# Benzophenone (CAS 119-61-9) — Complete Guide to Properties and Applications **Category:** Photoinitiator and UV Absorber | **Formula:** C₁₃H₁₀O | **MW:** 182.22 g/mol --- ## What Is Benzophenone? **Benzophenone (CAS 119-61-9)** is a photoinitiator and uv absorber with the molecular formula **C₁₃H₁₀O** and molecular weight **182.22 g/mol**. The IUPAC systematic name is **diphenylmethanone**. It appears as a **white crystalline solid with rose-like odor**. ## Frequently Asked Questions ### What is the CAS number of Benzophenone? The CAS Registry Number is **119-61-9**. This unique identifier is registered with the Chemical Abstracts Service and serves as the authoritative reference for chemical substance identification in scientific literature, regulatory filings, and commercial transactions. When ordering Benzophenone from any supplier, specifying the CAS number ensures you receive the correct compound regardless of naming variations. ### What is the molecular weight of Benzophenone? The molecular weight is **182.22 g/mol** based on the molecular formula **C₁₃H₁₀O**. This value is calculated from the standard atomic weights of the constituent elements and represents the mass of one mole of the compound. For synthetic planning, use this value to calculate molar equivalents and prepare solutions of known concentration. ### What is Benzophenone used for? Benzophenone is primarily used as a photoinitiator and uv absorber in organic synthesis and related chemical processes. The specific applications depend on the particular research or industrial context. For detailed application information, consult the product sections above or refer to the supplier's technical documentation and published synthetic protocols. ### How should Benzophenone be stored? Store Benzophenone in a cool, dry, well-ventilated area away from incompatible materials including strong oxidizing agents, strong acids, and sources of ignition. Keep the container tightly closed when not in use. Always consult the Safety Data Sheet (SDS) from your specific supplier for the most accurate and up-to-date storage recommendations, as conditions may vary by purity grade and formulation. ### Where can I buy Benzophenone? Benzophenone (CAS 119-61-9) is available from major chemical suppliers. Availability, pricing, and purity grades vary by supplier and region. Check the product sourcing section for CoreyChem availability or contact our sales team for sourcing assistance and bulk quotation. ### What is the purity of commercial Benzophenone? Commercial Benzophenone is typically available at ≥97% purity from major chemical suppliers. Higher purities (≥99%) may be available for specialized applications in pharmaceutical manufacturing and analytical standards. Always verify the specific purity grade and certificate of analysis (CoA) with your supplier before use in critical applications. ### What is the mechanism of benzophenone as a photoinitiator? Benzophenone functions as a Type II (hydrogen-abstraction) photoinitiator. Upon absorption of UV light (λ ≈ 250–350 nm), the carbonyl group is promoted from the singlet ground state (S₀, n orbital) to the excited singlet state (S₁, π* orbital), which undergoes rapid intersystem crossing (k_ISC ≈ 10¹¹ s⁻¹) to the triplet state (T₁). The T₁ state has a lifetime of approximately 10–50 μs in deoxygenated solution, sufficient for bimolecular reaction with a hydrogen donor (co-initiator). The n,π* triplet state is diradical in character — the oxygen atom carries significant spin density — and abstracts a hydrogen atom from the co-initiator (typically a tertiary amine such as N-methyldiethanolamine) to generate a ketyl radical and an α-aminoalkyl radical. The α-aminoalkyl radical initiates free-radical polymerization of acrylate and methacrylate monomers, while the benzophenone ketyl radical is too sterically hindered to initiate polymerization effectively. Oxygen inhibits the process by quenching the triplet state (k_q ≈ 2 × 10⁹ M⁻¹s⁻¹), so UV-curing formulations containing benzophenone must be processed under inert atmosphere or with oxygen scavengers. ### How does benzophenone differ from benzoin ether photoinitiators? Benzophenone belongs to the Type II (bimolecular) class of photoinitiators, requiring a co-initiator (typically a tertiary amine) to generate the initiating radical species. Benzoin ethers (e.g., benzoin methyl ether, benzoin isobutyl ether) are Type I (unimolecular) photoinitiators that undergo direct α-cleavage upon UV irradiation to generate benzoyl and α-alkoxybenzyl radicals, both of which initiate polymerization. Type I systems offer simpler formulation (single-component initiator) but suffer from yellowing and shorter shelf stability. Type II benzophenone-amine systems exhibit less yellowing, lower odor, and better deep-cure performance in thick films due to the photobleaching effect — benzophenone is consumed during the process, allowing UV light to penetrate deeper as curing progresses. ### What is benzophenone's role as a UV absorber? Benzophenone and its hydroxylated derivatives (oxybenzone, BP-3) are the most widely used UV absorbers in sunscreens and cosmetic formulations. The strong UV absorption (λmax ≈ 250 nm for benzophenone, ~288 and 325 nm for oxybenzone) stems from the π → π* and n → π* transitions of the benzoyl chromophore. After absorption, the excited-state energy is dissipated non-radiatively through intramolecular proton transfer in the hydroxybenzophenones, where the intramolecular hydrogen bond between the ortho-hydroxyl group and the carbonyl oxygen creates a six-membered ring that facilitates an excited-state intramolecular proton transfer (ESIPT) cycle. This ultrafast photoprotective mechanism converts absorbed UV energy to heat within picoseconds, preventing photochemical damage to skin and product formulations. ### How is benzophenone used in organic synthesis? Benzophenone serves two distinct roles in synthetic organic chemistry. First, as a protecting group precursor: benzophenone imine (Ph₂C=NH) is prepared from benzophenone and ammonia under dehydrating conditions and used to protect primary amines as the N-diphenylmethylene (benzophenone imine) derivative. This protecting group is stable to strong bases (LDA, n-BuLi) and nucleophiles, enabling amine-bearing substrates to participate in reactions that would otherwise protonate or coordinate through the free amine. Deprotection is achieved by mild acidic hydrolysis (1M HCl, THF/H₂O) or catalytic hydrogenation. Second, benzophenone ketyl radical anion — generated by single-electron reduction with sodium metal in THF or with photochemical reductants — is a powerful one-electron reductant (E° ≈ -1.8 V vs SCE) used for the deoxygenation of epoxides to alkenes, dehalogenation of aryl halides, and reductive cleavage of sulfonates. ## Key Applications in Industry and Research Benzophenone's unique combination of photochemical activity and thermal stability makes it indispensable across multiple industrial sectors. Its applications span from high-tech UV-curable coatings to everyday consumer products. ### UV-Curable Coatings, Inks, and Adhesives The largest industrial application of benzophenone is as a photoinitiator in UV-curable formulations. In clear coatings for wood flooring, furniture, and automotive parts, benzophenone (1–5 wt%) combined with a tertiary amine synergist (typically N-methyldiethanolamine at 2–5 wt%) enables curing within seconds under medium-pressure mercury UV lamps. The rapid cure eliminates solvent evaporation, dramatically reducing VOC emissions compared to conventional thermal curing systems. UV-curable printing inks based on benzophenone photoinitiation are the standard for high-speed offset, flexographic, and screen printing on non-porous substrates including plastics, metals, and glass. The instantaneous cure enables printing speeds exceeding 300 meters per minute with immediate post-print handling. UV-curable pressure-sensitive adhesives using benzophenone offer on-demand curing — the adhesive remains tacky until UV exposure triggers crosslinking, providing precise control over bond formation timing. ### Photostabilization of Polymers and Personal Care Products Benzophenone and its derivatives function as UV absorbers that protect materials from photodegradation. In polyethylene, polypropylene, and PVC outdoor applications (pipes, decking, agricultural films), benzophenone-type UV absorbers at 0.1–0.5 wt% dissipate absorbed UV energy as heat, preventing polymer chain scission, crosslinking, and discoloration. The mechanism relies on the ultrafast excited-state intramolecular proton transfer (ESIPT) in ortho-hydroxybenzophenones, which converts UV photon energy to vibrational energy within picoseconds — faster than competing photochemical degradation pathways. In sunscreens, oxybenzone (benzophenone-3) absorbs both UVB (280–315 nm) and UVA-II (315–340 nm) radiation. However, regulatory scrutiny has intensified due to concerns about coral reef toxicity and endocrine disruption potential, prompting the development of benzophenone-free sunscreen formulations in some markets. ### Organic Synthesis Building Block As a synthetic intermediate, benzophenone is the starting material for diphenylmethane derivatives through Clemmensen or Wolff-Kishner reduction, for diphenylmethanol (benzhydrol) through sodium borohydride reduction, and for benzophenone imine through condensation with ammonia. The benzophenone imine protecting group strategy is widely employed in the synthesis of primary amine-containing natural products and pharmaceutical intermediates, where the diphenylmethylene group masks the amine nitrogen from electrophilic attack and metal coordination during multi-step sequences involving organometallic reagents. ### Perfumery and Fragrance Applications Benzophenone's mild rose-like odor has led to its use as a fragrance fixative in perfumes, soaps, and cosmetics. It slows the evaporation of more volatile fragrance components, extending the longevity of the scent on skin or fabric. Typical use levels are 0.1–2% in fine fragrance and 0.01–0.5% in functional products. *Note: Benzophenone (CAS 119-61-9) is not currently in the CoreyChem catalog. Contact [email protected] for sourcing inquiries.* ## Industry and Regulatory Considerations Benzophenone is listed on the European Chemicals Agency (ECHA) Substance of Very High Concern (SVHC) Candidate List due to its classification as a substance of equivalent concern for endocrine disrupting properties. It is also included in California Proposition 65. Laboratories and manufacturers handling benzophenone should implement engineering controls (local exhaust ventilation), use appropriate PPE (nitrile gloves, safety goggles), and maintain updated SDS documentation. Despite these regulatory developments, benzophenone remains commercially available for industrial and research use from major chemical suppliers worldwide. ## Physical and Chemical Properties | Property | Value | Source | |----------|-------|--------| | CAS Number | 119-61-9 | | | Molecular Formula | C₁₃H₁₀O | | | Molecular Weight | 182.22 g/mol | | | IUPAC Name | diphenylmethanone | | | Appearance | white crystalline solid with rose-like odor | | | Melting Point | 47–49 °C | | | Boiling Point | 305 °C | | | Density | 1.11 g/cm³ | | ## Where to Buy ## Product Sourcing **Benzophenone (CAS 119-61-9)** is not currently listed in the CoreyChem catalog. Contact [email protected] for sourcing assistance.