# Mo(VI) Complexes Immobilized on SBA-15 as an Efficient Catalyst for 1-Octene Epoxidation
## 2 Results and Discussion
### Catalytic Performance in 1-Octene Epoxidation
#### 2.2.2 Influence of the Solvent  
As we have previously described, the influence of the nature of the solvent was evaluated by using different conventional organic solvents: tetrahydrofuran (THF), methanol, isopropanol, isopropylbenzene (cumene), toluene, and n-decane. These compounds were selected due to their very different polarity and handling easiness. All the reactions were carried out by using a molybdenum/1-octene molar ratio of 1:1000 and TBHP as oxidant. Figure 5 displays the obtained epoxide yields in the catalytic tests carried out within these solvents (during 6 h of reaction), pointing to very remarkable differences between the different organic solvents, and suggesting that the polarity of the reagents play a major role in olefin epoxidation in presence of these catalysts. As observed, less polar solvents lead to higher 1,2-exposioctane yields. This trend is in fairly good agreement with results obtained by [PERSON] et al. [25], and it is due to p-donor organic solvents capable of coordinating to molybdenum sites, hindering the coordination between these metal centers and the oxidant (TBHP), which is mandatory for the substrate epoxidation. Thus, the presence of oxygen atoms in the solvent, with an available electron pair that can effectively compete with TBHP to bind to Mo(VI) sites, involves an important inhibition of the epoxidation reaction [25; 26]. Since the coordination capacity of the electron pair increases by increasing the dipole moment of the solvent molecule, there should be a relationship between this parameter and the obtained epoxide yield. Figure 6 depicts the epoxide yield values obtained after 6 h of reaction versus the dipole moment of the used solvent, confirming the connection between both parameters. A drastic decrease of the epoxide production is observed by increasing the dipole moment above 1.6 D because, in these cases, metal centers are mainly coordinated to solvent instead to TBHP molecules. Figure 5: 1,2-epoxioctane yields obtained in presence of different solvents (Reaction conditions: Temperature = 75 °C; TBHP as oxidant; 1-octene:oxidant molar ratio of 1; Mo:1-octene = 1:1000). The influence of the epoxidation solvent was evaluated not only on the yield towards the desired oxirane, but also on the oxidant efficiency (\(\eta_{\text{TIBHP}}\)). This parameter is calculated as the ratio between the obtained epoxide amount and that corresponding to the converted oxidant. This calculation has been included in Equation (1). High oxidant efficiencies involve poor extension of the side reactions, not only related to the oxirane, like the ring opening of the epoxide to the diol, or its isomerization to an aldehyde [27], but also those involving the non-oxidative consumption of the oxidant, such as its thermal decomposition. \[\eta_{\text{TIBHP}}\left(\%\right)=\left(\text{Mol}\right)_{\text{epoxide}} /\left[\left(\text{Mol}\right)_{\text{TIBHP }t=0}\cdot\text{X}_{\text{TIBHP}}\right)\right]100, \tag{1}\]  
Figure 7 shows the oxidant efficiency progress by increasing reaction time for all the evaluated solvents. Figure 6: Relationship between 1,2-epoxioctane yield and dipole moment of the solvent (Reaction conditions: Temperature = 75 \({}^{\circ}\)C; TBHP as oxidant; 1-octeneoxidant = 1; Mo:1-octene = 1:1000). Figure 7: TBHP efficiency of 1-octene epoxidations carried out in presence of different solvents. As observed, less polar solvents (with low dipole moment) led to very high oxidant efficiency, indicating that TBHP is exclusively converted in the epoxidation reaction. On the contrary, the use of solvents with high polarity considerably reduces the oxidant efficiency because the interaction solvent-metal prevents the coordination TBHP-Mo(VI) and, thus, the oxygen transfer from the oxidant to the olefin is jeopardized. As a general trend, oxidant efficiency values are almost constant during all the reaction time, indicating that the kind of interaction established between solvent molecules and metal centers remains unaltered throughout the evaluated process.