## 3 Results and Discussion  
### Catalytic Conversion of \(\alpha\)-Pinene over Stannic Chloride Molten Salt Hydrates  
As previously mentioned in the introduction, what we have expected was that the Lewis acid-assisted Bronsted acidic nature of stannic chloride molten salt hydrates (SnCl\({}_{4}\)-5H\({}_{2}\)O) would work as a catalyst. In accordance with this expectation, the catalytic amount of SnCl\({}_{4}\)-5H\({}_{2}\)O was active for the conversion of \(\alpha\)-pinene in a solvent-less condition. As shown in Figure S1, the reaction products could be divided into four main groups (monomeric hydrocarbon, heteroatom-containing monomeric, dimeric, and trimeric product regions) on the basis of retention time in gas chromatography/flame ionization detector (GC/FID) chromatogram and molecular ion peaks in mass spectra. Figure S2A,B show the representative mass spectra of dimeric and trimeric hydrocarbons including molecular ion peaks at _m_/z 272 [C\({}_{20}\)H\({}_{32}\)]\({}^{+}\) and _m_/z 408 [C\({}_{30}\)H\({}_{48}\)]\({}^{+}\), respectively. Figure 1A shows that \(\alpha\)-pinene, which is the main constituent of turpentine, was consumed precipitously with increasing reaction temperature and the content thereof eventually stands at 0% in the reaction mixture heated above 90 \({}^{\circ}\)C. For the cases of dimeric and trimeric products, the contents increased approximately four-fold and eight-fold when the reaction temperature increased from 60 to 110 \({}^{\circ}\)C, standing at 60.9% and 15.4%, respectively, at 110 \({}^{\circ}\)C. There was a large discrepancy in the conversion of \(\alpha\)-pinene and yields of dimeric and trimeric products, which denotes the presence of other monomeric products formed from \(\alpha\)-pinene. Remarkably, our results differ from those of [PERSON] et al. who suggested that, when phosphotungstic acid supported on MCM-41 was applied, the isomerization of \(\alpha\)-pinene is the main reaction pathway at 100 \({}^{\circ}\)C and the dimeric products are formed mainly from the isomers at 160 \({}^{\circ}\)C [23]. As shown in Figure 1B, even at 70 \({}^{\circ}\)C of reaction temperature, 100% conversion of \(\alpha\)-pinene can be achieved by increasing the reaction time. Given that the dimeric products were produced without \(\alpha\)-pinene after 3 h of reaction, it can be thought that the monomeric products from \(\alpha\)-pinene also participated in the dimerization [8]. Unfortunately, several mass spectra involving an unexpected molecular ion peak at _m_/z = 290 (Figure S2C) were extracted from the dimeric product region in Figure 1B. Given the difference between the _m_/z of molecular ions, the molecular ion having _m_/z = 290 could be described as [C\({}_{20}\)H\({}_{34}\)O]\({}^{+}\), which means that oxygen-containing dimeric products, possibly dimeric alcohols or ethers, were also produced during the reaction. In the dimerization of monoterenes over acidic catalysts, dimeric products having _m_/z = 290 as a molecular ion have often been reported. [PERSON] et al. suggested a dimeric alcohol product in the dimerization of crude turpentine [23]. Moreover, heteropoly acid-catalyzed conversion of camphene furnished diisobornyl ether in a moderate yield and good selectivity [24]. Figure 2A,B show the main hydrocarbon product distribution in the monomeric hydrocarbon region in Figure S1B as a function of the reaction temperature. These monomeric hydrocarbons could be divided into two groups based on the tendency in the content thereof, according to the reaction temperature. Limonene, terpinolene, \(\alpha\)-terpinene, \(\gamma\)-terpinene, and camphene except for tricyclene presented a sudden decrease in their yield above 90 \({}^{\circ}\)C, meaning their participation in dimerization. On the other hand, the contents of menthenes and \(p\)-cymene increased with increasing reaction temperature until 100 \({}^{\circ}\)C. These have been reported to form by the disproportionation of \(p\)-menthalienes [25].