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 / Raman

spectroscopy) is exemplarily demonstrated by the means of two reactions as application

examples: the Lewis acid mediated formal [3+3] cyclocondensation reaction of a diene with a

ketenacetale and the heterogeneously catalysed asymmetric hydrogenation of imines. For both

reactions new reactors (deep-temperature cell, probe autoclave) have been developed enabling

in situ measurements under real reaction conditions

For the [3+3] cyclocondensation reaction it was demonstrated that the nature of the

formed product depends on the different intermediates formed between the ketenacetal and

the acids (complexation or acid catalysed rearrangement reaction). Furthermore the

mechanisms of similar reactions (including other Lewis acids like AlCl3, Al2O3 and TiO2 or

substrates like N-salicylideneaniline) could be successfully elucidated.

The effectiveness of the hydrogenation depends on the specific interaction of the

tested ketimines with the phosphoric acid ester used as chiral modifer. This interaction is

mainly influenced by the used solvent and leads to the formation of a carbocation (CH3OH) or

a contact ion pair in (CH2Cl2, CF3CH2OH). Furthermore, the detected strong adsorption of

imines and modifier on the Pt/Al2O3 catalyst affect their efficiency and activity in the

reaction.