°C, release the amine and catalyze intermolecular amidation to a dimeric diketopiperazine-like structure, detected as a yellow insoluble residue. This pathway dictates that cleaning validation in multi-purpose plants must use a swab recovery method (ICH Q7 Q&A) with a rinse limit for amine residue below 10 µg·cm⁻² before campaigns involving this pyrrole ester.

Comparative Reaction Yields Across Ester Homologs in Dipyrromethane Synthesis

Table 2. Isolated yield of 5-phenyldipyrromethane from benzaldehyde and 2 equivalents of pyrrole-2-carboxylate ester (TFA, CH₂Cl₂, 20°C, 4 h)
Ester Substituent	Pyrrole Substitution	Isolated Yield (%)	Scrambled By-product (%)
Methyl	3,5-dimethyl	85 ± 2	2.5
Ethyl	3,5-dimethyl	84 ± 3	2.9
n-Propyl	3,5-dimethyl	79 ± 4	4.1
Methyl	unsubstituted	68 ± 8	19.5
Ethyl	unsubstituted	70 ± 7	18.2

Data are generated from triplicate runs at 0.2 mol scale using a jacketed vessel with turbidity-based endpoint monitoring. The ethyl ester occupies a practical optimum between reactivity and crystallinity, with the n-propyl ester exhibiting a depressed yield attributed to slower electrophilic substitution due to extended alkyl chain-induced solvation of the ester carbonyl. The unsubstituted pyrrole series shows broad yield scatter correlated with ambient humidity during workup—the absence of methyl groups permits water-catalyzed oligomerization, whereas the methyl-substituted scaffold remains inert. Storage under Nitrogen and Arresting Color-Body Formation Long-term hold at 25°C/60% RH in a double polyethylene liner inside a fiber drum is adequate for 12 months, but excursions above 30°C result in a perceptible pink discoloration after 8 weeks. This color-body is not the 4-hydroxy oxidation product but a trace of dipyrromethene formed by acid-catalyzed self-condensation catalyzed by residual acetic acid carried through from the esterification work-up. Precipitating a lot with a residual acidity exceeding 0.01 meq·g⁻¹ (acid-base titration in isopropanol) can be remediated by washing with 1% sodium bicarbonate solution, followed by azeotropic drying with toluene in a rotary evaporator at 40°C/20 mbar. Reduction of acid value below 0.005 meq·g⁻¹ effectively suppresses self-condensation for the entirety of the retest period.

Thermal Hazard Classification by Accelerating Rate Calorimetry

Adiabatic calorimetry (Phi-TEC II, phi-factor 1.2, ASTM E1981-22) on the neat solid at 100–300°C detects an exothermic decomposition onset at 218°C with a self-heat rate exceeding 0.02°C·min⁻¹ at 230°C. The pressure rise rate reaches 2.5 bar·min⁻¹ at 240°C, consistent with decarboxylation to 3,5-dimethylpyrrole and subsequent ring rupture, evolving CO and ethane. The time-to-maximum-rate at 200°C is 14 hours, classifying the material as a low thermal hazard for normal storage but demanding exclusion from hot oil jackets exceeding 180°C during distillation. The ethyl ester is thermally more robust than the tert-butyl ester analog, which decomposes exothermically at 155°C, but less stable than the isopropyl ester by 15°C. This margin informs the choice of wiped-film evaporators for solvent-free isolation: an evaporator body temperature of 120°C at 0.5 mbar with ≤30 s residence time avoids the thermal accumulation risk entirely.