Acid catalyzed acetalization of aldehydes with diols resulting into the formation of fragrant cyclic acetals

Abstract

The influence of reaction conditions (amount and type of the catalyst, the reaction temperature, the type of the solvent) on the reaction course of the acetalization of aldehydes with diols was tested in this paper. The optimization of reaction conditions was performed on model reaction, acetalization of 2-methylpentanal by 2-methyl-2-propyl-1,3-propanediol leading to the formation of fragrant compound 2-(1-methylbutyl)-5-methyl-5-propyl-1,3-dioxane (Troenan). p-Toluenesulfonic acid was used as an active homogeneous catalyst. It appeared to be advantageous not to use any solvent in the reaction. Using 0.3 wt% of the catalyst the almost total conversion of 2-methylpentanal was achieved after 240 min of reaction at room temperature while the selectivity to the desired product was about 98%. The optimized reaction conditions were applied to the preparation of four cyclic fragrant acetals (namely 2-hexyl-1,3-dioxolane, 2-hexyl-4-methyl-1,3-dioxolane, 2-benzyl-5-hydroxy-1,3-dioxane and 2-(1-methylbutyl)-5-methyl-5-propyl-1,3-dioxane) in larger scale; and these were sensory evaluated after purification step. Prepared heterogeneous catalysts, acid modified montmorillonite (MMT) K-10 (treated by H₂SO₄, HNO₃, and HCl) were successful in the model reaction. The conversion of 2-methylpentanal over 90% was achieved using acid modified MMT after 300 min of reaction at room temperature, the selectivity to the desired product was about 98%. MMT/H₂SO₄ can be used in the model reaction four times without any change in the reaction course, what makes it promising for the further application.