Diapocynin (5,5'-dehydrodiacetovanillone) was synthesized by oxidative coupling of apocynin (acetovanillone, or 4-hydroxy-3-methoxyacetophenone). Diapocynin is a metabolite of apocynin, which has anti-inflammatory and anti-oxidative properties. The oxidizing agent was an in situ generated sulfate radical, produced by adding iron(II) sulfate and sodium peoxydisulfate to apocynin in boiling water. The diapocynin product was analyzed by FTIR, [to the first power]H NMR, and negative ion atmospheric pressure chemical ionization (APCI) LCMS. To minimize the quantity of triapocynin impurity, the reaction was stopped after five minutes. The product was re-dissolved in aqueous ammonia and re-precipitated with aqueous HCl. Small quantities of unreacted apocynin were removed by washing the product three times with boiling water. The FTIR spectrum was similar to that of apocynin, except in the fingerprint region. The [to the first power]H NMR indicated that one hydrogen was lost from each molecule of apocynin that reacted. The LC-MS indicated the presence of a [M-H[superscript -]] ion with m/z = 329.2 amu, consistent with a molar mass of 330.2 for diapocynin. (Contains 1 scheme and 2 figures.)