UV-531, known chemically as 2-hydroxy-4-n-octoxybenzophenone, is a premier ultraviolet (UV) absorber recognized for its exceptional performance in shielding polymers and coatings from harmful radiation. This compound absorbs UV light in the 240-340 nm range, with peak efficiency at 270-330 nm, and boasts key features like low toxicity, minimal migration, and excellent compatibility with resins. Widely used at concentrations of 0.1%-1%, UV-531 provides robust photostability in applications such as phenolic and alkyd varnishes, polyurethane coatings, acrylics, epoxies, automotive refinishes, powder coatings, and rubber products. Its synergy with additives like 4,4′-thio-bis(6-t-butyl-m-cresol) enhances its protective effects, delaying yellowing and physical deterioration in materials exposed to sunlight, thus solidifying its status as a critical additive in modern manufacturing.

Current industrial methods for synthesizing UV-531 face significant challenges that limit their viability. Phase-transfer catalysis, using agents like tetramethylammonium chloride with potassium carbonate or hydroxide, often leaves unreacted 2,4-dihydroxybenzophenone, complicating purification and reducing yields due to impurities. Solvent-based approaches, employing bromooctane in cyclohexanone with potassium carbonate, generate excessive byproducts, lower productivity, and suffer from operational inefficiencies. The one-pot method, involving catalysts like anhydrous zinc chloride and potassium iodide, shortens steps but results in subpar yields and costly, difficult post-processing. These drawbacks collectively hinder large-scale production, making novel, efficient synthesis pathways essential for advancing UV absorber technologies.

A breakthrough chlorooctane-based process overcomes these limitations by optimizing reaction conditions for enhanced efficiency and safety. The method begins with charging reactor with chlorinated octane heated to 95°C–100°C, followed by sequential addition of 2,4-dihydroxybenzophenone, PEG stabilizers like PEG-400 or PEG-600, potassium carbonate, and sodium carbonate. After mixing, the system is raised to 110°C–140°C for reflux dehydration. Post-reaction cooling enables water washing, phase separation, and distillation to isolate pure UV-531. Crucially, molar ratios are finely tuned: 1 mol of dihydroxybenzophenone to 0.03–0.05 mol PEG, 2.05–2.3 mol chlorinated octane, 0.01–0.04 mol of potassium salts, and 0.5–0.6 mol sodium carbonate. By substituting volatile bromooctane, this approach minimizes hazards and boosts raw material utilization, enabling a streamlined, cost-effective pathway.

Experimental trials validate the superior performance of this synthesis. In representative runs, initial temperatures at 95°C–100°C and reflux stages at 110°C–140°C yielded UV-531 with remarkable outcomes. For instance, one test combining chlorinated octane, dihydroxybenzophenone, PEG, and carbonates achieved a purity of >99% and a staggering yield of 95.2%. Similar results in multiple replicates confirmed consistency, with purity rates consistently exceeding 99% and yields staying above 95%. Such efficiency stems from the elimination of incomplete reactions and impurities that plague earlier techniques, with the optimized molar ratios enhancing reaction completeness and ease of isolation.

Compared to existing methods, this chlorooctane strategy delivers substantial industrial benefits. It drastically reduces costs by utilizing affordable chlorinated reagents instead of costly brominated alternatives, while the simplified procedure—relying on mild catalysts and routine operations—ensures safety and scalability. The high yield and purity translate to less waste and better resource efficiency, making UV-531 production more sustainable across polymer stabilization sectors. This innovation promises to expand access to high-performance UV absorbers for enhancing the lifespan of consumer and industrial materials in a rapidly evolving market.