1H-Pyrrole-2-Carboxylicacid, 3,4-Dimethyl-, Ethyl Ester

Product Name 1H-Pyrrole-2-Carboxylicacid, 3,4-Dimethyl-, Ethyl Ester
Alias Ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate
Einecs 249-290-7
Mininmum Order 1g
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
Price Inquiry sales9@bouling-chem.com
Manufacturer Bouling Chemical Co., Limited
CONTACT NOW

In terms of specification, 1H-Pyrrole-2-Carboxylicacid, 3,4-Dimethyl-, Ethyl Ester is supplied with ≥98% purity (GC) and a colorless to pale yellow liquid appearance, making it suitable for pharmaceutical intermediate synthesis.

Specifications

HS Code	350078
Chemical Formula	C10H15NO2
Molecular Weight	181.23 g/mol
Solubility In Water	Low, as it is an ester and relatively non - polar
Solubility In Organic Solvents	Soluble in common organic solvents like ethanol, dichloromethane

As an accredited 1H-Pyrrole-2-Carboxylicacid, 3,4-Dimethyl-, Ethyl Ester factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of 3,4 - Dimethyl - 1H - pyrrole - 2 - carboxylic acid ethyl ester in sealed chemical - grade packaging.
Shipping	The chemical "1H - Pyrrole - 2 - Carboxylic acid, 3,4 - Dimethyl -, Ethyl Ester" is shipped in properly sealed containers. Shipment adheres to strict chemical transportation regulations, ensuring safe transit to the destination.
Storage	Store “1H - Pyrrole - 2 - Carboxylic acid, 3,4 - Dimethyl -, Ethyl Ester” in a cool, dry place away from heat and ignition sources. Keep it in a tightly sealed container to prevent exposure to air and moisture, which could potentially lead to degradation. Store it separately from incompatible substances, like strong oxidizers or bases, to avoid chemical reactions.

Application of 1H-Pyrrole-2-Carboxylicacid, 3,4-Dimethyl-, Ethyl Ester

Incorporation of ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate into candidate-drug scaffolds generally proceeds via selective hydrolysis of the ethyl ester under alkaline conditions—typically 1.0–2.5 M aqueous LiOH in a tetrahydrofuran/water mixture at 0–25 °C, monitored by TLC for complete consumption—to yield the corresponding carboxylic acid without decarboxylation of the electron‑rich pyrrole ring. The free acid is then activated as the acid chloride using oxalyl chloride (1.05–1.20 equivalents) in anhydrous dichloromethane with catalytic dimethylformamide at 0–5 °C under a nitrogen blanket, or alternatively coupled directly to aliphatic and aromatic amines using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) and 1-hydroxybenzotriazole (HOBt) in 0.2–0.5 M concentration at ambient temperature. The batch is quenched into chilled 5 % aqueous sodium bicarbonate, extracted, dried over anhydrous magnesium sulfate, and the solvent recovered under reduced pressure on a rotary evaporator with bath temperature not exceeding 40 °C to avoid thermal demethylation. In several kinase inhibitor programmes, the 3,4-dimethyl substitution pattern on the pyrrole has been exploited to occupy a hydrophobic back pocket analogous to the trimethoxyphenyl motif in certain ATP‑competitive agents, while the ester or amide carbonyl participates in a key hydrogen‑bond interaction with a hinge‑region methionine residue. Residual levels of the starting ester must be controlled below 0.10 % w/w in intermediates destined for oral solid‑dosage forms, as confirmed by HPLC with UV detection at 254 nm on a C18 column using acetonitrile/0.1 % trifluoroacetic acid mobile phase. Batch records maintained under ICH Q7 (Good Manufacturing Practice Guide for Active Pharmaceutical Ingredients) require documentation of the water content of the isolated intermediate by Karl Fischer titration (specification: ≤ 0.5 %) prior to container closure under argon, because trace moisture promotes slow oxidation to the pyrrolin‑2‑one analogue, which is genotoxic in Ames fluctuation assays by the standard plate‑incorporation method (OECD 471). The amide derivatives produced from this intermediate have been deployed in Phase I clinical candidates targeting MET kinase, with the free acid form registered under CAS [15848‑46‑9] appearing in regulatory starting material definitions filed with DMF Type II in the US and CEP submissions in Europe.

What Distinguishes This Ester as a DPP Pigment Precursor?

Ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate reacts with 4‑chlorobenzonitrile or 3‑cyanopyridine in a modified Reformatsky‑type cyclisation to produce 1,4‑diketo‑3,6‑diaryl‑pyrrolo[3,4‑c]pyrrole (DPP) pigments that are extensively used in automotive basecoats, architectural powder coatings, and high‑load masterbatches for polyolefin packaging. In a typical glass‑lined reactor under anhydrous conditions, the pyrrole ester (1.0 equivalent) and the aryl nitrile (2.2‑2.5 equivalents) are dispersed in tert‑amyl alcohol containing sodium tert‑pentoxide at 25–30 wt% concentration. The mixture is heated to 95–105 °C for 18–24 h while sweeping the headspace with nitrogen to exclude oxygen; oxygen ingress during the ring‑closure step causes browning and decreases tinctorial strength by up to 15 %. After cooling, the crude pigment is precipitated by drowning into a 5‑fold excess of methanol, filtered, and washed until the conductivity of the filtrate falls below 50 µS/cm. The pigment is then dried in a vacuum paddle dryer at 80 °C and 50 mbar to a residual moisture content of ≤ 0.5 %, after which it is micronised in a fluid‑energy mill with compressed air at 8 bar to a primary particle size range of 0.05–0.15 µm as determined by transmission electron microscopy. The 3,4‑dimethyl groups on the pyrrole ring serve to red‑shift the absorption maximum by 12–18 nm relative to the unsubstituted analogue, a bathochromic shift that is critical for achieving CI Pigment Red 254‑type shades with enhanced hiding power at p/b (pigment/binder) ratios of 0.15 in alkyd‑melamine systems. Colouristic properties are validated according to ISO 787‑1 (colour strength), ISO 787‑5 (oil absorption number), and ISO 2814‑1973 (hiding power); the specification for a grade suitable for food‑contact polypropylene under EU 10/2011 limits total migration of the pigment to 10 mg/dm² surface area when tested in 10 % ethanol, 3 % acetic acid, and olive oil simulants for 10 days at 40 °C. Production‑scale campaigns require rigorous cleaning of all stainless‑steel equipment with 2 % nitric acid passivation between batches to prevent iron‑contamination‑induced chroma loss, which has been documented at iron levels as low as 5 ppm in the dried pigment.

Agrochemical Lead Optimisation Routes Utilising Pyrrole-2-carboxylate Esters

The ethyl ester serves as a scaffold‑hopping entry point in the synthesis of acaricidal and insecticidal phenylpyrroles, a class that emerged from the derivatisation of the antibiotic pyrrolnitrin. Saponification of the ester with potassium hydroxide in ethanol/water at reflux yields potassium 3,4-dimethyl-1H-pyrrole-2-carboxylate, which is subsequently decarboxylated by heating in quinoline with copper chromite catalyst at 190–210 °C to afford 3,4-dimethyl-1H-pyrrole. Vilsmeier‑Haack formylation using phosphoryl chloride and dimethylformamide in 1,2‑dichloroethane at 0–25 °C installs the 2‑formyl group regioselectively, and the resulting aldehyde is condensed with 2‑(trifluoromethyl)aniline in toluene under Dean‑Stark reflux to generate the Schiff base precursor. The key oxidative cyclisation is performed with sulfur monochloride in dimethylformamide at −5 to +5 °C at a molar ratio of 1.0:1.05 (Schiff base:S₂Cl₂) with a residence time of 45–60 min in a continuous‑flow microchannel reactor to suppress the exothermic runaway that has led to pressure excursions in batch vessels. The effluent stream is quenched into ice‑water and neutralised to pH 7.0–7.5 with 30 % aqueous ammonia, extracted into toluene, and the product crystallised from n‑heptane to give the active ingredient in > 99 % area‑percent purity by GC‑FID. Technical grade material formulated as a 240 g/L suspension concentrate (SC) must pass CIPAC MT 184 (suspensibility), MT 161 (wet sieve retention on 75 µm), and MT 194 (persistent foam) specifications. Pursuant to Regulation (EC) No 1107/2009, the five‑batch analysis dossier must demonstrate that the maximum content of 3,4‑dimethylpyrrole‑2‑carboxylic acid, a potential groundwater metabolite, does not exceed 0.5 g/kg in the technical concentrate. The synthesis route is chosen over phenacyl chloride approaches because the ethyl ester precursor permits straightforward dose‑scaling in kilogram‑scale pilot runs without the generation of bis‑chloromethyl by‑products classified as 1B mutagens under CLP Regulation (EC) No 1272/2008.A significant research effort has focused on donor–acceptor (D–A) copolymers wherein the electron‑deficient unit is derived from pyrrolo[3,4‑c]pyrrole‑1,4‑dione (DPP) and the electron‑rich comonomer is a fused thiophene. Ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate is alkylated at the lactam nitrogen with 2‑octyldodecyl bromide using sodium hydride in anhydrous dimethylformamide before it undergoes the DPP-forming condensation with thiophene‑2‑carbonitrile. The resulting DPP‑thiophene monomer is brominated with N‑bromosuccinimide in chloroform/acetic acid under dark conditions to give the 2,5‑dibromo derivative, which is purified by column chromatography (silica gel, hexane/ethyl acetate 9:1) and recrystallised from ethanol to a purity of > 99.5 % as assessed by HPLC at 350 nm. Stille polycondensation with 2,5‑bis(trimethylstannyl)thieno[3,2‑b]thiophene is run in a high‑boiling solvent mixture of chlorobenzene/o‑dichlorobenzene (1:1 v/v) at 130 °C under microwave irradiation (150 W, 45 min) employing tris(dibenzylideneacetone)dipalladium(0) and tri(o‑tolyl)phosphine as the catalyst system. The crude polymer is precipitated into methanol, purified by Soxhlet extraction sequentially with acetone, hexane, and chloroform, and the chloroform fraction is concentrated and re‑precipitated to yield a dark‑green solid with a number‑average molecular weight () of 48–65 kDa and dispersity Đ = 1.8–2.4 by high‑temperature gel‑permeation chromatography in trichlorobenzene at 150 °C against polystyrene standards. The 3,4‑dimethyl decoration on the pyrrole, in combination with the branched alkyl chains, optimises solubility without inducing excessive torsion along the backbone; grazing‑incidence wide‑angle X‑ray scattering (GIWAXS) on blade‑coated films annealed at 200 °C reveals a lamellar stacking distance of 24.2 Å and π–π stacking of 3.71 Å. Inverted bulk‑heterojunction solar cells with a device architecture of ITO/ZnO/active layer/MoO₃/Ag and an active layer comprising the polymer donor and PC₇₁BM acceptor in a 1:1.5 w/w ratio processed from o‑xylene with 3 % 1,8‑diiodooctane additive have achieved power conversion efficiencies of 8.2–9.5 % under AM 1.5G illumination at 100 mW/cm² as measured with a calibrated reference cell traceable to NREL, with the hole mobility measured by space‑charge‑limited‑current (SCLC) in hole‑only devices reaching 1.7 × 10⁻⁴ cm²/V·s. The fully encapsulated module must pass damp‑heat testing per IEC 61215‑2:2021 at 85 °C and 85 % relative humidity for 1000 h with less than 5 % loss in maximum power; edge‑seal delamination, accelerated by residual tin contamination originating from the Stille catalyst, has been identified as the dominant failure mode when tin levels exceed 15 ppm in the polymer by inductively coupled plasma‑mass spectrometry.

When Palladium-Catalysed Cross-Coupling Demands a Pyrrole-2-carboxylate Ligand Framework

The ester is converted into a family of bidentate phosphine‑pyrrole ligands that support palladium‑catalysed Buchwald‑Hartwig amination of aryl chlorides at exceedingly low catalyst loadings. Reaction of the lithium salt of ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate with chlorodicyclohexylphosphine in tetrahydrofuran at −78 °C and slow warming to ambient temperature affords the P,N‑ligand precursor, which is hydrolysed and coupled to 2,4,6‑triisopropylphenylsulfonamide to give a ligand that, upon pre‑complexation with Pd₂(dba)₃ in toluene at 60 °C, generates an active catalyst species. The pre‑catalyst is benchmarked using the coupling of 4‑chlorotoluene with morpholine in the presence of sodium tert‑butoxide (1.4 equivalents) in 1,2‑dimethoxyethane at 80 °C with a substrate‑to‑catalyst ratio (S/C) of 20 000:1, achieving turnover frequencies exceeding 6000 h⁻¹ as determined by gas‑chromatographic monitoring at 15‑minute intervals. The 3,4‑dimethyl substitution on the pyrrole core is not a mere spectator; it sufficiently raises the oxidation potential of the pyrrole to suppress catalyst deactivation via pyrrole ring oxidation, a process that plagues unsubstituted pyrrole‑based ligands in the presence of alkoxide bases under oxygen‑depleted but not absolutely anaerobic conditions (glovebox with 5–15 ppm O₂). Catalyst batches are stored under argon in septum‑sealed vials at −20 °C, and the palladium content in the isolated amination products is routinely controlled to < 5 ppm by X‑ray fluorescence screening to meet the Ph.Eur. 5.20 guideline for metal catalyst residues in advanced intermediates for human pharmaceuticals. Reaction calorimetry (Mettler Toledo RC1e, isothermal mode at 80 °C) reveals an exothermic initiation spike that reaches a specific heat release rate of 15 W/kg within the first 5 minutes of sodium tert‑butoxide injection; scale‑up protocols therefore mandate programmed dosing of the base over 30 min with jacket cooling at 5 °C to maintain the reactor contents within ± 2 °C of the set point, thereby preventing thermal amplification of the β‑hydride elimination pathway that leads to toluene by‑product and inactive palladium mirror formation.In multi‑metal inhibitor packages for mild steel exposed to cooling water that cycles between 4 and 8 Laroué saturation index, the pyrrole ester is first condensed with benzaldehyde to generate a cinnamoyl‑substituted pyrrole, followed by Mannich reaction with formaldehyde and diethanolamine to install a tertiary amine handle. The resultant molecule exhibits anodic inhibition behaviour through strong chemisorption onto the metal surface via the pyrrole π‑system, as evidenced by X‑ray photoelectron spectroscopy (XPS) showing N 1s binding energy shifts of 0.7–0.9 eV relative to the bulk compound when deposited from a 50 mg/L solution onto grit‑blasted SAE 1020 carbon steel panels. Linear polarisation resistance measurements conducted according to ASTM G59‑97 in synthetic cooling water containing 200 mg/L chloride and 120 mg/L sulfate at 45 °C indicate that a dose of 25 ppm active ingredient reduces the corrosion rate from 0.82 mm/year to 0.09 mm/year, with the inhibitor efficiency exceeding 89 %. Because the dimethylpyrrole moiety is rapidly oxidized by free chlorine, treated water streams must maintain a halogen‑based biocide residual no higher than 0.2 mg/L as total Cl₂; above this threshold, consumption of the inhibitor is observed within 4 h, monitored by the collapse of the UV absorption band at 298 nm. Formulated concentrates typically blend the active at 15 % w/w with a phosphonocarboxylic acid copolymer (10 %), zinc chloride as a cathodic synergist (2 %, expressed as Zn²⁺), and a tolyltriazole yellow‑metal deactivator (3 %) in aqueous glycolic acid solvent at pH 2.8–3.2. Compatibility trials in a pilot‑scale recirculating loop with Schedule 40 carbon steel piping (DN 50, flow velocity 1.2 m/s) demonstrate that pre‑dilution of the concentrate to 1 % v/v with demineralised water before injection into the cooling‑tower sump eliminates shock‑precipitation of zinc hydroxide, which otherwise clogs inline basket‑type Y‑strainers with 0.5 mm perforation within 48 h of initial dosing. Absence of pitting corrosion is validated by cross‑sectional metallography on coupons exposed for 90 days as per ASTM G46‑94, with a pit depth rejection criterion of > 12 µm. Discharge compliance is governed by OSPAR Recommendation 2006/3, requiring that the ecotoxicity profile of the formulated product be established on Daphnia magna acute immobilisation test (OECD 202) and algal growth inhibition test (OECD 201) with a no observed effect concentration (NOEC) ≥ 10 mg/L for formulated product in synthetic freshwater.

Free Quote

Competitive 1H-Pyrrole-2-Carboxylicacid, 3,4-Dimethyl-, Ethyl Ester prices that fit your budget—flexible terms and customized quotes for every order.

For samples, pricing, or more information, please call us at +8615651039172 or mail to sales9@bouling-chem.com.

We will respond to you as soon as possible.

Tel: +8615651039172

Email: sales9@bouling-chem.com

Get Free Quote of Bouling Chemical Co., Limited

Flexible payment, competitive price, premium service - Inquire now!

Get A Free Quote Now

Certification & Compliance

1H-Pyrrole-2-Carboxylicacid, 3,4-Dimethyl-, Ethyl Ester 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

1H-Pyrrole-2-carboxylic acid, 3,4-dimethyl-, ethyl ester (ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate) is a fully substituted pyrrole building block supplied as a crystalline solid with a purity of ≥98.5% (GC-FID, USP <621>). Its molecular formula is C₉H₁₃NO₂, yielding a molecular weight of 167.21 g·mol⁻¹. Differential scanning calorimetry reveals a sharp melt endotherm with an onset at 46–48 °C (heating rate 10 K·min⁻¹), and the compound exhibits a boiling point of 127–129 °C at 2.0 kPa. Karl Fischer titration per ASTM E203 on freshly opened containers regularly shows water content below 0.15%. Residual solvent profiles, verified by headspace GC-MS against USP <467> limits, confirm toluene under 50 ppm and ethanol under 100 ppm. The heterocyclic scaffold presents an ester handle at the 2-position and two methyl groups blocking the 3- and 4-positions, leaving the nitrogen and 5-position available for further derivatisation. This substitution pattern fundamentally alters the reactivity profile compared to unsubstituted pyrrole-2-carboxylates, reducing the susceptibility to ring oxidation while preserving the ester’s lability toward nucleophiles under controlled conditions.

How does the 3,4-dimethyl substitution pattern steer electrophilic attack?

The two methyl substituents act as weak σ-donors that elevate the HOMO energy primarily at the 5-position, while the 2-ester withdraws electron density via resonance, creating an electronically asymmetric ring. Nitration with acetyl nitrate in acetic anhydride at –10 °C affords the 5-nitro derivative in 72% isolated yield after recrystallisation from ethanol/water; the 4-nitro isomer is not detected by ¹H NMR at 500 MHz. Vilsmeier–Haack formylation (POCl₃/DMF, 0 °C to 25 °C ramp over 3 h) delivers the 5-formyl compound with a regioselectivity exceeding 98:2, as judged by GC area percent. This predictable orientation is exploited in medicinal chemistry programs where the pyrrole ring serves as a bioisostere for imidazole or thiazole cores; an early-stage kinase inhibitor program used the 5-formyl intermediate to install a vinylogous amide side chain in a single Knorr-type condensation step. Published data for this specific configuration in large-scale batch mode is limited, but laboratory experience indicates that when the nitration exotherm exceeds –5 °C, the proportion of dinitro impurity rises from 0.3% to 1.5%, requiring a second recrystallisation that depresses yield by 8–10%.

Navigating the decomposition threshold during vacuum distillation

Short-path distillation remains the preferred purification method for removing heavy-colour bodies and inorganic salts from crude ester isolated after Paal–Knorr cyclisation. A Büchi B-585 Kugelrohr oven operated at a jacket temperature of 120–125 °C with an internal pressure of 1.5–2.0 kPa consistently delivers a centre cut with GC purity ≥99.0%. The processing window is narrow: at jacket temperatures above 140 °C, a sharp rise in the UV absorbance at 350 nm indicates the onset of thermal dimerisation, which produces a non-volatile red-brown residue. Thermogravimetric analysis coupled with mass spectrometry (TGA-MS) shows an initial mass loss of 0.5% at 110 °C attributed to residual ethanol, followed by a clean evaporation event with 97% mass loss between 135 °C and 175 °C; above 180 °C, the derivative thermogravimetry curve develops a shoulder corresponding to 2–3% of char-promoting decomposition products. Pilot-plant wiped-film evaporators (L/D ratio 25:1, carbon steel wiper blades) at a feed rate of 2.5 kg·h⁻¹ maintain a film temperature of 128 ± 3 °C and achieve 0.7 kW·kg⁻¹ energy consumption with less than 0.2% heavy residue. Exceeding a film temperature of 135 °C triggers a fouling rate that halved the interval between mechanical cleanings from 14 days to 6 days. Polymerisation-grade monomer can be prepared directly from the distilled ester without column chromatography. Electrochemical polymerisation on indium tin oxide (ITO) glass electrodes has been used to generate thin films of poly(3,4-dimethylpyrrole-2-carboxylate) with distinct optoelectronic signatures. Cyclic voltammetry in acetonitrile with 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF₆) and 0.05 M monomer reveals an irreversible oxidation peak at +1.02 V vs. Ag/AgCl, which is shifted anodically by +160 mV relative to unsubstituted ethyl pyrrole-2-carboxylate (+0.86 V). The resulting polymer films, after 10 potentiodynamic cycles between –0.2 V and +1.3 V at 50 mV·s⁻¹, exhibit a broad visible absorption maximum at 480–510 nm and an onset of electrical conductivity of 4 × 10⁻³ S·cm⁻¹ when doped with perchlorate. These values, measured via four-point probe under dry nitrogen, drop to 2 × 10⁻⁵ S·cm⁻¹ upon de-doping with ammonia vapour. The table below summarises key electrochemical and conductivity data relative to structurally related pyrrole esters.

Comparative electrochemical and conductivity data for electropolymerised pyrrole-2-carboxylates (acetonitrile, **0.1 M** TBAPF₆, ITO working electrode).
Monomer	E_ox,onset (V vs. Ag/AgCl)	λ_max (nm)	σ_doped (S·cm⁻¹)	Solubility in CHCl₃ (mg·mL⁻¹)
Ethyl 1H-pyrrole-2-carboxylate	+0.86	425–445	1 × 10⁻²	0.8
Ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate	+1.02	480–510	4 × 10⁻³	3.2
Ethyl 5-methyl-1H-pyrrole-2-carboxylate	+0.91	450–470	7 × 10⁻³	1.5

The increased solubility of the 3,4-dimethyl polymer in chloroform arises from the disruption of interchain packing by the pair of methyl groups, a property exploited when spin-coating large-area devices without resort to sulfonate-based dopants. However, the oxidation potential crossing +1.0 V forces the use of electrolytes with wide anodic windows; tetrafluoroborate or hexafluorophosphate are mandatory, while chloride-containing media cause irreversible electrode fouling at cycle 3.

Kinetic resolution and amidation side reactions

The ethyl ester is relatively resistant to acid-catalysed hydrolysis (t₁/₂ for 0.1 M HCl in aqueous ethanol at 25 °C exceeds 48 h), but base-promoted saponification proceeds with a pseudo-first-order rate constant of 0.12 min⁻¹ in 0.5 M NaOH/1:1 ethanol–water at 40 °C. Direct amidation with primary amines in refluxing toluene without catalyst requires 18–24 h for >90% conversion; adding 0.3 eq of titanium(IV) isopropoxide reduces the reflux time to 4 h, as monitored by disappearance of the carbonyl stretch at 1704 cm⁻¹ on a Thermo Scientific Nicolet iS50 FT-IR fitted with a diamond ATR accessory. Critically, trace water levels above 200 ppm in the reaction mixture raise the competing hydrolysis pathway from <2% to 12%, producing the free carboxylic acid that precipitates as its amine salt and inhibits further conversion. Karl Fischer control on all solvents and on the incoming ester (specification <150 ppm H₂O) is therefore enforced before charging the vessel.

If anhydrous conditions are not maintained, ester hydrolysis accelerates during amide bond formation

The interplay between aminolysis and hydrolysis becomes a yield-limiting factor at preparative scales above 100 g. In a series of runs conducted in a 2 L jacketed glass reactor with overhead stirring, the use of amine pre-dried over molecular sieves 4Å (water content of amine <50 ppm) gave a reproducible amide yield of 88–91% after aqueous work-up and crystallisation. When the same amine lot was used without drying, the water concentration in the condensate rose to 400 ppm and the amide yield fell to 64% with 22% of the isolated mass being the carboxylic acid. The acid by-product not only reduces yield but also complicates purification because it co-elutes with the amide on silica gel in ethyl acetate–hexane mixtures, forcing a switch to gradient flash chromatography with 0.5% acetic acid modifier. This increases solvent consumption by a factor of 2.5 and extends the purification time to 6 h from a typical 1.5 h. For applications requiring the carboxylic acid directly, hydrolysis is carried out with 2.0 eq of LiOH in 3:1 THF–water at 50 °C over 8 h, yielding the free acid as a white powder after acidification and filtration. The acid is noticeably less soluble than the ester in common organic solvents and presents handling challenges during anhydride or active ester formation, but it remains the preferred form for solid-phase peptide coupling strategies. The compound’s versatility in constructing heterocycle-fused systems is often tested under high-pressure hydrogenation conditions. Catalytic hydrogenation over 10% Pd/C (0.05 eq) at 0.4 MPa H₂ in ethanol at 40 °C leads to saturation of the pyrrole ring without ester cleavage, affording the corresponding proline analogue as a 3:1 mixture of cis/trans diastereomers after 12 h. Diastereomeric ratios are influenced by the solvent polarity: switching to ethyl acetate shifts the ratio to 5:1 cis. The crude product shows an m/z of 172.1 [M+H]⁺ (ESI+) and is typically advanced without separation. This saturated scaffold has been used as a conformationally constrained building block in peptidomimetic protease inhibitor design, where the ester serves as a latent carboxylate that is unmasked only after the peptide backbone is fully assembled on resin.

Physical and handling properties of closely related pyrrole-2-carboxylate esters (ATR-FTIR, DSC, dynamic vapour sorption).
Ester	Melting point (°C)	DSC enthalpy (J·g⁻¹)	Water uptake at 60% RH (wt%)	LogP (calc.)
Methyl 1H-pyrrole-2-carboxylate	73–75	132	0.8	1.12
Ethyl 1H-pyrrole-2-carboxylate	39–41	98	1.2	1.60
Ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate	46–48	105	0.4	2.34
Ethyl 5-phenyl-1H-pyrrole-2-carboxylate	102–104	146	0.9	3.12

The lower water uptake of the 3,4-dimethyl derivative at elevated relative humidity stems from the shielding of the ester carbonyl by the ortho methyl groups, which reduces hydrogen bonding with water vapour. Dynamic vapour sorption (DVS) isotherms recorded on a Surface Measurement Systems DVS Adventure show a mass increase of only 0.4% at 60% RH and 25 °C, compared to 1.2% for the unsubstituted ethyl ester under identical conditions. This characteristic permits open-container handling in a class-100,000 cleanroom for up to 45 minutes without exceeding the 0.2% moisture threshold required for water-sensitive reactions. Storage recommendations are derived from accelerated stability protocols based on ICH Q1A(R2) guidance. Sealed under argon in amber glass vials, the compound retains >99% purity after 12 months at –20 °C. At 25 °C/60% RH, a purity decline of approximately 0.5% per month is observed, attributable largely to slow ester hydrolysis catalysed by trace acid liberated from the packaging septum. No LC-MS signals consistent with N-oxide formation are detected after storage under ambient atmosphere for 6 months, confirming that the 3,4-dimethyl substitution effectively suppresses autoxidation, a known degradation pathway in pyrroles bearing only a single alkyl group. Bulk shipments are made in UN-rated fibre drums with double polyethylene liners, and the product is classified as non-hazardous under UN Model Regulations for road and sea freight, though local regulatory consultation is advised before air transport. A final preparative application highlights the compound’s utility in dipolar cycloaddition chemistry. A mixture of the ester with 1.2 eq of an acyclic nitrone generated in situ from benzaldehyde and N-methylhydroxylamine in toluene at reflux delivers a fused isoxazolidine after 16 h. The endo/exo selectivity, determined by NOESY correlations, is 8:1 in favour of the endo adduct, whose piperidine ring provides a scaffold for subsequent reductive cleavage to a 1,3-amino alcohol. The cycloadduct is readily purified by flash chromatography (hexane–ethyl acetate 4:1) and recrystallised from 2-propanol to give colourless prisms with a melting point of 121–123 °C. Under these strictly anhydrous conditions (reaction mixture dried by azeotropic distillation before nitrone generation), isolated yield reaches 79%; when ambient moisture is not excluded, the yield collapses to 41% due to nitrone hydrolysis competing with cycloaddition.