## 2 Results and Discussion
### Influence of the Solvent  
The effect of the solvent on the reaction rate was also investigated by carrying out the model reaction in the presence of 0.05 g of Na\({}_{2}\)CaP\({}_{2}\)O\({}_{7}\) for 30 min with various solvents (1 mL), such as water, ethanol, dichloromethane (DCM), ethyl acetate (EtOAc), _n_-hexane, and acetonitrile (MeCN). Figure 2 summarizes the effects of various solvents on the percentage yield of 2-amino-3-cyanopyridine **5a**. We observed that when solvents were used, the yield decreased, indicating that the use of a solvent has a strong inhibitory effect on the reaction yield. This effect can be explained by the dilution of the reaction medium, which leads to a decrease in the interaction between the reactant and the catalyst (Na\({}_{2}\)CaP\({}_{2}\)O\({}_{7}\)). However, the highest yield of the desired product was achieved when the reaction was carried out under solvent-free conditions (Figure 7). After determining the optimal conditions for the synthesis of 2-amino-3-cyanopyridine **5a**, the reactions of different aromatic aldehydes containing substituents in the aromatic ring, such as Me, OMe, Cl, and NO\({}_{2}\), with malonomitrile **2**, acetophenone derivatives, or cyclohexanone **3** and ammonium acetate **4** were carried out under identical reaction conditions. The thirteen desired 2-amino-3-cyanopyridine derivatives 5(a-m) were obtained with good to excellent yields (84-94%), as shown in Table 2. The nature of aromatic ring substituents had no noticeable effect on the yields of synthesized 2-amino-3-cyanopyridines 5. All reactions with aromatic aldehydes proceed without the formation of byproducts. Figure 7: Influence of the solvent in the catalytic synthesis of 2-amino-3-cyanopyridine **5a**. \begin{table}
\begin{tabular}{c c c c c c} \hline Entry & R\({}_{1}\) & R\({}_{2}\) & R\({}_{3}\) & Product \({}^{[a]}\) & Yield \({}^{[b]}\) (\%) \\ \hline
**1** & H & Ph & H & 5a & CN & 94 \\
**2** & CH\({}_{3}\) & Ph & H & 5b & CN & 85 \\
**3** & CH\({}_{3}\)O & Ph & H & 5c & CN & 84 \\
**4** & Cl & Ph & H & 5d & CN & 95 \\
**5** & NO\({}_{2}\) & Ph & H & 5e & CN & 86 \\
**6** & NO\({}_{2}\) & Ph & H & 5f & CN & 93 \\ \hline \end{tabular}
\end{table} 
Table 2: Synthesis of 2-amino-3-cyanopyridine derivatives 5. In order to explain the formation of 2-amino-3-cyanopyridine 5, we propose a credible mechanism, which is shown in Scheme 3. \begin{table}
\begin{tabular}{c c c c c} \hline Entry & R\({}_{1}\) & R\({}_{2}\) & R\({}_{3}\) & Product [a] & Yield [b] (\%) \\ \hline
7 & H & \
\begin{tabular}{c} 4- \\ CH\({}_{3}\)C\({}_{6}\)H\({}_{4}\) \\ \end{tabular} & H & 5g &
\begin{tabular}{c} CN \\ \end{tabular} \\
8 & Cl & \
\begin{tabular}{c} 4- \\ CH\({}_{3}\)C\({}_{6}\)H\({}_{4}\) \\ \end{tabular} & H & 5h &
\begin{tabular}{c} CN \\ \end{tabular} \\
9 & H & \
\begin{tabular}{c} 4- \\ CH\({}_{3}\)OC\({}_{6}\)H\({}_{4}\) \\ \end{tabular} & H & 5i &
\begin{tabular}{c} CN \\ \end{tabular} \\
10 & Cl & \
\begin{tabular}{c} 4- \\ CH\({}_{3}\)OC\({}_{6}\)H\({}_{4}\) \\ \end{tabular} & H & 5j &
\begin{tabular}{c} CN \\ \end{tabular} \\
11 & H & \
\begin{tabular}{c} -(CH\({}_{2}\))\({}_{4}\)- \\ \end{tabular} & 5k &
\begin{tabular}{c} CN \\ \end{tabular} \\
12 & CH\({}_{3}\) & \
\begin{tabular}{c} -(CH\({}_{2}\))\({}_{4}\)- \\ \end{tabular} & 5l &
\begin{tabular}{c} CN \\ \end{tabular} \\
13 & Cl & \
\begin{tabular}{c} -(CH\({}_{2}\))\({}_{4}\)- \\ \end{tabular} & 5m &
\begin{tabular}{c} CN \\ \end{tabular} \\ \hline \end{tabular}  
[a] All products were characterized by \({}^{1}\)H, \({}^{13}\)C NMR, and IR spectral data (see Supplementary Data); [b] isolated yields.  
\end{table}