Synthesis of less acidic VO-salen complex grafted onto graphene oxide via functionalization of surface carboxyl groups f
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ORIGINAL ARTICLE
Synthesis of less acidic VO‑salen complex grafted onto graphene oxide via functionalization of surface carboxyl groups for the selective oxidation of norbornene Ravi S. Vithalani1 · Dikin Patel1 · Chetan K. Modi1 · Prafulla K. Jha2 · Himanshu Srivastava3 · Sanjeev R. Kane3 Received: 1 August 2020 / Revised: 24 September 2020 / Accepted: 6 October 2020 © Springer Nature Switzerland AG 2020
Abstract Oxidation of norbornene was carried out over oxovanadium Schiff base complex grafted on –OH and –COOH modified graphene oxide (GO) as heterogeneous catalysts using 30% H 2O2 as an oxidant and ethylene glycol as a solvent. Amongst them, the carboxylic acid group modified GO was found to be better for this transformation. The lower conversion with –OH modified catalyst was ascribed to the higher acidic nature of the catalyst. NH3-TPD study confirmed the less acidic sites on the –COOH modified catalyst and this less acidic nature and controlled addition of 30% H2O2 became the centre of action for this catalytic transformation. Absolute conversion of norbornene (100%) with 98.8% 2,3-epoxy norbornane was achieved at 60 °C in 1 h. This catalyst was recycled four times without significant loss of activity. This durability of the catalyst was believed to be due to strong π–π stacking interaction of GO sheet and an unsaturated ring of ligand and cyclic structure of ligand which protect the metal to leach out. Keywords VO-salen grafted on –COOH modified graphene oxide · NH3-TPD study · π–π stacking interaction of GO sheet and ligand · Selective epoxidation of norbornene
1 Introduction A large scale catalytic oxidation in all kinds of chemical industries has permitted for the development of a widely acceptable solid heterogeneous catalyst for the remedy of pollutants, production of energy and valuable chemicals [1]. A time ago, stoichiometric amounts of strong reagents and oxidants were involved in the development of oxidation reactions. However, these chemicals are noxious, erosive to the reaction vessel, unstable at ambient conditions, non-selective to product and forming scores of harmful by-products. In addition to this, the purification method of the key product * Chetan K. Modi [email protected] 1
Applied Chemistry Department, Faculty of Technology and Engineering, The Maharaja Sayajirao University of Baroda, Vadodara, Gujarat 390 001, India
2
Department of Physics, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara, Gujarat 390 002, India
3
Synchrotrons Utilisation Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, India
is very expensive, environment polluting, time-intensive and non-recyclable as well [2–5]. Hence, the developmental protocol involves the quest for the catalytic reaction which lessens toxic waste and production cost with little amount of catalyst [6, 7]. This exploration ends with the most flourishing material, graphite with typical distinct characteristics enthraling populace towards its own. Concomitantly, GO, an oxidi
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