**4.1.** *In situ* **kinetic study using NMR spectroscopy**

rate (**Figure 5**). Therefore, two working hypothesis were considered to explain such behavior. The first, under a strong acidic condition, the catalyst's ligand became protonated, and subsequently deco-ordinated from the Ru atom, followed by the loss of catalytic activity and the second one, in a large excess of hydrogenation mixture, the protonated triethylamine is also in large excess over the protonated substrate and sterically hinders active site of the

44 New Advances in Hydrogenation Processes - Fundamentals and Applications

**Figure 5.** Graphical summary of the results obtained in parametric study of ATH.

The variation of the ratio between formic acid and triethylamine, the two components of the hydrogenation mixture, could provide an insight into several subtle aspects of the reaction mechanism. Also, several visual differences between reaction mixtures containing different molar ratios of TEA and formic acid were observed, yellow color for mixtures containing higher molar ratio between formic acid and triethylamine and orange color for the mixture with higher amount of base. This fact indicates that the catalytic complex undergo some significant changes in excess of acid followed by loss of activity of the catalyst. Although, using higher amount of the TEA also showed that the reaction perform much more slowly than usual.

catalyst for substrate.

Implementation of the kinetic measurements of ATH of imines in flask brings some drawbacks. One of them is relatively complicated preparation of the sample for the following gas chromatography analysis. This preparation includes alkalinization of the reaction mixture for the release of the basic product and salt from formic acid, extraction of organic compounds into the diethyl ether, evaporating of the ether and dissolving of the sample with acetonitrile and analysis itself. For the practical reasons it is not possible to perform efficient enough kinetic measurements. To remove these drawbacks practical *in situ* NMR method of monitoring can be implemented. The core of this method lies in mixing of the catalyst together with the hydrogenation mixture (formic acid/TEA) dissolved in deuterated solvents like acetonitrile or dimethyl sulfoxide in NMR tube. The reaction is started by the addition of solution of substrate and in timely manner H1 -NMR spectra are acquired by automated software. By this, highquality kinetic profile of the reaction is obtained without an intervention from the ambient environment.
