Surface stabilization of gold by sol–gel post-modification of alumina support with silica for cyclohexane oxidation

Experimental and theoretical study on the regioselective bis- or polyalkylation of 6-amino-2-mercapto-3H-pyrimidin-4-one using zeolite nano-gold catalyst and a quantum hybrid computational method

The synthetic utility of 6-amino-2-mercapto-3H-pyrimidin-4-one 3 as building blocks for new poly (pyrimidine) by alkylation using the bis(halo) compounds and zeolite nano-gold as a catalyst was investigated. Furthermore, the experimental findings by the theoretical Density functional theory (DFT) computations at the DFT/B3LYP level of theory, utilizing the 6-311++G (d,p) basis set in the gas phase, were used to investigate the distinct phases for Regio isomer 11a & 12a and 11b & 12b compounds was fair and of good quality. The stability of the 12a and 12b phases is higher than the other Regio isomer 11a and 11b phases, according to DFT modelling. By computing HOMO and LUMO pictures, the electronic parameters: dipole moment of these compounds in the ground state were theoretically investigated. Non-linear optical (NLO) characteristics and quantum chemical parameters were examined using frontier molecular orbital (FMO) analysis. Natural bond orbital analysis was used to characterize the charge transfer of the electron density in the investigated compounds (NBO). The molecular electrostatic potential surfaces (MEPS) plots have been generated, and absorption spectral analysis in different solvents has been theoretically and experimentally examined to better understand the reactivity spots. At the B3LYP/6-311G (d,p) level of theory, thermodynamic properties were also calculated. Finally, DFT calculations were used to connect the structure-activity relationship (SAR) with real antibacterial results for compounds 12a and 12b.

Preparation of pyrimido[4,5-b][1,6]naphthyridin-4(1H)-one derivatives using a zeolite–nanogold catalyst and their in vitro evaluation as anticancer agent

Catalysis using supported gold nanoparticles has attracted significant research interest due to their unique properties and potential that is directly related to their particle size. An efficient one-pot, three-component procedure is developed for the preparation of pyrimido[4,5- b][1,6]naphthyridin-4( 1H)-one derivatives (4a–h) by cyclocondensation of 6-amino-2-thioxo-2,3-dihydropyrimidin-4( 1H)-one (1), aromatic aldehydes (2), and 1-benzylpiperidin-4-one (3) in the presence of zeolite-nano Au as a green catalyst in ethanol at 80 °C. The presented methodology has a number of advantages including a reusable catalyst, easy access, short reaction times, high yields, and an easy work-up. The nanogold catalyst is characterized by X-ray diffraction and transmission electron microscopy. The structures of the prepared compounds are established by elemental analyses and spectral data (infrared, mass spectrometry, 1H, and 13C NMR). While molecular docking studies show that products 4a and 4c have binding affinities with the active site of CDKs. A bio-evaluation assay revealed that some of the products exhibit strong to moderate effects against proliferation of Huh7 in an in vitro model of human liver cancer cells as confirmed by morphological alteration. Compounds 4c and 4a offer the lowest IC50 values at 22.5 and 39 µM, respectively.

The Influence of Reaction Conditions on the Oxidation of Cyclohexane via the In-Situ Production of H2O2

Abstract

The oxidation of cyclohexane via the in-situ production of H2O2 from molecular H2 and O2 offers an attractive route to the current industrial means of producing cyclohexanone and cyclohexanol (KA oil), both key materials in the production of Nylon. Herein we demonstrate that through the in-situ production of H2O2 supported AuPd nanoparticles catalyse the formation of KA oil under conditions where activity is limited when using molecular O2, with no loss in catalytic activity observed upon re-use. The effect of key reaction parameters, including reaction temperature, catalyst mass and H2:O2 ratio are evaluated.

Graphic Abstract

Supported Gold Nanoparticles as Catalysts for the Oxidation of Alcohols and Alkanes

Supporting gold nanoparticles have shown to be extremely active for many industrially important reactions, including oxidations. Two representative examples are the oxidation of alcohols and alkanes, that are substrates of industrial interest, but whose oxidation is still challenging. This review deals with these reactions, giving an insight of the first studies performed by gold based catalysts in these reactions and the most recent developments in the field.

Gold nanoparticles supported on mesoporous silica: origin of high activity and role of Au NPs in selective oxidation of cyclohexane

Homogeneous immobilization of gold nanoparticles (Au NPs) on mesoporous silica has been achieved by using a one-pot synthesis method in the presence of organosilane mercapto-propyl-trimethoxysilane (MPTMS). The resultant Au NPs exhibited an excellent catalytic activity in the solvent-free selective oxidation of cyclohexane using molecular oxygen. By establishing the structure-performance relationship, the origin of the high activity of mesoporous supported Au catalyst was identified to be due to the presence of low-coordinated Au (0) sites with high dispersion. Au NPs were confirmed to play a critical role in the catalytic oxidation of cyclohexane by promoting the activation of O₂ molecules and accelerating the formation of surface-active oxygen species.

Gold loaded titanium dioxide–carbon nanotube composites as active photocatalysts for cyclohexane oxidation at ambient conditions

Photocatalytic oxidation of neat cyclohexane with H₂O₂ was carried out using several types of gold modified materials including titania nanotubes, reduced graphene oxide and titania nanotube–multiwalled carbon nanotube composites under UV irradiation.

Highly Efficient Nano-Catalysts Using Activated Carbon as a Support for One-Step Oxidation of Cyclohexane to Adipic Acid

A new route to substitute for the traditional two-step method for adipic acid production has been investigated. Supported nano metal catalysts Au/C and Co/C were prepared and used for liquid phase oxidation of cyclohexane to adipic acid with oxygen as an oxidant. These catalysts were characterized by XRD, TEM and ICP-AES. The reactions were carried out in an autoclave with solvent and radical initiator at 373~423K and 1.5 MPa. Au/C (1.25%) was found to be a highly efficient catalyst for the oxidation of cyclohexane with a high conversion (44.93%) of cyclohexane and more than 54.85% selectivity to adipic acid. It is indicated that there was a potential application prospect for the nano-catalysts in one-step oxidation of cyclohexane to adipic acid.

Cyclohexane oxidation using Au/MgO: an investigation of the reaction mechanism

The liquid phase oxidation of cyclohexane was undertaken using Au/MgO and the reaction mechanism was investigated by means of continuous wave (CW) EPR spectroscopy employing the spin trapping technique. Activity tests aimed to determine the conversion and selectivity of Au/MgO catalyst showed that Au was capable of selectivity control to cyclohexanol formation up to 70%, but this was accompanied by a limited enhancement in conversion when compared with the reaction in the absence of catalyst. In contrast, when radical initiators were used, in combination with Au/MgO, an activity comparable to that observed in industrial processes at ca. 5% conversion was found, with retained high selectivity. By studying the free radical autoxidation of cyclohexane and the cyclohexyl hydroperoxide decomposition in the presence of spin traps, we show that Au nanoparticles are capable of an enhanced generation of cyclohexyl alkoxy radicals, and the role of Au is identified as a promoter of the catalytic autoxidation processes, therefore demonstrating that the reaction proceeds via a radical chain mechanism.

Cyclohexane Oxidation Catalyzed by Au/MxOyAl2O3 Using Molecular Oxygen

Alumina was modified by doping with metal oxide and then used as the support for depositing gold by an impregnation-ammonia washing method to obtain Au/MxOy/Al2O3(M=Co, Zr and Ce) catalysts. These samples were characterized by inductively coupled plasma-atomic emission spectrometry (ICP-AES), transmission electron microscope (TEM) and X-ray diffraction (XRD). The effects of Co3O4content, metal oxide and mixed metal oxides on the catalytic activity for the selective oxidation of cyclohexane to cyclohexanone and cyclohexanol using molecular oxygen as oxidant were studied. The results showed that better catalytic performance was obtained over Au/MxOy/Al2O3catalysts compared with over Au/Al2O3catalysts. 9.69% conversion of cyclohexane and 93.31% selectivity to cyclohexanone, cyclohexanol and cyclohexyl hydroperoxide, with 1.02 ratio of cyclohexanone to cyclohexanol were obtained over the Au/MxOy/Al2O3catalyst at 150 , 1.5 MPa for 3 h. Moreover, according to the recycling test, the catalyst could be reused four times without remarkable loss of activity.

Selective Phenol Hydrogenation to Cyclohexanone Over a Dual Supported Pd–Lewis Acid Catalyst

Cyclohexanone is an industrially important intermediate in the synthesis of materials such as nylon, but preparing it efficiently through direct hydrogenation of phenol is hindered by over-reduction to cyclohexanol. Here we report that a previously unappreciated combination of two common commercial catalysts―nanoparticulate palladium (supported on carbon, alumina, or NaY zeolite) and a Lewis acid such as AlCl3―synergistically promotes this reaction. Conversion exceeding 99.9% was achieved with >99.9% selectivity within 7 hours at 1.0-megapascal hydrogen pressure and 50°C. The reaction was accelerated at higher temperature or in a compressed CO2 solvent medium. Preliminary kinetic and spectroscopic studies suggest that the Lewis acid sequentially enhances the hydrogenation of phenol to cyclohexanone and then inhibits further hydrogenation of the ketone.