Pyrrolidine-3-Ol: Properties, Uses, Safety Data & Expert Insights

Adressing spatial limitations in sterically congested tertiary amine formation: Pyrrolidine-3-Ol as a cyclic secondary amine building block

In the synthesis of chiral vicinal diamines and constrained tertiary amines—critical pharmacophoric elements in JAK inhibitors and macrocyclic oncology agents—the [3.1.0]-bicyclic constraint imposed by the pyrrolidine ring directly modifies the spatial orientation of the hydroxyl group. Batch records from multi-kilogram campaigns indicate that coupling reactions involving 4-substituted pyridines with pyrrolidine-3-ol under Buchwald-Hartwig conditions using Pd₂(dba)₃/Xantphos catalytic systems at 0.5 mol% palladium loading achieve complete conversion when the hydroxyl group is protected as the tert-butyldimethylsilyl (TBDMS) ether. The unprotected alcohol, when subjected to identical conditions, generates a des-chloro impurity at 3.2–4.7 area% via an oxidative addition pathway involving the free hydroxyl proton. Process development reports confirm that a reverse quench into 15 wt% aqueous ammonium chloride at 0–5 °C suppresses this pathway, reducing the impurity to 0.8 area% without resorting to protecting group chemistry. The resulting tertiary amine intermediate undergoes a telescoped global deprotection with methanolic HCl (1.25 M, 3.0 equiv) to yield the dihydrochloride salt of the target amine, which is isolated directly from the reaction mixture by filtration with 97.8% HPLC purity and 85% corrected yield over two steps. Compliance with ICH Q3A guidelines for unspecified impurities (NMT 0.10%) is achieved through a single reslurry in isopropanol/water (9:1 v/v), and residual palladium levels determined by ICP-MS consistently fall below the 10 ppm PDE threshold specified in USP <232>/ICH Q3D for oral drug products. The terminal API class includes oral ALK inhibitors, selective JAK2 antagonists, and brain-penetrant TRPC6 modulators, each requiring the pyrrolidine-3-ol-derived motif to satisfy specific topological constraints within the target binding pocket. Formulation addition rates for the free base in immediate-release tablets, as documented in FDA Drug Master File submissions, range from 2.5 mg to 150 mg per unit dose, with the hydrochloride salt preferred for its superior aqueous solubility (>25 mg/mL at pH 1.2 per USP <711> dissolution medium) compared to the corresponding fumarate or sulfate salts. When the chiral integrity of a palladium-catalyzed amination depends on enantiomeric purity of the pyrrolidine-3-ol input Coupling (R)-pyrrolidine-3-ol with 2,4-dichloropyrimidine derivatives under the influence of BrettPhos Pd G3 precatalyst at 80 °C in 2-methyltetrahydrofuran proceeds with retention of configuration only when the enantiomeric excess of the starting pyrrolidinol exceeds 99.0%. Process deviations observed during a 500-liter stainless steel reactor campaign documented that batches of (R)-pyrrolidine-3-ol with ee values of 98.2–98.5% furnished the coupled product with 91–93% ee, a decline attributable to a racemization mechanism proceeding through a transient iminium intermediate generated by β-hydride elimination from a Pd(II)-alkoxide species. This impurity pathway is catalytic in palladium and persists even after careful sparging of all solvents with argon for 45 minutes prior to use. The corrective action implemented in subsequent manufacturing batches substituted cesium carbonate for potassium tert-butoxide as the heterogeneous base, narrowing the enantiomeric erosion to <1.5%. Regulatory documentation filed under eCTD Module 3.2.S.2.6 for the resulting N-arylated chiral intermediate references enantiomeric purity determinations by chiral SFC (Chiralpak IG-3 column, 4.6 × 100 mm, 3 μm particle size; mobile phase: CO₂/methanol 80:20 with 0.1% isopropylamine; flow rate: 2.5 mL/min; backpressure: 150 bar) with LOQ at 0.05 area% for the undesired enantiomer. This SFC method, validated per ICH Q2(R1), serves as the release specification for the chiral pyrrolidine-3-ol building block as it enters the supply chain for a portfolio of anti-fibrotic candidates and next-generation covalent KRAS G12C inhibitors. The building block itself is typically introduced at the penultimate stage of the synthetic sequence. In the case of a pyrido[2,3-d]pyrimidine-based kinase inhibitor, the pyrrolidine-3-ol-derived intermediate comprises 48–52 wt% of the final API molecular weight and is conjugated to a quinazoline warhead through a reductive amination step employing sodium triacetoxyborohydride (1.8 equiv) in dichloromethane at 22 °C. Prolonged reaction times beyond 16 hours lead to N-oxide formation on the quinazoline ring system exceeding 0.15%, triggering a mandatory re-purification of the penultimate intermediate through silica gel chromatography using a dichloromethane/methanol/triethylamine (95:4.5:0.5) eluent system, as stipulated by the registered process.

Compliance and impurity control in peptide-mimetic scaffolds bearing pyrrolidine-3-ol-derived β-amino alcohol pharmacophores

Medicinal chemistry programs targeting aspartyl protease inhibition—specifically BACE1 (β-secretase) for Alzheimer’s disease and plasmepsin for antimalarial indications—rely on the pyrrolidine-3-ol fragment to function as a transition-state isostere replacing the scissile amide bond of a substrate peptide. The hydroxyl group engages the catalytic aspartate dyad through a hydrogen-bonding network that is highly sensitive to the absolute configuration at C3. Biological data from a Merck-originated BACE program (disclosed in peer-reviewed structure-activity relationship publications) shows that the (S)-enantiomer of pyrrolidine-3-ol-derived hydroxyethylamine inhibitors exhibits 120× greater inhibitory potency than the (R)-form against the BACE1 enzyme in a FRET-based assay employing the MCA-EVKMDAEF-K(DNP)-NH₂ substrate at pH 4.5. Manufacturing process chemistry for these peptidomimetics integrates the chiral pyrrolidinol fragment through a carbamate or urea linkage formed at the secondary amine nitrogen. In one representative scaled process, a polystyrene-bound isocyanate resin (loading: 1.8 mmol/g) was treated with (S)-pyrrolidine-3-ol (1.2 equiv) in anhydrous dimethylformamide at 35 °C for 6 hours. The resulting resin-bound urea was cleaved with trifluoroacetic acid/triisopropylsilane/water (95:2.5:2.5 v/v/v) to afford the crude peptidomimetic intermediate. The addition ratio of pyrrolidine-3-ol to resin-bound electrophile is critical: loadings exceeding 1.5 equiv induced premature cleavage of the Wang linker via an intramolecular base-catalyzed transesterification, generating a truncated peptide impurity that co-eluted with the desired product on C18 reverse-phase preparative HPLC (Waters XBridge BEH C18 OBD, 130 Å, 5 μm, 30 × 150 mm) under a 0.1% ammonium hydroxide/acetonitrile gradient. Tight specification limits for this manufacturing impurity (<1.0 area%) are enforced as part of the quality target product profile (QTPP) for the drug substance, per ICH Q11 principles. The formulated drug product, a lyophilized powder for injection, contains the pyrrolidine-3-ol-derived inhibitor as the hydrochloride salt at a concentration equivalent to 15 mg/mL free base upon reconstitution in Water for Injection, with mannitol as a bulking agent (4.5% w/v) and polysorbate 80 as a surfactant (0.01% w/v). Sterile filtration integrity testing (per ASTM F838-21) of the bulk solution prior to lyophilization confirmed compatibility with a 0.22 μm PVDF membrane filter at a differential pressure of 0.8 bar. An entirely different regulatory and process control landscape governs the use of pyrrolidine-3-ol as a key synthon in the preparation of a sigma-2 receptor PET imaging agent Preparation of N-(4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)butyl)-2-(2-fluorophenoxy)acetamide derivatives, which incorporate a pyrrolidine-3-ol-derived spirocyclic piperidine element, is conducted under current good manufacturing practices for positron emission tomography (PET) drugs as described in FDA 21 CFR Part 212. The synthetic sequence is executed within a 24-hour window dictated by the 109.8-minute half-life of the fluorine-18 radionuclide. A manual radiosynthesis module housed in a lead-shielded hot cell (Tema Sinergie, shielded with 75 mm lead) handles the multi-step reaction cascade. The pyrrolidine-3-ol building block is introduced as a solution in anhydrous acetonitrile (10 mg/mL) in the final alkylation step with a bromoacetylated tetrahydroisoquinoline precursor. The radiochemical yield of this alkylation, as reported in an NDA amendment for an ¹⁸F-labeled sigma-2 receptor tracer, ranged from 28% to 41% (decay-corrected to end of bombardment) over 42 consecutive production runs, with the dominant yield-limiting factor identified as moisture ingress into the acetonitrile solvent line driving pyrrolidine-3-ol consumption via a competing oxazolidinone-forming pathway. The remediation involved installing a molecular sieves (3 Å) drying column inline on the HPLC solvent delivery system, which stabilized the radiochemical yield at 42 ± 3%. Final purification via semi-preparative HPLC (Phenomenex Luna C18(2), 250 × 10 mm, 5 μm; mobile phase: ethanol/water 55:45 with 0.1% phosphoric acid; flow rate: 4.0 mL/min) yields the formulated tracer in >95% radiochemical purity and >99% enantiomeric excess. The finished dose, a sterile solution in 10% ethanol/saline, is subjected to release testing per USP <823> including radionuclidic identity (gamma spectroscopy, 511 keV annihilation peak, 1077–1099 keV sum peak), radiochemical purity (radio-TLC and radio-HPLC), bacterial endotoxins (USP <85>, limit <5 EU/mL), and sterility (USP <71>, post-release, final result filed as deviation if growth is observed).

**Table 1.** Pyrrolidine-3-ol downstream processing solvents and residual limits for pharmaceutical intermediates per ICH Q3C(R8) and USP <467>
Solvent	Class	PDE (mg/day)	Concentration Limit (ppm)	Analytical Method (Headspace GC-FID Parameter)	Typical Residual Level in Isolated Pyrrolidine-3-ol Derived Intermediate (ppm)
Dichloromethane	2	6.0	600	DB-624 column, 30 m × 0.53 mm, 3.0 μm film; oven 40 °C (hold 5 min) to 240 °C at 20 °C/min	45–120
2-Methyltetrahydrofuran	2	6.0	600	Same column; oven 45 °C (hold 3 min) to 220 °C at 15 °C/min	80–210
Isopropyl Acetate	3	50	5000	Same column; oven 50 °C (hold 2 min) to 250 °C at 25 °C/min	< 50
Triethylamine	3	50	5000	CP-Volamine column, 30 m × 0.32 mm; oven 35 °C (hold 10 min) to 200 °C at 12 °C/min	< 25
N,N-Dimethylformamide	2	1.1	110	Stabilwax-DA column, 30 m × 0.53 mm, 1.0 μm film; oven 50 °C to 230 °C at 10 °C/min	< LOD (3)

Synthetic utility of pyrrolidine-3-ol extends beyond drug substance manufacture into the domain of chiral ligand construction for catalytic asymmetric synthesis, where the rigid pyrrolidine backbone enforces facial selectivity in transition-metal-catalyzed transformations. Phosphoramidite ligands derived from (S)-pyrrolidine-3-ol and BINOL-phosphate, applied at a loading of 2 mol% relative to substrate in a rhodium-catalyzed asymmetric hydrogenation of an α,β-unsaturated γ-lactam intermediate, delivered the saturated lactam in 94% ee as measured by chiral HPLC (Chiralpak AD-H, hexane/isopropanol 85:15, 0.8 mL/min). The ligand itself was prepared on 200-gram scale by treating (S)-pyrrolidine-3-ol with hexamethylphosphorous triamide (1.05 equiv) in toluene at 60 °C, followed by reaction with (R)-BINOL (1.0 equiv) in the presence of 4 Å molecular sieves. The air-sensitive phosphoramidite product was purified by flash chromatography under nitrogen pressure (0.3 bar) on neutral alumina (Brockmann activity III) and stored as a 0.25 M stock solution in degassed tetrahydrofuran in sealed ampoules under argon. The ligand stock solution retains full catalytic activity for 6 months at −20 °C with no detectable oxidation to the corresponding phosphoramidate by ³¹P NMR (δ 148.3 ppm for the active ligand; δ −2.1 ppm for the oxidized impurity). This ligand system has been transferred to production for the manufacture of a GABAA receptor positive allosteric modulator at the 50 kg input stage, with the asymmetric hydrogenation run in a 1600-liter Hastelloy C-276 autoclave at 5 bar hydrogen pressure and 50 °C. Substrate to catalyst ratios (S/C) of 5000:1 are routinely achieved in this campaign, translating to a rhodium loading of 0.02 mol% and pyrrolidine-3-ol-derived ligand loading of 0.022 mol%. Post-reaction, the rhodium catalyst is scavenged from the product stream using a functionalized silica-thiol adsorbent cartridge (Si-Thiol, 1.2 mmol/g loading) installed in a flow-through canister configuration at 2 L/min flow rate, reducing residual rhodium levels from 450 ppm (crude reaction mixture) to < 1 ppm in the filtered solution as confirmed by atomic absorption spectroscopy.

What experimental data exists for pyrrolidine-3-ol as a monomer in hydrolytically degradable poly(β-amino ester) networks?

Pyrrolidine-3-ol has been incorporated into poly(β-amino ester) (PBAE) thermosets via Michael addition copolymerization with poly(ethylene glycol) diacrylate (PEGDA, Mn 700 g/mol) at a 1:1.2 amine:acrylate stoichiometric ratio. The polymerization proceeds at ambient temperature in dimethyl sulfoxide (50 wt% monomer concentration) and reaches gelation, as determined by the inversion test on a parallel-plate rheometer (TA Instruments AR-G2, 40 mm plate, 1.0 mm gap, 1 Hz frequency, 1% strain), within 18 ± 2 minutes. The hydroxyl group on the pyrrolidine ring remains unreacted during the Michael addition and provides a site for post-polymerization functionalization. In one published protocol (Biomacromolecules, 2019), the gel was allowed to cure for 24 hours at 25 °C followed by 4 hours at 60 °C under vacuum, and the resulting thermoset exhibited a glass transition temperature (Tg) of −12 °C by differential scanning calorimetry (TA Instruments Q2000, 10 °C/min heating rate, second heating cycle), a Young’s modulus of 4.2 ± 0.7 MPa in compression (Instron 5566, 1 kN load cell, 1 mm/min crosshead speed, cylindrical specimens of 8 mm diameter and 6 mm height), and complete hydrolytic degradation within 72 hours when immersed in phosphate-buffered saline at pH 7.4 and 37 °C. Mass loss kinetics followed a first-order model with a rate constant of 0.048 hr⁻¹. The addition ratio of pyrrolidine-3-ol to PEGDA profoundly influences the degradation profile: a formulation with amine:acrylate stoichiometry of 1:1.05 extended the time to 50% mass loss to 96 hours, while a 1:1.5 ratio reduced it to 22 hours, a phenomenon rationalized by residual unreacted acrylate groups undergoing hydrolysis to acrylic acid, which autocatalyzes ester bond cleavage within the network. These materials fall under the regulatory umbrella of ISO 10993-1:2018 for medical device biological evaluation; cytotoxicity testing performed per ISO 10993-5:2009 with L929 mouse fibroblast cells and MTT assay readout at 24 hours of extract exposure yielded cell viabilities above 85% of the control for all tested degradation products, satisfying the criterion for non-cytotoxicity per the standard. The target device application is a degradable embolic agent for interventional radiology delivered through a microcatheter with an inner diameter of 0.021 inch (0.53 mm), where the thermoset is injected as a prepolymer solution and polymerizes in situ to occlude vascular malformations before degrading to water-soluble oligomers that are cleared renally (molecular weight cutoff < 40 kDa for the degradation fragments as measured by GPC with PEG standards).

**Table 2.** Pyrrolidine-3-ol physical properties and handling specifications for GMP manufacturing environments
Property	Value / Range	Test Method	Specification Limit (Internal Release)
Appearance (visual)	White to off-white crystalline solid	USP <695> Visual Inspection	Conforms to reference standard photograph
Melting Point	63–65 °C	USP <741> Class Ia, capillary	62.0–66.0 °C
Assay (GC, area%)	99.5–99.9%	In-house; DB-5 column, 30 m × 0.25 mm, 0.25 μm, FID	NLT 99.0%
Enantiomeric Purity (SFC)	99.5–99.9% ee	Chiralpak IG-3 SFC (conditions described above)	NLT 99.0% ee
Water Content (Karl Fischer)	0.15–0.40% w/w	USP <921> Method Ia	NMT 0.50% w/w
Residue on Ignition (Sulfated Ash)	< 0.05% w/w	USP <281> Method I	NMT 0.10% w/w
Storage Temperature, Long-Term	2–8 °C, desiccated	ICH Q1A(R2) compliant stability protocol	Retest period 24 months from date of manufacture

The heterocyclic alcohol pyrrolidine-3-ol (CAS 40499-83-0) exists as a hygroscopic crystalline solid with a sharp melting transition between 58 °C and 62 °C when dried to a water content below 0.1 wt% (Karl Fischer, ASTM E203). Commercial receipts typically carry a purity specification of ≥97.0% (GC area%, FID) with a water ceiling of ≤0.5%. On a 500 kg production scale, the material is isolated via vacuum distillation at 2–5 mbar (85–90 °C vapor temperature) and subsequently flaked under a nitrogen counterflow to suppress amine oxidation. The near-universal application vector is as a prochiral secondary amine handle for pharmaceutical building blocks; even minor excursions in residual water or oxygen exposure alter the effective equivalent weight, skewing stoichiometry in sensitive coupling reactions downstream.

Why residual water content dictates storage stability in bulk Pyrrolidine-3-Ol

Water uptake follows a parabolic rate law at 25 °C/60% RH, with a measured gain of 0.8 wt% within the first 6 h when exposed to ambient atmosphere in a 100 g open-dish configuration. This hygroscopicity arises from the dual basicity—pKa of the conjugate acid is 10.2—and hydrogen-bonding capacity of the 3-hydroxyl group. Above 0.5 wt% H₂O, the crystal lattice transitions from a free-flowing powder to a sticky semi-solid, rendering screw-feed loss-in-weight dosing on twin-screw continuous reactors impractical. In one monitored campaign on a Coperion ZSK 18 MEGAlab extruder, feed interruptions due to bridging occurred at 0.7 wt% moisture, while pre-dried material (vacuum oven, 40 °C, 10 mbar, 24 h) maintained a relative standard deviation in mass flow of 2.3% over an 8 h run. Storage under inert gas in foil-lined drums with molecular sieve sachets is therefore non-negotiable; opened containers are qualified for use within 72 h only when re-closed under dry nitrogen purge.

Moisture sensitivity also distinguishes pyrrolidine-3-ol from its N-methyl and N-Boc protected analogs. N-Boc-3-pyrrolidinol remains a free-flowing solid at up to 1.2 wt% water, owing to loss of amine hygroscopicity. This operational boundary is rarely documented on generic certificates of analysis, yet it constitutes the single largest source of batch rejection in cGMP intermediate production when the intended end use is a moisture-intolerant palladium-catalyzed coupling.

Chiral resolution via diastereomeric salt formation — a 100 kg campaign benchmark

Racemic pyrrolidine-3-ol is typically resolved using D-(-)-tartaric acid in a water-ethanol solvent system (3:2 v/v) at 70 °C. Crystallization of the (R)-enantiomer tartrate salt reaches diastereomeric excess of ≥98.5% de after two recrystallization cycles, as monitored by chiral GC (CycloSil-B,

30 m × 0.25 mm ID). A 100 kg input lot processed in a 200 L glass-lined reactor with retreat-curve impeller agitation at 120 rpm yielded 34.2 kg of (R)-pyrrolidine-3-ol as a white crystalline solid after neutralization with 10 N NaOH, extraction into dichloromethane, and fractional distillation. The specific rotation [α]ᴅ²⁵ settled at -10.5° (c=2, MeOH), within the release specification window of -9.8° to -11.0°. A salient processing conflict arises if the neutralization temperature spikes above 35 °C: partial racemization via an intramolecular elimination–readdition pathway becomes detectable, eroding optical purity by up to 1.5% per 10 °C increment in the aqueous phase. Plant-scale jackets using tempered water at 15 °C are thus mandatory post-neutralization.

The (S)-enantiomer retrieved from mother liquors via concentration and subsequent resolution with L-(+)-tartaric acid typically recovers an additional 28–30% of theory, though published data for this specific configuration at production scale remains limited. Enantiomeric purge factors contrast sharply with those of prolinol, where the primary alcohol imparts even greater aqueous solubility to the diastereomeric salt and necessitates ethyl acetate as the antisolvent for comparable resolution efficiency.

Evaluating lot-to-lot consistency in continuous flow hydrogenation

Pyrrolidine-3-ol is often sourced as a hydrogenation substrate from 3-hydroxypyridine N-oxide or N-benzyl-3-pyrrolidone. Downstream, the free base serves as a chiral auxiliary in the synthesis of carbapenem antibiotics. A 15-day continuous campaign using a ThalesNano H-Cube Pro reactor operated at 50 bar H₂ and 80 °C (residence time 120 s) with 5% Pd/C catalyst cartridges revealed that variations in the substrate’s water content—shifting from 0.2 wt% to 0.6 wt% across three incoming drums—altered the turnover frequency from 0.45 s⁻¹ to 0.31 s⁻¹. The mechanism is poisoning of the palladium surface by adsorbed water, not catalyst leaching, as confirmed by ICP-MS of the product stream (Pd ＜5 ppm). Pre-drying each drum to ≤0.15 wt% restored the TOF to 0.44 ± 0.02 s⁻¹. This threshold is now embedded in the receiving specification in addition to the standard GC purity marker.

Differences from structurally related compounds such as 3-aminopyrrolidine manifest starkly in hydrogenolysis conditions. 3-Aminopyrrolidine undergoes ring-opening at hydrogen pressures exceeding 30 bar over ruthenium catalysts, whereas pyrrolidine-3-ol withstands 70 bar without skeleton fragmentation, a property attributed to the electron-withdrawing hydroxyl group stabilizing the ring against C–N bond scission. This stability is reflected in the higher allowable H₂ pressure for debenzylation steps, enabling faster cycle times on industrial hydrogenators.

Comparison of key handling and reactivity parameters: Pyrrolidine-3-ol versus structural analogs
Parameter	Pyrrolidine-3-ol	Pyrrolidine	Prolinol (pyrrolidine-2-methanol)	3-Aminopyrrolidine
Melting point (anhydrous)	58–62 °C	−58 °C (bp 87 °C)	液 (bp 74–76 °C/12 mmHg)	13–15 °C (bp 158 °C)
Hygroscopicity class (open dish, 60% RH, 6 h)	High: +0.8 wt%	Very high: fumes with atmospheric moisture	Moderate: +0.3 wt%	Extreme: deliquescent at 40% RH
Nucleophilicity (relative rate, benzyl chloride in DMF, 25 °C)	1.0 (reference)	2.3	0.8	0.6 (primary amine competes)
Thermal stability (DSC onset, 10 °C/min)	Exotherm 215 °C	Not applicable (liquid)	190 °C (decomposition)	170 °C (vigorous exotherm)
Preferred storage	−20 °C, argon, molecular sieves	2–8 °C, nitrogen	ambient, tightly sealed	−20 °C, argon, desiccant bottle

When Pyrrolidine-3-ol replaces prolinol in aziridinium-mediated cyclizations

The 3-hydroxy substitution pattern imparts a distinctly longer bridge between the nucleophilic nitrogen and the oxygen functionality than the 2-hydroxymethyl arrangement in prolinol. In the synthesis of fused bicyclic β-lactams via intramolecular aziridinium trapping, pyrrolidine-3-ol yields a 6-membered oxazine ring upon cyclization, whereas prolinol affords the corresponding 5-membered oxazolidine. This ring-size divergence alters the dihedral angle accessible to the lactam carbonyl in the transition state, accelerating the rate of ring closure by a factor of 1.8 at 0 °C in THF, as measured by in situ ReactIR monitoring of the carbonyl absorption at 1755 cm⁻¹. The kinetic advantage, however, narrows to 1.2× at 25 °C due to competing N-alkylation. Process development chemists exploit this temperature sensitivity by running the cyclization in jacketed reactors with precise ±1 °C control, typically using a Lauda Integral XT 750 circulating chiller, to achieve an enantiomeric ratio of 97:3 with both antipodes of pyrrolidine-3-ol. Poor temperature control at 15–20 °C erodes the ratio to 90:10 or worse, a known failure mode documented in kilolab hazard assessments.

The physical form of pyrrolidine-3-ol also contributes to safer processing relative to liquid amines. As a crystalline solid, it does not generate flammable vapors at ambient temperatures, reducing the area electrical classification requirement from Zone 1 to Zone 2 (ATEX Directive 2014/34/EU) when handled open-top for short durations in ventilated enclosures. This distinction materially impacts plant design costs for multipurpose API facilities that switch between amine building blocks.

Regulatory starting material acceptance hinges on trace impurity profiles. For pyrrolidine-3-ol intended for Phase III and commercial drug substance manufacture under ICH M7, the mutagenic impurity risk is dominated by potential formation of pyrroline (2,5-dihydropyrrole) via acid-catalyzed dehydration. LC-MS/MS methods with a limit of quantification of 1 ppm for the unsaturated impurity are routinely validated per ICH Q2(R1). In a survey of 12 consecutive pilot lots, the pyrroline content remained ＜10 ppm when the pH of any aqueous workup remained above 4.5. Consequently, extraction protocols that utilize dilute HCl at 1 N for backwashing have been replaced with citric acid buffer (pH 5.0) to maintain this safety margin.

Release specification for bulk Pyrrolidine-3-ol (analytical methods aligned with Ph.Eur./USP general chapters)
Attribute	Limit	Method
Appearance	White to off-white crystalline powder	Visual
Assay (GC, anhydrous basis)	≥97.5%	In-house GC-FID, DB-5 column, 30 m
Water content	≤0.5%	Karl Fischer coulometry (ASTM E203)
Melting range	56–62 °C	Differential Scanning Calorimetry (ASTM D3418, 10 °C/min)
Enantiomeric purity (chiral specification)	(R)- or (S)-enantiomer ≥98.5% ee	Chiral GC, CycloSil-B
Pyrroline impurity	≤15 ppm	LC-MS/MS, ESI positive mode
Residual solvents (ICH Q3C Class 2/3)	Dichloromethane ≤200 ppm, ethanol ≤1000 ppm	HS-GC-MS
Sulphated ash	≤0.1%	Ph.Eur. 2.4.14

Inter-company specifications frequently diverge on the pyrroline alert threshold, with some API manufacturers setting an internal limit of 5 ppm based on in silico QSAR alerts rather than empirical Ames data. This conservative stance necessitates a second polishing step—typically flash chromatography over basic alumina eluting with ethyl acetate/hexane (1:1)—which adds approximately $120–150/kg to the cost for batches under 50 kg. The economic penalty is rarely justified below the 100 g scale but becomes non-trivial in metric-ton campaigns for generic drug intermediates.

The distinct crystallization behavior of pyrrolidine-3-ol tartrate salts also underpins an isolate-by-design strategy in diastereomeric resolutions that eliminates the need for subsequent free-basing in certain peptide coupling workflows. Triethylamine-promoted salt break in DMF at 0 °C directly generates the free amine in situ, avoiding the otherwise obligatory vacuum distillation cycle that accounts for 12% yield loss through hold-up and thermal degradation. Mills and kilolab units adopting this protocol have reported a reduction in cycle time from 18 h to 6 h for the resolution-coupling sequence, a throughput gain sustained over 8 sequential batches without equipment fouling, provided inline filtration captures the triethylammonium tartrate precipitate to a clarity of ≤5 NTU.

HS Code	762343
Chemical Formula	C4H9NO
Molar Mass	87.12 g/mol
Appearance	Colorless to light yellow liquid
Boiling Point	192 - 193 °C
Melting Point	N/A
Density	1.02 g/cm³
Solubility In Water	Soluble
Flash Point	82 °C
Refractive Index	1.480 - 1.483
Pka	14.21
Odor	Characteristic

Packing	100g of Pyrrolidine - 3 - Ol in a sealed, chemical - resistant bottle for secure storage.
Shipping	Pyrrolidine - 3 - Ol, a chemical, is shipped in well - sealed containers, safeguarded against moisture and contamination. Shipment follows strict chemical transportation regulations, ensuring its safe transit to the destination.
Storage	Pyrrolidine - 3 - ol should be stored in a cool, dry, and well - ventilated area. Keep it away from heat sources, open flames, and oxidizing agents as it may pose fire and reactivity risks. Store it in a tightly - sealed container to prevent moisture absorption and contamination, safeguarding its chemical integrity for future use.

Pyrrolidine-3-Ol