Markus Allmendinger

In situ ATR-IR spectroscopy: a powerful tool to elucidate the catalytic oxidation of veratryl alcohol in aqueous media

The Co(salen) catalyzed oxidation of veratryl alcohol by molecular oxygen in aqueous media was studied by online ATR-IR spectroscopy. The introduction of dioxygen into the reaction mixture initiated the formation of the aldehyde. Only product observed was veratryl aldehyde and its amount was noted to increase linearly with reaction time when reaction conditions are not changed. Addition of NaOH during the reaction increases the reaction rate as the amount of active cobalt species increases. During the reaction a strong vibration is observed in the range of cobalt–oxygen complexes at frequencies 981–993 cm−1. Based on these results we suggest here that in the catalytic oxidation of veratryl alcohol by Co(salen) complexes in basic aqueous solution, a cobalt–superoxo complex is formed, which can oxidize veratryl alcohol to veratraldehyde.

High Yield Synthesis, Separation and Structural Characterization of New [n+n]-Polyazamacrocycles

t-Bu- and isopropyl-substituted aromatic dialdehydes (la-c) and diamines (2a-f) were used to synthesize a series of imine macrocycles (3a-m). The highly selective cyclization reaction resulted either in a [2+2] stoechiometry or in a mixture of different [n+n] cycles, depending on the diamine building block. For some defined macrocycles (3b, 3d, 3e) the structure was elucidated by single crystal X-Ray diffraction that revealed a column-like arrangement of the macrocycles in the solid state. Mixtures of macrocycles were investigated with a combination of MALDI-Tof and analytical GPC which brought significant improvements in the determination of the exact size distribution. Isolated higher homologues of polyimine cycles were made available by preparative GPC for the first time. The possibility to reduce the imine macrocycles quantitatively to their corresponding amine analogues was demonstrated exemplary by the reduction of two pyridine containing cycles (4a-b).