1-Methyl-2-(2-Nitroethenyl)-Pyrrole

When hydrogenating the exocyclic nitroethenyl group en route to 2-(2-aminoethyl)-1-methylpyrrole, a critical pharmacophoric fragment for a class of selective 5-HT_1B/1D receptor modulators under investigation for acute migraine therapy, the substrate concentration in methanol must not exceed 0.35 M at a catalyst loading of 5% w/w Raney Ni slurry (moisture-free, type A-7063, activated by pre-washing with deionised water followed by absolute ethanol). Batch hydrogenation is conducted in a 500 mL Hastelloy C-276 stirred autoclave fitted with a hollow-shaft gas-inducing impeller; hydrogen uptake is monitored via a Brooks SLA5850 mass flow controller. A two-stage pressure profile is employed: initial pressurisation to 1.0 bar(g) at 25 °C until 60% of the theoretical uptake is recorded, followed by a ramp to 3.0 bar(g) and 38 °C for endpoint completion, typically within 110–140 min. Termination is triggered by a real-time in-line ReactIR 15 probe monitoring attenuation of the 1520 cm⁻¹ asymmetric NO₂ stretch to a signal-to-noise ratio below 3:1. Failure to maintain dissolved hydrogen above 0.003 mol/L during the ramp phase induces accumulation of the hydroxylamine intermediate, which subsequently forms a mutagenic bis-alkylated dimer exceeding the 1.5 µg/day threshold of toxicological concern (TTC) as defined in ICH M7(R2) for an exposure duration of 1–12 months. Post-reaction, the catalyst is removed by inline depth filtration through a 0.2 µm polypropylene filter capsule, and the filtrate is acidified with HCl gas to pH 2.8 to precipitate the amine hydrochloride. Recrystallisation from isopropanol/water (4:1 v/v) yields a solid of 99.4% purity by HPLC (Ascentis® C18, 150 × 4.6 mm, 5 µm, 220 nm). The final drug substance manufactured from this intermediate must be controlled for residual 1-methyl-2-(2-nitrovinyl)pyrrole as a Class 2 mutagenic impurity per ICH M7, with an acceptable intake limit derived from a TD₅₀ of 0.042 mg/kg/day in rodent models, requiring a LC-MS/MS method with a LOQ of 0.15 ppm.

If the chromophore is poled at 85 °C under 60 V/µm in PMMA, the electro-optic coefficient r₃₃ reaches 12 pm/V at 1550 nm

1-Methyl-2-(2-nitrovinyl)pyrrole functions as a compact push-pull chromophore wherein the N-methylpyrrole donor and nitro acceptor are linked by a short π-conjugated ethenyl bridge. When dispersed as a guest dopant in poly(methyl methacrylate) (PMMA, M_w ~ 120 000 Da, Tg 105 °C) at 20 wt%, the binary blend is spin-cast from cyclopentanone onto an ITO-coated glass substrate pre-patterned with a 200 nm gold bottom electrode. Film thickness is regulated at 2.8 ± 0.2 µm measured by stylus profilometry (ISO 4287:1997). Contact poling is executed using a corona discharge needle at 6 kV with a grid bias to maintain a constant poling field of 60 V/µm across the film, while the substrate stage is held at 85 °C for 30 min, after which the heater is deactivated and the field maintained while cooling to 25 °C at 2 °C/min. The resulting electro-optic activity is characterised by a modified Teng-Man reflection interferometer (IEEE P1521) at 1550 nm, yielding r₃₃ values tabulated below. The chromophore population must be homogenously distributed; local aggregation detected by UV-vis microscopy as a red-shift of the charge-transfer band beyond 460 nm triggers domain scattering losses. Thermal stability of the dipole orientation is probed by a ramped depolarisation experiment at 10 °C/min from 40 °C to 120 °C; the orientational decay half-life at 85 °C exceeds 600 h. For telecom-grade reliability testing (Telcordia GR-468-CORE, damp heat 85 °C/85% RH), the electro-optic coefficient degrades by less than 15% after 2000 h when a 50 nm SiO₂ barrier layer is deposited by plasma-enhanced CVD over the poled stack.

Electro-optic performance and glass transition of PMMA-based guest-host films at varying chromophore loading (poling field fixed at 60 V/µm, 1550 nm).

At 25 wt%, a marked plasticisation depresses T_g below the practical poling window and increases scattering, causing r₃₃ to plateau despite higher chromophore concentration. Published data for this specific configuration in packaged Mach-Zehnder modulators is limited; however, the 20 wt% system demonstrates a figure of merit (n³r₃₃) of 540 pm/V, competitive with Chromophore CLD-1-based composites.

Methine dye synthesis via active methylene condensation

Condensation of 1-methyl-2-(2-nitrovinyl)pyrrole with malononitrile at a 1:1.05 molar ratio in refluxing ethanol containing 2 mol% piperidine as base catalyst yields a deep red methine dye, systematically named 2-[2-(1-methylpyrrol-2-yl)vinyl]-1,1,3,3-tetracyanopropene when a subsequent Knoevenagel cascade is suppressed by maintaining the temperature strictly at 78 °C and a reaction time of 45 min. The crude product is purified by column chromatography (silica gel 60, 230–400 mesh, dichloromethane/ethyl acetate 95:5) and obtained as dark red crystals in 73% yield, mp 168–170 °C. A 0.5 mM solution in acetonitrile exhibits λ_max at 487 nm with a molar extinction coefficient (log ε) of 4.48. When adsorbed onto a 10 µm transparent TiO₂ photoanode (P25, doctor-bladed on FTO glass, sintered at 450 °C for 30 min) via a 16 h immersion in a 0.3 mM dye solution, the sensitised electrode assembled with an iodide/triiodide redox electrolyte (0.6 M BMII, 0.03 M I₂, 0.5 M 4-tert-butylpyridine in acetonitrile/valeronitrile 85:15) and a platinum counter electrode produces a short-circuit photocurrent density (J_sc) of 8.7 mA/cm², an open-circuit voltage (V_oc) of 0.64 V, and a fill factor of 0.68 under AM 1.5G illumination (100 mW/cm², Wacom WXS-155S-L2 solar simulator, calibrated to JIS C 8912). Power conversion efficiency is 3.8%, significantly lower than N719 controls (7.2%) due to narrower absorption bandwidth; electron injection yield estimated by nanosecond transient absorption at 780 nm is 0.72. Long-term light soaking per ISO 10677:2011 reveals 20% efficiency loss after 1000 h owing to dye desorption at the TiO₂ interface, mitigated partially by co-adsorption of chenodeoxycholic acid at 1 mM.

In the fabrication of dual-layer organic photoreceptor drums for high-speed laser printers, a charge generation layer (CGL) comprising a 1:1 charge transfer complex of 1-methyl-2-(2-nitrovinyl)pyrrole and 2,4,7-trinitrofluorenone (TNF) dispersed in a poly(4,4′-cyclohexylidene bisphenol) carbonate (PCZ, M_w 45 000 Da) binder at a pigment:binder ratio of 40:60 by weight is formulated through 72 h of ball milling in a Fritsch Pulverisette 5 using 2 mm yttria-stabilised zirconia beads at 200 rpm. The resulting dispersion, filtered through a 1.0 µm absolute-rated nylon membrane, is dip-coated onto a 30 mm diameter aluminium drum substrate pre-coated with a 0.5 µm undercoat layer of alcohol-soluble nylon 6/66/12 terpolymer (Amilan CM8000). A wet film thickness of 18 µm yields a dry CGL of 0.25 ± 0.03 µm after forced-air drying at 80 °C. The charge transport layer consists of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) in the same polycarbonate (TPD:PCZ 50:50) deposited at 18 µm dry thickness. Electrostatic cycling fatigue (ASTM F-929-85, reapproved 2002) conducted with a charge corona of −5.8 kV and erase illumination at 780 nm (LED, 1.0 µJ/cm²) demonstrates an initial dark decay of 12 V/s and a residual potential below 20 V after 10 000 cycles, meeting the drum specification for printing speeds up to 45 ppm. Sensitivity at 780 nm is measured as 0.45 cm²/µJ (half-decay exposure). The complex is hygroscopic; processing rooms require 20 ± 5% RH to prevent binder clouding. This photoreceptor configuration has been validated for compliance with RoHS (2011/65/EU) due to the absence of cadmium sulfide-based CGLs.

What happens when thiol-functionalised 4-arm PEG reacts with the nitrovinyl moiety?

The terminal β-nitrostyrene-like double bond in 1-methyl-2-(2-nitrovinyl)pyrrole undergoes rapid Michael-type addition with thiols in aqueous buffered media, enabling formation of covalent thioether crosslinks without requiring a photoinitiator or metal catalyst. In a typical hydrogel precursor solution, the nitrovinyl compound is first dissolved in a 5% v/v DMSO/phosphate-buffered saline (PBS, pH 7.4) co-solvent at a concentration of 80 mM, then combined with an equimolar solution (per thiol group) of 4-arm PEG-thiol (Mw 10 kDa, end-group functionality >95%, JenKem Technology USA) under nitrogen purge. Gelation kinetics are tracked by dynamic oscillatory time-sweep rheology using a TA Instruments DHR-2 controlled-stress rheometer equipped with a 20 mm parallel plate geometry, a 0.5 mm gap, and a frequency of 1 Hz at 0.5% strain at 37 °C. The gel point, defined as the crossover of storage modulus G′ and loss modulus G″, shifts from 18 ± 2 min at pH 7.4 and a 1:1 thiol:ene stoichiometry to 5 ± 1 min at pH 8.0, consistent with base-catalysed thiolate formation. At a 1.2:1 thiol:ene molar excess, the equilibrium swelling ratio in PBS at 37 °C is 14.2 ± 1.1, and the compressive modulus (confined compression, 10%/min ramp) is 28 kPa, suitable for soft tissue sealant applications per ISO 10993-5:2009 cytotoxicity testing (L929 fibroblast extraction method, cell viability >70% at 24 h). Residual unreacted nitrovinyl groups can act as Michael acceptors for serum albumin in situ, which must be monitored by Ellman's assay of free thiols remaining in the network; after 4 h gelation, less than 5% of initial thiols are detectable. Shelf-life studies of the lyophilised nitrovinyl-PEG precursor stored under argon at −20 °C indicate 90% retention of thiol coupling activity over 12 months as quantified by ¹H NMR integration of the vinyl proton at δ 7.05 ppm (DMSO-d₆).

Effects of formulation parameters on gelation point and equilibrium mechanical properties of a PEG-thiol/nitrovinyl hydrogel system (all tests at 37 °C, 1:1 stoichiometry unless noted).

Sterilisation of the pre-gel solution by filtration through a 0.22 µm PVDF syringe filter prior to application is mandatory; ethylene oxide treatment post-gelation leads to nitro group reduction and crosslink cleavage, reducing G′ by 85% and rendering the material non-viable for implant use.

Certified reference material for HPLC-MS impurity profiling

1-Methyl-2-(2-nitrovinyl)pyrrole is supplied as a quantitative ¹H qNMR-certified reference standard (99.82 ± 0.15% purity, traceable to NIST SRM 350b benzoic acid) for use in the development and validation of HPLC-UV/MS methods targeting potential genotoxic impurities (PGIs) in pyrrole-containing active pharmaceutical ingredients. The standard is stored in sealed amber ampoules under argon at 2–8 °C and reconstituted in acetonitrile at 1.0 mg/mL for preparation of calibration curves across the range 0.05–5.0 µg/mL (LOQ 0.03 µg/mL on a Waters ACQUITY UPLC H-Class with a Cortecs C18+ column (2.1 × 100 mm, 1.6 µm), MRM transition m/z 153.1→106.0). Lot-specific certificates of analysis include chromatographic purity, water content by Karl Fischer (≤0.1%), and residual solvents by headspace GC-FID (meets ICH Q3C Option 2 limits).