Di(hydroperoxy)adamantane adducts: synthesis, characterization and application as oxidizers for the direct esterification of aldehydes.

The di(hydroperoxy)adamantane adducts of water (1) and phosphine oxides -TolPO·(HOO)C(CH) (2), -TolPO·(HOO)C(CH) (3), and CyPO·(HOO)C(CH) (4), as well as a CHCl adduct of a phosphole oxide dimer (8), have been created and investigated by multinuclear NMR spectroscopy, and by Raman and IR spectroscopy. The single crystal X-ray structures for 1-4 and 8 are reported. The IR and P NMR data are in accordance with strong hydrogen bonding of the di(hydroperoxy)adamantane adducts. The Raman (O-O) stretching bands of 1-4 prove that the peroxo groups are present in the solids. Selected di(hydroperoxy)alkane adducts, in combination with AlCl as catalyst, have been applied for the direct oxidative esterification of -nonyl aldehyde, benzaldehyde, -methylbenzaldehyde, -bromobenzaldehyde, and -hydroxybenzaldehyde to the corresponding methyl esters. The esterification takes place in an inert atmosphere, under anhydrous and oxygen-free conditions, within a time frame of 45 minutes to 5 hours at room temperature. Hereby, two oxygen atoms per adduct assembly are active with respect to the quantitative transformation of the aldehyde into the ester.