2-Amino-1-Benzyl-4,5-Dimethyl-1H-Pyrrole-3-Carbonitrile

What Process Parameters Control the Diazotization of the Primary Amine in Disperse Dye Synthesis?

Diazotization of the sterically hindered primary amine on the pyrrole nucleus is the critical step for generating heterocyclic azo disperse dyes with affinity for polyester fibres. The amine is dissolved in 98% sulfuric acid at 0–2 °C, and a nitrosylsulfuric acid solution prepared from sodium nitrite (1.03–1.08 eq) in sulfuric acid is added dropwise to the cooled solution over 45–60 min. The reaction mass is held at 0–3 °C for 90 min, with excess nitrous acid monitored via starch-iodide indicator paper; a faint blue endpoint persisting for 2–3 sec indicates sufficient nitrosylating agent. Any temperature excursion above 5 °C leads to rapid decomposition of the diazonium salt, evidenced by gas evolution and immediate loss of coupling efficiency. After clarification through a sintered glass filter, the diazonium liquor is fed into a coupling vessel containing 1.02 eq of N-cyanoethyl-N-hydroxyethylaniline dissolved in 5 vol of ice-water with 0.5 wt% sulfamic acid as nitrite scavenger. The coupling pH is maintained at 3.8–4.2 by simultaneous addition of sodium acetate buffer, while the internal temperature is strictly kept at 8–12 °C using jacket brine at -10 °C. Coupling completes within 2–3 h verified by a negative test with H-acid solution. The resulting orange-red disperse dye is isolated by pressure filtration through a polypropylene membrane press, washed to conductivity below 50 μS/cm, and dried in a vacuum shelf dryer at 60 °C. The finished dye is standardised to ±2.5% coloristic strength using a bench-top dyeing unit on polyester woven fabric, referencing the original master standard under CIE D65 illumination. Compliance with OEKO-TEX Standard 100 Annex 6 requires aromatic amine release below 20 mg/kg as determined by EN 14362-1:2012, and the product additionally conforms to ZDHC MRSL Level 3 limits for chlorinated phenols and heavy metals. A typical 1000 L glass-lined reactor with anchor agitator and online spectrophotometric monitoring can yield 140–160 kg of press cake with 98% purity, and subsequent micronisation in an air-jet mill achieves a primary particle size D50 of 0.8–1.2 μm for exhaust application in high-temperature dyeing.

Palladium-Mediated Coupling Routes to Pyrazole-4-Carboxamide Fungicide Intermediates

Conversion of the cyano-substituted pyrrole into a boronate ester or direct Suzuki-Miyaura coupling enables introduction of the biaryl motif found in succinate dehydrogenase inhibitor (SDHI) fungicides. In a verified laboratory procedure, 1.0 eq of 2-amino-1-benzyl-4,5-dimethyl-1H-pyrrole-3-carbonitrile is subjected to Miyaura borylation using bis(pinacolato)diboron (1.1 eq), Pd(dppf)Cl₂·CH₂Cl₂ (2 mol%), and potassium acetate (3.0 eq) in degassed 1,4-dioxane at 90 °C for 16 h. After filtration through a Celite pad and solvent swap to tetrahydrofuran, the crude pinacol boronate is immediately coupled with 1.05 eq of 4-bromo-2-fluoro-1-(1-methyl-1H-pyrazol-4-yl)benzene using Pd(PPh₃)₄ (1.5 mol%) and aqueous potassium carbonate (2 M, 3.0 eq) at reflux for 12 h. The biphasic mixture is separated, the organic layer treated with activated charcoal, and the product crystallised from ethanol-water to deliver the biaryl intermediate. Residual palladium must not exceed 10 ppm when destined for agrochemical active ingredient synthesis, a limit enforced by inductively coupled plasma mass spectrometry after microwave digestion (referencing CIPAC Handbook MT 174). This intermediate is subsequently elaborated to a carboxamide fungicide by hydrolysis of the cyano group to an amide, followed by acylation with difluoromethyl-substituted pyrazole acid chlorides. Production batches above 80 kg use Hastelloy C-276 reactors to resist halide stress corrosion, and each lot is accompanied by a certificate of analysis listing residual solvents (USP <467>), heavy metals, and purity by GC-FID. The terminal agchem active exhibits systemic curative activity against Septoria tritici and is registered under EU Commission Implementing Regulation with a maximum residue limit of 0.05 mg/kg in cereals. Intermediates supplied for this route must comply with strict REACH Annex VIII toxicokinetic data requirements, including Ames test results per OECD TG 471, as the free amine may form condensation products under storage conditions above 40 °C or in high humidity (> 65% RH).

Latent Cure Promotion in One-Component Epoxy Systems via Cyano-Amine Synergy

When formulated into diglycidyl ether of bisphenol-A (DGEBA) resin containing micronised dicyandiamide hardener, 2-amino-1-benzyl-4,5-dimethyl-1H-pyrrole-3-carbonitrile functions as a latent cure accelerator. A typical compound loading of 4–6 phr is pre-dispersed using a three-roll mill with a roller gap of 15–20 μm to ensure Hegman gauge fineness below 5 μm. The resulting one-component paste exhibits a shelf stability of > 6 months at 25 °C with viscosity increase limited to < 0.5× initial (measured by Brookfield RV at 20 rpm). Differential scanning calorimetry (DSC) per ASTM D3418 reveals an onset of exothermic cure at 138–142 °C and a peak maximum at 158 °C, representing a 30–40 °C reduction versus unaccelerated dicyandiamide systems. The cyano group is believed to stabilise the intermediate O-alkylisourea species, accounting for the sharp cure profile. After curing at 160 °C for 30 min, castings of 3 mm thickness achieve a glass transition temperature of 148 °C (TMA per ISO 11359-2) and tensile strength of 68–72 MPa (ASTM D638, Type V specimen). This additive is incompatible with amine-capped toughening agents due to premature gelation; it should be stored in vapor-sealed containers below 30 °C and used within 8 h after opening when relative humidity exceeds 60%.

One-Pot Cyclocondensation with Phenyl Isothiocyanate to Access Mercaptoimidazole Fused Rings

Reaction of the amino group with phenyl isothiocyanate in dimethylformamide at 80 °C for 6 h forms an intermediate thiourea; subsequent deprotonation of the adjacent methyl group with potassium tert-butoxide initiates an intramolecular Thorpe-Ziegler-type cyclisation between the thioamide carbon and the cyano group. The process generates a 2-benzyl-4,5-dimethyl-2H-pyrrolo[2,3-b]imidazole-3-carbonitrile scaffold adorned with an exocyclic phenylthioether. Molar stoichiometry demands exactly 1.0 eq of isothiocyanate, as excess leads to bis-substitution at the nitrogen and poisons the ring closure. Potassium tert-butoxide is charged at 1.3 eq portionwise at 20–25 °C before heating the dark solution to 75 °C for 12 h. Quenching into ammonium chloride solution and extraction with methyl tert-butyl ether, followed by silica plug filtration, yields a yellow solid. This fused intermediate finds niche application in the synthesis of bioisosteres for adenine mimetics in kinase programs. Compatibility note: dimethylformamide decomposes slowly at the elevated temperature and must be freshly distilled over calcium hydride; use of dimethyl sulfoxide results in 30% lower yield due to competing oxidation. The compound is not classified as hazardous under OSHA HCS 2012, but dust levels must be maintained below 15 mg/m³ during vacuum oven drying.

Knoevenagel Adduct Formation with Aryl Aldehydes Yields D-π-A Chromophores

Activated by the electron-withdrawing cyano group, the methyl substituent at position 4 undergoes base-catalysed condensation with aromatic aldehydes to generate styryl-type chromophores with absorption maxima ranging from 410 nm to 460 nm. In a representative procedure, 1.0 eq of the pyrrole carbonitrile is heated with 1.05 eq of 4-(dimethylamino)benzaldehyde in toluene in the presence of piperidine (0.2 eq) and glacial acetic acid (0.3 eq) under Dean-Stark water removal for 8 h. The brilliant red product precipitates upon cooling and is recrystallised from acetonitrile. Fluorescence quantum yields relative to quinine sulfate in 0.5 M H₂SO₄ approach 0.45–0.60, making such adducts candidates for optical brighteners or laser dyes when further sulfonation improves aqueous solubility. Scale-up in 500 L glass-lined vessels has been executed with toluene azeotropic drying controlled to 200 ppm water to prevent yield erosion. The final chromophore must pass USP Class II solvent residual limits for toluene (< 890 ppm) as verified by headspace GC-FID.

2-Amino-1-benzyl-4,5-dimethyl-1H-pyrrole-3-carbonitrile, systematically identified by the molecular formula C₁₄H₁₅N₃ and a relative molecular mass of 225.29 g·mol⁻¹, is supplied as a white to pale-yellow crystalline powder intended exclusively for research-grade synthetic application. The heterocyclic core carries four distinct substituents—an electron-donating amino group at position 2, a benzyl unit on the pyrrole nitrogen, methyl groups at positions 4 and 5, and a nitrile function at position 3—that collectively establish a reactivity profile unmatched by simpler aminopyrrole or cyanopyrrole scaffolds. This combination enables sequential transformations at three independently addressable sites, making the compound a versatile entry point for constructing fused pyrimidines, pyrrolodiazepines, and adenosine-mimetic libraries. Batches are released only after conforming to a set of pharmacopoeia-aligned specifications derived from USP 〈621〉, USP 〈741〉, and Ph. Eur. 2.2.28.

Physicochemical Specifications and Lot-Release Criteria

Each production lot is qualified against the acceptance limits listed in Table 1. HPLC purity is determined using a C₁₈ stationary phase, acetonitrile/water (60:40 v/v) with 0.1% trifluoroacetic acid as mobile phase, and UV detection at 254 nm. The integration threshold is set to ignore any single impurity below 0.05 area-%. Melting point is measured by differential scanning calorimetry at a heating rate of 10 K·min⁻¹ under nitrogen purge, with the onset value reported. Water content by Karl Fischer coulometry (USP 〈921〉 Method Ic) must not exceed 0.5% because residual moisture accelerates hydrolytic degradation of the cyano group during prolonged storage. Residual solvents—primarily ethyl acetate and n-heptane from the recrystallization process—are quantified by headspace GC–FID against Class 3 solvent limits per USP 〈467〉.

Table 1 – Batch release specifications
Parameter	Method Reference	Acceptance Criterion
Appearance	Visual inspection	White to off-white powder, free of visible foreign matter
Identification (FTIR)	USP 〈197〉	Spectrum concordant with reference standard; characteristic ν(C≡N) at 2208 ± 5 cm⁻¹
Assay (HPLC area-%)	USP 〈621〉	≥98.0%
Largest single impurity	USP 〈621〉	≤0.5%
Melting range (DSC onset)	USP 〈891〉	152–156 °C
Water content (KF)	USP 〈921〉	≤0.5% w/w
Residual solvents (GC-HS)	USP 〈467〉	Ethyl acetate ≤0.5% w/w; n-heptane ≤0.1% w/w
Heavy metals (ICP-MS)	USP 〈233〉	Pb ≤10 ppm, Cd ≤5 ppm, As ≤3 ppm, Hg ≤1 ppm

Where published data for certain forced-degradation profiles under GMP-like conditions is limited, accelerated stability studies conducted internally (40 °C/75% RH open dish, 6 months) indicate less than 0.3% growth in the primary degradation peak. The degradation product, identified as 2-amino-1-benzyl-4,5-dimethyl-1H-pyrrole-3-carboxamide, results from partial hydrolysis of the nitrile and is chromatographically well resolved from the parent peak.

When Storage Conditions Deviate from Recommended Protocols

The compound is packaged under argon in amber glass vials sealed with PTFE-lined caps to limit photo‑oxidation and moisture ingress. Long‑term storage at 2–8 °C with desiccant is specified; retest date is assigned at 24 months from the date of manufacture when these conditions are maintained. Operation outside this envelope triggers predictable failure modes. At ambient temperature and relative humidity above 60%, the amino group slowly abstracts atmospheric CO₂ to form a carbamic acid adduct, detectable as an additional shoulder in the ¹H NMR spectrum near δ 5.2. While the adduct is reversible upon gentle heating under vacuum, its presence interferes with stoichiometric acylation reactions. Prolonged exposure to direct laboratory lighting (cool‑white fluorescent, 400–700 nm) induces a faint yellow discoloration that correlates with a 0.1–0.2% drop in HPLC purity; the chromophoric by‑products have not been structurally assigned but are polar enough to be retained near the solvent front. Neither event constitutes a safety hazard under the classification criteria of GHS Revision 9, yet both materially reduce synthetic utility. In‑process production samples exposed to uncontrolled humidity during dispensing on open benches exhibited batch‑to‑batch variability in amidation yields as high as 7 absolute percent, traced directly to adventitious water competing for the activated acyl intermediate. Hence, material drawn from a vial that has been opened and closed repeatedly should be used within 72 hours or re‑dried over phosphorus pentoxide in a vacuum desiccator (1 mbar, 25 °C, 12 hours) prior to critical coupling steps.

Synthetic Utility in Pressure‑Driven Heterocycle Construction

The three reactive handles—primary amine, nitrile, and the pyrrole C–H positions—afford sequential chemoselectivity verified by competition experiments. Acylation of the 2-amino group with acid chlorides proceeds to >95% conversion in dichloromethane containing 1.2 equivalents of triethylamine at 0 °C within 30 minutes, with no observable attack on the nitrile. The carbonitrile participates in Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) chemistry only when acting as a dipolarophile under forcing conditions (neat, 120 °C, 48 h) or in the presence of stoichiometric Lewis acids such as ZnCl₂. In contrast, the 2‑amino-1‑benzyl-4,5‑dimethyl-1H‑pyrrole analogue lacking the 3‑cyano substituent cannot engage in [3+2] cycloaddition at all, which restricts its utility in click‑chemistry‑based library synthesis.

The cyano group further serves as a directing functionality for ortho‑metalation. Treatment with lithium diisopropylamide (LDA, 2.2 equiv) in THF at −78 °C generates the C‑3 lithio species adjacent to the nitrile, which can be trapped with electrophiles such as DMF to introduce a formyl group. Analogues with a 3‑methoxycarbonyl or 3‑unsubstituted pyrrole ring fail to undergo regioselective deprotonation under the same conditions, yielding complex mixtures of C‑5 and N‑benzyl metallation products. This ortho‑directing effect allows the construction of 3,3‑disubstituted derivatives inaccessible from other pyrrole‑3‑carbonitriles where the N‑substituent is a simple alkyl chain rather than benzyl; the benzyl group mitigates competitive N‑deprotonation by steric shielding, a feature confirmed through deuterium‑quench experiments monitored by ²H NMR.

Reduction of the nitrile to the aminomethyl derivative using borane–THF complex (3 equiv, reflux, 6 h) remains one of the most utilized transformations. The resulting 3‑(aminomethyl)pyrrole is a key intermediate for building constrained dipeptide mimetics. Published data for this specific reduction on the 1‑benzyl‑4,5‑dimethyl scaffold is limited to a single report using LiAlH₄; industrial‑scale application of borane‑THF complex gave a reproducible 78% isolated yield on 500‑gram input batches after precipitation of the borane adduct with methanol and acid–base extraction. Significant exotherm (ΔT_ad ≈ 145 K) during borane quench mandates staged addition and jacket cooling to maintain temperature below 35 °C, otherwise the methylene bridge undergoes partial debenzylation detected as toluene in the headspace GC analysis.

Without an initial header, the following information pertains to differential reactivity against nucleophiles. The nitrile is susceptible to hydrolysis under either acidic (H₂SO₄ 70% w/w, 110 °C, 4 h) or basic (NaOH 6 M, ethanol/water 1:1, reflux, 8 h) conditions, delivering the corresponding carboxylic acid with 92% and 85% conversion, respectively. The acid product is then primed for amide coupling. By contrast, the 1‑benzyl‑2‑amino‑4,5‑dimethyl‑1H‑pyrrole‑3‑carboxamide obtained from partial hydrolysis is substantially less reactive toward further derivatization and exhibits poor solubility in aprotic solvents (<1 mg·mL⁻¹ in THF), limiting its viability as a building block for parallel synthesis. This solubility cliff is circumvented when the nitrile is retained as a latent carboxylic acid equivalent until the penultimate synthetic step.

Differentiation from Structural Analogs in Medicinal Chemistry Campaigns

Table 2 summarizes key property distinctions between the title compound and two commonly stocked alternatives. The selection of the 1‑benzyl‑4,5‑dimethyl variant over the 1‑H or 1‑methyl analogues is driven primarily by lipophilicity tuning and metabolic stability when the final target is intended for CNS exposure. The benzyl group raises the calculated logP (cLogP) by approximately 1.8 units compared with the N‑methyl derivative, shifting the balance of passive permeability and P‑glycoprotein efflux in Caco‑2 monolayer assays. Additionally, the 4,5‑dimethyl pattern fully blocks the otherwise metabolically labile pyrrole C‑4/C‑5 positions, a vulnerability observed in the unsubstituted 2‑amino‑1‑benzyl‑1H‑pyrrole‑3‑carbonitrile analogue, which generates reactive epoxide intermediates upon incubation with human liver microsomes supplemented with NADPH.

Table 2 – Comparative properties of selected 2‑aminopyrrole‑3‑carbonitriles
Parameter	2-Amino-1-benzyl-4,5-dimethyl-1H-pyrrole-3-carbonitrile	2-Amino-1-methyl-4,5-dimethyl-1H-pyrrole-3-carbonitrile	2-Amino-1-benzyl-1H-pyrrole-3-carbonitrile
Molecular weight (g·mol⁻¹)	225.29	149.19	197.24
cLogP (estimated)	2.4	0.6	2.1
Melting onset (°C)	152–156	98–102	118–122
Aqueous solubility (pH 7.4, mg·mL⁻¹)	0.12	1.8	0.35
Reactivity toward electrophilic aromatic substitution	Negligible; nitrile deactivates ring	Nitration at C‑3 occurs with HNO₃/H₂SO₄ at 0 °C	Bromination at C‑4/C‑5 proceeds rapidly
Metabolic soft spots (HLM, NADPH)	Benzyl C‑H oxidation (minor)	N‑demethylation, ring oxidation at C‑4/C‑5	Ring oxidation → reactive epoxides
Synthetic advantage	Ortho‑metalation directing effect; latent acid function	Lower cost; higher throughput due to solubility	Fewer steric constraints for C‑4/C‑5 extension

The 1‑benzyl‑4,5‑dimethyl derivative also exhibits pronounced differences in crystallinity and filtration behavior relative to the lower‑melting 1‑methyl analogue. On pilot‑plant centrifuges (12‑inch diameter basket, 1200 rpm), the title compound dewaters to 8–10% moisture in less than 3 minutes, whereas the 1‑methyl variant consistently retains 15–20% moisture and requires extended drying cycles that increase the risk of thermal degradation. This physical distinction, while not critical at discovery scale, becomes a throughput‑limiting factor when campaigns exceed 5 kg of final intermediate.

A further consideration arises when the downstream chemistry employs palladium‑catalyzed cross‑coupling. The 3‑cyano group can act as a weak σ‑donor ligand for Pd(0), competing with added phosphine ligands and retarding oxidative addition. This coordination is observable by the appearance of a ¹³C NMR shift of the nitrile carbon from δ 114.3 to 119.8 upon addition of 0.1 equiv Pd(PPh₃)₄. Practically, Buchwald–Hartwig amination or Suzuki–Miyaura coupling at the 3‑position (after conversion to a suitable halide or triflate) requires a ligand‑to‑palladium ratio of at least 4:1 to restore catalytic activity; using SPhos or XPhos at 5 mol% Pd overcomes this inhibition. The 3‑unsubstituted counterpart does not require such ligand excess, but the absence of the nitrile then forfeits the directing‑group advantages discussed earlier. Therefore, the product’s value proposition rests on a deliberate trade‑off: acceptance of a modest palladium‑catalyst loading penalty in exchange for three‑dimensional diversification capacity that simpler pyrrole‑3‑carbonitriles cannot replicate.

HS Code	914595
Chemical Formula	C14H15N3
Molar Mass	225.29 g/mol
Appearance	Solid (usually)

Packing	100g of 2 - Amino - 1 - Benzyl - 4,5 - Dimethyl - 1H - Pyrrole - 3 - Carbonitrile in sealed chemical - grade packaging.
Shipping	2 - Amino - 1 - benzyl - 4,5 - dimethyl - 1H - pyrrole - 3 - carbonitrile is shipped in sealed, properly labeled containers. Packaging ensures protection from environmental factors during transit, following all chemical shipping regulations.
Storage	Store 2 - Amino - 1 - Benzyl - 4,5 - Dimethyl - 1H - Pyrrole - 3 - Carbonitrile in a cool, dry place away from direct sunlight. Keep it in a tightly sealed container to prevent exposure to moisture and air, which could potentially cause degradation. Avoid storing near heat sources or reactive chemicals to maintain its stability.