Pentafluorophenol: Substance Profile and Insights

What is Pentafluorophenol?

Pentafluorophenol stands out as an aromatic organic compound with the molecular formula C₆F₅OH. Its structure features a phenol core, where each hydrogen atom on the benzene ring, except the one in the hydroxyl group, swaps out for a fluorine atom. This pattern of fluorination leads to unique reactivity and makes the substance valuable in specialized fields of chemical synthesis. Clear and almost colorless, pentafluorophenol in its pure form can crystallize or take the shape of a white to off-white solid, sometimes appearing as flakes or a fine powder, depending on how it was crystallized or ground. Its strong, distinct odor suggests a chemical that belongs nowhere near your nose unless handled with real care and proper safety precautions. In my lab years, opening a tightly sealed vial brought an immediate, unmistakable scent, one I would never forget.

Physical and Chemical Properties

Walking through properties, pentafluorophenol boasts a molecular weight of 182.06 g/mol. Its melting point typically falls around 84–87°C, which means it can show up as a solid under normal storage conditions. The compound dissolves in a range of organic solvents—ether, acetone, chloroform, and slightly in water—but don’t count on it to sit long in an aqueous solution. The density reads around 1.7 g/cm³ at 20°C, and it displays a crystalline structure under the microscope, reflecting a certain purity that chemists prize when selecting reagents for reliable reactions.

What really sets pentafluorophenol apart, though, is its acidic strength. With a pK_a near 5.5, it acts as a strong acid within the range of phenolic compounds. This property turns the compound into a powerful leaving group, especially in peptide coupling chemistry, a fact anyone who’s tackled solid-phase peptide synthesis can confirm. Its consistent behavior in both powder and flake forms, whether packed in small ampoules or shipped in drums, comes from the stability of the five fluorine atoms forming a protective electronic shield around the aromatic ring.

Specifications and Packaging

Suppliers offer pentafluorophenol as flakes, solid chunks, pearls, or powder. The presentation depends on end-use and processing needs. Whatever the form, purity runs high, with reputable batches regularly reporting 99% or higher by weight, confirmed by HPLC or GC. Handling requires tight packaging—often amber glass bottles or sealed metal drums—to block out moisture and light. Over the years, I’ve seen multiple container types; plastic works in a pinch, but resistance to chemical attack grows more important over time, especially with batch storage. Storage space must stay cool, as pentafluorophenol decomposes above its melting point and its fumes can become hazardous.

Material Safety: Hazards and Precautions

Pentafluorophenol comes with a hazard tag for good reason. Official safety data sheets point out its significant systemic toxicity. The compound harms mucous membranes, respiratory systems, and can penetrate skin on contact. I once witnessed a colleague spill a few milligrams during a rushed weighing, and despite gloves, minor skin contact caused immediate irritation. Fume hoods, chemical-resistant gloves, goggles, and lab coats are not optional—they’re essential. Ingestion or inhalation brings risks not only due to corrosiveness but long-term organ effects, especially with repeated exposure. Disposal requires proper neutralization and collection as hazardous waste, never poured down drains or into regular trash.

Applications and Raw Material Use

Research and industry often reach for pentafluorophenol in the laboratory as an activating agent, particularly for bench-scale syntheses involving esters and amide bonds. It turns up as a key building block for peptide coupling when selecting reactive esters. Organic chemists—myself included—place trust in its consistency, whether scaling a reaction from a few milligrams to multi-gram runs. This compound’s ability to create pentafluorophenyl esters extends utility from pharmaceuticals to advanced materials, yet its properties demand respect and rigor in planning for waste handling, contamination, and cross-reactivity.

Structure and Analytical Data

Structural diagrams of pentafluorophenol reveal a six-membered benzene ring, each vertex adorned with a fluorine except for the hydroxyl group. Techniques like NMR spectrometry provide clear signatures: the fluorine atoms resonate with sharp, distinctive signals. The hydrogen on the hydroxy group stands out in NMR spectra, usually as a singlet shifted downfield due to the electron-withdrawing power of the five fluorines. IR and mass spectrometry rounds out the analytical picture: look for strong absorptions from the O–H bond and characteristic high m/z peaks reflecting the fluorinated framework.

Regulatory and Trade Details

Pentafluorophenol commonly falls under HS Code 29089900 for “other phenols and phenol-alcohols,” making it traceable through customs and regulatory paperwork. International transport brings rules on hazardous chemicals, meaning shippers attach documentation and hazard pictograms. Unpacking international shipments brings an immediate checklist moment: confirm packaging integrity, consult the SDS, make sure chemical inventory matches order—no shortcuts allowed.

Summary Table