Amine‐Catalyzed Aldol Addition of Dihydroxyacetone for Bio‐Based Flame Retardants

Abstract A new catalytic method was developed for synthesizing a sustainable phosphorus‐based flame retardant (PFR) from dihydroxyacetone (DHA), a triose derived from hexoses or glycerol oxidation, e.g., for PUR applications. The study first investigates alkyl amine catalysts for self‐aldol addition of DHA to form the branched hexose dendroketose. Short‐chain, non‐functionalized secondary and tertiary amines showed the best balance between aldol activity and branching selectivity. Triethylamine (Et 3 N) was chosen for process optimization, enabling scale‐up to a 10 L process using 500 g/L DHA and 1 mol % Et 3 N, achieving a productivity of 109 g/(L·h)—approximately 7.5 times higher than the current state of the art. The resulting dendroketose was hydrogenated to produce dendroketol, a branched hexitol with three primary alcohol groups suitable for further functionalization. To prevent product loss during hydrogenation due to base‐catalyzed retro‐aldol addition, various amine neutralization methods were evaluated, with equimolar HCl addition proving most effective and economical. Finally, dendroketol was purified and phosphorylated with P 2 O 5 to yield the PFR. Flame‐retardant testing, conducted under EU standard BS 7175 (for bedding materials), confirmed compliance, underscoring the industrial potential of the process.