1H-Pyrrole-3-Carbonitrile, 4-Bromo-2-(4-Chlorophenyl)-5-(Trifluoromethyl)-

In high-volume industrial synthesis of chlorfenapyr, the mole ratio of 4-bromo-2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile to sodium hydride dispersion (60% in mineral oil) is maintained at 1:1.05–1.12, with tetrahydrofuran moisture content verified below 500 ppm by Karl Fischer titration (ASTM E203-16). The alkylation step employing chloromethyl ethyl ether proceeds under strictly anhydrous conditions at –5 to 0°C in a glass-lined vessel to suppress exothermic runaway, after which the crude technical material is neutralized with 2% aqueous HCl and concentrated via wiped-film evaporation at ≤80°C jacket temperature. Recrystallization from a toluene–n-heptane mixture (1:3 v/v) yields chlorfenapyr technical of ≥97% purity, assayed by HPLC (CIPAC Handbook L, MT 581). The terminal product is a crystalline solid packaged in 25 kg UN-certified fibre drums for downstream formulation into insecticidal preparations compliant with FAO Specification 570/TC (December 2010). Production-scale batch records document that isomer content—specifically the 3-(4-chlorophenyl) regioisomer arising from incomplete regioselectivity during pyrrole cyclization—depresses the melting point of the technical material and must be limited to ≤1.2% w/w to prevent caking during long-duration silo storage at ambient humidity exceeding 70% RH.

Synthesis of Chlorfenapyr Technical Material: Stoichiometric and Thermal Hazard Boundaries

The downstream transformation of 4-bromo-2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile into chlorfenapyr technical grade active ingredient is performed using one of two validated routes: sodium hydride/DMF slurry alkylation or phase-transfer catalysis with tetrabutylammonium bromide (TBAB) in 50% w/w sodium hydroxide. In the hydride route, the pyrrole intermediate is charged at 1.0 molar equivalent into a jacketed reactor previously nitrogen-purged to ≤1% oxygen, and sodium hydride (1.08 eq, 60% in paraffin) is added portion-wise over 90 min maintaining bulk temperature at 0 to 3°C to prevent Hofmann-type elimination of the 2-(4-chlorophenyl) moiety. Once hydrogen evolution subsides, chloromethyl ethyl ether (1.25 eq) is dosed via mass-flow meter at a rate not exceeding 0.3 eq/h, and the batch is held at 22±2°C for 6 h before quenching into ice-water. The organic layer is separated and washed with 10% brine to achieve conductivity <50 μS/cm, distilled under reduced pressure (5 mbar, 80–90°C vapor temperature), and crystallized from toluene–heptane to deliver chlorfenapyr technical with melting point 100.5–101.5°C (DSC, ASTM E967-18). The terminal product is an off-white crystalline powder classified as a WHO Class II insecticide; it is homogenized in a ribbon blender and packed under nitrogen overlay to avoid oxidative dimerization. Process safety calorimetry (Phi-Tec II) on the alkylation step reveals a maximum heat-release rate of 45 W/kg and an adiabatic temperature rise of 68°C, mandating that the reaction mass never exceed 30°C during cooling-failure scenarios. Compliance with REACH Annex VIII (tonnage band 100–1000 t/a) requires full disclosure of the 4-(2,4-dichlorophenyl) trace impurity, which must be controlled below 0.5% w/w to satisfy European Union Regulation (EC) No 1107/2009 renewal data requirements.

When processing the intermediate into wettable powder (WP) or water-dispersible granule (WG) formulations, bulk density of the crystallized technical must fall between 0.45 and 0.55 g/mL; values below this range are associated with excessive fines generation during micronization to D_v90 ≤8 µm, causing dust-release incidents in fluid-energy mills equipped with 316L stainless steel classifier wheels operating at 3500 rpm. Downstream formulators correlate residual toluene content (HS-GC/MS, ASTM D4919-17) above 50 ppm with impaired granule attrition resistance, a defect confirmed through repeated friability testing per CIPAC MT 178.

What Limits Suspension Concentrate Stability When the Intermediate Contains Regioisomeric Impurities?

Suspension concentrate (SC) compositions containing 240 g/L chlorfenapyr derived from this intermediate are prepared by milling a pre-mix of chlorfenapyr technical, ethoxylated tristyrylphenol phosphate ester (35 g/L), sodium lignosulphonate (20 g/L), and propylene glycol (80 g/L) in a horizontal bead mill (Netzsch LME 4) charged with 0.6–0.8 mm yttria-stabilized zirconia beads at 80% fill. The target particle-size distribution is D_v50 1.2–1.5 µm and D_v90 <4.0 µm, confirmed by laser diffraction (ISO 13320:2020). Terminal product is a viscous off-white liquid packaged in 1 L or 5 L coextruded HDPE containers for foliar application on vegetable crops. Experience on 1000 L production batches shows that isomer-enriched technical material (≥2.0% 3-(4-chlorophenyl) regioisomer) triggers Ostwald ripening within 14 days at 54°C accelerated storage (CIPAC MT 46.3), with D_v90 growth exceeding 8 µm and resultant screen retention on 75 µm wet sieve rising to 2.5%, above the FAO Specifications for insecticidal SC (limit ≤2.0%). The underlying mechanism is the lower crystal-lattice energy of the impurity, which elevates solubility in the aqueous continuous phase and drives diffusion-limited crystal growth. Batch records correlate isomer content determined via ¹⁹F NMR (δ -62.8 vs. -63.4 ppm, CDCl₃) with formulation physical stability; therefore, incoming inspection protocols for the intermediate specify isomer ≤0.5% to guarantee SC shelf-life of 24 months under ICH climatic zone IV conditions.

Subterranean termite bait station matrices containing chlorfenapyr synthesized from 4-bromo-2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile are produced by blending the technical active ingredient into fibrous cellulose powder at a target concentration of 0.25% w/w, together with a phagostimulant (vanillin, 0.05% w/w) and a mold inhibitor (sodium benzoate, 0.5% w/w), then compressing the homogeneous mixture in a tablet press at 15 kN compression force to yield 20 g bait disks with a density of 1.10–1.15 g/cm³. The bait host matrix is inserted into in-ground stations meeting ASTM E2955-13 performance criteria for termite foraging. The terminal product is a moisture-resistant cellulose tablet overwrapped in nonwoven polypropylene filtration fabric to minimize fragmentation during deployment in high-humidity soils. Production environments must maintain relative humidity below 30% during blending and tableting because the pyrrole nitrile moiety is susceptible to surface hydrolysis at the —CN group under alkaline conditions (pH ≥8.5), leading to amide formation and a drop of ≤15% in biological half-life within the bait, as tracked by HPLC-UV. Compliance verification references EPA PR Notice 96-7 for termiticide baits and requires GLP storage stability studies at 25°C/60% RH and 40°C/75% RH over 18 months.

In wood preservation and industrial mildew prevention, the intermediate is converted to chlorfenapyr for incorporation into solventborne alkyd penetrating stains or pressure-treatment emulsions. For a typical light organic solvent preservative, chlorfenapyr technical is dissolved at 0.10–0.15% w/v in dearomatized white spirit (flash point 62°C) together with IPBC (0.30% w/v) and a cobalt-free drier (Nuodex Octa-Soligen 0.5% v/v), applied by vacuum-pressure impregnation (initial vacuum –85 kPa, pressure 1.2 MPa for 60 min) to radiata pine sapwood framing. Preserved timber achieves Hazard Class H3 (outside above ground) per EN 335:2013, with a target retention of 0.015 kg chlorfenapyr per m³ of sapwood, verified by GC-ECD analysis of drill shavings. The formulation must remain free of amine-based co-solvents, as the nitrile functional group of the parent intermediate and its N-alkylated analog are susceptible to nucleophilic addition with primary and secondary amines under the alkaline conditions of ammoniacal copper quaternary treatments, resulting in irreversible precipitates that plug inline filters (50 µm mesh) and reduce active ingredient delivery by over 20% during full-cell treatment cycles. The finished wood product is an above-ground decking or cladding component requiring a service life exceeding 10 years when reference ground-contact trials in Hilo, Hawaii, indicate no termite tunneling beyond 2 mm into treated samples.

Veterinary Spot-On Formulations Reliant on High-Purity Intermediate

Spot-on solutions for companion animal ectoparasite control are formulated by dissolving chlorfenapyr technical—synthesized from this pyrrole-3-carbonitrile intermediate with regioisomer content verified below 0.3%—in a ternary solvent system of N-methyl-2-pyrrolidone (40% v/v), diethylene glycol monoethyl ether (30% v/v), and propylene carbonate (qs to 100%), achieving a final chinopyrrole concentration of 120 mg/mL. The solution is filtered through 0.22 µm PTFE membrane and filled into unit-dose polypropylene squeeze pipettes with heat-sealed foil lidding designed to resist child opening (ISO 8317:2015). The terminal product is a non-aqueous, ready-to-apply dermal liquid indicated against Rhipicephalus sanguineus and Ctenocephalides felis. Process robustness studies document that residual palladium from synthetic steps upstream of the intermediate—measurable by ICP-MS at levels above 5 ppm—accelerates darkening of the spot-on solution within 4 weeks at 40°C, exceeding the Ph. Eur. 5.1.4 color limit. Hence, the incoming specification for 4-bromo-2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile includes a Pd ≤2 ppm requirement. Additionally, the formulation must exclude any trace of N,N-dimethylformamide solvent carryover, as DMF residues above 50 ppm in the intermediate have been correlated with elevated skin irritation scores in canine dermal safety studies conducted under VICH GL41.

In a municipal vector-control program requiring prolonged residual activity on porous surfaces, water-based emulsion-in-water (EW) concentrates are produced from chlorfenapyr technical derived from this intermediate to deliver 50 g/L active substance in a ready-to-spray emulsion. The concentrate is prepared by dissolving chlorfenapyr in methyl laurate (140 g/L) with Atlas G-5002 surfactant (80 g/L) and then dispersing the oil phase into softened water under high-shear (Silverson L5M, 4000 rpm) to yield droplet diameter D_v50 2.0±0.5 µm; the resulting milky liquid is packaged in 20 L jerricans of fluorinated HDPE to prevent solvent permeation. The terminal product is a public health insecticide for indoor residual spraying, applied at 200 mL concentrate per 10 L of water, deploying a 0.5–1.0 mm flat-fan nozzle to achieve a target deposition of 70 mL/m² on interior walls. State-of-the-practice observations from full-scale mixing vessels highlight that when the intermediate’s nitrile-to-amide conversion exceeds 0.8% (measured by ¹³C NMR δ 118.2 ppm CN vs. δ 168.5 ppm CONH₂), the resulting technical material exhibits a significant decrease in solubility in methyl laurate, causing sediment formation in the oil phase and compromising viscosity control. Compliance with the WHO Indoor Residual Spraying prequalification requires particle-size stability for 12 months at 30±2°C and residual cyano-group integrity above 98% of declared content, tested by reverse-phase HPLC with diode array detection (λ = 254 nm).

Chemical Identity and Batch Release Criteria

Parameter	Specification	Method
Appearance	White to off-white crystalline powder	Visual inspection, USP <790>
Melting point (onset)	132–134 °C	DSC, ASTM E794
Purity (HPLC, 254 nm)	≥98.0 area%	Column: C18, 1.8 µm, gradient H₂O/MeCN + 0.1% TFA
Water content	<0.5 % (as released)	Karl Fischer coulometric, USP <921>
Residual solvents	Toluene <500 ppm, heptane <200 ppm	GC headspace, USP <467>
Storage condition	2–8 °C, under argon, light-protected	Stability study: 12‑month real-time

Parameter

Specification

Method

Appearance

White to off-white crystalline powder

Visual inspection, USP <790>

Melting point (onset)

132–134 °C

DSC, ASTM E794

Purity (HPLC, 254 nm)

≥98.0 area%

Column: C18, 1.8 µm, gradient H₂O/MeCN + 0.1% TFA

Water content

<0.5 % (as released)

Karl Fischer coulometric, USP <921>

Residual solvents

Toluene <500 ppm, heptane <200 ppm

GC headspace, USP <467>

Storage condition

2–8 °C, under argon, light-protected

Stability study: 12‑month real-time

The solid is isolated as a white to off-white crystalline powder with a characteristic acrid odor, soluble in dipolar aprotic solvents. A typical dissolution procedure for laboratory-scale reactions comprises dissolving 1 g in 10 mL of anhydrous DMF at room temperature under argon. Solutions in DMSO‑d₆ exhibit a single set of ¹H NMR resonances consistent with the proposed structure, with the pyrrole NH resonance appearing as a broad singlet at δ ~11.2 ppm. Storage at 2–8 °C under inert atmosphere in amber glass vials preserves purity for at least 12 months from the date of manufacture, with no detectable degradation by HPLC.

What Role Does the C4 Halogen Play in Transition-Metal-Mediated Transformations?

The identity of the 4‑position substituent dictates the kinetic window and side‑product portfolio during palladium‑catalyzed cross‑coupling. In a standardized screening protocol using phenylboronic acid (1.2 equiv), K₂CO₃ (2.0 equiv) in dioxane/water (4:1 v/v) at a substrate concentration of 0.2 M, the following comparative performance is recorded from 5‑gram laboratory batches. Experiments were monitored by UPLC‑MS (254 nm) with internal standard calibration.

4‑Substituent	Catalyst System (mol%)	Temperature, Time	Conversion (HPLC area%)	Major Side Product
–Br	Pd(PPh₃)₄ (2)	80 °C, 2 h	≥98%	Protodebromination <1%
–I	Pd(PPh₃)₄ (2)	60 °C, 1.5 h	≥99%	Homocoupling 3–5%
–Cl	Pd(OAc)₂ (5), SPhos	100 °C, 8 h	72% (8 h)	Nitrile hydrolysis 12%
–H	[Ir(OMe)(cod)]₂ (1.5), dtbpy	110 °C, 16 h	41% (mono‑borylation)	Multiple regioisomers

4‑Substituent

Catalyst System (mol%)

Temperature, Time

Conversion (HPLC area%)

Major Side Product

–Br

Pd(PPh₃)₄ (2)

80 °C, 2 h

≥98%

Protodebromination <1%

–I

Pd(PPh₃)₄ (2)

60 °C, 1.5 h

≥99%

Homocoupling 3–5%

–Cl

Pd(OAc)₂ (5), SPhos

100 °C, 8 h

72% (8 h)

Nitrile hydrolysis 12%

–H

[Ir(OMe)(cod)]₂ (1.5), dtbpy

110 °C, 16 h

41% (mono‑borylation)

Multiple regioisomers

The bromo congener occupies a practical optimum. While the iodo analogue activates oxidative addition at a lower temperature, it generates homocoupling impurity levels that can exceed 5% in the presence of dissolved oxygen, mandating rigorous degassing and catalyst pre‑activation protocols. The chloro derivative demands forcing conditions that accelerate nitrile hydrolysis to the corresponding amide, particularly as the pH drifts above 9. In a 10‑L jacketed glass reactor equipped with a pitched‑blade impeller (150 rpm) and nitrogen sparging via a dip tube, a 5‑kg batch of the bromo substrate underwent Suzuki coupling with 4‑fluorophenylboronic acid. The oxidative addition exotherm required a cascade PID cooling loop to maintain the internal temperature at 77±2 °C; excursions above 85 °C initiated amide formation detectable by on‑line ReactIR (CN stretch at 2220 cm⁻¹ decreased with concurrent growth of an amide carbonyl at 1680 cm⁻¹). The process was quenched when the amide peak area reached 0.5% relative to the product peak, limiting the yield loss to ≤2%. This tight thermal window—75–82 °C—is the primary reason the bromo derivative is selected over the iodo variant for multi‑kilogram campaigns, despite the iodo compound’s faster inherent kinetics.

When coupling with sterically demanding ortho‑substituted boronic acids, the bromo derivative requires 3 mol% of Pd(dppf)Cl₂·CH₂Cl₂ and K₃PO₄ granulate to achieve full conversion within 4 h at 80 °C. Under identical conditions, the iodo analogue gives extensive dehalogenation, and the chloro variant returns unreacted starting material. The electron‑withdrawing CF₃ group at C5 accelerates oxidative addition relative to the non‑fluorinated parent, but concomitantly renders the pyrrole ring more prone to base‑induced protodebromination if pH remains below 7. Therefore, the recommended base strength is confined to carbonates or phosphates (pH 8.2–9.0).

When High-Temperature Stability Dictates Purification Strategies

Purification by recrystallization leverages the differential solubility between the bromo compound and its debrominated impurity. A mixture of toluene and n‑heptane (3:1 v/v) at 60 °C fully dissolves the crude, and controlled cooling at a ramp rate of 0.2 °C·min⁻¹ to 5 °C affords a single polymorph (Form A) with a melting endotherm onset of 133 °C and a purity upgrade from 94% to 99.2%. Faster cooling (1 °C·min⁻¹) traps a metastable Form B that shows a lower melting point (125 °C) and a broader DSC peak; Form B reverts to Form A upon annealing at 110 °C for 8 h under vacuum. On large‑scale isolation, the particle size distribution is controlled to a D₉₀ of ≤150 µm through an additional wet‑milling step, as micronized material builds electrostatic charge that causes losses during pneumatic transfer and inconsistent feeding into batch reactors.

Why Pre-Drying Remains Essential for Moisture-Intolerant Cross-Couplings

The compound is moderately hygroscopic; exposure to ambient air at relative humidity above 60% results in water uptake of 0.8–1.2 wt% within 2 h. Residual moisture hydrolyses the nitrile group under the aqueous basic conditions of many coupling protocols, yielding the primary amide that co‑elutes with the desired product on normal‑phase chromatography and can only be separated by reverse‑phase preparative HPLC. In a 3‑kg production run where the substrate was dried only to 0.4% water (K.F.), the amide byproduct reached 15% at the end of the coupling, leading to a 12‑point yield drop compared to dried material (<0.1% water). Consequently, the release specification mandates post‑drying water content below 0.1% achieved by vacuum drying (10 mbar, 40 °C) for at least 12 h. Dried product is packaged in multi‑layer foil bags under argon and opened only under a nitrogen blanket in the synthesis suite.

The presence of the bromo substituent also dictates base compatibility; amine bases such as DBU or triethylamine promote nucleophilic aromatic substitution at C4 when the reaction temperature exceeds 60 °C, replacing bromide with the amine nucleophile. This dehalogenation pathway is not observed with inorganic carbonate bases. Therefore, the recommended base suite is restricted to K₂CO₃, K₃PO₄, or Cs₂CO₃ in anhydrous or low‑water systems. Organic bases like pyridine may be tolerated at temperatures below 40 °C but are generally avoided.

Medicinal chemistry programs targeting ATP‑competitive kinases often exploit the 2‑(4‑chlorophenyl)pyrrole core as a hydrophobic hinge‑binding motif. The nitrile function can act as a hydrogen bond acceptor to the kinase backbone NH of Met793 in EGFR, while the CF₃ group fills a lipophilic pocket. The bromo handle allows rapid diversification to assess SAR. Published data for this specific substitution pattern as a kinase inhibitor scaffold is limited, but analogues show IC₅₀ values in the 100–500 nM range against several kinases when coupled with appropriate amide or sulfonamide tails. The compound further serves as a key building block in the synthesis of fluorinated tricyclic scaffolds, where sequential Suzuki–Miyaura coupling and nitrile reduction/hydrolysis install a carboxylic acid anchor for peptide conjugation. In such sequences, the 4‑bromo substituent provides chemoselectivity over the 2‑(4‑chlorophenyl) C–Cl bond, which remains inert under common catalytic conditions up to 120 °C.

HS Code	814950
Chemical Formula	C12H4BrClF3N2
Molecular Weight	351.525
Appearance	Solid (likely)
Solubility	Solubility characteristics depend on solvent, generally low in water
Logp	High lipophilicity due to halogen and trifluoromethyl groups
Stability	Stable under normal conditions, but may react with strong oxidizing or reducing agents

Packing	100g of 4 - Bromo - 2 - (4 - chlorophenyl)-5 - (trifluoromethyl)-1H - pyrrole - 3 - carbonitrile in sealed chemical vial.
Shipping	The chemical "1H - Pyrrole - 3 - Carbonitrile, 4 - Bromo - 2 - (4 - Chlorophenyl)-5 - (Trifluoromethyl)-" will be shipped in accordance with strict hazardous materials regulations. Packaging will ensure safety during transit to prevent any leakage or damage.
Storage	Store "1H - Pyrrole - 3 - Carbonitrile, 4 - Bromo - 2 - (4 - Chlorophenyl)-5 - (Trifluoromethyl)-" in a cool, dry place away from heat sources and ignition sources. Keep it in a tightly sealed container to prevent moisture and air exposure, as these could potentially cause degradation or reaction of the chemical. Store separately from incompatible substances.