## 1 Introduction  
Aspirations for alternative biofuel have emerged vigorously worldwide, amid increasing concern about fossil fuel sustainability and environmental pollution. In this respect, cellulosic biomass-derived chemicals such as furural, 5-hydroxymethylfurfural, 2-methylfuran, levulinic esters, and angelica lactone have attracted considerable attention as renewable resources for the sustainable production of biofuels [1; 2; 3]. Another promising renewable chemical in order to produce synthetic fuel is turpentine. Turpentine can be obtained by either the distillation of oleoresins or the kraft pulping process as a side-product and it is mainly composed of \(\alpha\)-pinene and lesser amounts of isomers (\(\beta\)-pinene, camphene, and limonene), which all belong to monoterperone hydrocarbons [4]. Because fuel properties depend on what consists of the fuel, the fact that hydrocarbons make up the majority of turpentine is an advantage of itself as the resource of biofuels [5]. It has been reported that the blends of monoterenes and petroleum-based fuel could be utilized as drop-in fuels [6; 7]. When it comes to the application of fuel to an aerospace field and ramjet engines, however, drop-in fuels are required for much higher energy density than neat turpentine. To synthesize high-energy density fuel from turpentine (\(\alpha\)-pinene), dimerization over acid catalysts has been devised to increase density, thereby increasing energy density [5]. With the advantage of facile separation, various heterogeneous Bronsted acid catalysts have been studied to carry out the dimerization [8; 9]. Because the four-membered ring of \(\alpha\)-pinene is labile to acidic conditions, the ring is easily opened or extended to five-membered ring. This furnishes isomers including both monocyclic monoterpene hydrocarbons such as limonene and bicyclic monoterpene hydrocarbons such as camphene. Thus, the acid-catalyzed dimerization of \(\alpha\)-pinene always accompanies the isomerization, which is followed by inevitable cross-dimerization and makes the reaction mixture consist of not only the isomers of \(\alpha\)-pinene but also the various dimers [8]. It has been found that a dimer fraction has too high viscosity to apply it to a field where the fuel is exposed to extremely low temperatures [10]. To come up with this problem, blending the dimer faction with monoterpene hydrocarbons or the partial dimerization of \(\alpha\)-pinene has been devised [5]. Inorganic molten salts hydrates, such as ZnCl\({}_{2}\)-3H\({}_{2}\)O, are the hydrated form of inorganic salts that easily melted like butter at an elevated temperature. A chemical reaction system exploiting the inorganic molten salts hydrates as a reaction medium has been applied to several processes, particularly biopolymer conversion. It has been reported that an acidic LiBr salt hydrates can hydrolyze both the \(\beta\)-1,4 glycosidic bond of cellulose [11] and the aryl ether bond of lignin [12] and co-produce boromomethylfurural and furfural directly from lignocellulosic biomass within the biphasic system [13]. In addition to LiBr salt hydrates, ZnCl\({}_{2}\) and SnCl\({}_{4}\) salts hydrates have been used for the synthesis of isosorbide from cellulose [14] and 5-hydroxymethylfurfural from fructose, inulin, glucose, and chitosan [15; 16; 17; 18]. Herein, we focused on the acidic nature of stannic chloride molten salt hydrates (SnCl\({}_{4}\).5H\({}_{2}\)O). [SnCl\({}_{4}\).L\({}_{2}\)] complexes in anhydrous conditions have been reported as Lewis acid-assisted Bronsted acid catalysts when the L\({}_{2}\) are 2\({}^{\prime}\)-methoxy-[1,1\({}^{\prime}\)-binaphthalene]-2-ol (BINOL-Me), 2\({}^{\prime}\)-isopropyl-[1,1\({}^{\prime}\)-binaphthalene]-2-ol (BINOL-irP), 2-methoxyphenol (guaiacol), or 2,6-dimethoxyphenol (syringol), because they can coordinate to the stannic (Sn\({}^{\text{(IV)}}\)) center via the vicinal hydroxy and alkoxy groups in a bidentate manner [19; 20; 21].