K3PO4-catalyzed carbonylation of amines to formamides

• K3PO4 showed superior catalytic activity to others for the carbonylation of amines.
• Up to 99% of formaldehydes were produced using K3PO4 at mild conditions.
• PO43− of K3PO4 is capable of forming a strong hydrogen bond with an amine.
• PO43− functions as a proton shuttle as well as an amine activator.
• Small portion of K3PO4 was transformed into K2HPO4 during the carbonylation.

Synthesis of formamides from the catalytic carbonylation of amines with CO is of great interest due to their wide applications of formamides as synthetic intermediates and aprotic polar solvents. Up to now, the most commonly used catalysts are either expensive noble metal compounds or difficult-to-handle alkali metal alkoxides. We have found that a solid base, K3PO4 is a highly active and selective catalyst for the carbonylation of primary and cyclic secondary amines, producing corresponding formaldehydes in yields up to 99% at relatively mild conditions. Spectroscopic and quantum mechanical calculation results indicate that such high activity of K3PO4 is closely related to the strong hydrogen bonding ability of PO43− with the amino group of an amine, thereby enhancing the nucleophilicity of the amino group enough to interact with a neutral molecule, CO and mediating proton transfer from the amino group to the carbonyl group. Characterization of spent catalyst by FT-IR and XRD implies that small portion of K3PO4 is converted into less active K2HPO4 during the carbonylation reaction.

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