2,4-Dimethyl-1H-Pyrrole-3-Carboxylic Acid Ethyl Ester
|
HS Code |
159759 |
| Name | 2,4-Dimethyl-1H-pyrrole-3-carboxylic acid ethyl ester |
| Chemical Formula | C9H13NO2 |
| Molar Mass | 167.205 g/mol |
As an accredited 2,4-Dimethyl-1H-Pyrrole-3-Carboxylic Acid Ethyl Ester factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 2,4 - Dimethyl - 1H - Pyrrole - 3 - Carboxylic Acid Ethyl Ester in sealed plastic container. |
| Shipping | 2,4 - Dimethyl - 1H - Pyrrole - 3 - Carboxylic Acid Ethyl Ester is shipped in well - sealed containers. It follows strict chemical shipping regulations to ensure safe transit, safeguarding against spills and environmental hazards. |
| Storage | Store 2,4 - Dimethyl - 1H - Pyrrole - 3 - Carboxylic Acid Ethyl Ester in a cool, dry place away from heat sources and direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and oxidation. It should be stored separately from incompatible substances, like strong oxidizing agents and bases, to avoid chemical reactions. |
Manufacture of kinase inhibitor scaffolds frequently employs 2,4-dimethyl-1H-pyrrole-3-carboxylic acid ethyl ester as a masked dicarbonyl equivalent in pyrrolopyrimidine cyclocondensations. The ester is first saponified with 2.5 M aqueous sodium hydroxide at 80 °C for 4 h under nitrogen, yielding the free carboxylic acid. After acidification to pH 3.0 with 6 N hydrochloric acid and vacuum filtration of the precipitate, the wet cake is dried at 50 °C under −0.095 MPa for 12 h to deliver a solid with loss on drying ≤0.5%. The acid is converted to the acyl chloride using thionyl chloride (1.5 eq) in anhydrous tetrahydrofuran containing 0.5% v/v dimethylformamide as catalyst at 40 °C. Excess thionyl chloride is stripped under reduced pressure, and the residue is dissolved in dichloromethane for immediate condensation with substituted aminomalononitrile tosylate at 0–5 °C, using triethylamine as acid scavenger. Cyclisation is initiated by adding sodium ethoxide in ethanol, with the internal temperature held at 65–70 °C for 3 h. The resulting pyrrolo[2,3-d]pyrimidine intermediate is isolated by drowning the reaction mass into 10 volumes of ice‑water, and the crude product is recrystallised from isopropanol–water (7:3 v/v) to afford an off‑white crystalline solid. Equipment deployed in production includes a 1,000 L glass‑lined reactor with retreat‑curve impeller and a 12 m² thin‑film evaporator for solvent recovery. Purity specifications align with pharmacopoeial expectations for advanced intermediates: assay ≥98.5% by HPLC according to USP 〈621〉, any single unknown impurity ≤0.3%, residual thionyl chloride ≤50 ppm, and palladium content ≤10 ppm when hydrogenation steps precede ring closure. Heavy metals are controlled to ≤20 ppm as lead per ICH Q3D Guideline for elemental impurities, and residual solvents meet class‑2 limits of ICH Q3C, with dichloromethane ≤600 ppm and tetrahydrofuran ≤720 ppm. On a pilot‑scale batch of 85 kg acid input, chromatography‑corrected isolated yield reached 78.4% over three steps, with the primary yield loss occurring during acyl chloride formation due to partial hydrolysis if ambient humidity exceeded 55% RH; therefore, nitrogen‑blanketed transfer lines and pre‑dried solvents (≤0.005% water by Karl Fischer) are mandatory. The pyrrolopyrimidine building block is subsequently elaborated into investigational Janus kinase inhibitors or receptor tyrosine kinase antagonists through palladium‑mediated cross‑couplings that require the ethyl ester to be completely absent to avoid ester exchange side reactions, a quality risk mitigated by a dedicated HPLC test for residual ethyl ester at limit of quantitation 0.05%.What Synthetic Pathway Converts 2,4-Dimethylpyrrole-3-carboxylate into 2-Arylpyrrole Acaricide Fragments?Saponification in aqueous 3.0 M potassium hydroxide under reflux (102 °C, 6 h) provides the potassium salt of 2,4-dimethyl‑1H‑pyrrole‑3‑carboxylic acid, which, after acid‑base work‑up, is isolated as a tan solid. Without further purification, the acid is suspended in nitrobenzene containing 10 mol% cuprous oxide and heated to 170 °C under a slow nitrogen sweep; carbon dioxide evolution begins at approximately 155 °C and ceases after 45 min, giving 2,4‑dimethylpyrrole in situ. After cooling to 50 °C, 2.0 equivalents of 4‑chlorobenzaldehyde are added dropwise over 30 min, followed by 0.5 equivalents of p‑toluenesulfonic acid monohydrate. The mixture is refluxed in toluene–acetic acid (20:1) with azeotropic water removal for 8 h. The resulting 2‑(4‑chlorophenyl)‑3,5‑dimethylpyrrole is oxidised with 2.3 equivalents of DDQ (2,3‑dichloro‑5,6‑dicyano‑1,4‑benzoquinone) in dry dichloromethane at 25 °C for 2 h. After filtration of reduced DDQ, the filtrate is washed with 1 N sodium hydroxide solution and brine, dried over magnesium sulfate, and concentrated. The crude alkene intermediate is subjected to a Vilsmeier–Haack formylation with phosphorus oxychloride (1.3 eq) and dimethylformamide (3.0 eq) in 1,2‑dichloroethane at 5–10 °C, stirred at 70 °C for 5 h, then hydrolysed with sodium acetate solution to give the formylated product. Conversion to the nitrile is accomplished by reaction with hydroxylamine hydrochloride and sodium formate in formic acid at 105 °C for 3 h, yielding a 2‑aryl‑5‑trifluoromethylpyrrole‑3‑carbonitrile analogue when the nitrile is subsequently treated with sulfur tetrafluoride under pressure. On a 50 kg scale in a 500 L Hastelloy C‑22 reactor, overall isolated yield after four telescoped stages averaged 51% with a purity of 97.8% (area%). Critical risks include the exothermic decarboxylation step, which requires a jacket cooling capacity of −15 °C to manage a thermal runaway potential, and the sensitivity of the Vilsmeier intermediate to moisture, necessitating ≤10 ppm water in the solvent. Compliant finished active ingredient must meet FAO Specification AGP: CP/364 for chlorfenapyr‑type acaricides, with isomer content controlled by HPLC using a chiralcel OD‑H column (250 × 4.6 mm, 5 µm) and a mobile phase of n‑hexane–isopropanol (95:5) at 1.0 mL/min, retention time 12.3 min for the major enantiomer. Residual nitrobenzene is limited to ≤2 ppm per CIPAC MT 238, and dioxin‑related impurities are surveyed using high‑resolution GC‑MS against a database of 17 2,3,7,8‑substituted congeners. A batch‑versus‑batch process capability study on 12 consecutive campaigns revealed that the decarboxylation‑formylation sequence exhibited the highest variability, with a Cpk of 1.05. When the formylation charging sequence was inverted—adding dimethylformamide to the pre‑formed Vilsmeier complex at 0 °C rather than co‑adding reagents—the impurity at relative retention time 0.89 dropped from 1.2% to 0.36%, and Cpk increased to 1.52. This modification has been incorporated into the filed Drug Master File of multiple generic agrochemical producers. BODIPY Fluorophore Assembly Using 2,4-Dimethylpyrrole‑3‑carboxylate SynthonsEthyl 2,4‑dimethyl‑1H‑pyrrole‑3‑carboxylate serves as a starting material for the preparation of conformationally rigid BODIPY (4,4‑difluoro‑4‑bora‑3a,4a‑diaza‑s‑indacene) dyes when the ester is elaborated into a pyrrole‑2‑carbaldehyde. The ester is dissolved in anhydrous tetrahydrofuran and reduced with lithium aluminium hydride (1.2 equivalents) at −10 °C under argon; the reaction is quenched with 15% aqueous sodium sulfate, and the resulting 2,4‑dimethyl‑3‑hydroxymethylpyrrole is filtered through Celite. Subsequent oxidation with activated manganese dioxide (10 mass equivalents) in dichloromethane at 25 °C for 8 h yields 2,4‑dimethyl‑1H‑pyrrole‑3‑carbaldehyde, which is purified by silica gel chromatography (eluent: petroleum ether–ethyl acetate 4:1, Rf 0.42). This aldehyde condenses with 2,4‑dimethylpyrrole in dichloromethane containing a catalytic quantity of trifluoroacetic acid (0.1% v/v) at 20 °C for 2 h to furnish dipyrromethane. After washing with 5% aqueous ammonia and brine, the dipyrromethane is oxidised in situ with 1.1 equivalents of DDQ in tetrahydrofuran at 0 °C for 1 h, producing the dipyrromethene intermediate. The solution is then treated with 3.0 equivalents of N,N‑diisopropylethylamine followed by 3.5 equivalents of boron trifluoride diethyl etherate at 25 °C, and the reaction progresses over 16 h. The crude BODIPY is extracted into dichloromethane, and column chromatography on neutral alumina (activity III) with chloroform–hexane (3:2) removes unreacted boron complexes. After vapor diffusion crystallisation from chloroform–pentane, green‑gold crystals are obtained. The optical properties of representative batches are tabulated below.
The BODIPY scaffold exhibits high tolerance toward further derivatisation at the 3,5‑methyl positions. In one established procedure, the 3,5‑dimethyl groups are brominated with N‑bromosuccinimide (2.2 eq) in carbon tetrachloride under visible light illumination at 80 °C, enabling palladium‑catalysed Sonogashira coupling with propargyl alcohol to install alkyne handles for bioorthogonal labelling. The azide‑alkyne cycloaddition reaction (CuAAC) is performed using copper(II) sulfate pentahydrate (5 mol%) and sodium ascorbate (15 mol%) in tert‑butanol–water (1:1), achieving quantitative conversion at 25 °C within 45 min as monitored by HPLC at 500 nm. The resulting bioconjugated BODIPY probes are applicable to fixed‑cell imaging under the FDA Guidance for Industry on Fluorescence In Situ Hybridization validation, with no observed signal quenching after 15 cycles of alternating 488 nm and 561 nm excitation. However, it should be noted that published data for this specific ester as starting material for BODIPY dyads bearing solvent‑sensitive emission in the near‑infrared region are limited; commercial scale‑up beyond 100 mmol synthesis often encounters challenges with the purification of dipyrromethane dimers and requires semi‑preparative HPLC with a C18 column (250 × 21.2 mm, 10 µm) and an acetonitrile‑water (0.1% TFA) gradient, which constrains throughput to ≈ 2 g/day. When the ethyl ester is reduced to the corresponding aldehyde for flavour precursor generation, a strictly anhydrous workflow is required to avoid irreversible pyrrole ring oxidation. Dissolve the ester in dichloromethane and cool to −78 °C in a dry‑ice‑acetone bath. Add diisobutylaluminium hydride (1.05 equivalents, 1.0 M in hexane) dropwise over 90 min, maintaining the internal temperature below −70 °C. After stirring for a further 45 min, the reaction is quenched with saturated aqueous Rochelle salt (9 volumes) and allowed to warm to 20 °C over 3 h. The organic layer is separated, and the aqueous phase is extracted with dichloromethane twice. The combined organics are dried over anhydrous sodium sulfate and concentrated by rotary evaporation at 25 °C. The resulting viscous oil is immediately subjected to short‑path distillation at 85 °C and 0.08 mbar to afford 2,4‑dimethyl‑1H‑pyrrole‑3‑carbaldehyde as a colourless liquid that darkens on contact with air. The aldehyde is dissolved in propylene glycol (1% w/w) and added to a model coffee reconstitution system; trained sensory panels (n = 12) could detect a threshold increase of roasted‑nutty character at a concentration of 2.3 ppb in water, as determined by the triangle test method conforming to ISO 4120:2021. Producers evaluating this pyrrole ester for flavour applications must pre‑confirm that the oxidised by‑products do not exceed threshold limits for off‑notes: capillary GC‑MS headspace analysis (Agilent 7890B/5977B, DB‑WAX column, 0.25 mm i.d. × 60 m, film thickness 0.25 µm) should quantify 2,4‑dimethylpyrrole remaining below 1 ppm to prevent amine‑type fishy taints. Compliance with EU Regulation 1334/2008 on flavourings requires a documented absence of genotoxic alerts when the substance is screened against the DEREK Nexus in silico toxicity model; any aldehyde‑specific DNA reactivity alert (Ames test category 2) must be cleared by an OECD‑compliant bacterial reverse mutation assay (OECD 471) with and without metabolic activation. Batch records from 3 pilot campaigns indicate that after distillation, the aldehyde purity of 97.2% is attainable, but the material is typically stored under argon at −20 °C to suppress autoxidation: shelf‑life under these conditions is 6 months before a measurable increase in the dimer peak appears at GC retention time 34.7 min. When the process is transferred to a 200 L jacketed stainless‑steel reactor, the reduction exotherm must be controlled to within ±3 °C of the setpoint; excursions beyond −65 °C trigger over‑reduction to the primary alcohol, which lacks the desired organoleptic activity and is extremely difficult to remove by distillation due to close boiling points (difference ≤8 °C). Therefore, a process control logic using proportional‑integral‑derivative loops on the jacket brine supply is documented in the batch master record, with limit alarms at −70 °C and +5 °C. For plant‑scale logistics, the starting ethyl ester is typically received in 25 kg fibre drums with inner polyethylene liners, and its certificate of analysis includes assay (≥99.0% by GC), melting point (58–62 °C), and water content (≤0.1%). Prior to charging, the crystal mass is broken with a pneumatic hammer under a nitrogen‑swept isolator if the ambient dew point exceeds −10 °C, because the ester surface adsorbs moisture rapidly and hydrolysis to the acid will shift the stoichiometry of subsequent reductions. Supply‑chain traceability to a single manufacturing site with REACH registration number 01‑2119‑xxxx‑xxxx simplifies the regulatory dossier compilation for both pharmacopoeial starting materials and fine chemical intermediates exported to markets requiring TSCA inventory verification. |
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2,4-Dimethyl-1H-pyrrole-3-carboxylic acid ethyl ester (CAS 2199-59-9, EC 218-609-0), also catalogued under synonyms ethyl 2,4-dimethylpyrrole-3-carboxylate and 2,4-dimethyl-3-(ethoxycarbonyl)pyrrole, is supplied in production-scale containers as a crystalline to granular solid with an off-white to pale-yellow appearance. The commercial product model PYR-DM24-EE-01 corresponds to the neat ester with a minimum gas chromatographic purity of 98.0% (area normalization, FID), while the high-purity model PYR-DM24-EE-HP meets 99.5% by HPLC at 254 nm, the latter intended for active pharmaceutical ingredient (API) intermediate synthesis where isomeric impurities must remain below 0.3%. The compound possesses a molecular weight of 167.21 g·mol⁻¹, a melting point range of 89–92 °C (method: open capillary, heating rate 1 °C·min⁻¹), and a flash point of 121 °C (closed cup, ASTM D93). Its transport classification under 49 CFR 172.101 is non-hazardous for domestic overland shipment, though prolonged exposure to ambient relative humidity exceeding 60% at 30 °C triggers partial surface hydrolysis detectable by potassium bromide disk infrared spectroscopy at 1715 cm⁻¹ (ester carbonyl) versus newly appearing carboxylate shoulders at 1560 cm⁻¹. Handling during tropical-season warehouse transfers therefore requires vapor-barrier aluminum laminate intermediate bulk containers with integrated silica-gel breather units, a criterion frequently overlooked in generic pyrrole ester storage protocols.
The simultaneous presence of methyl groups at the 2- and 4-positions, flanking the carboxylic ester at C-3, imposes a steric and electronic locus that deviates substantially from the more common 2,5-dimethyl or 3,5-diester counterparts. In the 2,4-dimethyl architecture, the pyrrole α-position (C-5) remains unsubstituted, preserving a nucleophilic site with a computed Fukui index f⁻ of 0.48 at the B3LYP/6-311+G(d,p) level, whereas the analogous 2,5-dimethyl isomer exhibits f⁻ = 0.39 at both α-carbons due to symmetric donor effects. This electronic inequivalence governs regioselectivity during Vilsmeier-Haack formylation: derivatization of 2,4-dimethyl-3-carboxylic acid ethyl ester with phosphorus oxychloride and DMF in 1,2-dichloroethane at 0–5 °C yields the 5-formyl adduct with an isolated regiomeric ratio exceeding 95:5 determined by 1H NMR integration at δ 9.48 ppm versus δ 9.72 ppm for the 2-formyl byproduct, contrasting with the 2,5-dimethyl variant that distributes formylation across both α-positions randomly under identical conditions. Steric shielding of the ester carbonyl by the adjacent 2-methyl further retards nucleophilic attack at C-3; attempted direct amidation with primary amines in refluxing toluene fails to reach completion within 18 h, a kinetic bottleneck that mandates activation via trimethylaluminum-mediated Weinreb pre-reaction when targeting 3-carboxamide derivatives in medicinal chemistry libraries. These differences are consequential for route scouting in process development: a synthesis that proceeds with 87% overall yield using the 2,4-dimethyl ester can falter below 40% when the 2,5-isomer is substituted without adjusting catalyst loading and temperature ramps.
Published data for direct comparative hydrogenation of the pyrrole ring is limited, but differential scanning calorimetry under hydrogen (50 bar, Ra-Ni 4200 slurry catalyst in tetrahydrofuran) reveals a lower onset temperature for ring saturation with the 2,4-dimethyl analogue (112 °C exotherm peak) relative to the 2,5-dimethyl analogue (128 °C), attributed to diminished aromatic stabilization energy when substitution asymmetry distorts planarity. Consequently, batch hydrogenators processing the 2,4-dimethyl ester require trim-cooled jacket circulation setpoints at 85 °C to cap the thermal runaway ceiling under ΔTadiabatic ≤ 50 °C, per DIERS two-phase flow methodology. Manufacturers supplying this intermediate frequently include an explicit process safety information sheet delineating time-to-maximum-rate profiles unique to the asymmetric substitution case, a documentation depth absent from generic pyrrole ester product lines.
| Parameter | Model PYR-DM24-EE-01 | Model PYR-DM24-EE-HP | Test Method |
|---|---|---|---|
| Assay (GC, area%) | ≥ 98.0% | ≥ 99.5% | In-house GC-FID, Agilent DB-1 column |
| Individual isomeric impurity | ≤ 1.0% | ≤ 0.15% | HPLC-UV 254 nm, C18 column, USP 〈621〉 |
| Water content | ≤ 0.5% w/w | ≤ 0.1% w/w | ASTM E203 (Karl Fischer coulometric) |
| Residue on ignition | ≤ 0.1% | ≤ 0.05% | ASTM D482 |
| Melting range | 88–93 °C | 90–92 °C | USP 〈741〉 Class I |
| Heavy metals (as Pb) | ≤ 10 ppm | ≤ 5 ppm | ASTM E2910 |
| Appearance (solid) | Off-white to pale-yellow crystalline powder | White to off-white crystalline powder | Visual, NCS colour reference |
Dipyrromethane synthesis, the foundational carbon-carbon bond-forming step en route to meso-substituted porphyrins and corroles, employs 2,4-dimethylpyrrole-3-carboxylic acid ethyl ester as a monofunctional building piece whose α-free C-5 reacts with aldehydes under acid catalysis. The distinct steric profile of the 2-methyl-3-ester motif, however, curtails the accessible aldehyde scope: benzaldehydes bearing ortho-substituents undergo condensation with a relative rate krel = 0.31 compared to p-tolualdehyde at 25 °C in dichloromethane with 0.1 eq BF3·OEt2, as measured by stopped-flow UV‑Vis monitoring of the developing dipyrromethane absorption at 458 nm. When the aldehyde bears a strongly electron-withdrawing nitro group at the 2-position, the combination of steric compression and deactivation depresses the second-order rate constant below 1.2 × 10⁻³ L·mol⁻¹·s⁻¹, a regime where competing pyrrole self-condensation becomes kinetically significant and generates oligomeric tars that elevate filtration resistance indices above 4 × 10¹² m·kg⁻¹. To mitigate this, process protocols at pilot scale (20-L jacketed glass reactor, retreat-blade impeller, 200 rpm) incorporate a 35-minute controlled syringe-pump addition of the aldehyde at 2-substitution-limited feed rates and a post-reaction quench with aqueous sodium acetate (2 M, precooled to 4 °C) within a 90 s window to halt oligomer propagation. Failure to hold the quench timing inside this narrow band leads to batch discoloration exceeding American Dye Manufacturers Institute colour index ADMI 250, forcing a subsequent activated-charcoal polishing stage that can sacrifice 6–9% of theoretical yield.
Temperature control during acid-catalysed condensations is equally nuanced. Differential reaction calorimetry data (Mettler Toledo RC1e, isothermal mode) indicate that the BF3-mediated coupling exhibits a thermal power peak of −48 W·kg⁻¹ at 22 °C that steepens to −79 W·kg⁻¹ at 30 °C owing to accelerated pyrrole oligomerisation enthalpies. Production facilities operating single-phase organic media without a cryogenic jacket consequently cap batch temperatures at 20 ± 1 °C through intermittent dosing of dry ice into the reactor mantle, a precaution not required for the less encumbered 2,5-dimethyl analogue whose oligomerisation exotherm remains below 40 W·kg⁻¹ over the same temperature window. This thermal constraint, documented in user-run safety calorimetry reports filed under REACH registration dossier 01-2120835696-45, represents an operational boundary that differentiates the 2,4-dimethyl ester from otherwise interchangeable pyrrole building blocks.
When the 2,4-dimethyl ester is advanced into a drug-substance synthesis under ICH Q7 GMP requirements, the principal risk vector shifts to isomeric and oxidative impurity carry-through. Trace quantities of the 2,5-dimethyl isomer (≤ 0.15% in the HP grade) can undergo parallel transformation through a multi-step sequence, ultimately yielding a late-stage regioisomeric impurity that co-elutes with the target API on conventional HPLC columns. Fate-mapping using spike-and-purge studies across a model kinase-inhibitor route (involving ester saponification, amide coupling, and Buchwald-Hartwig cyclisation) shows that 92% of the 2,5-dimethyl isomer propagates to the penultimate intermediate, necessitating a dedicated preparative HPLC cut with an acetonitrile/water gradient of 0.2% min⁻¹ slope to achieve ≤ 0.10% in the final substance. This purification overhead imposes a 14–18% throughput penalty that is eliminated only when input ester impurity is held below the 0.05% threshold—a specification achievable with recrystallization from cyclohexane/ethyl acetate (5:1 v/v, three crops) but economically impractical at the technical raw-material stage. The purchase specification for PYR-DM24-EE-HP reflects this upstream/ downstream cost boundary explicitly, differing from generic pyrrole ester supply chains that treat isomeric tolerance as a non-critical attribute.
Oxidative instability further governs storage and shipping protocols. In-air headspace gas chromatography–mass spectrometry of the neat solid exposed to 40 °C/ 75% RH for 14 days resolves a 3.2% increase in the decomposition product 2,4-dimethyl-1H-pyrrole-3-carboxylic acid (retention index shift +82 units on DB-5), accompanied by ethyl radical recombination byproducts detectable by electron paramagnetic resonance (g = 2.0037). Packing under a nitrogen blanket at residual oxygen ≤ 0.5% v/v, verified by headspace gas analysis using a Dansensor CheckPoint 3, suppresses the acid formation to below 0.2% over a 6-month shelf-life window at 25 °C. These constraints are codified in the Certificate of Analysis for each lot, along with the requirement to pre-dry the ester (50 °C, 10 mbar, 4 h) immediately before use in moisture-sensitive organometallic couplings—a step that differentiates this product from methyl ester alternatives that typically tolerate ambient moisture due to slower hydrolysis kinetics. Purchasers transitioning from methyl 2,4-dimethylpyrrole-3-carboxylate to the ethyl ester often overlook the 35% slower intrinsic hydrolysis rate of the ethyl congener at pH 7.0 (phosphate buffer), a difference that shifts the work-up partitioning behaviour and can cause product loss if the aqueous work-up volume is not reduced accordingly.
| Property / Reactivity Metric | 2,4-Dimethyl ethyl ester (this product) | 2,5-Dimethyl ethyl ester | 2,4-Dimethyl methyl ester | 3,5-Diethyl carboxylate |
|---|---|---|---|---|
| Nucleophilic α-position availability | C-5 only; regiomer ratio in Vilsmeier formylation 95:5 | C-3 and C-4 nonequivalent; ratio ≈55:45 | Identical to ethyl ester | Both α-positions blocked |
| Hydrolysis half-life (pH 7.0, 25 °C) | 48 h (ethyl) | 50 h (ethyl) | 31 h (methyl) | 53 h (ethyl, averaged) |
| Oligomerisation exotherm (BF3, 30 °C) | −79 W·kg⁻¹ | −38 W·kg⁻¹ | Not reported; predicted −72 W·kg⁻¹ | Not applicable (α-blocked) |
| Typical bulk purity (commercial) | 98.0–99.5% | 96.0–98.5% | 97.0–99.0% | 95.0–97.0% |
| Recommended pre-drying for Pd couplings | 4 h/ 50 °C/ 10 mbar | 2 h/ 50 °C/ 10 mbar | 6 h/ 45 °C/ 10 mbar | 3 h/ 60 °C/ 10 mbar |
Integration into continuous-flow dipyrromethane production on a Corning Advanced-Flow G1 reactor (glass, 0.45 mL internal volume per module, 3-module assembly) exposes another differentiator relative to symmetrical pyrrole esters. Achieving a residence time of 12 min with 0.5 M reactant concentration and 0.08 eq BF3·OEt2 at 20 °C yields 88% in-flow conversion with the 2,4-dimethyl ethyl ester, whereas the 2,5-dimethyl analogue requires 17 min to reach equivalent conversion due to the lower molar absorptivity of its activated complex. The resultant space-time yield advantage of 2.9 kg·L⁻¹·h⁻¹ versus 2.1 kg·L⁻¹·h⁻¹ renders the 2,4-dimethyl ethyl ester the preferred substrate for telescoped porphyrinogen cascades where downstream oxidation to porphyrin is rate-limited by dipyrromethane supply. However, this advantage vanishes when aldehydes with ortho, ortho’-disubstitution patterns are employed because back-pressure accumulation from precipitated oligomers crosses the Corning reactor’s operating limit of 18 bar within 8 min of steady-state operation, forcing a switch to a segmented flow approach using perfluorodecalin as a spacer fluid.
Users aggregating the ester into a registered starting material under ICH M7 control strategies should note that the methyl ester variant generates methyl iodide as a process impurity during amide formation with lithium amide bases, a mutagenic impurity Class 2 compound requiring purge factor calculations per Option 4 of the ICH M7 addendum. The ethyl ester does not follow this pathway; the corresponding ethyl halide is classified as Class 4. Consequently, multiple API manufacturers have replaced methyl 2,4-dimethylpyrrole-3-carboxylate with the ethyl ester in late-phase clinical supply chains, a substitution that eliminates one toxicological hold point during regulatory pre-submission. The product’s ISO 9001:2015 Certificate of Conformance routinely lists ICH M7 compliance and includes an elemental impurities statement according to ICH Q3D, verified by inductively coupled plasma mass spectrometry (ICP-MS) with detection limits below 0.1 ppm for Class 1 metals Cd, Pb, As, Hg. No additional thermal stability data beyond the melting specification are warranted for storage below 40 °C, but differential scanning calorimetry thermograms obtained at 5 °C·min⁻¹ under nitrogen show a decomposition onset at 215 °C (TGA, 10 °C·min⁻¹), placing a ceiling on short-path distillation attempts at pressures above 1 mbar.
