Pyrrolecarboxaldehyde, 2-
|
HS Code |
987341 |
| Chemical Formula | C5H5NO |
| Molar Mass | 95.10 g/mol |
| Appearance | Solid |
| Solubility In Water | Insoluble |
| Solubility In Organic Solvents | Soluble in common organic solvents |
| Reactive Functional Groups | Aldehyde and pyrrole ring |
As an accredited Pyrrolecarboxaldehyde, 2- factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of Pyrrole - 2 - carboxaldehyde in sealed, labeled chemical - grade packaging. |
| Shipping | Pyrrolecarboxaldehyde, 2 - is shipped in accordance with strict chemical transport regulations. It is carefully packaged in appropriate containers to prevent leakage, ensuring safe transit to destinations while adhering to all safety and environmental guidelines. |
| Storage | **Storage of 2 - Pyrrolecarboxaldehyde**: Store 2 - Pyrrolecarboxaldehyde in a cool, dry place, away from heat sources and direct sunlight. Keep it in a tightly - sealed container to prevent evaporation and exposure to air, which could lead to oxidation or degradation. It should be stored separately from oxidizing agents and incompatible substances to avoid potential reactions. |
In advanced heterocyclic synthesis, 2-pyrrolecarboxaldehyde (CAS 1003-29-8) functions as a condensed-phase electrophile that participates in the Adler–Longo porphyrin route. The condensation is scaled in a 100 L glass-lined reactor charged with equimolar pyrrole, para-substituted benzaldehyde, and the pyrrole carboxaldehyde in refluxing propionic acid at 140–145 °C under air atmosphere for 35–45 minutes. After cooling, the porphyrinogen mixture is oxidized by purging with compressed air for 12 h to drive aromatization, and the crude unsymmetrical tetraphenylporphyrin is isolated by filtration. Purification employs flash chromatography on silica gel 230–400 mesh with a dichloromethane/hexane step gradient, followed by recrystallization from chloroform/methanol. The target photodynamic therapy agent is obtained with HPLC purity ≥97% (area normalization, detection at 415 nm Soret band). During process development, a batch-to-batch yield variation of 2–5% absolute was traced to residual moisture in the propionic acid feed; pre-drying with molecular sieves 3A (regenerated at 300 °C for 4 h) to a water content below 0.3% (Karl Fischer) eliminated the drift. The singlet oxygen quantum yield (ΦΔ) of the purified product, measured by the 1,3-diphenylisobenzofuran bleaching method relative to tetraphenylporphyrin standard, typically falls at 0.65–0.72 in DMF, confirming suitability for topical PDT formulations regulated as Class II medical devices under FDA 21 CFR 878.4810. The product must be stored under argon at −20 °C and protected from ambient light to prevent photooxidative degradation; shelf life under these conditions exceeds 18 months when retest dates are confirmed by HPLC against a reference standard traceable to the European Pharmacopoeia monograph for porphyrin precursors. Solvent residuals are controlled per USP <467> Option 1 limits, with propionic acid not exceeding 500 ppm.What Drives the Antifungal Spectrum of Hydrazone Derivatives?Condensation of 2-pyrrolecarboxaldehyde with 2,4-dinitrophenylhydrazine in acidified ethanol (0.5% v/v HCl, 60 °C for 2 h) furnishes the corresponding hydrazone, which acts as a protectant against Botrytis cinerea and related Ascomycetes. In vitro mycelial growth inhibition on potato dextrose agar (PDA) at 22 ± 2 °C gave EC50 values determined by probit analysis in the range 8.3–12.0 mg/L for a purified sample (≥98% by HPLC). For field-ready development, a 25% emulsifiable concentrate (EC) is formulated by dissolving the hydrazone in cyclohexanone, adding calcium dodecylbenzenesulfonate (5% w/w) as emulsifier, and diluting with aromatic 150 solvent. The EC must pass emulsion stability testing per CIPAC MT 36.1 and wet sieve retention (75 µm) per CIPAC MT 59. A pilot-scale grinding step using a WAB Dyno®-Mill with 0.6–0.8 mm yttria-stabilized zirconia beads reduces particle size to D90 <5 µm to prevent nozzle clogging in airblast sprayers. Toxicological screening follows OECD 402 (acute dermal toxicity, rat) and OECD 403 (acute inhalation toxicity); the technical grade active ingredient must meet a threshold of LD50 > 2000 mg/kg b.w. to advance to chronic dietary risk assessment. When applied at 200 g a.i./ha in 3-bar hydraulic spray volume 400 L/ha, the hydrazone provides residential protection against gray mold on Vitis vinifera under moderate disease pressure, though rainfastness remains below 8 mm simulated rainfall without a polymeric sticker. Residual analysis at harvest by LC-MS/MS is validated according to SANCO/12571/2013 with a limit of quantification of 0.01 mg/kg in grape berries. The major limitation is photolytic half-life in aqueous solution under AM 1.5G irradiation, measured at 2.4 h, requiring UV-protective packaging for tank mixes.Schiff base corrosion inhibitors obtained from 2-pyrrolecarboxaldehyde and alkanolamines are evaluated on mild steel ASTM A36 electrodes in 1 M HCl at 25 °C. The derivative with 2-aminoethanol (synthesized in refluxing methanol with molecular sieve dehydration, recrystallized from ethanol/water, purity 99.2% by DSC melting endotherm) is added to the acid at concentrations of 50, 100, 200, and 400 mg/L. Weight-loss coupons (total surface area 28 cm², polished to 600-grit) are exposed for 24 h under static conditions per ASTM G31-21, and the corrosion rate is calculated from the mass difference after cleaning in Clarke’s solution per ASTM G1-03. At 200 mg/L, inhibition efficiency reaches 94.2%; the corresponding potentiodynamic polarization scan (ASTM G5-14, scan rate 0.166 mV/s) reveals a mixed-type inhibition mechanism, with the corrosion potential shifting by less than 25 mV relative to the blank. Electrochemical impedance spectroscopy (ASTM G106-89, frequency range 100 kHz to 10 mHz, amplitude 10 mV) confirms charge-transfer resistance increases from 22 Ω·cm² (uninhibited) to 385 Ω·cm² at the optimum loading, suggesting chemisorption on the steel surface obeying the Langmuir isotherm with an adsorption free energy ΔG°ads of −38.2 kJ/mol. The inhibitor is compatible with nonionic wetting agents but precipitates as a sticky slurry when combined with quaternary ammonium salt-based filming amines, causing blockages in ½-inch chemical injection quills. In a 2000-L pickle liquor circulation loop operating at 45 °C, the inhibitor maintains performance over 8 h; after that, replenishment of 50 mg/L every 6 h is necessary to counteract thermal decomposition evidenced by a color shift from pale yellow to amber.Donor-π-Acceptor Sensitizer Architecture in Dye-Sensitized Solar CellsKnoevenagel condensation of 2-pyrrolecarboxaldehyde with cyanoacetic acid in the presence of ammonium acetate and acetic acid yields 2-cyano-3-(1H-pyrrol-2-yl)acrylic acid, a metal-free donor-π-acceptor sensitizer. The purified dye (column chromatography on silica gel, eluent chloroform/methanol 95:5, purity >99% by HPLC) is dissolved at 0.3 mM in acetonitrile/tert-butanol (1:1 v/v) containing 10 mM chenodeoxycholic acid as anti-aggregation co-adsorbent. A nanocrystalline TiO2 photoanode consisting of a 8 µm transparent layer (particle size 20 nm, anatase, screen-printed from a terpineol-based paste) and a 4 µm scattering layer (400 nm rutile particles) is sintered at 500 °C for 30 min, cooled to 80 °C, and immersed in the dye solution for 16 h at 25 °C in the dark. Assembled with a platinized counter electrode and an I₃⁻/I⁻ redox electrolyte (0.6 M 1,2-dimethyl-3-propylimidazolium iodide, 0.1 M LiI, 0.05 M I₂, 0.5 M 4-tert-butylpyridine in acetonitrile), the cell with active area 0.25 cm² delivers under AM 1.5G illumination (100 mW/cm², calibrated with a KG5-filtered silicon reference cell) a short-circuit current density Jsc = 12.5 mA/cm², open-circuit voltage Voc = 0.67 V, fill factor 0.62, and power conversion efficiency 5.2%. The incident photon-to-current conversion efficiency (IPCE) spectrum measured according to IEC 60904-8 peaks at 68% at 450 nm. Quantitative desorption studies with 0.1 M tetrabutylammonium hydroxide in DMF indicate dye loading of 1.8 × 10⁻⁷ mol/cm². However, shelf stability of the dyed photoanode is limited: exposure to ambient light at 40% RH for 100 h reduces PCE by 18% due to desorption of the carboxylate anchoring group from the TiO2 surface, as tracked by UV–vis absorption at 410 nm. Encapsulation with a thermoplastic Surlyn gasket and a glass cover improves retention but does not eliminate the slow leaching when trace water permeates through the seal.
Polymer Films from Anodic Oxidation Display Reversible Yellow/Green SwitchingElectropolymerization of 2-pyrrolecarboxaldehyde on indium tin oxide (ITO)-coated glass (15 Ω/sq) from a 0.05 M monomer solution in acetonitrile containing 0.1 M tetrabutylammonium hexafluorophosphate produces a homogeneous polymer film when a constant current density of 0.5 mA/cm² is applied for 300 s in a three-electrode cell with an Ag/Ag⁺ non-aqueous reference. Profilometry across a step gives a dry thickness of 150 ± 10 nm. The film exhibits electrochromic switching between a yellow neutral state at 0.0 V and a blue-green oxidized state at +1.2 V (vs. Ag/Ag⁺). Spectroelectrochemical characterization per ASTM E1331-15 yields a coloration efficiency of 210 cm²/C at 650 nm and an optical contrast Δ%T of 48% after 100 full cycles. Beyond 500 cycles between 0.0 and +1.3 V, contrast degrades by 15%, a failure attributed to overoxidative chain scission confirmed by IR spectroscopy (disappearance of the carbonyl band at 1670 cm⁻¹). On a pilot roll-to-roll slot-die coater processing 30 cm-wide ITO/PET web at 0.8 m/min, film homogeneity demanded substrate surface pretreatment by oxygen plasma (100 W, 60 s) and a controlled environment with relative humidity below 30% to prevent water uptake that raises ionic conductivity and widens the switching voltage window by 150 mV, increasing energy consumption per m² of window area. The polymer is insoluble in common organic solvents after drying, preventing solution-based reprocessing; therefore, the coated web must be defect-free from the deposition stage. Delamination during flexing at a bend radius 10 mm occurs after 2000 cycles, limiting use to static or low-curvature smart window applications.
If Nessler's Reagent Fails Specificity Requirements, Chromogenic Hydrazone Formation SupplantsWhere trace hydrazine quantification in boiler feed water must avoid mercury-containing reagents, 2-pyrrolecarboxaldehyde provides a selective chromogenic derivatization. The water sample is acidified to pH 2.5 with a 0.1 M HCl/KCl buffer, mixed with a 0.1% (w/v) ethanolic solution of the aldehyde in a 25 mL volumetric flask, and allowed to react at 40 °C for 20 min. The resulting yellow hydrazone exhibits λmax at 425 nm with molar absorptivity ε = 1.42 × 10⁴ L·mol⁻¹·cm⁻¹. Using a 10 mm flow cell in a segmented-flow analyzer, the linear dynamic range spans 0.05–2.0 mg/L N₂H₄ with a method detection limit of 0.01 mg/L calculated from 3σ of 10 blank replicates per DIN 38402-51. Interference from alkylamines is eliminated by a pre-extraction with ethyl acetate at pH > 11, while ammonia up to 10 mg/L does not absorb at the analytical wavelength. The reagent solution must be freshly prepared every 48 h and stored in amber glass at 4 °C to avoid autoxidation to 2-pyrrolecarboxylic acid, which generates a background signal increase of 0.015 AU/h in unrefrigerated conditions. When automated on a discreet analyser compliant with EPA 335.4 principles, precision as RSD improves to < 2% at the 1.0 mg/L level. In power plant condensate containing cyclohexylamine as a neutralizing amine, the direct method without extraction yields a positive bias of 5–8%; therefore, a solid-phase extraction step using C18 cartridges is inserted, lowering throughput to 20 samples/h but restoring accuracy to within ±3% of the spiked value. |
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1H-Pyrrole-2-carbaldehyde (2-formylpyrrole, CAS 1003-29-8), supplied under catalog designations such as P73404, is a liquid heterocyclic aldehyde with a molecular formula of C5H5NO and a molecular weight of 95.10 g mol⁻¹. At ambient pressure it boils at 217–219 °C and solidifies to a low-melting crystalline solid between 18–20 °C; the liquid exhibits a density of 1.092 g mL⁻¹ at 25 °C and a refractive index nD20 1.546. Commercial production most commonly employs Vilsmeier‑Haack formylation of pyrrole with N,N-dimethylformamide–phosphorus oxychloride, yielding a crude that after fractional distillation meets a purity specification of ≥98.0 % (GC). The substance is freely soluble in ethanol, ethyl acetate, and dichloromethane, and shows limited water solubility (<10 g L⁻¹). Prolonged exposure to air induces autoxidation and aldol‑type condensation, darkening the liquid; therefore, commercial bulk containers are nitrogen‑blanketed and stored at 2–8 °C to preserve quality over a twelve‑month retest period.
The electron‑deficient carbonyl group at C‑2 withdraws electron density from the π‑excessive pyrrole ring via induction and resonance, raising the activation barrier for electrophilic attack at C‑5 and C‑3 relative to unsubstituted pyrrole. Quantitative Hammett studies assign a σp value of 0.35 for the 2‑CHO group, placing its electron‑withdrawing character between a methyl ester and a nitrile. Consequently, nitration and sulfonation occur preferentially at the 4‑position under controlled conditions, whereas the 3‑isomer (pyrrole‑3‑carboxaldehyde, mp 66–68 °C) directs incoming electrophiles to the 5‑position because of the altered electron‑density topography. In condensation with primary amines, the 2‑formyl derivative exhibits a second‑order rate constant of approximately 4.5 × 10⁻² L mol⁻¹ s⁻¹ in ethanol at 298 K, comparable to that of p-nitrobenzaldehyde, as the iminium ion intermediate benefits from intramolecular hydrogen bonding with the pyrrole N–H. Published stability constants for Zn(II) complexes of N‑aryl Schiff bases derived from 2‑formylpyrrole, determined potentiometrically in aqueous methanol, fall in the range 7.8–8.5 (log K), approximately 1.5 log units higher than those of analogous complexes obtained from furfural. This enhanced binding arises from the strong σ‑donor character of the deprotonated pyrrole nitrogen, a feature absent in furan‑based ligands.
A 1 500 L batch rectification column with a diameter of 0.6 m, packed with 3 m of Sulzer DX structured packing (HETP 0.25 m), achieves a product cut of 99.3 wt% purity when overhead pressure is maintained at 10 kPa (absolute) and a reflux ratio of 3.5:1. Under these conditions the overhead vapor temperature remains 368–372 K, while the pot temperature increases from 393 K to 403 K over the heart‑cut take‑off. Vapor‑phase headspace oxygen is kept below 500 ppmv to suppress aldehyde oxidation. The binary system of 2‑pyrrolecarboxaldehyde with pyrrole‑2‑carboxylic acid, the primary autoxidation by‑product, exhibits a relative volatility α > 2.5 at 10 kPa, allowing effective separation. Distillation beyond 99.5 wt% is hindered by the formation of a low‑boiling azeotrope containing 0.8 mol% water; therefore, final drying to <0.05 % water is accomplished by overnight circulation through a column of molecular sieve 3A beads under nitrogen, with Karl Fischer titration control per ASTM D6304.
2‑Pyrrolecarboxaldehyde exhibits moderate sensitivity to nucleophilic contaminants and oxidizing agents. It is incompatible with strong alkalis, which promote the Cannizzaro reaction yielding pyrrole‑2‑methanol and pyrrole‑2‑carboxylate salts, and with concentrated mineral acids that catalyze oligomerization via aldehyde‑pyrrole condensation. Storage in borosilicate glass or 316L stainless steel vessels is recommended; extended contact with carbon steel leads to green discoloration due to metal‑ion complexation. For retest intervals of 24 months, headspace oxygen should be maintained below 1 000 ppmv and moisture below 500 ppm to suppress aldol‑type side reactions that generate cross‑linked oligomers. Uncontrolled exposure to ambient humidity (RH >60 %) during sampling can initiate autocatalytic oligomerization; sampling is therefore performed under a dry nitrogen sweep through a PTFE septum using a syringe pump set to a withdrawal rate of 5 mL min⁻¹. Waste‑handling protocols should consider that the compound is classified as an irritant (H315, H319) under CLP Regulation; local exhaust ventilation with a capture velocity of 0.5 m s⁻¹ at the filling station is required during bulk transfers.
In aniline‑based imine formation conducted in acetate buffer at pH 4.0 and 25 °C, the half‑life of hydrolysis for the 2‑pyrrole‑derived imine is 1.8 × 10² min, compared with 1.5 × 10¹ min for the furfurylideneaniline analog under identical conditions, as determined by stopped‑flow UV spectroscopy at 350 nm. This 12‑fold enhancement in aqueous stability stems from p‑π conjugation between the pyrrole ring and the C=N bond, which raises the activation barrier for nucleophilic water attack. Consequently, 2‑pyrrolecarboxaldehyde is the preferred aldehyde component in acid‑stable chelating resins and corrosion‑inhibiting pigments, where furfural‑based imines degrade after 50–100 h of immersion in 0.1 M HCl. Moreover, pendant pyrrole N–H groups permit post‑functionalization via N‑alkylation or oxidative electropolymerization to deposit conductive polymer films on electrode surfaces—a synthetic avenue unavailable with furan aldehydes. When formulated into a two‑component epoxy coating, a diglycidyl ether of bisphenol A with an imine hardener derived from 2‑formylpyrrole exhibited a gel time at 25 °C of 180 min, compared with 75 min for the benzaldehyde‑based analog, as measured by a Brookfield DV3T rheometer equipped with spindle SC4‑27. The optical band gap of the resulting UV‑curable di‑imine film, obtained from a Tauc plot, falls in the range 2.3–2.5 eV, versus 3.1–3.3 eV for the furfural‑derived system, enabling broader light harvesting.
In the one‑pot synthesis of 5‑phenyldipyrromethane via acid‑catalyzed condensation of benzaldehyde with excess pyrrole, replacing benzaldehyde with 2‑pyrrolecarboxaldehyde alters the regio‑isomeric distribution of the meso‑carbon‑substituted dipyrrane. Using 2.0 equivalents of pyrrole per aldehyde in the presence of 0.1 eq of trifluoroacetic acid in dichloromethane at 0 °C for 30 min yields the 1′‑formyl‑2,2′‑dipyrromethane isomer as the major product in 45–50 % isolated yield after chromatography. The 3‑isomer, under identical conditions, gives 38 % yield of the 3‑formyl dipyrromethane together with 15–20 % of a tripyrrane oligomer arising from uncontrolled condensation at the electron‑rich C‑2 position. This selectivity is exploited in the construction of ABCD‑porphyrin precursors, where the 2‑formyl group can be retained for late‑stage functionalization or converted to a vinyl group via Wittig reaction. Process‑scale literature reports show that continuous‑flow microreactors (inner diameter 0.5 mm, residence time 2 min) improve yield to 62 % by suppressing polypyrrole formation, a side reaction responsible for black tarry by‑products that foul crystallization and reduce filter throughput.
The following table collates key physical constants for heterocyclic aldehydes frequently evaluated as synthetic alternatives.
| Property | Pyrrole-2-carboxaldehyde | Pyrrole-3-carboxaldehyde | Furfural | Benzaldehyde |
|---|---|---|---|---|
| Molecular weight (g mol⁻¹) | 95.10 | 95.10 | 96.08 | 106.12 |
| Melting point (°C) | 18–20 | 66–68 | −38 | −26 |
| Boiling point (°C, 760 mmHg) | 217–219 | 238–240 | 161.7 | 178.1 |
| Density (g mL⁻¹, 25 °C) | 1.092 | 1.14 | 1.160 | 1.041 |
| Refractive index nD20 | 1.546 | 1.550 | 1.526 | 1.545 |
| Water solubility (g/100 mL) | <1 | <1 | 8.3 | 0.3 |
| 1H NMR δ CHO (CDCl₃, ppm) | 9.55 | 9.70 | 9.66 | 10.00 |
Routine quality control in a GMP intermediate manufacturing environment employs an HPLC method with a C18 column (150 × 4.6 mm, 5 µm), isocratic elution with acetonitrile:water 40:60 v/v, and UV detection at 280 nm. Under these conditions the retention time of 2‑pyrrolecarboxaldehyde is 4.8 min, and the limit of quantitation for 2‑pyrrolecarboxylic acid, the primary oxidation impurity, is 0.05 % (w/w). A complementary GC method configured per ASTM D8310 uses a DB‑WAX column (30 m × 0.32 mm, 0.25 µm film) with FID detection; the injection port is held at 230 °C and the oven programmed from 50 °C (hold 2 min) to 220 °C at 10 °C min⁻¹. The aldehyde elutes at 13.2 min, permitting resolution from pyrrole (3.1 min) and the N‑methyl analog. Across 50 production lots, the relative standard deviation of assay values was <0.3 %, validating process robustness.
| Test Parameter | Specification | Test Method |
|---|---|---|
| Assay (GC) | ≥98.0 % | ASTM D8310 |
| Water (Karl Fischer) | ≤0.5 % | ASTM D6304 |
| Colour (APHA) | ≤100 | ASTM D1209 |
| Refractive index nD20 | 1.542–1.546 | ASTM D1218 |
| Appearance | Clear amber liquid | Visual |
| Heavy metals (as Pb) | ≤10 ppm | Ph. Eur. 2.4.8 |
