Catalytic three-phase diastereoselective hydrogenation of o-toluic and 2-methyl nicotinic acid derivatives: In situ FTIR/ATR investigation

Catalytic diastereoselective hydrogenation of o-toluic and 2-methyl nicotinic acids covalently bound to various chiral auxiliaries was carried out in a three-phase slurry reactor and followed in real time by means of in situ Fourier transform infrared/attenuated total reflection (FTIR/ATR) spectroscopy. The measurements show that the catalytic hydrogenation of o-toluic acid derivatives undergoes direct transformation to corresponding cyclohexanoic compounds. On the contrary, the presence of the nitrogen atom in the nicotinyl ring affects deeply the mechanism of hydrogenation by favoring the accumulation of tetrahydropyridine intermediate in the liquid phase, which is probably caused by modifying the adsorption mode on the metallic surface. It was demonstrated that data provided by examining corresponding IR stack plots by employing a chemometric, self-modeling curve resolution algorithm are more reliable than data derived from off-line GC analysis.