1-Methyl-1H-Pyrrole-2-Carboxylate

What Limits Electropolymerization Efficiency When the Ester Serves as a Latent Monomer?

When fabricating poly(1‑methylpyrrole) coatings for neural electrode arrays, the methyl ester of 1‑methylpyrrole‑2‑carboxylic acid is deliberately chosen as a pro‑monomer. Direct electropolymerisation of 1‑methylpyrrole itself proceeds efficiently, but the ester offers a latent strategy: alkaline hydrolysis in the electrolyte solution triggers decarboxylation to generate the active pyrrole monomer in situ, enabling control over nucleation density on microfabricated platinum sites. The practical limitation arises from incomplete conversion and carbonate by‑product accumulation. A typical bath consists of 0.1 M ester in acetonitrile containing 0.1 M tetrabutylammonium hexafluorophosphate and 0.05 M tetrabutylammonium hydroxide monohydrate as the internal hydrolysis initiator. Purging with argon for 30 min reduces dissolved oxygen to <0.5 ppm (Orbisphere sensor). Cyclic voltammetric growth on a Pt disc electrode (3 mm diameter) between -0.2 V and +1.2 V versus Ag/AgCl at 50 mV/s for 20 cycles yields a coherent film. However, the carbonate anion generated during decarboxylation oxidises at potentials above +0.9 V, introducing parasitic current that lowers the coulombic efficiency to 55–65 %. To circumvent this, a two‑step protocol is adopted: ex‑situ hydrolysis of the ester in 1.0 M KOH/ethanol (50 °C, 2 h) followed by neutralisation with CO₂ and extraction with dichloromethane gives 1‑methylpyrrole with >99.9 % monomer purity after spinning‑band distillation. This monomer is then electropolymerised in a fresh electrolyte of 0.1 M LiClO₄ in propylene carbonate, leading to faradaic efficiency exceeding 95 %. The coated electrodes, intended for chronic intracortical recording, undergo biocompatibility assessment per ISO 10993‑5 and 10993‑10. Extracts prepared in phosphate‑buffered saline at 37 °C for 72 h must show <5 % reduction in L929 fibroblast viability (MTT assay) to pass. In a manufacturing context, the critical control point is the residual ester content in the pre‑hydrolysed monomer, which must be ≤0.1 % (GC‑MS limit) to avoid film delamination during steam sterilisation at 121 °C for 20 min. Film adhesion on polyimide substrates is measured by a cross‑hatch tape test (ASTM D3359‑17) with a requirement of 5B classification.

Can the C2-Carboxylate Route Deliver BODIPY Fluorophores with Quantum Yield Above 0.85?

The 1‑methylpyrrole‑2‑carboxaldehyde, an essential precursor for 8‑methyl‑BODIPY dyes, is conventionally sourced by Vilsmeier‑Haack formylation. A more atom‑economical sequence starting from the methyl ester circumvents the use of phosphorus oxychloride and dimethylformamide on the pyrrole ring itself, instead reducing the ester to the aldehyde with diisobutylaluminum hydride. Under strict inert atmosphere in a double‑walled glass reactor (Schlenk‑type, 1 L), the ester is dissolved in anhydrous toluene (0.3 M) and cooled to –78 °C. DIBAL‑H (1.2 eq, 1.0 M in toluene) is added via a syringe pump at 0.5 mL/min over 3 h to limit local exotherms. After 2 h of equilibration at –78 °C, the reaction is quenched with methanol (2 eq relative to DIBAL‑H) and allowed to warm to 0 °C. Filtration through a pad of Celite and fractional distillation (bp 78–81 °C at 15 mmHg) routinely yields a 92 % isolated yield of 1‑methylpyrrole‑2‑carboxaldehyde, with residual ester below 0.3 %. The aldehyde is immediately protected from light and stored under nitrogen to prevent autoxidation. BODIPY core assembly proceeds in a separate reactor: the aldehyde (1.0 eq) and 2,4‑dimethylpyrrole (2.2 eq) are dissolved in dry dichloromethane at 25 °C, followed by addition of trifluoroacetic acid (0.1 eq) as catalyst. After 12 h, 2,3‑dichloro‑5,6‑dicyano‑1,4‑benzoquinone (DDQ, 1.0 eq) is added for oxidation, and the mixture is stirred for 4 h. The dipyrromethene salt is then treated with triethylamine (3.0 eq) and boron trifluoride diethyl etherate (3.0 eq) at 0 °C for 6 h. The product is purified by silica gel chromatography (cyclohexane/ethyl acetate 9:1) to give deep red fluorescent crystals. Table 1 collects photophysical data for a series of conditions, measured with a calibrated integrating‑sphere system (Hamamatsu Quantaurus‑QY) in accordance with ISO 20473.

Entries 3 and 4 demonstrate that a slight excess of pyrrole coupled with elevated BF₃·OEt₂ pushes the quantum yield above 85 %. All measurements were conducted in aerated toluene at 25 °C with an excitation wavelength of 470 nm. The 8‑methyl‑BODIPY product finds use as a non‑toxic probe in fluorescence immunoassay conjugates, where low interference from serum autofluorescence is critical. Conjugation to proteins is carried out through an activated succinimidyl ester handle derived from the corresponding carboxylic acid obtained by hydrolysis of the original methyl ester with 1.0 M NaOH in MeOH/H₂O (3:1) at 50 °C for 6 h. The bioconjugate must exhibit a degree of labelling between 3 and 5 moles of dye per mole of IgG, as verified by UV‑vis spectrometry (ε ≈ 80 000 M⁻¹cm⁻¹ at λ_max). Storage of the dye powder is prescribed at –20 °C in amber vials under argon; exposure to ambient fluorescent light for more than 8 h attenuates fluorescence intensity by up to 15 %.

When Continuous Flow Reduces Aldehyde Over-Reduction in Fragrance Intermediate Synthesis

1‑Methyl‑2‑acetylpyrrole, a key impact chemical imparting roasted coffee and nutty notes, is commonly manufactured via nucleophilic addition of methylmagnesium chloride to the methyl ester of 1‑methyl‑1H‑pyrrole‑2‑carboxylic acid. Batch‑mode execution in a 20 L glass‑jacketed reactor frequently suffers from double addition to form the tertiary alcohol impurity, 2‑(2‑hydroxypropan‑2‑yl)‑1‑methylpyrrole, which is difficult to separate by distillation and depresses the organoleptic quality, contributing an off‑note characterised as camphoraceous. Switching to a continuous‑flow platform suppresses this pathway by enforcing a residence time of 30 s in a PFA coil reactor (1.0 mm ID, 10 mL internal volume) immersed in a –10 °C ethylene glycol bath. The ester (0.5 M in THF) and MeMgCl (1.05 eq, 3.0 M in THF) are pumped separately at equi‑volumetric flow rates using peristaltic pumps calibrated against a back‑pressure regulator set at 3.5 bar. At the reactor outlet, the stream is quenched in‑line with 2 M HCl (2 eq) and directed to a liquid‑liquid membrane separator to split the organic phase instantly. Concentration and vacuum distillation (bp 88–92 °C at 10 mmHg) yield 1‑methyl‑2‑acetylpyrrole with a typical purity of 99.2 % and tertiary alcohol content of 0.4 %, compared to 6–9 % in a standard batch process. The flavour compound is subsequently diluted to a 1 % solution in triacetin for safety evaluation. Regulatory compliance is demonstrated against the IFRA Standard (category 4) and FEMA GRAS 4716. Usage levels in savoury flavours do not exceed 2 ppm in the finished food product. The process analytical technology (PAT) approach monitors the UV absorbance at 280 nm via an in‑line flow cell; a deviation in absorption above 0.5 AU triggers automated diversion to waste to prevent accumulation of out‑of‑spec material. Stainless steel components in contact with the Grignard reagent must be electropolished to Ra ≤0.4 µm to minimise metal‑catalysed Wurtz coupling.

Solvothermal Preparation of Mixed-Linker Zr-MOFs Incorporating Hydrolysed Pyrrole-2-Carboxylic Acid

Although the methyl ester must be converted into the free carboxylic acid prior to metal coordination, a one‑pot hydrolysis‑crystallisation route has been established to integrate 1‑methyl‑1H‑pyrrole‑2‑carboxylic acid directly into the UiO‑66 framework. A 100 mL PTFE‑lined stainless‑steel autoclave is charged with zirconium tetrachloride (1.0 mmol, 233 mg), terephthalic acid (0.8 mmol), 1‑methylpyrrole‑2‑carboxylic acid (0.2 mmol, freshly prepared by saponification of the ester with 2.0 M NaOH at 70 °C for 4 h followed by acidification to pH 2 with 6 M HCl and extraction), dimethylformamide (15 mL), and glacial acetic acid (2.5 mL) as modulator. The sealed vessel is heated at 120 °C for 24 h, yielding a pale brown microcrystalline powder after centrifugation and washing with DMF and methanol. Powder X‑ray diffraction confirms the fcu topology is retained with minor lattice expansion (peak at 2θ = 7.4° shifts by 0.1° compared to pristine UiO‑66). Nitrogen adsorption at 77 K (Micromeritics ASAP 2020) gives a BET surface area of 1180 m²/g, marginally lower than the 1250 m²/g of the parent framework due to pore occupancy by the methylpyrrole moiety. The pyrrole ring exhibits Brønsted basicity (pK_a of conjugate acid ≈ -0.2) that enhances CO₂ uptake: at 298 K and 1.0 bar, the CO₂ adsorption capacity reaches 2.8 mmol/g, a 22 % increase over unfunctionalised UiO‑66, as measured on a gravimetric sorption analyser (IGA‑002, Hiden Isochema) following outgassing at 150 °C for 12 h. The compound is handled as a fine dust; respiratory protection conforms to EN 149 FFP3 and local exhaust ventilation must achieve 0.5 mg/m³ as the inhalable fraction. The mother liquor, containing residual DMF and zirconium species, is treated with polymeric flocculant and passed through a 0.2 µm membrane filter before waste release compliant with German AbwV Annex 40. The mixed‑linker MOF is being evaluated as a solid‑phase extraction sorbent for heterocyclic amines in aqueous food simulants, with validation per EU Regulation 10/2011 and total migration limits respecting <10 mg/dm².

Bromination-Directed C5-Functionalisation for Phosphorescent OLED Hosts

The electron‑rich nature of 1‑methyl‑1H‑pyrrole‑2‑carboxylate dictates that electrophilic halogenation occurs exclusively at the 5‑position, furnishing a versatile intermediate for cross‑coupling chemistry aimed at deep‑blue host materials. In a typical batch, the methyl ester (100 g, 0.72 mol) is dissolved in anhydrous dimethylformamide (600 mL) in a 2 L round‑bottom flask wrapped in aluminium foil to exclude light. N‑Bromosuccinimide (1.05 eq, 135 g) is added in four equal portions at 0 °C over 1 h, keeping the temperature below 5 °C. After 3 h at 0–5 °C, the reaction is poured onto ice‑water, extracted with ethyl acetate, washed with sodium metabisulfite solution to eliminate excess bromine, and dried. Distillation under reduced pressure (bp 120–123 °C at 10 mmHg) provides methyl 5‑bromo‑1‑methyl‑1H‑pyrrole‑2‑carboxylate in 85 % yield with >99 % regiochemical purity as confirmed by ¹H NMR (absence of the 4‑H signal at δ 6.85 ppm). This bromide undergoes Suzuki‑Miyaura coupling with 4‑(9H‑carbazol‑9‑yl)phenylboronic acid (1.1 eq) using Pd(PPh₃)₄ (0.5 mol%) in a toluene/ethanol/water mixture (4:1:1) containing potassium carbonate (2.5 eq). The biphasic system is refluxed under nitrogen for 16 h, leading to the coupled ester that is subsequently reduced with lithium aluminum hydride (2.0 eq, 1.0 M in THF, 0 °C) to the benzyl alcohol, which serves as the monomer for the host polymer matrix. The final polymeric host, processed by spin‑coating from chlorobenzene (10 mg/mL) onto ITO substrates, yields a phosphorescent organic light‑emitting diode (PhOLED) with an external quantum efficiency of 18.2 % at 500 cd/m² and Commission Internationale de l’Éclairage coordinates of (0.15, 0.16) when doped with fac‑tris(2‑phenylpyridine)iridium as the emitter. Device stability is assessed under constant current at 10 mA/cm²; half‑life LT50 exceeds 1500 h at an initial luminance of 1000 cd/m². The brominated ester must be stored at –20 °C under inert atmosphere; exposure to moisture accelerates de‑esterification, generating hydrobromic acid that autocatalytically degrades the product within 48 h if the relative humidity exceeds 60 %. All synthetic operations involving lithium aluminum hydride and palladium catalysts comply with HSE guidelines on pyrophoric and toxic metals, and the waste stream is treated with iron chloride to precipitate palladium before incineration.