Unexpected nucleophilic participation and rearrangement of DBU in reactions with saccharin derivatives

DBU attacks saccharin derivatives with subsequent rearrangement to give rise to 3-[3'-(1"-azepin-2"-onyl)propylamino]-1,2-benzisothiazole-1,1-dioxide 2 after work-up

SOME OBSERVATIONS ON THE STIMULATION OF ERYTHROPOIESIS BY HUMORAL FACTORS

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71621/1/j.1749-6632.1959.tb36931.x.pd

On the development of kinetic models for solvent-free benzyl alcohol oxidation over a gold-palladium catalyst

Bimetallic Au-Pd nanoparticles supported on TiO2 have shown excellent catalytic activity and selectivity to benzaldehyde in the solvent-free transformation of benzyl alcohol to benzaldehyde, where toluene is the main observed by-product, together with smaller amounts of benzoic acid, benzyl benzoate and dibenzyl ether. However, despite the industrial relevance of this reaction and importance of tuning the selectivity to the desired benzaldehyde, only a few attempts have been made in the literature on modeling the reaction kinetics for a quantitative description of this reaction system. A kinetic model for the oxidation of benzyl alcohol over Au-Pd is proposed in this paper. It has been found satisfactory after a model discrimination procedure has been applied to a number of simplified candidate models developed from microkinetic studies. Despite its relative simplicity, the proposed model is capable of representing the reactant conversion and distribution of products observed in experiments carried out at different temperature, pressure and catalyst mass in a stirred batch reactor. Major findings included the quantitative evaluation of the impact of hydrogenolysis and disproportionation pathways on benzaldehyde production. At low temperature the disproportionation reaction was the dominant route to toluene formation, while hydrogenolysis dominated at high temperature

Tuning of catalytic sites in Pt/TiO2 catalysts for chemoselective hydrogenation of 3-nitrostyrene

The catalytic activities of supported metal nanoparticles can be tuned by appropriate design of synthesis strategies. Each step in a catalyst synthesis method can play an important role in preparing the most efficient catalyst. Here we report the careful manipulation of the post-synthetic heat treatment procedure—together with control over the metal loading—to prepare a highly efficient 0.2 wt% Pt/TiO2 catalyst for the chemoselective hydrogenation of 3-nitrostyrene. For Pt/TiO2 catalysts with 0.2 and 0.5 wt% loading levels, reduction at 450 °C induces the coverage of TiOx over Pt nanoparticles through a strong metal–support interaction, which is detrimental to their catalytic activities. However, this can be avoided by following calcination treatment with reduction (both at 450 °C), allowing us to prepare an exceptionally active catalyst. Detailed characterization has revealed that the peripheral sites at the Pt/TiO2 interface are the most likely active sites for this hydrogenation reactio

Author correction: Tuning of catalytic sites in Pt/TiO2 catalysts for the chemoselective hydrogenation of 3-nitrostyrene

Correction to: Nature Catalysis https://doi.org/10.1038/s41929-019-0334-3, published online 16 September 2019. In the version of this Article originally published, the Fig. 3 panels were mislabelled and the mean particle size in Fig. 3e, which is now labelled Fig. 3b, was incorrectly given as ‘1.2 nm’. From left to right, the top row of panels should have been labelled a, c, e and g and the bottom row of panels should have been labelled b, d, f and h. The mean particle size in Fig. 3b should have been ‘1.0 nm’. This has been corrected in the online versions of this Article

The controlled catalytic oxidation of furfural to furoic acid using AuPd/MgIJ(OH)2

© 2017 The Royal Society of Chemistry. The emphasis of modern chemistry is to satisfy the needs of consumers by using methods that are sustainable and economical. Using a 1% AuPd/Mg(OH) 2 catalyst in the presence of NaOH and under specific reaction conditions furfural; a platform chemical formed from lignocellulosic biomass, can be selectively oxidised to furoic acid, and the catalyst displays promising reusability for this reaction. The mechanism of this conversion is complex with multiple competing pathways possible. The experimental conditions and AuPd metal ratio can be fine-tuned to provide enhanced control of the reaction selectivity. Activation energies were derived for the homogeneous Cannizzaro pathway and the catalytic oxidation of furfural using the initial rates methodology. This work highlights the potential of using a heterogeneous catalyst for the oxidation of furfural to furoic acid that has potential for commercial application

Tuning of catalytic sites in Pt/TiO₂ catalysts for the chemoselective hydrogenation of 3-nitrostyrene

The catalytic activities of supported metal nanoparticles can be tuned by appropriate design of synthesis strategies. Each step in a catalyst synthesis method can play an important role in preparing the most efficient catalyst. Here we report the careful manipulation of the post-synthetic heat treatment procedure—together with control over the metal loading—to prepare a highly efficient 0.2 wt% Pt/TiO2 catalyst for the chemoselective hydrogenation of 3-nitrostyrene. For Pt/TiO2 catalysts with 0.2 and 0.5 wt% loading levels, reduction at 450 °C induces the coverage of TiOx over Pt nanoparticles through a strong metal–support interaction, which is detrimental to their catalytic activities. However, this can be avoided by following calcination treatment with reduction (both at 450 °C), allowing us to prepare an exceptionally active catalyst. Detailed characterization has revealed that the peripheral sites at the Pt/TiO2 interface are the most likely active sites for this hydrogenation reactio

Investigating catalytic properties which influence dehydration and oxidative dehydrogenation in aerobic glycerol oxidation over Pt/TiO2

The use of heterogeneous catalysts to convert glycerol into lactic acid has been extensively investigated in recent years. Several different strategies have been employed, but importantly, the highest production rates of lactic acid are achieved through aerobic oxidation under alkaline conditions. Despite the progress made in this area, insight into how the catalytic properties influence the selectivity of the competing pathways, oxidative dehydrogenation and dehydration, remains limited. Developing a deeper understanding is therefore critical, if process commercialization is to be realized. Using a model Pt/TiO2 catalyst, we set out to investigate how the supported metal particle size and support phase influenced the selectivity of these two pathways. Both these parameters have a profound effect on the reaction selectivity. Using a range of characterization techniques and through adopting a systematic approach to experimental design, important observations were made. Both pathways are first instigated through the oxidative dehydrogenation of glycerol, leading to the formation of glyceraldehyde or dihydroxyacetone. If these intermediates desorb, they rapidly undergo dehydration through a reaction with the homogeneous base in solution. Based on the experimental evidence we therefore propose that selectivity to lactic acid is influenced by surface residence time

Kinetic analysis to describe co-operative redox enhancement effects exhibited by bimetallic Au-Pd systems in aerobic oxidation

Recent work has demonstrated that for bimetallic Au–Pd systems, the rate of catalytic alcohol and formyl dehydrogenation (DH) is intrinsically linked to the rate of oxygen reduction (ORR) within the same system. Herein, the rate enhancement as a result of the coupling between these two processes is assessed via kinetic analysis for the oxidative dehydrogenation of 5-hydroxymethylfurfural. The influence of the Au and Pd molar ratio is explored for a physical mixture of carbon-supported catalysts by changing the mass of each 1 wt% catalyst. Importantly, the activity of the bimetallic system exceeds the sum of the monometallic analogues, at all molar ratios. It is shown that by considering the coupling between two individual reactions (DH and ORR), the kinetic analysis of the system predicts where the maxima in monometallic and bimetallic activity will be observed. The accuracy of the model provides further evidence and understanding of cooperative redox enhancement (CORE) effects observed in bimetallic, heterogeneous catalytic systems

Enhancing the understanding of the glycerol to lactic acid reaction mechanism over AuPt/TiO2 under alkaline conditions

The oxidation of glycerol under alkaline conditions in the presence of a heterogeneous catalyst can be tailored to the formation of lactic acid, an important commodity chemical. Despite recent advances in this area, the mechanism for its formation is still a subject of contention. In this study, we use a model 1 wt. % AuPt/TiO2 catalyst to probe this mechanism by conducting a series of isotopic labeling experiments with 1,3-13C glycerol. Optimization of the reaction conditions was first conducted to ensure high selectivity to lactic acid in the isotopic labeling experiments. Selectivity to lactic acid increased with temperature and concentration of NaOH, but increasing the O2 pressure appeared to influence only the rate of reaction. Using 1,3-13C glycerol, we demonstrate that conversion of pyruvaldehyde to lactic acid proceeds via a base-promoted 1,2-hydride shift. There was no evidence to suggest that this occurs via a 2,1-methide shift under the conditions used in this study