Iron-Catalyzed Synthesis of 4-oxo-1,3-dioxolanes (DOXs) Using Lactic Acid: From Homogeneous to Heterogeneous Behaviors

This work investigates the use of simple iron(III) and iron(II) salts (FeSO₄, Fe(NO₃)₃, Fe(OAc)₂, FeCl₂, FeBr₂, Fe(ClO₄)₂, Fe(BF₄)₂, FeCl₃, and Fe(ClO₄)₃) as catalysts for the ketalization of α-hydroxy acids (i.e., lactic and glycolic acids) to obtain 4-oxo-dioxolanes. These compounds find application in polymer science and, more recently, have been proposed as green polar aprotic solvents. Lactic acid and acetone were chosen as benchmark reactants. The results show that catalytic activity depends on the oxidation state of the metal ion, the nature of its counterion, the cosolvent used, and the molar ratio between the reactants. The most effective catalyst was revealed to be iron(III) perchlorate, which precipitates as iron(III) lactate that can be recycled in consecutive runs once separated from the reaction mixture. This beneficial prerogative couples the efficiency of homogeneous catalysis with the advantage of heterogeneous catalysis. Compared to other methods proposed in the literature, the proposed process is more sustainable, given its high efficiency, low energy consumption, ease of purification, and the absence of auxiliary substances and byproducts.

Preparation of DOXs by α-hydroxy acid ketalization promoted by iron(III) catalysts. With lactic acid, the in situ formation of iron(III) lactate allows its easy separation and recycling.