Journal of Molecular Catalysis A: Chemical 426 (2017) 534–541 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical jou rnal h om epa ge: www.elsevier.com/locate/molcata Magnetically recoverable copper oxide catalysts for aerobic allylic oxidation of cyclohexene Fernanda Parra da Silva a , Renato V. Gonc ¸ alves b , Liane M. Rossi a,∗ a Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, 05508-000, São Paulo, SP, Brazil b Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970, São Carlos, SP, Brazil a r t i c l e i n f o Article history: Received 24 June 2016 Received in revised form 16 July 2016 Accepted 25 July 2016 Available online 26 July 2016 Keywords: Magnetic separation Allylic oxidation Cyclohexene 2-cyclohexene-1-one Copper oxide a b s t r a c t Magnetically recoverable copper oxide catalysts prepared by sol-immobilization method exhibited inter- esting properties for the allylic oxidation of cyclohexene with molecular oxygen as the sole oxidant. The catalysts were prepared by immobilization of pre-synthesized PVA (polyvinyl alcohol)-stabilized Cu 2 O nanoparticles (NPs) on a magnetically recoverable support; the catalyst was further oxidized to CuO NPs after calcination at 600 ◦ C. Both catalysts can selectively oxidize cyclohexene through allylic oxidation to give 2-cyclohexene-1-one as the main product, but CuO was identified as the most active species provid- ing 90% cyclohexene conversion and 96% selectivity for allylic products under 100 ◦ C and 4 bar pressure of O 2 for 6 h of reaction time. The catalysts were magnetically recovered without metal leaching and could be reused in at least six consecutive runs. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The functionalization of allylic C H bonds of alkenes represents a powerful approach to the synthesis of ,-unsaturated deriva- tives, which find widespread application as synthetic intermediates and as products in the commodity chemical, fine chemical, and pharmaceutical industries [1–4]. The allylic oxidation of alkenes is a valuable organic transformations for the synthesis of value-added products such as ,-unsaturated alcohols, esters and ketones from simple precursors [4]. Classically, these oxidations were performed using chromium reagents (first stoichiometric or then catalytic with the aid of oxidants), but due to the radical character, metals that undergo one-electron redox processes, such as Mn, Rh, Fe, Cu or Co, have been used in the development of environmentally friendly metal-catalyzed methods [4–8]. Many of these metal-catalyzed systems are not compatible with the use of molecular oxygen and require unfriendly oxidants, such as PhIO, NaClO, H 2 O 2 , tBuOOH; to achieve catalytic turnover [9–15]. Molecular oxygen should be preferred as an ideal oxidant due to its natural, highly economical, environmentally benign and abundant characters [16,17]. Limita- tions in reaction scope and selectivity as well as safety concerns have hindered the application of aerobic oxidations in the fine chemical, pharmaceutical, and related industries. ∗ Corresponding author. E-mail address: lrossi@iq.usp.br (L.M. Rossi). An ideal clean oxidation may use molecular oxygen as the primary oxidant along with catalysts that can be recycled and non- toxic solvents. Yin et al. [18] and Silva et al. [19] reported the allylic oxidation of alkenes using molecular oxygen as the sole oxi- dant with easily recoverable cobalt catalysts. Copper catalysis also received attention for selective aerobic oxidative functionalization of C H bonds [20–22]. The facile aerobic oxidation of Cu(I) ions to Cu(II) is widely recognized, and a number of important synthetic Cu-catalyzed aerobic oxidation reactions exist, including industrial applications, with high catalytic activities and a wide functional groups tolerance. Herein we explored the preparation of supported copper oxide nanoparticles (NPs) as catalyst for the allylic oxidation of alkenes with molecular oxygen as the sole oxidant. Many catalytic pro- cesses with copper make use of metal complexes or enzyme mimetics [23–25]; however, due to its excellent conductivity, availability and low cost, the use of copper as an heterogeneous cat- alyst receives attention. Metallic copper nanoparticles and cuprous oxide have been used as catalysts for various reactions, includ- ing Ullmann coupling [26–28], cycloaddition of terminal alkynes and azides [29,30], hydrogenation of alkynes [31,32], oxidative dehydrogenation of alcohols [33], degradation of pollutants [34] and oxidation of olefins [35]. Copper tetramers supported on alu- mina showed excellent activity in carbon dioxide reduction into methanol at low partial pressure of CO 2 [36]. Allylic oxidation of cyclohexene by copper supported on expanded graphite [22] or http://dx.doi.org/10.1016/j.molcata.2016.07.044 1381-1169/© 2016 Elsevier B.V. All rights reserved.