Cleavage and Oligomerization of Malondialdehyde

Malondialdehyde (MDA) slowly self-condensates in aqueous solution at pH 4.5–6 and room temperature yielding (E)-(3′-oxo-1′-propenyl)malondialdehyde and 2,4-dihydroxymethylene-3-(2′-oxoethyl)glutaraldehyde. The latter compound exists in solution in equilibrium with 4-(1,3-dioxopropan-2-yl)-5-formyl-2-hydroxy-3,4-dihydro-2H-pyran, the trans-form of which can be readily isolated as a crystalline hemipotassium salt. Cleavage of MDA also occurs under these conditions leading to acetaldehyde, which further reacts with the excess of MDA to form 2,4-dihydroxymethylene-3-methylglutaraldehyde.