Selective Ammoximation of Ketones via In Situ H₂O₂ Synthesis

Abstract

The ammoximation of ketones to the corresponding oxime via the in situ production of H 2 O 2 offers a viable alternative to the current means of industrial-scale production, in particular for the synthesis of cyclohexanone oxime, a key precursor to Nylon-6. Herein, we demonstrate that using a bifunctional catalyst, consisting of Pd-based bimetallic nanoparticles immobilized onto a TS-1 carrier, it is possible to bridge the considerable condition gap that exists between the two key distinct reaction pathways that constitute an in-situ approach (i.e., the direct synthesis of H 2 O 2 and ketone ammoximation). The formation of PdAu nanoalloys is found to be crucial in achieving high reactivity and in promoting catalytic stability, with the optimal formulation significantly outperforming both alternative Pd-based materials and the monometallic Pd analogue.

Selective Oxidation Using In Situ-Generated Hydrogen Peroxide

“…24,25 It is the overcoming of these challenges that has motivated extensive research from our laboratory, with particular focus placed on the application of Pd-based catalysts for (i) alkane upgrading, 26−31 (ii) alcohol oxidation, 3,32−34 and recently (iii) the ammoximation of cyclohexanone (and other cyclic ketones) to the corresponding oxime. 4,35,36 Regarding alkane oxidation, we direct the reader to our recent Account on methane valorization for an extensive discussion of our contribution to this field. 37 The development of the titanosilicate TS-1 by EniChem can be considered to be one of the most important innovations in industrial heterogeneous catalysis in recent decades, offering exceptional activities and selectivities for the oxidative transformation of many small molecules, as dictated by the relatively limited pore size of TS-1 (∼5.5 Å), which consists of a 10membered ring (MFI) framework.…”

“…24,25 It is the overcoming of these challenges that has motivated extensive research from our laboratory, with particular focus placed on the application of Pd-based catalysts for (i) alkane upgrading, 26−31 (ii) alcohol oxidation, 3,32−34 and recently (iii) the ammoximation of cyclohexanone (and other cyclic ketones) to the corresponding oxime. 4,35,36 Regarding alkane oxidation, we direct the reader to our recent Account on methane valorization for an extensive discussion of our contribution to this field.…”

“…These include poor selective H 2 utilization, rapid catalyst deactivation, and the formation of complex product mixtures, necessitating extensive purification and the inclusion of promoters. Indeed, in many cases, it is the presence of H 2 , required to generate H 2 O 2 in situ, that largely promotes the formation of such byproducts. , Such concerns are not limited to alkene epoxidation, with product distributions for a range of transformations influenced by competitive unselective hydrogenation pathways. , It is the overcoming of these challenges that has motivated extensive research from our laboratory, with particular focus placed on the application of Pd-based catalysts for (i) alkane upgrading, − (ii) alcohol oxidation, ,− and recently (iii) the ammoximation of cyclohexanone (and other cyclic ketones) to the corresponding oxime. ,, Regarding alkane oxidation, we direct the reader to our recent Account on methane valorization for an extensive discussion of our contribution to this field …”

“…Such systems, utilized either as a physical mixture of two separate catalysts or as a composite material that can catalyze both individual reaction pathways, have been demonstrated to offer exceptional reactivity and selectivity toward a range of oximes, with yields comparable to that achieved by the current state-of-the-art industrial process (Figure B). In particular, the formation of AuPd nanoalloys has been found to offer improved performance compared to Pd-only analogues or alternative Pd-based formulations (Figure C,D) despite the enhanced rate of H 2 O 2 synthesis observed over monometallic Pd formulations, under conditions optimized for the stability of the oxidant. Such observations may be attributed to the improved stability of bimetallic AuPd species compared to that of monometallic Pd analogues and the increased selective utilization of H 2 over alloyed surfaces …”

A comparative study of palladium-gold and palladium-tin catalysts in the direct synthesis of H2O2

“…in situ for use in chemical transformations. [11][12][13] While Pd-based catalysts have been well reported to offer high activity towards H 2 O 2 production via the direct route, 14,15 limited catalytic selectivity has typically necessitated the use of acidic or halogenated stabilising agents. [16][17][18][19] Alternatively, there has been extensive investigation into the alloying of Pd with secondary metals, primarily other precious metals [20][21][22][23][24] to improve catalytic performance.…”