Abstract: Nowadays, considerable attention is focused on the development of new solid Lewis catalysts, which can solve the well-known problems of traditional homogeneous acid catalysts, such as ZnCl2, AlCl3 and FeCl3, in isomerization of terpene oxides. Isomerization of terpene oxides is one of the important reactions for synthesis of intermediates for production of drugs, vitamins and fragrances. α-Pinene oxide (PO) is one of the key examples, which isomerizes rapidly in the presence of acids, thereby forming many products (Reaction 1). Campholenic aldehyde (CA) and trans-carveol (trans-carv) are industrially the most desired products of PO isomerization, because they are highly valuable ingredients for the production of flavors. (1) The aim of this study was to investigate the dependence of activity and selectivity of the rearrangement of PO to campholenic aldehyde (CA) on the textural and acid-base properties of new Fe-containing materials, such as Fe-containing mesoporous mesophase silica materials (Fe-MMM-2), microporous Fe-containing nickel phosphate molecular sieves (Fe-VSB-5), Al-containing silica materials (Al-SiO2 magnetic Al-SiO2/Fe3O4) and porous metal-benzenetricarboxylates (Al-BTCs), such as MIL-X(Al) (X = 96, 100 and 110) and isostructural family MIL-100(М) (М – Al, Fe and Cr). The catalytic performance of these materials was investigated with a combination of physicochemical and catalytic approaches. The investigation of Lewis acidity was done by EPR and IR spectroscopy using 2,2',6,6'-tetramethyl-1-piperidinyoxyl radical (TEMPO) and benzonitrile/pyridine/CO as the probe molecules, respectively. It was demonstrated that these materials favour the rearrangement of PO to CA in dichloroethane under mild conditions. For Al-BTCs,The reaction rate and selectivity towards CA were found to decrease in order MIL-100 > MIL-110 > MIL-96 that was in agreement with the change of the amount of Lewis acid sites (LAS). A relatively good correlation between selectivity towards CA and the electronegativity of the metal ion was found for isostructural MIL-100(Al, Fe and Cr). The selectivity towards CA decreased in the order: MIL-100(Al) > MIL 100(Fe) > MIL-100(Cr). The high selectivity towards CA in the presence of MIL-100 has been suggested to originate from the unique structure of this material, which favors shape selectivity In the presence of Al-SiO2, Fe-VSB-5 and Fe-MMM-2 reaction rate and selectivity towards CA depended on Fe and Al content, which affected the oligomeric state of Fe and Al and Lewis acidity. Correlations between the strength of Lewis acid sites (LAS) and conversion of PO are presented in Fig. 1. Experimental data point that conversion of PO rises with increasing the strength of LAS. However, in contrast to Fe-VSB-5 and Al-SiO2, selectivity towards CA decreases with increasing the amount of LAS that is related to the formation of a large oligomeric iron oxides species. This result indicates that the high selectivity is a result of well-dispersed Lewis acid sites in a matrix. Figure 1. Correlations between conversion of PO and strength of BAS, and correlation between selectivity of CA and amount of LAS for Al-SiO2, Fe-VSB-5 and Fe-MMM-2 (Reaction conditions: 0.25 mmol of PO in 2 mL dichloroethane, 5 mg of catalyst, 303 K, 30 min). We compared the selectivities towards CA and productivities of reaction in the presence of Al-SiO2 and Al-SiO2/Fe3O4 magnetically recoverable catalyst with Al-containing containing materials demonstrated in literature (Table 1). It was found that in the presence of 12%Al-SiO2 selectivity and productivity are comparable with Al2O3-SiO2 commercial system. At the same time in the presence of 12%Al-SiO2/Fe3O4 the selectivity is not very high, while the productivity is high, when compared with the best systems reported in the literature. Table 1. The comparison of catalytic properties of Al-containing materials in isomerization of PO 12%Al-SiO2 12%Al-SiO2/Fe3O4 Al2O3-SiO2 commercial HY (Si/Al 10.4) HY (Si/Al 60) Selectivity of CA, % 72 63 72 49 66 Productivity, (mmol PO/(gcat•h) 58 41 57 33 12 Therefore, we may conclude that the magnetic 12%Al-SiO2/Fe3O4 material is more active than HY (Si/Al 10.4 and 60). Moreover, it was demonstrated that 12%Al-SiO2/Fe3O4 can be used repeatedly without significant loss of catalytic activity during at least four catalytic cycles (Fig. 2). Figure 2. TEM micrographs and photo of 12% Al-SiO2/Fe3O4 in reaction mixture and its separation from the reaction mixture by the external permanent magnet. 12% Al-SiO2/Fe3O4 recycling during the isomerisation of PO. (Reaction conditions: 0.25 mmol of PO in 2 mL dichloroethane, 5 mg of catalyst, 303 K, 30 min).

Cite: Timofeeva M.N. , Panchenko V.N. , Abel A.A. , Hasan Z. , Kirillov V.L. , Volcho K.P. , Martyanov O.N. , Jhung S.H.
Isomerization of α-Pinene Oxide to Campholenic Aldehyde over Fe-and Al-Containing Materials
The 5th Asian Symposium on Advanced Materials: Chemistry, Physics & Biomedicine of Functional and Novel Materials 01-04 Nov 2015