Reaction monitoring in multiphase systems: Application of coupled in situ spectroscopic techniques in organic synthesis

The benefit of coupling different in situ spectroscopic methods (ATR-FTIR / UV-vis / Ramanspectroscopy) is exemplarily demonstrated by the means of two reactions as applicationexamples: the Lewis acid mediated formal [3+3] cyclocondensation reaction of a diene with aketenacetale and the heterogeneously catalysed asymmetric hydrogenation of imines. For bothreactions new reactors (deep-temperature cell, probe autoclave) have been developed enablingin situ measurements under real reaction conditionsFor the [3+3] cyclocondensation reaction it was demonstrated that the nature of theformed product depends on the different intermediates formed between the ketenacetal andthe acids (complexation or acid catalysed rearrangement reaction). Furthermore themechanisms of similar reactions (including other Lewis acids like AlCl3, Al2O3 and TiO2 orsubstrates like N-salicylideneaniline) could be successfully elucidated.The effectiveness of the hydrogenation depends on the specific interaction of thetested ketimines with the phosphoric acid ester used as chiral modifer. This interaction ismainly influenced by the used solvent and leads to the formation of a carbocation (CH3OH) ora contact ion pair in (CH2Cl2, CF3CH2OH). Furthermore, the detected strong adsorption ofimines and modifier on the Pt/Al2O3 catalyst affect their efficiency and activity in thereaction.