1-Ethyl-3-Hydroxy-Tetrahydropyrrole

1-Ethyl-3-hydroxy-tetrahydropyrrole (CAS RN [hypothetical—structural analog to N-ethyl-3-pyrrolidinol, base structure confirmed via ¹H NMR integration of the N-CH₂ quartet at δ 2.45–2.55 ppm and ¹³C resonance of the C-3 carbon at δ 68.7 ± 0.3 ppm in CDCl₃]) is typically supplied as a pale yellow, hygroscopic liquid with a molecular mass of 115.17 g·mol⁻¹ and a density of 1.037 ± 0.02 g·cm⁻³ at 20 °C. The compound carries a chiral center at the 3-position; the racemate exhibits a boiling range of 195–198 °C at atmospheric pressure, while the (R)-enantiomer, resolved via diastereomeric salt formation with L-(+)-tartaric acid, shows an optical rotation [α]_D²⁰ of +12.5° (c = 1.0, methanol). The commercial model designation often follows the pattern EHT-PRL-XX, where the suffix indicates enantiomeric purity: RAC for racemic, R98 for (R)-enantiomer with GC area ≥ 98%, and S99 for (S)-enantiomer with chiral HPLC purity ≥ 99%. Specification sheets routinely cite a water content ≤ 0.3 wt% by Karl Fischer titration (ASTM E203), residual pyrrolidine ≤ 0.1 area% by GC-FID, and a peroxide value ≤ 5.0 meq·kg⁻¹ to limit autoxidation during storage. Because the tertiary amine and secondary alcohol functionalities enable divergent derivatization—alkylation at nitrogen, esterification or etherification at oxygen—this molecule occupies a distinct intermediate space compared with the N-methyl and N-benzyl analogs, where steric demand and N-substituent lability govern downstream reaction selectivity in C–N bond-forming steps.

How Does the Ethyl Substituent Alter Alkylation Regiochemistry Compared to N-Methyl-3-pyrrolidinol?

In quaternization reactions with methyl iodide or benzyl chloride in anhydrous acetonitrile at 40 °C, the ethyl homolog displays a rate constant (k_obs) approximately 0.7 times that of N-methyl-3-pyrrolidinol under identical conditions, as measured by ¹H NMR disappearance of the N-CH₂ signal. This kinetic retardation, attributable to the increased steric bulk of the N-ethyl group, shifts the selectivity window during bis-quaternary ammonium salt formation when the C-3 hydroxyl group is concurrently protected. In pilot-scale batches processed in a 50-L glass-lined reactor with a retreat-blade impeller, maintaining a molar ratio of alkylating agent to substrate at 1.05:1.00 and a dosing time of 90 minutes suppressed dialkylation to 1.8 area% by IPC-HPLC. The N-methyl analog, in contrast, generated 4.2 area% dialkylated byproduct under the same parameter set. This differential is amplified when the reaction solvent contains trace water (≥ 0.1% v/v), which preferentially solvates the smaller N-methyl ammonium transition state and accelerates the second alkylation. Processing specifications therefore recommend a pre-drying step of the substrate over activated 3Å molecular sieves to <50 ppm H₂O, verified by in-line NIR spectroscopy, before charging the alkyl halide.

Electrolyte Additive Performance in High-Voltage Lithium-Ion Cells

Addition of 0.5–1.5 wt% 1-ethyl-3-hydroxy-tetrahydropyrrole to a baseline electrolyte formulation of 1.0 M LiPF₆ in EC:EMC (3:7 v/v) shifts the onset of oxidative decomposition, as determined by linear sweep voltammetry on a glassy carbon electrode at a scan rate of 0.5 mV·s⁻¹, from 5.1 V to 5.35 V vs. Li/Li⁺. The mechanism involves preferential oxidation of the tertiary amine to form a thin, passivating film comprising poly(vinylidene fluoride)-coordinated fragments, confirmed by XPS N 1s peaks at 399.8 eV and 402.3 eV assigned to neutral amine and oxidized quaternary species, respectively. In NMC811||graphite pouch cells (nominal capacity 2.0 Ah) cycled at 1C/1C between 3.0–4.35 V at 45 °C, the capacity retention after 500 cycles improved from 78% (baseline) to 91% with 1.0 wt% additive. However, impedance rise measured by electrochemical impedance spectroscopy at 10 kHz revealed a contact resistance increase of 12 mΩ·cm² over the cycle life when the additive level exceeded 1.2 wt%, indicating a critical upper loading threshold. Published data for this specific configuration is limited, and cell manufacturers typically validate compatibility with nickel-rich cathode surfaces via post-mortem TOF-SIMS depth profiling before production qualification.

Differences from structurally related electrolyte additives such as N-methylpyrrole or N-butyl-3-hydroxypiperidine stem from the combination of a five-membered ring geometry and an N-ethyl chain length short enough to maintain solubility in carbonate solvents (log P 0.61 calculated via Molinspiration) yet long enough to impede intermolecular hydrogen bonding between hydroxyl groups, which reduces bulk viscosity contribution. When 2.0 wt% N-methyl-3-pyrrolidinol was blended into the same electrolyte, viscosity rose by 1.8 cP at 25 °C, versus a 1.2 cP increase for the ethyl variant (both measured on an Anton Paar Lovis 2000 M rolling-ball viscometer, ISO 12058-1). This disparity affects wetting speed on polyolefin separators; the ethyl compound achieved complete separator saturation in 22 seconds vs. 31 seconds for the methyl analog at 25 °C, determined by optical absorption edge tracking.

When Enzymatic Resolution Offers Enantiomeric Excess Exceeding 99%

Kinetic resolution of racemic 1-ethyl-3-hydroxy-tetrahydropyrrole has been demonstrated using immobilized lipase B from Candida antarctica (Novozym 435) in methyl tert-butyl ether at 35 °C with vinyl acetate as the acyl donor. Under continuous-flow conditions in a packed-bed reactor (column ID 10 mm, bed height 150 mm, residence time 8 minutes), the (R)-enantiomer was preferentially acetylated, leaving the (S)-alcohol in solution. The enantiomeric excess (ee) of the residual alcohol reached 99.2% as determined by chiral GC (CycloSil-B column, 30 m × 0.25 mm, isothermal at 110 °C). Throughput was 12.6 g·day⁻¹ of resolved (S)-enantiomer per gram of immobilized enzyme, with catalyst productivity maintaining >80% of initial activity over 15 consecutive batches. This contrasts sharply with N-benzyl-3-hydroxypyrrolidine, which undergoes debenzylation under the same conditions, releasing benzyl alcohol as a contaminant and poisoning the lipase active site. The ethyl group’s stability under these mild conditions circumvents the need for protective-group strategies, a limitation frequently encountered with the N-benzyl derivative in pharmaceutical intermediate synthesis where metal residues from hydrogenolysis must be controlled to <10 ppm Pd by ICP-MS per ICH Q3D guidelines.

Thermal Stability and Distillation Behaviour Under Reduced Pressure

Short-path distillation of the racemate at 0.5 mbar yields a center cut with GC purity ≥ 99.5 area%, provided the evaporation temperature does not exceed 92 °C. Differential scanning calorimetry (DSC, heating rate 10 K·min⁻¹, N₂ purge) records an endothermic event at 102 °C attributed to onset of thermal dehydration, forming the corresponding 3-pyrroline via β-elimination of water. Thermogravimetric analysis (TGA) under nitrogen shows a 5% mass loss at 138 °C and a catastrophic decomposition step beginning at 210 °C with an exotherm of −487 J·g⁻¹. This narrow processing window mandates jacketed reactor systems capable of maintaining an internal bulk temperature within ±2 °C of setpoint during any distillative purification and prohibits the use of hot-oil systems with overshoot >5 °C. By comparison, N-methyl-3-pyrrolidinol exhibits 5% mass loss at 125 °C, narrowing its safety margin during scale-up. Industrial incidents involving N-alkyl pyrrolidinols have been traced to inadequate temperature control during batch concentration, where localized film temperatures at the reactor wall triggered auto-catalytic dehydration, producing flammable pyrroline vapor and non-condensable gases. Consequently, specification sheets for the ethyl derivative invariably stipulate storage at 2–8 °C under nitrogen and mandate a peroxide test prior to any thermal operation if the container has been opened for more than 48 hours.

Aqueous solubility of the racemate exceeds 500 g·L⁻¹ at 20 °C, with a pH of a 10% (w/w) solution measuring 11.2 ± 0.2. This alkalinity is exploited in water-based cooling-tower corrosion inhibitor formulations where the amine acts as a neutralizing agent and metal passivator. Blends containing 3–5 wt% of the compound along with phosphonobutane tricarboxylic acid (PBTC) and zinc chloride, when tested according to ASTM G31-21 on C1018 carbon steel coupons in synthetic cooling water at 40 °C for 168 hours, reduced the corrosion rate to 0.8 mils per year (mpy) compared to 4.2 mpy for the blank. The ethyl chain length augments the film persistency on the metal surface relative to the methyl analog, as measured by electrochemical impedance at 10 mHz, where polarization resistance remained above 2.5 kΩ·cm² after 24 hours of static exposure, versus 1.7 kΩ·cm² for N-methyl-3-pyrrolidinol under the same conditions.

Avoiding Amine-Based Additive Incompatibilities in Epoxy Curing Formulations

When 1-ethyl-3-hydroxy-tetrahydropyrrole is considered as a reactive diluent or accelerator component in two-part epoxy-amine thermosets, its tertiary amine structure accelerates the ring-opening polymerization of bisphenol A diglycidyl ether (DGEBA) at ambient temperature. The gel time of a stoichiometric DGEBA–isophoronediamine mixture, measured by a Gelnorm® device at 23 °C, decreased from 72 minutes to 23 minutes upon incorporation of 10 phr of the ethyl compound. However, the presence of the free hydroxyl group introduces a competing pathway: at temperatures above 60 °C, the alcohol initiates homopolymerization of epoxide groups, liberating heat and causing localized runaway that can carbonize the resin matrix in thick sections (> 5 mm). This property restricts its use to thin-film applications cured below 50 °C. The N-ethyl substituent also reduces the amine’s tendency to bloom to the surface compared with the methyl variant—surface energy measurements by contact angle goniometry showed a surface N concentration, quantified by XPS, that was 40% lower after 7-day ambient cure, attributable to the marginally higher molecular weight and integration into the network. Nonetheless, formulators must avoid combination with anhydride curing agents, as the tertiary amine catalyzes anhydride hydrolysis in the presence of atmospheric moisture, leading to formation of carboxylic acid that precipitates as an incompatible phase, evidenced by haze and a drop in tensile strength (ASTM D638-14) of more than 30% compared to anhydride-only cured samples.

Differences between this ethyl derivative and the widely used N-methyl or N-H analogs become most pronounced in agrochemical intermediate synthesis, where the 3-hydroxyl group serves as a handle for introducing leaving groups for nucleophilic displacement. Treating the alcohol with thionyl chloride in dichloromethane at 0–5 °C yields the corresponding 3-chloro compound with 89% isolated yield after aqueous workup. The N-ethyl group’s increased lipophilicity shifts the log D (pH 7.4) of the resulting chloride to 1.48 versus 0.92 for the N-methyl chloride, a parameter that influences foliar uptake rates in systemic fungicide candidates under evaluation. Field trial data linking this physicochemical parameter to efficacy remains proprietary; however, greenhouse translocation studies on Triticum aestivum using radiolabeled (¹⁴C) analogs indicated a xylem mobility factor approximately 1.7-fold greater for the ethyl-labeled congener, suggesting translocation advantages that are product-specific and require full toxicological profiling under REACH Annex VII before commercialization.

Production-scale handling data from a multi-purpose batch facility equipped with a 2000-L glass-lined reactor and a triple-layer stainless steel condenser (effective area 12 m²) indicate that the exotherm during the reductive amination step—employing ethylamine and 3-pyrrolidone over Raney nickel at 40 bar H₂—must be controlled with a jacket cooling ramp not exceeding −0.5 °C·min⁻¹ to prevent catalyst sintering and subsequent batch failure. The reduction endpoint, confirmed by in situ ReactIR monitoring of the C=O stretch at 1715 cm⁻¹, dictates the final impurity profile. Batches with incomplete reduction show residual ketone ≥ 0.5% that forms Schiff-base oligomers upon storage, increasing color beyond specification within 90 days at 25 °C. These oligomeric species are absent in the N-methyl process due to faster imine reduction kinetics, presenting a distinct manufacturing challenge particular to the ethyl derivative.