## 2 Materials and Methods
### Thermodynamic Analysis of the Hydrogenation/Dehydrogenation Reactions
#### 3.5.2 Liquid-Phase Standard Molar Enthalpies of Formation of the \"Hydrogen Reach\" Reactants
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Compound** & \(\Delta_{t}H_{m}^{o}\) **(gas)** HL a & \(\Delta_{t}^{\text{g}}H_{m}^{o}\)**b & \(\Delta_{t}H_{m}^{o}\) **(liq)** HL c & \(\Delta_{t}H_{m}^{o}\) **(liq)** HL & \(\Delta_{t}H_{m}^{o}\) **(liq)** * & \(\Delta_{t}H_{m}^{o}\) **(liq)/H2 f \\ \hline
1 & 2 & 3 & 4 & 5 & 6 & 7 \\ \hline pyridine [55] & 139.1 & 40.2 & 98.9 & \(-\)86.4 & \(-\)185.3 & \(-\)61.8 \\
2-methylpyridine [55] & 97.4 & 42.5 & 54.9 & \(-\)124.9 & \(-\)179.8 & \(-\)59.9 \\
3-methylpyridine [55] & 104.5 & 44.6 & 59.9 & \(-\)123.6 & \(-\)183.5 & \(-\)61.2 \\
4-methylpyridine [55] & 102.2 & 44.8 & 57.4 & \(-\)123.5 & \(-\)180.9 & \(-\)60.3 \\
2-ethylpyridine & 78.5 & 45.9 & 32.6 & \(-\)158.0 & \(-\)190.6 & \(-\)63.5 \\
3-ethylpyridine & 85.7 & 48.0 & 37.7 & \(-\)158.0 & \(-\)195.7 & \(-\)65.2 \\
4-ethylpyridine & 83.4 & 48.6 & 34.8 & \(-\)158.0 & \(-\)192.8 & \(-\)64.3 \\ quinoline [14] & 200.5 & 59.3 & 141.2 & \(-\)166.2 & \(-\)307.4 & \(-\)61.5 \\
2-methylquinoline & 155.6 & 61.7 & 93.9 & \(-\)204.0 & \(-\)297.9 & \(-\)59.5 \\
3-methylquinoline & 163.2 & 63.7 & 99.5 & \(-\)204.0 & \(-\)303.5 & \(-\)60.7 \\
4-methylquinoline & 161.3 & 64.1 & 97.2 & \(-\)204.0 & \(-\)301.2 & \(-\)60.2 \\
2-ethylquinoline & 134.2 & 64.2 & 70.0 & \(-\)237.8 & \(-\)307.8 & \(-\)61.6 \\
3-ethylquinoline & 141.7 & 66.8 & 74.9 & \(-\)237.8 & \(-\)312.7 & \(-\)62.5 \\
4-ethylquinoline & 141.8 & 67.7 & 74.1 & \(-\)237.8 & \(-\)311.9 & \(-\)62.4 \\
2-phenyl-quinoline & 286.6 & 92.7 & 193.9 & \(-\)283.3 & \(-\)477.2 & \(-\)59.7 \\ \hline \hline \end{tabular}  
* Gas-phase enthalpies of formation of the fully dehydrogenated molecules are shown (HL = “hydrogen lean” = substituted pyridine or quinoline) from Table 10, column 5, or from experiment [55]. b Evaluated enthalpies of vaporization of the fully dehydrogenated molecules from Tables 2 and 3. c Liquid-phase enthalpies of formation of the fully dehydrogenated molecules as the difference between column 2 and 3 in this table. d Liquid-phase enthalpies of formation of the fully hydrogenated molecules (HR = hydrogen reach = dehydrogenated pyridines and quinolines calculated according to the ”centerpiece” approach). e Enthalpies of reactions according to Figure 1. f Enthalpies of reactions according to Figure 1 per mole H\({}_{2}\).  
\end{table} 
Table 11: Calculation of the _liquid-phase_ reaction enthalpies, \(\Delta_{t}H_{m}^{o}\) (liq), of the dehydrogenation of pyridines to piperidines and quinolines to decahydroquinolines, at \(T\) = 298.15 K (\(p^{o}\) = 0.1 MPa, in kJ\(\cdot\)mol\({}^{-1}\)) a.  
Figure 4: Calculation of enthalpies of formation, \(\Delta_{\rm{f}}H_{\rm{m}}^{\rm{o}}({\rm{liq}})\), of alkyl-substituted decahydroquinolines using the H\(\rightarrow\)CH\({}_{3}\) (\(-\)37.8 \(\pm\) 0.8) and H\(\rightarrow\)CH\({}_{2}\)CH\({}_{3}\) (\(-\)71.6 \(\pm\) 1.8) increments for piperidine ring (see Figure 3). Figure 3: Evaluation of increments H\(\rightarrow\)CH\({}_{3}\) for \(\Delta_{\rm{f}}H_{\rm{m}}^{\rm{o}}({\rm{liq}})\) responsible for exchange of H-atom in piperidine ring with the methyl group. The averaged increment (\(-\)37.8 \(\pm\) 0.8) kJ-mol\({}^{-1}\) for the H\(\rightarrow\)CH\({}_{3}\) substitution was derived as it shown in Figure S4. The increment H\(\rightarrow\)CH\({}_{2}\)CH\({}_{3}\) was calculated based on the enthalpies of formation of piperidine, 4-ethyl-piperidine (numerical data are given in Table S6). The liquid-phase enthalpies of formation of the \"hydrogen reach\" alkyl-pyridine and alkyl-quinoline derivatives, calculated according to the centerpiece approach (for details see Table S7), are given in Table 11, column 5. This means that all data for calculating the hydrogenation/dehydrogenation enthalpies for reactions according to R1-R3 (Figure 1) are complete.