Vol.:(0123456789) 1 3 Journal of Porous Materials https://doi.org/10.1007/s10934-018-0578-3 Enhanced catalytic oxidation of monoterpenes by zeolite-Y entrapped iron complex: spectral studies and mechanistic vision Jignasu P. Mehta 1  · Digvijaysinh K. Parmar 1  · Haresh D. Nakum 1  · Dinesh R. Godhani 1  · Nisheeth C. Desai 1 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract [Fe(L) 2 (H 2 O) 2 ]–Y complex (where, L = (Z)-2-((4-hydroxybenzylidene)-amino)benzoic acid) has been synthesized by Flex- ible Ligand (FL) method and characterized by chemical analysis (CHN, ICP-OES, TGA, AAS), difraction method (XRD), absorption spectroscopy (FTIR, UV–Vis), BET and SEM techniques. To investigate the catalytic performance (activity, stabil- ity, and reusability), [Fe(L) 2 (H 2 O) 2 ]–Y was employed as heterogeneous catalyst in the liquid phase oxidation of α-pinene and limonene with H 2 O 2 oxidant. [Fe(L) 2 (H 2 O) 2 ]–Y catalyzed the oxidation of α-pinene via free radical formation as confrmed by in-situ IR and DR UV–Vis spectroscopy. [Fe(L) 2 (H 2 O) 2 ]–Y showed conversion of α-pinene (67%) and limonene (79%) with better TONs, which is far better performance than neat iron complex. Keywords Metal complex · Zeolite-Y · Heterogeneous catalysis · Oxidation · Monoterpenes 1 Introduction Oxyfunctionalized derivatives of monoterpenes are key raw materials of great importance as they used in the perfumery, aromatherapy and herbal remedies owing to their pleasant fragrance [1–3]. Increasingly strict environmental regula- tions have compelled the modifcation of a number of chemi- cal processes including the oxidation of monoterpenes which improved number of times from the usage of homogeneous systems viz., mineral acids, transition metals, and metal complexes [4, 5] to eco-friendly heterogeneous systems viz., mixed metal oxides [6, 7], supported Ionic Liquid catalyst [8], biocatalytic epoxidation [9], zeolite-Y entrapped com- plexes [10–12], MCM-41 [13], SBA-15 [14], and polymer supported catalyst [15]. In particular, zeolite-Y hold the exchangeable sodium cations which allow the introduction of diferent metal ions. Moreover, due to the porous structure, zeolite-Y can act as “host materials” for incoming guest molecules which make them interesting and valuable for heterogeneous catalysis. In contrast to homogeneous systems, the metal complexes entrapped within a zeolite-Y, providing unlimited structural and chemical variations [16] through electrostatic, [17–19] covalent, [20] and dative [21] binding, which is nothing but an alternate way for the heterogenization, with additional advantages viz., easy separation, shape selectivity, site isola- tion, and thermal stability [22–24]. The metal complex, once formed inside the cavity, does not difuse out and pass in the liquid phase during the catalytic reaction. The heterogene- ously catalyzed oxidation of monoterpenes [10–12] gave a remarkably superior TONs and therefore much increased conversion to oxyfunctionalized derivatives as compared to their homogeneous counterparts. Our group is principally engaged to identify the nature of zeolite-Y entrapped metal complexes on selective oxida- tion reactions [25–27]. Herein we report the catalytic acts of zeolite-Y entrapped iron complex in the liquid phase oxida- tion of monoterpenes using 30% H 2 O 2 as an oxidant. 2 Materials and methods All chemicals used in this work are of AR grade and are used as received from Aldrich. The elemental analysis of the synthesized materials was carried out on Perkin Elmer, USA 2400-II CHN analyzer. The content of Na(I), Al(III), Si(IV) and Fe(II) ions were determined by ICP-OES using * Jignasu P. Mehta jpm1569@yahoo.co.in 1 Department of Chemistry, (UGC NON-SAP & DST-FIST Sponsored Department), Mahatma Gandhi Campus, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar, Gujarat 364 002, India