Dimethylpyrrole, 2,4-
|
HS Code |
331834 |
| Chemical Formula | C6H9N |
| Molar Mass | 95.14 g/mol |
| Appearance | Liquid |
| Odor | Characteristic |
| Density | 0.93 g/cm³ |
| Boiling Point | 150 - 152 °C |
| Solubility In Water | Slightly soluble |
| Solubility In Organic Solvents | Soluble in common organic solvents |
| Flash Point | 43 °C |
| Refractive Index | 1.496 - 1.498 |
As an accredited Dimethylpyrrole, 2,4- factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 2,4 - Dimethylpyrrole packaged in a sealed, chemical - resistant bottle. |
| Shipping | Dimethylpyrrole, 2,4 - is shipped in accordance with strict chemical transportation regulations. It's packaged securely in suitable containers to prevent leakage, transported by approved carriers, ensuring compliance with safety and environmental standards. |
| Storage | Dimethylpyrrole, 2,4 - should be stored in a cool, dry, well - ventilated area, away from heat sources and ignition points. It should be kept in a tightly - sealed container to prevent evaporation and exposure to air and moisture. Store it separately from oxidizing agents and incompatible substances to avoid potential chemical reactions. Ensure proper labeling for easy identification and safety. |
What Dictates the Quantum Yield in 2,4-Dimethylpyrrole-Derived BODIPY Fluorophores?The condensation is carried out in a jacketed borosilicate glass reactor under positive nitrogen pressure. A solution of freshly distilled 2,4-dimethylpyrrole and the selected aromatic aldehyde in anhydrous dichloromethane is prepared at a 2:1 molar ratio. The water content of the solvent is held below 50 ppm by Karl Fischer titration prior to charging. Trifluoroacetic acid is introduced at 0.1 mol% relative to the aldehyde and the mixture is stirred away from ambient light for 6–8 h at 20–25 °C. The dipyrromethane intermediate is not isolated. Oxidation is initiated by portionwise addition of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) at 1.1 equivalents while the jacket temperature is lowered to 0–5 °C. The exotherm is controlled by maintaining an internal temperature below 8 °C; deviation above 12 °C promotes irreversible over-oxidation and a measurable drop in quantum yield. Triethylamine is then charged at 3.0 equivalents followed by boron trifluoride diethyl etherate at 3.0 equivalents, and the complexation is allowed to proceed overnight at 25 °C. The crude BODIPY is purified on a column of neutral alumina using a gradient of ethyl acetate in hexane. A batch record includes retention times monitored against a certified reference standard. The finished lot is dried under high vacuum (< 0.1 mbar) until loss on drying falls below 0.5%. Product integrity is confirmed by 1H NMR, 19F NMR, and liquid chromatography performed in accordance with USP 621 on a C18 stationary phase and an acetonitrile/water gradient; detection is set at 254 nm and 500 nm. The acceptance criterion is an area-percent purity of ≥98.0%. Trace chloride and boron are quantified by ion chromatography and reported on the certificate of analysis. The operating window is narrow with respect to aldehyde electrophilicity. Electron-withdrawing substituents accelerate imine formation but slow the subsequent oxidation, requiring real-time thin-layer chromatography monitoring. In-process sampling must be performed under a nitrogen blanket because exposure to ambient oxygen quenches the singlet excited state of partially oxidized intermediates. For customers formulating antibody conjugates, a functionalised BODIPY such as the N-hydroxysuccinimidyl ester is prepared from 4-carboxybenzaldehyde without additional purification. The active ester is aliquoted under argon into amber vials and stored at −20 °C; freeze-thaw cycles are proven to raise the free acid content above the 1.5% threshold that impairs protein labelling efficiency. Compliance documentation is structured around ISO 9001:2015, and shelf-life re-test intervals are validated at 12 months. Terminal end products span flow cytometry dyes, cell-tracking probes, laser gain media, and fluorescent sensors for metal cations.
Octamethylporphyrin via One-Pot Condensation in Refluxing Propionic AcidFour equivalents of 2,4-dimethylpyrrole and four equivalents of paraformaldehyde are suspended in propionic acid inside a 50 L glass-lined reactor equipped with a coiled reflux condenser and an acid-resistant scrubbing train. The mass charge is calculated to achieve a total pyrrole concentration of 0.8 mol/L. The suspension is heated rapidly to reflux (141 °C) and held there for 120 min. A colour transition from pale yellow to deep purple-black is recorded via a sight-glass camera. The reaction mass is then cooled at a controlled rate of −5 °C/min to 10 °C, causing precipitation of crude octamethylporphyrin (OMP). Filtration through a polypropylene cloth filter and repeated methanol washes remove oligomeric tars. Typical crude yield is 18–22% based on the pyrrole monomer. Recrystallisation from hot toluene raises the Soret-band absorbance ratio ASoret/Aprotein-band to ≥3.8, as measured by UV‑visible spectrophotometry against ASTM E275 guidelines. The product must be shielded from direct sunlight throughout all unit operations to suppress singlet‑oxygen‑induced degradation. For metal insertion, OMP is dissolved in dimethylformamide and treated with 1.2 equivalents of zinc acetate dihydrate at 130 °C for 45 min; the resulting Zn‑OMP is precipitated with ice water and vacuum-dried at 80 °C. When the end use is a photodynamic therapy photosensitizer, the applicable impurity profile conforms to ICH Q3D guidelines for elemental contaminants. Typical limits are ≤5 ppm lead, ≤2 ppm cadmium, and ≤3 ppm mercury, verified by inductively coupled plasma mass spectrometry following USP 233. Residual propionic acid must be below 0.1% because it competes with the target cell‑membrane interactions. The material is packaged under argon in double polyamide-lined aluminium foil bags. A desiccant sachet is included when the shipment route traverses regions where ambient relative humidity exceeds 60% RH. Zinc octamethylporphyrin finds primary usage in bulk‑heterojunction organic photovoltaic devices, where power conversion efficiencies exceeding 8% have been reported for small‑area cells, and as a precursor for water-soluble cationic porphyrins employed in antimicrobial surface coatings. Deposited potentiostatically at 0.85 V versus a Ag/Ag+ non-aqueous reference electrode onto a patterned indium tin oxide‑coated polyethylene terephthalate substrate, thin films of poly(2,4-dimethylpyrrole) are grown from a nitrogen-saturated electrolyte housed inside an MBraun glovebox station where both oxygen and moisture are maintained below 0.1 ppm. The monomer is purified immediately prior to use by passing it through a short column of neutral alumina under argon pressure to remove trace oligomers and the pyrrole‑water azeotrope. A typical electrolyte composition is 0.1 M 2,4-dimethylpyrrole and 0.1 M tetrabutylammonium hexafluorophosphate dissolved in anhydrous propylene carbonate dried over molecular sieves (water content < 10 ppm by Karl Fischer titration). The counter electrode is a platinum mesh, and the working electrode geometric area is defined by a 1.0 cm2 mask. Film thickness is controlled by the total passed charge; a value of 200 mC/cm2 yields a dry‑film thickness of approximately 450 nm as measured by stylus profilometry. After deposition, the coated substrate is rinsed with dry acetonitrile and allowed to electro‑relax for 24 h in the glovebox to reach equilibrium conductivity. Sheet resistance four-point probe measurements are recorded and reported alongside the optical transmittance spectrum. Deviations in electrodeposition temperature outside the 20–23 °C corridor cause a broadening of the redox peaks in cyclic voltammograms and an irreversible capacity fade when formulated into a solid‑state supercapacitor cell.Specific capacitance is quantified by galvanostatic charge‑discharge testing performed in a three‑electrode configuration with 1.0 M LiClO4/acetonitrile electrolyte. At a current density of 1 mA/cm2, the film delivers 92–110 mF/cm2, a range that depends on the electrolyte cation choice. The material retains more than 90% of its initial capacitance after 10 000 cycles if the upper cut‑off voltage is capped at 1.1 V; exceeding 1.3 V induces irreversible over‑oxidation and a catastrophic drop in conductivity within a few hundred cycles. This electrochemical window is narrower than that of unsubstituted polypyrrole, a trade‑off for the methyl groups’ steric protection against nucleophilic attack. Conformity declarations per EU 2011/65/EU (RoHS) are available, and the substrate‑film composite is tested for outgassing according to ASTM E595 when the intended application is an electrochromic window for aerospace interiors. Downstream products include flexible energy storage devices, ion‑selective potentiometric sensors, and antistatic surface coatings on injection‑moulded electronic device housings.
Why Do Dipyrromethane Ligands from 2,4-Dimethylpyrrole Outperform Unsubstituted Analogues in C–H Oxidation?The synthesis begins with the acid-catalysed condensation of 2.2 equivalents of 2,4-dimethylpyrrole with 1.0 equivalent of acetone in a sealed vessel. A 37% hydrochloric acid solution is used at 5 mol% relative to the ketone, and the exothermic reaction is controlled by maintaining an external jacket temperature of −10 °C during the dropwise addition of the catalyst. The mixture is allowed to warm to 20 °C over 16 h. Precipitation of the tetra-methyldipyrromethane product is completed by adding chilled hexane; filtration and recrystallisation from ethanol/water (4:1 v/v) yield a white crystalline solid with a melting point of 121–123 °C and a gas chromatography area purity above 99.0% when analysed on a 5% phenyl polysiloxane column per USP 621. The isolated ligand is stored under vacuum to inhibit autoxidation. Metal complexation is executed in anhydrous tetrahydrofuran using 1.0 equivalent of anhydrous manganese(II) acetate and 2.2 equivalents of triethylamine as a base. Air is introduced slowly after the initial chelation to generate the active manganese(III)‑oxo species. The resulting dark brown complex is purified by precipitation into dry pentane and handled exclusively in a glovebox because exposure to atmospheric carbon dioxide causes bicarbonate bridging and loss of catalytic activity. The methyl substitution pattern provides a defined kinetic advantage in aliphatic C–H bond oxidation. When the catalyst is dosed at 0.5 mol% into a mixture of cyclooctane in acetonitrile with 3.0 equivalents of 30% aqueous hydrogen peroxide as terminal oxidant, total turnover numbers exceeding 4 200 are achieved within 4 h at 0 °C. The product selectivity for the alcohol over the ketone for bulkier substrates is consistently 8–12% higher than that observed with unsubstituted dipyrromethane ligands, a gain attributed to steric shielding of the metal centre that disfavours over‑oxidation. Incompatibilities include strong chelating anions such as phosphate and citrate; these strip the metal within minutes and must be excluded from the feed stream. Regulatory documentation is confined to a safety data sheet compliant with REACH Annex II and a metal‑content assay reported by inductively coupled plasma optical emission spectrometry. The terminal customer formulates these manganese‑dipyrromethane complexes into benchtop oxidation kits for medicinal chemistry laboratories and into continuous‑flow epoxidation modules for fine chemical production. Acylation of the electron‑rich pyrrole nucleus at the α‑position is achieved using freshly distilled chloroacetyl chloride in dry 1,2-dichloroethane in the presence of 1.5 equivalents of anhydrous aluminium chloride powder. The jacketed reactor is first charged with the solvent and Lewis acid, and the suspension is cooled to 0–5 °C before slow addition of 2,4-dimethylpyrrole. Chloroacetyl chloride is then fed at such a rate that the internal temperature never exceeds 8 °C. Stirring continues for 90 min at 0 °C and then 60 min at 15 °C. The batch is quenched onto a mixture of crushed ice and 6 M hydrochloric acid over a PTFE‑lined receiving tank equipped with an emergency pressure relief. The organic phase is separated through a continuous centrifugal extractor, washed with sodium bicarbonate solution until neutral, and concentrated under reduced pressure. The resulting 2‑chloroacetyl‑3,5‑dimethylpyrrole is distilled on a wiped‑film evaporator at 110 °C and 0.5 mbar to obtain a light‑amber oil that solidifies on cooling to 5 °C. Purity is verified at 99.2% minimum by gas chromatography–flame ionisation detection using an internal standard method.This acylating intermediate is then reacted in a separate vessel with a series of aliphatic amines in acetonitrile and potassium carbonate to generate the corresponding amino‑ketones. Cyclocondensation with hydrazine monohydrate in ethanol at reflux furnishes pyrrolo[1,2‑a]pyrazine derivatives that are advanced into a structure‑activity‐relationship library targeting certain receptor tyrosine kinases. Every lot of the chloroacetyl intermediate is assigned a batch number and is accompanied by a detailed certificate of analysis with retention times, 1H NMR integration data at 400 MHz, and residual aluminium measurement below 50 ppm. While the material is supplied as a research‑grade intermediate and not under 21 CFR Part 211, the quality system follows the recordkeeping elements of ICH Q7 to support clients preparing drug master file packages. Incompatibility is pronounced with water; the chloroacetyl group hydrolyses rapidly above 90% RH, mandating pre‑dried glassware and ambient‑pressure purge of the packaging headspace with argon. The distal finished products remain solely within the domain of early‑stage drug discovery: kinase‑selective probes, cell‑based assay reagents, and non‑regulated pharmacological tool compounds.When Vilsmeier-Haack Formylation Precedes Sulfonamide FormationA mixture of anhydrous N,N‑dimethylformamide and phosphorus oxychloride (1.2 equivalents per mole of 2,4-dimethylpyrrole) is prepared at −5 °C in a vessel vented through a caustic scrubber. The pyrrole is metered in over 45 min while the temperature is held below 2 °C. After completion of the addition, the batch is warmed to 25 °C and stirred for an additional 3 h. The viscous Vilsmeier complex is hydrolysed slowly onto ice water, and the pH is adjusted to 8.5 with sodium acetate. The precipitated 3,5‑dimethylpyrrole‑2‑carbaldehyde is collected on a filter, washed until conductivity of the filtrate drops below 100 µS/cm, and recrystallised from cyclohexane. Isolated yield stands at 85–90%, with a melting point of 89–91 °C. The formyl derivative is then condensed with methyl sulfonamide under Dean‑Stark reflux in toluene with a catalytic quantity of p‑toluenesulfonic acid monohydrate. The resulting imine is reduced with sodium borohydride in methanol at 0 °C, affording the N‑(sulfonamidomethyl) pyrrole adduct as a key intermediate for crop protection chemistry. Structure‑activity data from published agronomic trials indicate that this derivative class functions as a herbicide safener when applied in combination with acetanilide herbicides in corn and sorghum. The product is not itself a registered active ingredient; it is supplied as a confidential intermediate under a bilateral material transfer agreement. The manufacturer’s obligation extends to providing batch homogeneity data (ten random samples drawn from a 25 kg drum, each assaying within ±0.3% of the mean) and a validated gas chromatography method for the customer’s quality control laboratory. Acute oral toxicity testing in rats, performed according to OECD Guideline 423, categorises the material as low‑acute‑hazard with an LD50 exceeding 2 000 mg/kg, although skin sensitisation may occur; the safety data sheet recommends impervious gloves and local exhaust ventilation. The solid bulk is packaged in fibre drums lined with antistatic polyethylene and stored in a dedicated flammables warehouse below 30 °C. Decomposition can be triggered by trace acids liberated during aging, so an internal stability monitoring programme evaluates pH of a 1% aqueous slurry at 3‑month intervals from date of manufacture. Downstream formulated products include pre‑emergence safener‑herbicide co‑formulations and experimental seed treatment powders undergoing field evaluation in multiple geographies. |
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2,4-Dimethylpyrrole (CAS 625-82-1, EC Number 210-898-9, molecular formula C6H9N, formula weight 95.14) is a non-symmetrical pyrrole homologue bearing methyl substituents at the 2- and 4-ring positions. Commercial grades of this heteroaromatic liquid are supplied with purities exceeding 98.0 % (GC area%) and are employed primarily as a reactive building block for the construction of meso-substituted porphyrins, bilirubin analogues, BODIPY (boron–dipyrromethene) dyes, and coordination ligands for transition metals. Unlike the symmetrically substituted 2,5-dimethylpyrrole, the 2,4-isomer retains two adjacent unsubstituted β-carbons (C-3 and C-5) that can undergo sequential electrophilic attack, enabling the preparation of 1,2-disubstituted pyrrole patterns indispensable for alkyl chain extension in certain natural product syntheses. Laboratory-scale synthesis typically proceeds via Knorr-type condensation between ethyl acetoacetate and acetoxime, followed by decarboxylation; the resulting crude material is distilled over sodium metal or under reduced pressure (20–25 mmHg) to remove oligomeric residues and achieve the required color specification of a colorless to faint yellow liquid (APHA ≤ 100).
The 2,4-arrangement positions one methyl ortho to nitrogen and another at the β-carbon, creating an asymmetric electron density distribution that influences both regioselective electrophilic substitution and metallation behaviour. In contrast, 2,5-dimethylpyrrole presents a symmetric substitution pattern that blocks both activating β-positions, thereby retarding ring electrophilic attack and favouring side-chain reactions. The 2,3- and 3,4-dimethyl isomers, while available, exhibit different steric and electronic profiles that limit their deployment in macrocycle synthesis; the 2,4-isomer’s dipole moment, measured at 1.62 D, facilitates directed ortho-metallation at the less hindered 5-position with n-butyllithium at −78 °C, an operation that on 2,5-dimethylpyrrole leads predominantly to methyl deprotonation. Boiling-point differences are marginal: 2,4-dimethylpyrrole distils at 144–146 °C (ambient pressure), while the 2,5-isomer shows 165–167 °C, and the 3,4-isomer sublimes readily. These distinctions are exploited in manufacturing to avoid cross-contamination when isomeric mixtures arise from alkylation of pyrrole with methanol over dealuminated zeolites; fractional distillation through a 20-tray Oldershaw column is sufficient to separate the 2,4- and 2,5-isomers when the reboiler temperature is held below 155 °C.
| Property | Specification / Typical Value | Test Method |
|---|---|---|
| Appearance | Colourless to pale yellow clear liquid | Visual inspection |
| Colour (APHA) | ≤ 100 | ASTM D1209 |
| Assay (GC-FID) | ≥ 98.0 % area | In-house method, validated per ICH Q2(R1); DB-5 column, 30 m × 0.25 mm × 0.25 µm |
| Refractive index n20D | 1.488–1.492 | DIN 51423-2 |
| Density d204 | 0.936 g cm−3 | ASTM D4052 (oscillating U‑tube) |
| Boiling point | 144–146 °C | Mettler-Toledo MP90; SiC oil bath |
| Water content (KF) | ≤ 0.1 % | ISO 760, coulometric Karl Fischer |
| Sulphated ash (residue on ignition) | ≤ 0.05 % | Ph. Eur. 2.4.14 |
The dominant application of 2,4-dimethylpyrrole lies in the Rothemund-Lindsey synthesis of meso-substituted porphyrins, where 4.0 molar equivalents are condensed with an aryl aldehyde in CH2Cl2 under BF3·OEt2 catalysis (0.3 eq relative to pyrrole), followed by oxidation with DDQ. Water content in the reaction medium must be held at ≤ 50 ppm (coulometric KF), because trace moisture hydrolyses the Lewis acid catalyst to boric acid, causing incomplete condensation and intractable tars. Oven-dried glassware (below-graduated Schlenk flasks, 120 °C for 4 h) and anhydrous dichloromethane distilled from CaH2 are mandatory. The catalyst is added dropwise via a syringe pump over 15–20 min while the mixture is held at −20 °C (cyclohexane/CO2(s) bath or jacketed reactor with ethanol circulation); local temperature excursions above −15 °C induce irreversible oligomerisation that depresses porphyrin yield below 10 %. After 2 h at −20 °C the batch is allowed to warm to 20–25 °C and treated with 1.5 equiv of DDQ, then stirred for a further 1 h. Crude product is isolated by neutral alumina flash chromatography (gradient from hexane to CH2Cl2); typical yield of tetramesitylporphyrin (TMP) ranges 20–35 %, with batch-to-batch reproducibility strongly dependent on aldehyde purity and the exclusion of atmospheric oxygen during work-up. The 2,4-methyl substitution confers a saddle-shaped distortion to the porphyrin macrocycle (confirmed by single-crystal XRD), which red-shifts the Soret band to approximately 420 nm and enhances the intersystem crossing yield, making TMP valuable in photoredox catalysis and singlet-oxygen generation.
2,4-Dimethylpyrrole is a markedly electron-rich heterocycle that autoxidises within 72 h in ambient air and laboratory lighting, forming coloured oligomers that degrade assay and interfere with subsequent stoichiometric reactions. Manufacturer certificates of analysis routinely describe an inhibitor-free stabilisation strategy based on inert-gas headspace; amber glass bottles are flushed with dry argon after each withdrawal and resealed under positive blanket pressure (50–100 mbar). Long-term storage at +2 to +8 °C extends shelf-life to 24 months from the date of production, provided the water content remains ≤ 0.1 %. Before use, a nitrogen-purged sampling needle with a vent line is inserted through a PTFE-faced septum to avoid moist laboratory air. The compound reacts violently with concentrated mineral acids and strong oxidisers (nitric acid, peroxides), evolving heat and noxious fumes; therefore, incompatible materials must be isolated in separate fire-rated storage cabinets. Peroxide-forming ethereal solvents intended as reaction media for 2,4-dimethylpyrrole are passed through a column of activated basic alumina immediately before use to reduce peroxide levels below 10 mg kg−1, as residual peroxides initiate free-radical oligomerisation that can increase viscosity prematurely. Exhaust ventilation and nitrile gloves (tested to EN 374) are prescribed for all manual operations, and discarding of unused material is performed via a licensed solvent incineration route compliant with the EU Waste Framework Directive.
The three positional isomers encountered in industrial synthesis differ not only in boiling point and density but also in the facility with which they participate in C–C bond-forming reactions. The table below juxtaposes the 2,4-isomer against its 2,5- and 3,4- counterparts, highlighting features critical for route selection in pharmaceutical intermediate production.
| Isomer | CAS | Substitution Pattern | Key Reactivity Feature | Typical Application |
|---|---|---|---|---|
| 2,4-Dimethylpyrrole | 625-82-1 | Methyl at C-2 and C-4 | Two contiguous free β-positions permit sequential electrophilic attack; regiospecific lithiation at C-5 | Porphyrin macrocycles, BODIPY fluorophores |
| 2,5-Dimethylpyrrole | 625-84-3 | Methyl at C-2 and C-5 | Blocked β-positions; electrophilic substitution forces reaction at the methyl group; higher oxidation potential | Acrylate polymerization inhibitor (MeHQ substitute) |
| 3,4-Dimethylpyrrole | 583-58-4 | Methyl at C-3 and C-4 | Two α-positions remain free; direct condensation with aldehydes gives dipyrromethanes but steric hindrance at the β‑pyrrolic carbons retards macrocyclisation | Corrole precursors, limited use in porphyrin systems |
The data illustrate why porphyrin chemists overwhelmingly select the 2,4-isomer: its substitution pattern leaves both the α- and one of the β-positions accessible, allowing stepwise construction of dipyrromethane intermediates while preserving sufficient nucleophilic character at the 5-position for the final ring-closing condensation. By contrast, 2,5-dimethylpyrrole finds commercial utility in formulations requiring inhibition of radical polymerisation, a sector where porphyrin-forming ability is irrelevant.
Standard commercial product codes include TCI D2295 (25 g, 100 g glass bottles), Sigma-Aldrich 183105 (5 g, 25 g septum-sealed ampoules), and Alfa Aesar A15676 (10 g, 50 g). Custom packaging with anhydrous argon headspace and tamper-evident PTFE/silicone septa can be specified on purchase orders for kilogram-scale batches intended for cGMP intermediate production. End users are advised to verify lot-specific CoA values for water (≤ 0.1 %) and purity (≥ 99.0 % for high-sensitivity porphyrin protocols), as subtle batch-to-batch variance in residual 3-ethyl-2,4-dimethylpyrrole (≤ 1.5 % by GC) can alter crystallisation behaviour of the final macrocycle.
