Scientists have developed a groundbreaking eco-friendly synthesis method for producing antimony mercaptide, a crucial heat stabilizer widely used in the plastics industry. This novel process utilizes ionic liquids as both a catalyst and reaction solvent, overcoming significant drawbacks associated with traditional production techniques that rely on corrosive and hazardous concentrated acids like sulfuric or hydrochloric acid.

Conventional synthesis faces challenges like high reaction temperature (often exceeding 100°C), operational risks due to the use of controlled substances, severe equipment corrosion, and generation of hazardous waste. Crucially, the old catalysts could not be recovered. The new method directly tackles these issues. By employing specific Bronsted acidic sulfonic acid-functionalized ionic liquids – such as 1-butyl-3-methylimidazolium hydrogensulfate [BMIM][HSO₄] – the reaction becomes homogenous, significantly lowering mass transfer resistance and reducing activation energy.

The streamlined process involves reacting antimony trioxide (Sb₂O₃) with isooctyl thioglycolate in the chosen ionic liquid, under remarkably mild conditions: temperatures ranging from 15-35 °C and reaction times as short as 0.5 to 2 hours. Recommended mass ratios are Isocotyl thioglycolate : Sb₂O₃ : Ionic Liquid = 1600 : (350-420) : (1700-1900). Following the reaction, the crude antimony mercaptide undergoes vacuum distillation at temperatures between 80-110 °C and pressure ranging from -0.1 MPa to -0.01 MPa. This step purifies the target product and, critically, recovers the ionic liquid catalyst for reuse.

Extensive experimental results, detailed in multiple examples, demonstrate the method's superiority. Reaction times are drastically shortened by 2-3 hours compared to the traditional acid-catalyzed process requiring over 5 hours. Temperatures are reduced dramatically by 70-90 °C, enhancing safety. Product yields consistently exceed 99%, often reaching up to 99.8%, with purity levels above 99%. Perhaps most impressively, the ionic liquid catalyst achieves recovery rates exceeding 99% across several cycles tested, proving its practicality and cost-effectiveness. Notably, the process eliminates the formation of toxic byproducts or waste residues.

A critical advantage identified is the significantly lower corrosiveness towards industrial equipment. Corrosion tests involved immersing carbon steel nails (simulating equipment material) in different ionic liquids versus concentrated hydrochloric acid for 24 hours. While the acid caused severe corrosion, rust, and iron salt formation, the ionic liquids, including [BMIM][HSO₄], showed practically no visible damage to the nails, drastically reducing maintenance costs and safety risks.

Antimony mercaptide is prized as a cost-effective and low-toxicity alternative to expensive organotin stabilizers, offering excellent initial color retention in PVC and other polymers. This new green synthesis method addresses the major production hurdles, promising safer operations, enhanced sustainability through catalyst recycling, reduced environmental impact, and potentially lower operating costs for the rapidly growing heat stabilizer market. "Replacing hazardous acids with reusable ionic liquids represents a significant step towards greener industrial chemistry," noted researchers involved in the development.