2,3,4,5,6-Pentafluorobenzene Pharma Grade API for Oral & Injectable

How Is Pentafluorobenzene Converted to Pentafluorophenyl Ester Intermediates for Sterile Injectable APIs?

Pentafluorobenzene conversion to pentafluorophenyl ester intermediates for sterile injectable APIs proceeds through a two-stage sequence in which the aromatic ring is first converted to pentafluorophenol; industrial routes may select hexafluorobenzene as the starting material for pentafluorophenol when higher yields are required. The activated pentafluorophenyl ester is then used to acylate the N-terminus of a protected peptide or amino acid in solution-phase coupling because the electron-withdrawing pentafluorophenyl group accelerates amide bond formation under mild conditions. For an injectable application, the reaction solvent is typically dimethylformamide or N-methyl-2-pyrrolidone, both controlled for peroxide and water content below 100 ppm before use. The coupling is conducted in a stainless steel or glass-lined vessel equipped with temperature control at 0 °C to 25 °C. N-methylmorpholine is added slowly to avoid an exotherm exceeding 3 °C/min. After coupling, the pentafluorophenol leaving group is extracted into aqueous sodium bicarbonate, and the aqueous phase is monitored by high-performance liquid chromatography with UV detection at 210–254 nm to verify residual pentafluorophenol removal. For injectable-grade manufacture, the final peptide is subjected to tangential flow filtration, sterile filtration through a 0.22 µm polyvinylidene fluoride membrane, and lyophilization. The endotoxin specification is derived from the maximum intended dose and typically requires a limit not exceeding 0.25 EU/mL for water for injection systems, with testing according to USP <85> or Ph. Eur. 2.6.14. Particulate matter in the reconstituted injection is controlled to USP <788> limits of not more than 6000 particles per container for ≥10 µm and not more than 600 particles per container for ≥25 µm. Residual solvents are controlled under ICH Q3C, and any solvent not listed in the guideline is justified with a toxicological risk assessment. Batch-to-batch variability arises mainly from incomplete activation of the carboxylic acid to the pentafluorophenyl ester. The reaction is monitored by in-line attenuated total reflectance infrared spectroscopy for the disappearance of the carboxylic acid carbonyl band at 1700–1750 cm⁻¹. Because the ester hydrolyzes in aqueous media, transfer and storage are performed under nitrogen in sealed containers at 2–8 °C. Published data for this specific configuration is limited; the limits above reflect compendial injectable requirements rather than a proprietary monograph.

When Finished Dosage QC Demands Electron-Capture Derivatization of Non-Chromophoric Impurities

In finished tablet, capsule, granule, and injection QC, residual carboxylic acids, phenols, and amines without a suitable chromophore are converted to pentafluorobenzoyl derivatives for gas chromatography with electron-capture detection. Pentafluorobenzene serves as a building block for pentafluorobenzoyl chloride through lithiation, carbonation with carbon dioxide to pentafluorobenzoic acid, and subsequent chlorination with thionyl chloride or oxalyl chloride. The resulting derivatization reagent reacts with polar impurities in a two-phase system of dichloromethane and aqueous bicarbonate. Extraction and evaporation are performed in automated vortex evaporators before splitless injection into a GC-ECD system fitted with a 5% phenyl-95% methylpolysiloxane capillary column. Electron-capture detection of pentafluorobenzoyl derivatives provides method detection limits in the low picogram on-column range for primary amines and phenols, although method-specific verification under ICH Q2(R1) is required for each impurity profile. The technique is applied in release testing of granule intermediates, where residual acetate or benzoate salts from wet granulation are derivatized and quantified against a calibration curve of three replicates at five concentration levels. For injectable products, the same derivatization is used to profile trace leachables or residual amine buffers that are otherwise masked by inorganic salts in LC-UV. The derivatization step is itself a source of variability: excess reagent must be evaporated at ≤40 °C to avoid thermal decomposition of the electron-capturing tag, and carryover is minimized by a sequence of blank dichloromethane injections until the baseline ECD signal returns to ≤1% of the analyte peak height. Compliance with GMP documentation is maintained under FDA 21 CFR 211.194 for laboratory records and USP <621> for chromatographic system suitability. Published data for this exact pentafluorobenzene-derived reagent configuration is limited; the performance range above is based on general pentafluorobenzoyl derivatization methodology.

Alternatively, nucleophilic aromatic substitution on pentafluorobenzene generates tetrafluoroaniline, tetrafluorophenol, and tetrafluoro thioether intermediates used in the synthesis of fluorinated drug candidates. The reaction relies on the activating effect of five fluorine atoms, which directs the incoming nucleophile to the para position relative to the hydrogen. With anhydrous ammonia in a pressure reactor, the product is 2,3,5,6-tetrafluoroaniline, while hydroxide or alkoxide nucleophiles yield tetrafluorophenol or tetrafluoroalkoxybenzene intermediates. On a production line, the amination is conducted in a pressure-rated stainless steel vessel at temperatures between 60 °C and 100 °C and pressures not exceeding 5 bar. The addition rate of ammonia is controlled to keep the exotherm below 2 °C/min. The reaction mass is then cooled, vented through a caustic scrubber, and extracted into ethyl acetate; the organic layer is washed with water and dried over sodium sulfate. The isolated tetrafluoroaniline is tested for assay by gas chromatography with flame ionization detection, residual pentafluorobenzene by headspace GC, and total impurities by HPLC. These tetrafluorinated intermediates are used in medicinal chemistry because the fluorine substitution pattern increases metabolic stability at the para position while retaining a reactive amine or hydroxyl handle for subsequent acylation or coupling. In tablet and capsule routes, the resulting API may require additional control of residual fluoride ion below 100 ppm by ion chromatography, because fluoride release during storage can corrode uncoated aluminum blister cavities and alter dissolution performance. Published data for this specific configuration is limited, and the 100 ppm limit is a process-validation value rather than a compendial monograph.

Residual Palladium, Ionic Fluoride, and Endotoxin Boundaries in Dual-Use Manufacturing

The principal conflict in dual-use manufacturing is that a process designed only for oral tablets may meet oral limits but fail injectable limits without additional purification. Palladium-catalyzed cross-coupling with pentafluorophenylboronic acid leaves residual palladium in the crude intermediate. The ICH Q3D oral PDE for palladium is 100 µg/day, while the injectable PDE is 10 µg/day. A process intended only for oral tablets may use a trimercaptotriazine scavenger and filtration to reduce palladium to approximately 15–30 ppm in the isolated intermediate, which is often adequate for a 100–200 mg oral dose but cannot support a 20 mg injectable dose unless additional crystallization or chelating resin treatment is added. The second boundary is ionic fluoride, which is not directly addressed by ICH Q3D but is controlled as a specific impurity because defluorination of pentafluorobenzene during SNAr or lithiation generates inorganic fluoride. Ion chromatography with conductivity detection is used to monitor fluoride in the final API. Oral tablet processes may accept up to 500 ppm if supported by stability data, while injectable routes typically require less than 50 ppm for compatibility with glass vials, rubber stoppers, and sterilizing filters. Published data for this specific configuration is limited, and the numerical limits are process-validation values rather than a monograph. The third boundary is endotoxin. Oral intermediates are not required to meet a bacterial endotoxin limit, but any pentafluorobenzene-derived intermediate entering an injectable API route must be handled in depyrogenated equipment and tested by USP <85>, with a limit derived from the maximum dose. Particulate matter in the injectable finished product is controlled to USP <788> limits of not more than 6000 particles per container at ≥10 µm and not more than 600 particles per container at ≥25 µm. When a single manufacturing train is used for both oral and injectable intermediates, the changeover procedure must include an aqueous detergent wash, a deionized water rinse, and a dried nitrogen purge, with swab sampling for residual pentafluorobenzene and palladium before the next batch. FDA 21 CFR 211.67(a) requires written cleaning procedures, and ICH Q7 requires validation of cleaning methods for residues that may carry over.

Control parameter	Oral tablet/capsule route	Injectable route	Reference method
Palladium residual	100 µg/day PDE	10 µg/day PDE	USP <233> ICP-MS, ICH Q3D Table A.2.1
Ionic fluoride	≤500 ppm with stability data	≤50 ppm	Ion chromatography with conductivity detection
Bacterial endotoxin	Not tested at intermediate stage	Dose-derived; WFI system 0.25 EU/mL	USP <85>, Ph. Eur. 2.6.14
Particulate matter	Not applicable to API	≤6000/container ≥10 µm; ≤600/container ≥25 µm	USP <788>
Residual solvents	ICH Q3C with toxicological justification	ICH Q3C with lower in-process limits for Class 2 solvents	Headspace GC-FID

Control parameter

Oral tablet/capsule route

Injectable route

Reference method

Palladium residual

100 µg/day PDE

10 µg/day PDE

USP <233> ICP-MS, ICH Q3D Table A.2.1

Ionic fluoride

≤500 ppm with stability data

≤50 ppm

Ion chromatography with conductivity detection

Bacterial endotoxin

Not tested at intermediate stage

Dose-derived; WFI system 0.25 EU/mL

USP <85>, Ph. Eur. 2.6.14

Particulate matter

Not applicable to API

≤6000/container ≥10 µm; ≤600/container ≥25 µm

USP <788>

Residual solvents

ICH Q3C with toxicological justification

ICH Q3C with lower in-process limits for Class 2 solvents

Headspace GC-FID

The fluoride limits in the table are route-specific process validation values, not compendial monograph limits.

The Organolithium Intermediate Demands Cryogenic Control and In-Line Monitoring

When pentafluorobenzene is lithiated at the only aromatic hydrogen using n-butyllithium, the resulting pentafluorophenyllithium is a highly reactive intermediate that imposes cryogenic temperature control and strict oxygen and moisture exclusion. The reaction is performed in anhydrous tetrahydrofuran at −78 °C to −65 °C in a glass-lined reactor equipped with a secondary heat exchange loop using a silicone-based heat transfer fluid. The n-butyllithium is added by a jacketed dosing line over 1–3 h, and the addition rate is adjusted to maintain the internal temperature below −60 °C. If the temperature rises above −50 °C, the organolithium species can attack the ethereal solvent or eliminate fluoride to form benzyne-type intermediates, although published kinetic data for this exact substrate is limited. In-line process analytical technology, typically an attenuated total reflectance infrared probe, tracks the disappearance of the C–H stretch of pentafluorobenzene at approximately 3100 cm⁻¹; this supports endpoint control without opening the reactor. After complete lithiation, the intermediate is quenched with trimethyl borate at −78 °C to form pentafluorophenylboronic acid, which is then hydrolyzed with aqueous ammonium chloride at 0 °C and extracted into methyl tert-butyl ether. The organolithium route is preferred over Grignard formation when low levels of residual magnesium in the final API would create bioinorganic concerns. The water content of the solvent must be maintained below 100 ppm, and the atmosphere must contain less than 10 ppm oxygen. Batch-to-batch variability is observed when the cooling system does not recover fast enough after the exotherm, producing a temperature overshoot that raises the level of defluorinated by-products by 0.5–1.0 area percent in the GC fingerprint. For injectable-grade downstream use, the resulting pentafluorophenylboronic acid is recrystallized from a toluene/hexane mixture and dried at 40 °C under vacuum. Residual lithium and boron are monitored by ICP-OES against process validation limits. This route is relevant to tablet and capsule APIs where a pentafluorophenyl group improves oxidative metabolic stability at the para position of an aromatic ring, and the same organometallic intermediate may be used in injectable candidates provided the elemental impurity profile meets ICH Q3D. Published data for this specific configuration is limited, and the analytical markers above are route-specific indicators rather than compendial acceptance criteria.

2,3,4,5,6-Pentafluorobenzene is supplied as a pharmaceutical-grade fluorinated aromatic API under supplier code PFB-100-API for oral, tablet, capsule, granule, and injectable dosage-form development. The compound has the molecular formula C₆HF₅, CAS Registry Number 363-72-4, and molecular weight 168.06 g/mol. At 25 °C it is a clear, colourless, mobile liquid with a density of 1.448 g/cm³, a refractive index of 1.3880, a boiling point of 85.0 °C, and a melting point of −47.4 °C. The neat liquid is not a directly compressible solid and is not administered as supplied. For tablet and granule applications the fluid is adsorbed onto a high-surface-area carrier; for capsule applications it may be filled as a cooled liquid or as an adsorbed solid; for injectable applications it is formulated as a non-aqueous or emulsified system. Packaging is 100 mL, 500 mL, and 1 L amber borosilicate glass with PTFE-lined closures under dry nitrogen, with storage at 2–8 °C protected from light. The supplier releases each lot against a certificate of analysis covering appearance, identity, assay, water content, residual solvents, sulfated ash, and elemental impurities. Published pharmacological endpoint data for this precise fluorinated hydrocarbon as an active pharmaceutical ingredient are limited; development programmes must therefore supply their own nonclinical and clinical evidence before use.

What Differentiates the 2,3,4,5,6-Substitution Pattern Among Fluorobenzene Intermediates?

The single ring hydrogen in 2,3,4,5,6-pentafluorobenzene is the principal structural differentiator. It provides one chemically accessible C–H position for late-stage functionalization, metabolic modification, or analytical derivatization. Hexafluorobenzene, by contrast, is fully substituted and has no C–H bond; its chemistry is dominated by electron-deficient π interactions rather than hydrogen replacement. The physical-processing difference is equally important: 2,3,4,5,6-pentafluorobenzene has a boiling point of 85.0 °C and density 1.448 g/cm³, while hexafluorobenzene has a boiling point of 80.1 °C and density 1.606 g/cm³. The lower density of pentafluorobenzene changes volumetric capsule fill calculations, and the slightly higher boiling point offers marginally less vapour pressure at 20–25 °C. Compared with 1,2,4,5-tetrafluorobenzene, the absence of a second ring hydrogen in the pentafluoro compound eliminates positional-isomer formation in downstream transformations. Published direct comparative formulation data for 1,2,4,5-tetrafluorobenzene as a tablet component is limited; therefore, the following comparison is restricted to the two fully characterised fluorobenzene liquids.

Comparative physical-property data for fluorobenzene liquids
Substance	CAS Registry Number	Boiling point at 101.3 kPa	Density at 25 °C	Structural consequence
2,3,4,5,6-Pentafluorobenzene	363-72-4	85.0 °C	1.448 g/cm³	One C–H position; liquid at room temperature
Hexafluorobenzene	392-56-3	80.1 °C	1.606 g/cm³	Fully substituted; no C–H position

For liquid-filled capsule manufacture, the density differential means that a 0.5 mL fill of 2,3,4,5,6-pentafluorobenzene corresponds to approximately 724 mg, whereas the same volume of hexafluorobenzene corresponds to approximately 803 mg. Fill weight calculations must therefore use the lot-specific density value.

Release limits for PFB-100-API are tracked against the compendial and validated in-house methods shown in the table below. The material is released only when no unidentified volatile impurity above 0.10% is reported. Water content is controlled at ≤0.1% because dry packaging is required to prevent container-headspace corrosion during long-term storage. For injectable development, the user is responsible for the sterile filtration step and for validating the container-closure system for volatile headspace at 40 °C and 75% relative humidity.

Release specification and analytical methods
Parameter	Limit	Method
Appearance	Clear, colourless liquid; no suspended matter	Ph. Eur. 2.2.1; USP <631>
Identification	Infrared spectrum consistent with reference file	Ph. Eur. 2.2.24
Assay by gas chromatography	≥99.5% area normalisation	USP <621>; Ph. Eur. 2.2.28
Total related fluorinated impurities	≤0.5%	USP <621>
Water content	≤0.1%	USP <921>; Karl Fischer
Residual solvents	ICH Q3C Option 1 limits	USP <467> headspace GC
Sulfated ash	≤0.1%	USP <281>
Elemental impurities	ICH Q3D oral and injectable limits	USP <233> ICP-MS

When Oral Solid Dosage Processing Requires a Liquid-to-Solid Adsorption Step

Pentafluorobenzene cannot be compressed as a neat liquid. The tablet or granule intermediate is prepared by adsorbing the fluid onto a high-surface-area carrier. Neusilin US2, a magnesium aluminometasilicate, has an oil-adsorption capacity of 2.0–3.0 mL/g; therefore, the maximum practical loading is held at 200–250 mg/g to preserve flow and tabletability. In a top-spray fluid-bed granulator with liquid feed rate 10–20 kg/h, the spray is directed onto a fluidised carrier at inlet air temperature ≤40 °C, product temperature ≤30 °C, atomising air pressure 1.5–2.5 bar, and exhaust dew point ≤5 °C. Standard tray drying above 40 °C is unsuitable because the boiling point of 85.0 °C produces vapour-phase loss in unsealed vessels; vacuum drying below 30 °C is preferred. When loading exceeds 250 mg/g, production-scale tumble dryers have produced cohesive agglomerates and delayed blend uniformity under near-infrared monitoring, so the adsorption limit is treated as a critical process parameter.

For immediate-release tablets, the adsorbed granule is blended with croscarmellose sodium at 2–5% w/w, microcrystalline cellulose as diluent, and magnesium stearate at 0.5–1.0% w/w before compression on a rotary tablet press to hardness 40–80 N. For granule-based oral products intended for reconstitution or sachet filling, the adsorbed carrier is milled through a 1.0 mm screen and filled into foil-lined sachets at loss-on-drying ≤1.0%. Blending is performed in a diffusion mixer at 15–25 rpm for 10–20 min; the acceptance criterion for blend uniformity is an individual sample relative standard deviation ≤5.0%. Because the active is volatile, the sachet headspace is flushed with nitrogen and the seal is checked by vacuum decay at −30 kPa.

For capsules, size 0 HPMC capsules are filled at 0.4–0.6 mL neat liquid on cooled lines at 5–10 °C, followed by sealing or banding. Cold-form aluminium foil is recommended over polyvinyl chloride blister material because the active is volatile. Published data for a directly compressed tablet of the neat liquid is limited; the liquid-to-solid adsorption step is a necessary formulation conversion.

Injectable product manufacture requires either dissolution in a parenteral-grade oil or preparation of an injectable emulsion. For an oil-in-water emulsion, the dispersed phase is passed through a high-pressure homogeniser at 800–1200 bar until the globule-size distribution meets USP <729>: mean droplet diameter ≤500 nm and the volume fraction of droplets greater than 5 μm does not exceed 0.05%. The emulsion is then filtered through a 0.22 μm polyvinylidene fluoride membrane and aseptically filled. The finished injectable must meet USP <71> sterility, USP <85> bacterial endotoxins, and USP <788> particulate matter. Because the active compound is hydrophobic and volatile, aqueous solubility is insufficient for direct dissolution; a polysorbate 80 or soybean-oil emulsion containing a lipophilic stabiliser is required. Terminal steam sterilisation at 121 °C for 15 min is not recommended for unsealed vessels because the low boiling point generates headspace vapour. If terminal sterilisation is required for a sealed parenteral, it must be performed in pressure-rated containers with validated headspace gas composition and moisture content.

Manufacturing experience with liquid hydrophobic APIs indicates that holding an unsealed emulsion at 40 °C during transfer can cause droplet growth and volatile loss; jacketed vessels should be cooled to 5–10 °C during homogenisation and filling. Process analytical technology for globule size should be used at-line rather than relying solely on release testing. Published data for this specific pentafluorobenzene injectable configuration is limited; the above globule-size targets are compendial requirements for injectable emulsions, not compound-specific clinical results.

Residual Solvent and Elemental Impurity Control Boundaries

The supplier applies ICH Q3C Option 1 limits by headspace GC. Typical manufacturing-related solvent limits are benzene ≤2 ppm, dichloromethane ≤600 ppm, methanol ≤3000 ppm, and toluene ≤890 ppm. Lot-specific data are reported on the certificate of analysis. For elemental impurities, ICH Q3D route-specific limits are applied to both oral and injectable finished-product risk assessments. For injectable finished products, cadmium is controlled at ≤2 μg/g, lead at ≤5 μg/g, arsenic at ≤15 μg/g, and mercury at ≤3 μg/g unless the marketing authorisation specifies lower values. Oral products apply the same lead, arsenic, and mercury limits with cadmium at ≤5 μg/g. Validation batches are monitored by ICP-MS using USP <233>, and residual solvents are confirmed by USP <467> headspace GC.

The material should not be combined with primary or secondary amines in heated preformulation stress studies without monitoring for nucleophilic aromatic substitution of fluoride. Transfers are conducted under nitrogen in stainless-steel lines with mechanical seals; product-contact surfaces of 316L stainless steel, PTFE, and PVDF are used. Closed handling with local exhaust ventilation and grounded transfer lines is required because the liquid has a low flash point and a measurable vapour pressure at ambient temperature.

HS Code	649937
Product Name	2,3,4,5,6-Pentafluorobenzene Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable
Chemical Name	Pentafluorobenzene
Iupac Name	1,2,3,4,5-Pentafluorobenzene
Cas Number	363-72-4
Einecs Number	206-660-8
Molecular Formula	C6HF5
Molecular Weight	168.06 g/mol
Appearance	Colorless to pale yellow liquid
Purity	≥99.0%
Grade	Pharma Grade
Dosage Forms	Tablet, Capsule, Granule, Injection
Routes Of Administration	Oral, Injectable
Solubility	Insoluble in water; soluble in organic solvents
Boiling Point	85-87 °C
Melting Point	-48 °C
Density	1.511 g/mL at 25 °C
Refractive Index	n20/D 1.392
Flash Point	13 °C (closed cup)
Storage Conditions	Store in a cool, dry, well-ventilated area away from heat, sparks, and open flames
Hazard Classification	Flammable liquid; irritant; harmful if swallowed
Packaging	Amber glass bottle with PTFE-lined cap
Shelf Life	24 months when stored as directed

Packing	2,3,4,5,6-Pentafluorobenzene Pharma Grade API supplied in 25 kg double-lined, sealed HDPE drums suitable for oral and injectable use.
Container Loading (20′ FCL)	20′ FCL container loading of 2,3,4,5,6-pentafluorobenzene pharma-grade API for tablet, capsule, granule, injection; oral and injectable, palletized and secured.
Shipping	Ship Pentafluorobenzene API in UN-approved, sealed, inert-atmosphere containers with temperature/humidity control, protected from light and moisture. Comply with IATA/ADR/IMDG, GDP, and SDS requirements for flammable/irritant materials. Include COA, SDS, packing list, and chain-of-custody documents. Use validated lanes, tamper-evident seals, and qualified handlers throughout transit. Maintain documented temperature records. Keep away from ignition sources.
Storage	Store 2,3,4,5,6-Pentafluorobenzene Pharma Grade API in tightly closed, original, labeled containers under controlled room temperature in a cool, dry, well-ventilated, fire-safe area. Protect from light, moisture, heat, ignition sources, static discharge, and incompatible substances such as oxidizers. Maintain GMP-compliant segregation, cleanliness, secure access, and secondary containment. Keep away from food, feed, and consumables. Suitable for oral and injectable dosage manufacturing.
Shelf Life	Shelf life: Typically 24–36 months when stored sealed, dry, protected from light at controlled room temperature; retest before pharmaceutical use.

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2,3,4,5,6-Pentafluorobenzene Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable