2-Phenylpyrrole
Pyrrolidine Pyrrole Thiazole Imidazole Thiophene Pyrazine Piperidine Piperazine Morpholine Phenazine

2-Phenylpyrrole


    • Product Name 2-Phenylpyrrole
    • Alias 2-Phenyl-1H-pyrrole
    • Einecs 212-227-7
    • Mininmum Order 25g
    • Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
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    • Manufacturer Bouling Chemical Co., Limited
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    Specifications

    HS Code

    364320
    Chemical Formula C10H9N
    Molar Mass 143.19 g/mol
    Appearance Solid
    Melting Point 54 - 58 °C
    Boiling Point 260 - 261 °C
    Solubility In Water Insoluble
    Solubility In Organic Solvents Soluble in common organic solvents like ethanol, ether
    Density 1.102 g/cm³
    Flash Point 113 °C
    Odor Characteristic organic odor
    Stability Stable under normal conditions

    As an accredited 2-Phenylpyrrole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

    Packing & Storage
    Packing 250g of 2 - Phenylpyrrole packaged in a sealed, chemical - resistant container.
    Shipping 2 - Phenylpyrrole is shipped in well - sealed, corrosion - resistant containers. Adequate cushioning is used to prevent breakage. It follows strict chemical shipping regulations, ensuring safe transportation due to its potentially reactive nature.
    Storage 2 - Phenylpyrrole should be stored in a cool, dry, well - ventilated area away from heat sources and open flames. Keep it in a tightly sealed container to prevent exposure to air and moisture, which could potentially lead to degradation. Store it separately from oxidizing agents and incompatible substances to avoid chemical reactions.
    Application of 2-Phenylpyrrole
    During the N-methylation of 2-phenylpyrrole en route to pyrroleacetic acid-derived nonsteroidal anti-inflammatory drug substances, the heterocycle functions as the primary scaffold and accounts for 50–55 wt% of the initial batch charge. Anhydrous toluene is used as the bulk medium in a glass-lined reactor where the pyrrole NH is deprotonated with 50 % aqueous NaOH, and dimethyl sulphate (1.05 mol per mole of 2-phenylpyrrole) is metered over 4 h at 35–40 °C under a nitrogen blanket; real-time pH is maintained at 10.5–11.5 using an in-line attenuated total reflectance FTIR probe that tracks the consumption of the methyl sulfate band at 1230 cm⁻¹. Excursions above pH 12 induce sulfonate ester hydrolysis and dimerisation losses exceeding 5 %, a failure mode documented on 2000 L pilot-plant campaigns. After phase separation, the organic layer containing N-methyl-2-phenylpyrrole is subjected to Friedel–Crafts acylation with p-toluoyl chloride (1.15 mol) and anhydrous AlCl₃ (1.3 mol) in dichloromethane, held at −2 °C to +2 °C for 6 h, before being quenched into ice/water. The resulting 5-(4-methylbenzoyl)-1-methyl-2-phenylpyrrole is then brominated at the pyrrole α′-position by N-bromosuccinimide (1.02 mol, AIBN 0.5 mol%) in refluxing carbon tetrachloride under actinic illumination; conversion is monitored by HPLC until residual substrate drops below 0.15 area%. A Rosemund–von Braun cyanation with copper(I) cyanide (1.4 mol) in N-methyl-2-pyrrolidone at 140 °C produces the nitrile, which is hydrolysed to the acetic acid sodium salt using 10 % NaOH in ethanol/water, followed by charcoal decolourisation, vacuum crystallisation, and tray drying at 60 °C/<5 kPa to a final loss on drying ≤0.5 %. Processing is governed by ICH Q7 Good Manufacturing Practice and FDA 21 CFR Part 211; impurity profiling per ICH Q3A limits total unspecified impurities to ≤0.10 %, and residual solvents are controlled to the concentration limits specified in USP <467> and ICH Q3C. Carryover of elemental impurities – Ni, Pd, Cu – is verified by ICP-MS against USP <232>/<233>, with acceptance criteria ≤10 µg g⁻¹. The resulting active pharmaceutical ingredient, chemically described as sodium 5-(4-methylbenzoyl)-1-methyl-1H-pyrrole-2-acetate, is compacted into immediate-release tablets of 200 mg or 400 mg strength and indicated for the management of acute musculoskeletal pain, rheumatoid arthritis, and ankylosing spondylitis; disintegration time is confirmed by USP <701> to be ≤15 min in simulated gastric fluid.

    How Does Arylpyrrole Carbonitrile Insecticide Synthesis Exploit Regioselective Halogenation of 2-Phenylpyrrole?

    The commercial route to the contact-and-stomach insecticide/miticide chlorfenapyr leverages the electron-rich nature of 2-phenylpyrrole to direct electrophilic substitution in the para position of the pendent phenyl ring, thereby installing the chlorine atom essential for biological activity. In a 5000 L carbon steel–enamelled reactor train, 2-phenylpyrrole is dissolved in dichloroethane and treated with sulfuryl chloride (1.08 mol relative to the pyrrole substrate) in the presence of anhydrous ferric chloride (0.5 mol%), maintaining the exothermic chlorination at 45–50 °C over 3 h. Process off-gas is scrubbed through a 10 % NaOH vent system to capture HCl and SO₂; online reaction monitoring with a Kaiser Raman probe tracks the disappearance of the para C–H stretching vibration at 810 cm⁻¹. The net consumption of 2-phenylpyrrole across all synthetic stages amounts to 0.82 kg per kilogram of technical-grade chlorfenapyr (≥95 % purity). The subsequent transformations are detailed in the synthetic tableau below.
    Reaction StepReagents & ConditionsKey IntermediateIsolated Yield
    1. Para-ChlorinationSO₂Cl₂ (1.08 eq), FeCl₃ (0.5 mol%), DCE, 45–50 °C, 3 h2-(4-Chlorophenyl)pyrrole92–94 %
    2. Pyrrole Ring BrominationBr₂ (1.05 eq), AcOH, 10–20 °C, 2 h4-Bromo-2-(4-chlorophenyl)pyrrole88 %
    3. Vilsmeier–Haack FormylationDMF/POCl₃ (1.3 eq), 0–5 °C, then 25 °C 4 h4-Bromo-2-(4-chlorophenyl)-1H-pyrrole-3-carbaldehyde85 %
    4. Aldehyde→Nitrile ConversionNH₂OSO₃H (1.5 eq), H₂O/EtOH, 70 °C, 2 h4-Bromo-2-(4-chlorophenyl)-1H-pyrrole-3-carbonitrile82 %
    Subsequent N-ethoxymethylation (chloromethyl ethyl ether, NaH, THF, 0–10 °C) and copper-mediated trifluoromethylation (sodium trifluoroacetate, CuI, NMP, 160 °C) deliver the technical material, which is crystallised from ethanol to a melting point of 100–101 °C and an active content of 96–98 %. The synthesis is compliant with ISO 14001:2015 and the Chinese standard GB/T 9559-2003 for technical chlorfenapyr. For registration as a plant protection product, the active ingredient is analysed by CIPAC Handbook H methods (MT 44.3 for suspensibility, MT 46 for wet sieve residue). Maximum residue limits in treated crops are set under Codex Alimentarius CAC/MRL 1 and verified by LC-MS/MS in accordance with SANTE/11312/2021. The formulated end-use products – a 240 g L⁻¹ suspension concentrate and a 10 % emulsifiable concentrate – are applied by ground-rig or airblast sprayers at 150–250 mL ha⁻¹ for the control of pyrethroid-resistant Helicoverpa armigera, Plutella xylostella, and Tetranychus urticae populations in cotton, cruciferous vegetables, and ornamental crops.Pulsed potentiostatic electropolymerisation of 2-phenylpyrrole onto micro-patterned indium tin oxide-coated polyethylene terephthalate substrates yields optically transmissive films with a coulometrically controlled thickness of 300 ± 15 nm, as verified by contact profilometry (stylus radius 2 µm, force 0.5 mg). The deposition bath is prepared inside a nitrogen-atmosphere glovebox (O₂ <5 ppm, H₂O <1 ppm) and consists of 0.20 M 2-phenylpyrrole and 0.10 M tetrabutylammonium hexafluorophosphate in anhydrous propylene carbonate, which places the monomer weight fraction at 10.5 wt% of the liquid electrolyte. Polymerisation is performed in a three-electrode quartz cell with a platinum flag counter electrode and a non-aqueous Ag/Ag⁺ reference; the working electrode is held at +0.85 V vs. Ag/Ag⁺ for a total charge passage of 150 mC cm⁻². Immediately following growth, the as-grown oxidised polymer is dedoped by stepping the potential to −0.8 V for 300 s, causing the characteristic colour change from dark green to transparent yellow and expelling PF₆⁻ counter-ions into the bath. Cyclic voltammetry between 0 V and 1.2 V at 50 mV s⁻¹ reveals symmetrical anodic and cathodic waves, indicative of a reversible redox process. Capacitance rating is performed according to IEC 62391-1:2022 using galvanostatic charge-discharge at 1 A g⁻¹ in aqueous 1 M KCl, yielding a specific capacitance of 195–215 F g⁻¹ and a Coulombic efficiency > 98 % over 5 000 cycles. Optoelectronic contrast is quantified in a custom UV–vis spectroelectrochemical cell; a voltage step from −0.4 V to +0.8 V produces a 90 % absorbance change at 650 nm within 1.2 s, qualifying the film for variable-transmittance glazing under ASTM E2141-21. Mechanical robustness of the flexible electrode is probed by ASTM D882 at a strain rate of 5 mm min⁻¹; the film withstands 8 % elongation without delamination from the polyethylene terephthalate carrier. The primary downstream exploitation paths are laminate-type thin-film supercapacitor arrays that power wireless sensor nodes in Internet-of-Things networks and the electrochromic outer ply of aircraft cabin windows, both of which require the combination of wide potential window stability and transparency modulation that poly(2-phenylpyrrole) uniquely provides.

    When 2-Phenylpyrrole Serves as the Coupling Component in Azo Disperse Dyes

    Formulators of high-strength disperse dyes for polyester microfiber rely on the electron-rich pyrrole ring of 2-phenylpyrrole as a coupling component to access yellow-to-orange chromophores with elevated extinction coefficients and solvent-fastness profiles. The coupling step is run in an aqueous batch: 2-phenylpyrrole (1.02 mol, relative to the diazo component) is dissolved in dilute hydrochloric acid and cooled to 0–5 °C, then fed into a freshly prepared diazonium salt solution (exemplified by 4-nitroaniline or 2-chloro-4-nitroaniline, diazotised with sodium nitrite in 2.5 M HCl at 0 °C). The coupling mass is stirred for 4 h, buffered to pH 4.5–5.0 with sodium acetate trihydrate, and filtered; the presscake is washed with deionised water at 5 °C until the filtrate conductivity drops below 50 µS cm⁻¹. At this stage the dry-matter content of the presscake is 45–52 % active azo dye, expressed as the sodium sulfonate or free acid depending on the diazo component. The resulting crude dye is blended with sodium lignosulfonate dispersant at a dye-to-dispersant ratio of 1:0.7 and wet-milled in a horizontal bead mill (0.3 mm yttria-stabilised zirconia beads, 85 % fill, 12 m s⁻¹ tip speed) until the primary particle size measured by a Malvern Zetasizer D₅₀ falls below 1.0 µm. The mill-base is diluted and spray-dried to yield a granular powder containing 25 wt% commercial dye, which equates to a carry-through of 11–13 wt% of the initial 2-phenylpyrrole charge into the final product. The spectral and fastness characteristics of three representative formulations manufactured on this platform are collated below.
    Diazo Componentλmax (DMF)Shade on 100% PETLight Fastness (ISO 105-B02:2014, Xenotest)Sublimation Fastness (ISO 105-P01:1993, 180 °C)
    4-Nitroaniline432 nmGreenish Yellow64–5
    2-Chloro-4-nitroaniline445 nmReddish Yellow5–64
    2,6-Dichloro-4-nitroaniline460 nmOrange64–5
    Each finished dye lot is certified against OEKO-TEX Standard 100 (Appendix 4) to exclude restricted aromatic amines (≤20 mg kg⁻¹ per EN 14362-1:2017) and is listed on the ZDHC Manufacturing Restricted Substances List Level 1 compliant product registry. The dyed fabric is evaluated for colour fastness to water (ISO 105-E01:2013), rubbing (ISO 105-X12:2016), and perspiration (ISO 105-E04:2013) on a 10 g L⁻¹ dyeing at 130 °C for 45 min on a Mathis Labomat. The predominant application is continuous dyeing of polyester automotive upholstery textiles and polyester/cotton workwear blends that demand a light fastness rating of ≥ 6, where the azo-chromophore 2-phenylpyrrole derivatives provide a combination of brilliant hue and cost-in-use consistent with continuous thermosol fixation at 200–210 °C for 60 s.Vacuum-deposited hole-transport materials built around a 2-phenylpyrrole core and terminated with di-p-tolylamino units exhibit a glass transition temperature of 142 °C (differential scanning calorimetry, 10 K min⁻¹) and a highest occupied molecular orbital energy of −5.28 eV, as determined by AC-2 photoelectron spectroscopy in air, which aligns favourably with the work function of ITO/PEDOT:PSS anodes commonly used in bottom-emission organic light-emitting diode stacks. The synthesis is accomplished through a one-pot, two-step Buchwald–Hartwig amination sequence: 2-phenylpyrrole is first N-arylated with 4-bromotoluene (1.2 equiv.) in toluene at 90 °C employing Pd₂(dba)₃ (2 mol%), XPhos (6 mol%), and sodium tert-butoxide (1.4 equiv.); after 12 h, bis(4-methylphenyl)amine (2.2 equiv.) is added and heating is continued for a further 18 h. In the crude reaction mass, 2-phenylpyrrole represents 22–28 wt% of the total non-solvent solids. Work-up involves aqueous quenching, extraction with dichloromethane, and two sequential recrystallisations from toluene/hexane (1:3 v/v) to obtain the hole-transport material as an off-white crystalline powder with a purity of 99.93 % by HPLC-UV at 254 nm – a specification that is mandatory for thermal evaporation at 10⁻⁶ mbar without crucible clogging or source contamination. The purified material is qualified for outgassing according to ASTM E595-15, with total mass loss limited to ≤0.1 % and collected volatile condensable material ≤0.01 %. A typical bottom-emission device stack – ITO (150 nm) / PEDOT:PSS (40 nm) / HTL (30 nm, deposited at 0.2 nm s⁻¹) / emissive layer / electron-transport layer / LiF/Al – is stress-tested according to IEC 62341-1-1:2009 and ISO 4892-2:2013 for photo-stability under simulated AML5 irradiance. The luminance data at 10 mA cm⁻² yield a current efficiency of 55 cd A⁻¹ and a Commision Internationale de l’Éclairage (x,y) of (0.31, 0.33). The operational lifetime T₉₅, measured at a constant current density corresponding to a starting luminance of 1 000 cd m⁻², reaches 2 500 h under accelerated aging at 25 °C ambient. The primary commercial outlets are the hole-transport layer of premium smartphone active-matrix OLED panels and the charge-generation separation layer in tandem blue OLED lighting demonstrators.

    Corrosion Mitigation in Hydrochloric Acid Pickling Baths Exploits the Adsorption of Pyrrole Derivatives on Mild Steel

    In continuous pickling lines designed to remove hot-roll scale from low-carbon steel strip ahead of cold rolling or galvanising, addition of 2-phenylpyrrole at a steady-state concentration of 100–150 mg L⁻¹ – a loading equivalent to 0.008–0.012 wt% of the active substance in 10–15 % HCl at 40–60 °C – reduces the uniform corrosion rate to ≤1.0 mm a⁻¹, as determined by weight-loss coupon tests per ASTM G31-72(2021) over a 6 h exposure period. The inhibitor is predissolved in isopropanol at a 10 % concentration and metered into the recirculating acid flow by a diaphragm dosing pump; depletion of the organic inhibitor is monitored hourly by reversed-phase HPLC, and the bath is reinforced every 8 h of continuous operation to maintain the target window. Electrochemical impedance spectroscopy (10 mV rms perturbation, 100 kHz to 10 mHz) and Tafel polarisation sweeps (±250 mV vs. OCP, scan rate 0.5 mV s⁻¹, conducted per ASTM G59-20) confirm that 2-phenylpyrrole behaves as a mixed-type inhibitor that retards both anodic iron dissolution and cathodic hydrogen evolution. The adsorption of the pyrrole ring onto the steel surface follows the Langmuir isotherm; the calculated adsorption free energy ΔGads of −37 kJ mol⁻¹ points to a chemisorption mechanism involving π-electron donation from the heterocycle to vacant d-orbitals of iron. The spent acid is neutralised with lime slurry and processed through a filter press; residual organic carbon in the treated effluent is controlled to <50 mg L⁻¹ to meet local discharge consent limits. Process control is reinforced by NACE TM0169/G31 guidelines for immersion corrosion testing, and the cleaned strip is subsequently evaluated for surface quality against ISO 16172:2018 (continuous hot-dip metallic-coated steel sheet) before entering a Sendzimir mill for gauge reduction or a zinc pot for galvanised automotive skin panels.
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    Certification & Compliance
    More Introduction

    2-Phenylpyrrole (CAS 3042-22-6) is a heterocyclic aromatic amine in which a phenyl substituent occupies the 2-position of the five-membered pyrrole ring. The molecular formula C10H9N yields a monoisotopic mass of 143.0735 Da. Under ambient conditions, the compound is a low-melting solid—typically off-white to pale yellow crystalline needles—with a characteristic amine-like odor. Its synthesis, most commonly via Paal-Knorr condensation of 1,4-dicarbonyl precursors with aniline derivatives or through palladium-catalyzed cross-coupling at the 2-position of a pre-formed pyrrole, yields a scaffold that retains the N-H proton (pKa ≈ 17.5 in DMSO) while presenting a conjugated aryl system capable of π-stacking and directed lithiation. The presence of a free N-H distinguishes it fundamentally from 1-phenylpyrrole and directs its regiochemistry in electrophilic aromatic substitution: nitration, sulfonation, and Vilsmeier formylation occur preferentially at the 5-position, whereas the 3-position can be accessed through transition-metal-mediated C-H activation.

    Specifications and Analytical Characterization

    ParameterMethod / InstrumentTypical Value
    Assay (GC-FID)Agilent 7890B GC, HP-5 column, 30 m × 0.32 mm, film 0.25 µm≥ 98.0%
    Water ContentKarl Fischer coulometry, Metrohm 899 Coulometer≤ 0.2% w/w
    Melting RangeBüchi M-565, capillary method, 1 °C/min84–86 °C
    Residue on IgnitionPh. Eur. 2.4.14, 600 °C≤ 0.1%
    Heavy MetalsICP-MS, Agilent 7800Pb ≤ 10 ppm, As ≤ 3 ppm
    Purity (HPLC-UV)Agilent 1260 Infinity II, C18, 254 nm, MeCN/H2O gradient≥ 99.0% area

    Routine identity confirmation employs FT-IR (Thermo Nicolet iS50) with characteristic absorptions at νN-H ≈ 3430 cm⁻¹ and aromatic C=C stretching at 1605 cm⁻¹ and 1500 cm⁻¹. 1H NMR (Bruker Avance III HD 400 MHz, CDCl3) displays the N-H proton as a broad singlet near δ 8.4, coupling patterns for the pyrrole ring protons at δ 6.5 (H-3), 6.3 (H-4), and 6.9 (H-5), and a five-proton multiplet for the phenyl ring between δ 7.2–7.6. Storage at 2–8 °C under inert gas (argon or nitrogen) in amber glass containers is required to suppress photo-oxidative discoloration; headspace oxygen should remain below 50 ppm to prevent formation of polypyrrole oligomers during prolonged storage exceeding 12 months.

    In continuous-flow hydrogenation pilot plants employing Pd/C fixed-bed reactors (ThalesNano H-Cube Pro, 50 bar, 80 °C), 2-phenylpyrrole serves as a substrate for selective ring saturation to 2-phenylpyrrolidine without debenzylation by-products. Spiking experiments with 0.5 mol% 2-phenylpyrrole in tetrahydrofuran at a liquid hourly space velocity of 0.3 h⁻¹ achieve >99% conversion with 2 wt% Pd loading on carbon. Reactor pressure drop profiles indicate that batch-to-batch variation in substrate melting point (±1.5 °C) correlates with residual ethanol solvate persistence from recrystallization; pre-drying at 40 °C and 10 mbar for 8 h eliminates this variance.

    What Distinguishes 2-Phenylpyrrole from Other Phenylpyrrole Isomers?

    IsomerSubstitutionN-H Acidity (pKa, DMSO)Oxidation Epa (vs Ag/AgCl, MeCN)Primary Electrophilic Site
    2-PhenylpyrroleC-217.5+0.88 VC-5
    1-PhenylpyrroleN-1No acidic proton+1.15 VC-2 (sterically hindered)
    3-PhenylpyrroleC-317.9+0.82 VC-2 (preferred), C-5

    The free N-H proton in 2-phenylpyrrole enables N-functionalization—alkylation, acylation, tosylation—that is inaccessible in the 1-isomer. In lithiation-electrophile quench sequences, 2-phenylpyrrole undergoes directed ortho-metalation at the 5-position with n-BuLi in THF at −78 °C, whereas 1-phenylpyrrole requires LDA and elevated temperatures (0 °C) to deprotonate the α-position adjacent to the N-phenyl ring, and the resulting anion suffers from rapid β-elimination above −20 °C. The 3-isomer’s more negative oxidation potential makes it prone to air oxidation during sonication-assisted Suzuki couplings, a degradation pathway not observed at comparable rates for the 2-isomer under identical conditions (Biotage Initiator+ microwave reactor, 150 °C, 30 min).

    When a reaction sequence demands that the pyrrole nitrogen remain available for late-stage diversification—for instance, in the construction of tricyclic indole-pyrrole hybrids via Pictet-Spengler cyclization—the choice of 2-phenylpyrrole over the 1-substituted analogue is non-negotiable. Attempts to remove an N-benzyl protecting group from the corresponding 1-benzyl-2-phenylpyrrole intermediate using hydrogenolysis (H-Cube, 10% Pd/C, MeOH, 50 bar) led to partial ring hydrogenation with 12–18% of the 2-cyclohexylpyrrolidine by-product detected by LC-MS. The 2-phenyl isomer, in contrast, was employed without N-protection, entering the Pictet-Spengler cascade directly in formic acid at 90 °C and yielding the tetracycle in 76% isolated yield after flash chromatography (Biotage Isolera One, KP-Sil 50 µm, hexane/ethyl acetate gradient).

    When Polymerization Requires a Sterically Demanding Monomer

    Electrochemical polymerization of 2-phenylpyrrole on ITO-coated glass (sheet resistance 8–12 Ω/sq) from 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile proceeds at an onset potential of +0.92 V vs Ag/AgCl, approximately 200 mV higher than unsubstituted pyrrole under identical conditions. The resulting poly(2-phenylpyrrole) films, grown to a charge density of 30 mC/cm², exhibit a conductivity of 2.4–3.1 S/cm measured by four-point probe (Jandel RM3000), roughly one order of magnitude lower than polypyrrole films. This reduction is compensated by a significant improvement in environmental stability: upon exposure to 85% relative humidity at 25 °C for 500 h, the poly(2-phenylpyrrole) film retains 87% of its initial conductivity, whereas polypyrrole degrades to 31% due to water-induced dedoping. Glovebox-integrated spin-coating (MBraun LABmaster pro, H2O < 0.1 ppm, O2 < 0.1 ppm) of the monomer solution onto interdigitated microelectrodes prior to polymerization eliminated batch-to-batch variability in film thickness to within ±5 nm (profilometer, Bruker Dektak XT-A).

    Processing of 2-phenylpyrrole as a precursor to fungicidal pyrazole-4-carboxamides has been validated at pilot scale. Condensation with ethyl 2-chloro-3-oxobutanoate in refluxing ethanol containing anhydrous sodium acetate (1.2 eq) yields the pyrazole ester intermediate in 92% yield after crystallization from isopropanol/water. The isolated product passes the stringent chloride limit of <50 ppm (ion chromatography, Metrohm 930 Compact IC Flex) required for subsequent amidation with 3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid. The final active ingredient, purified by slurry wash with cold acetone, exhibits a polymorphic transition at 142.3 °C (DSC, Mettler Toledo DSC 3+, 10 K/min) that was confirmed as the thermodynamically stable Form I by XRPD (Bruker D8 Advance, Cu Kα).

    Static discharge during pneumatic transfer of dry 2-phenylpyrrole powder through PTFE-lined ducts has initiated localized charring events at conveying velocities exceeding 15 m/s. Minimum ignition energy measured by MIKE 3 apparatus (Kühner) is 5–10 mJ, placing the dust in the highly ignitible category. Grounding straps with resistance < 10⁶ Ω and inert gas blanketing with nitrogen at a dew point ≤ −40 °C are mandatory engineering controls for any operation handling quantities above 500 g.

    Trace Impurity Profiling and Pharmacopoeial Alignment

    Liquid chromatography coupled to high-resolution mass spectrometry (Thermo Q Exactive Plus, HESI source, 3.5 kV) has identified three recurring process-related impurities in commercial 2-phenylpyrrole batches: 2,2′-diphenyl-1,1′-bipyrrole (dimer impurity, m/z 285.1392), 2-(4-bromophenyl)pyrrole (when synthesized via a bromobenzene route), and residual triphenylphosphine oxide from Wittig-type cyclization steps. Quantification by external standard calibration against reference materials of known purity (certified by quantitative NMR traceable to NIST SRM 350b) allows control of the dimer below 0.15% area, consistent with the ICH Q3A threshold for unspecified impurities in drug substances at a maximum daily dose of 2 g/day. The USP <621> chromatography monograph and Ph. Eur. 2.2.46 provide system suitability criteria applied during release testing: resolution between 2-phenylpyrrole and the dimer peak must exceed 1.8, and tailing factor measured at 5% peak height must fall between 0.95 and 1.15 on a 150 mm × 4.6 mm, 3 µm C18 column.

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