Haresh G. Manyar

Microwave Irradiation for the Facile Synthesis of Transition-Metal Nanoparticles (NPs) in Ionic Liquids (ILs) from Metal–Carbonyl Precursors and Ru-, Rh-, and Ir-NP/IL Dispersions as Biphasic Liquid–Liquid Hydrogenation Nanocatalysts for Cyclohexene

Stable chromium, molybdenum, tungsten, manganese, rhenium, ruthenium, osmium, cobalt, rhodium, and iridium metal nanoparticles (M-NPs) have been reproducibly obtained by facile, rapid (3 min), and energy-saving 10 W microwave irradiation (MWI) under an argon atmosphere from their metal-carbonyl precursors [M(x)(CO)(y)] in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF(4)]). This MWI synthesis is compared to UV-photolytic (1000 W, 15 min) or conventional thermal decomposition (180-250 degrees C, 6-12 h) of [M(x)(CO)(y)] in ILs. The MWI-obtained nanoparticles have a very small (<5 nm) and uniform size and are prepared without any additional stabilizers or capping molecules as long-term stable M-NP/IL dispersions (characterization by transmission electron microscopy (TEM), transmission electron diffraction (TED), and dynamic light scattering (DLS)). The ruthenium, rhodium, or iridium nanoparticle/IL dispersions are highly active and easily recyclable catalysts for the biphasic liquid-liquid hydrogenation of cyclohexene to cyclohexane with activities of up to 522 (mol product) (mol Ru)(-1) h(-1) and 884 (mol product) (mol Rh)(-1) h(-1) and give almost quantitative conversion within 2 h at 10 bar H(2) and 90 degrees C. Catalyst poisoning experiments with CS(2) (0.05 equiv per Ru) suggest a heterogeneous surface catalysis of Ru-NPs.

Highly selective and efficient hydrogenation of carboxylic acids to alcohols using titania supported Pt catalysts

Selective hydrogenation of carboxylic acids to alcohols and alkanes has been achieved under remarkably mild reaction temperatures and H(2) pressures (333 K, 0.5 MPa) using Pt/TiO(2) catalyst.

Novelties of synthesis of acetoveratrone using heteropoly acid supported on hexagonal mesoporous silica

Abstract Friedel–Crafts acylations are often used for synthesis of important aromatic ketones such as acetoveratrone, which is the intermediate for synthesis of papavarine alkaloids. This is produced by conventional homogeneous catalysts and HY and Hβ zeolites which are known to deactivate. The current study reports the development of environmentally benign route for acetoveratrone synthesis. Twenty percent dodecatungstophosphoric acid supported on hexagonal mesoporous silica (DTP/HMS) was synthesized. This catalyst was found to be very active and also stable without any deactivation. The catalyst was characterised for its ultrastructural features by using X-ray diffraction, SEM, framework IR and nitrogen sorption techniques. Based on the experimental data a suitable mathematical model is proposed to describe the reaction kinetics. It was possible to determine the adsorption equilibrium constant and reaction rate constant from the same set of data and the reaction follows the Eley Rideal mechanism. The results are novel.

Selective Hydrogenation of α,β‐Unsaturated Aldehydes and Ketones using Novel Manganese Oxide and Platinum Supported on Manganese Oxide Octahedral Molecular Sieves as Catalysts

The selective hydrogenation of α,β‐unsaturated aldehydes and ketones has been studied using ketoisophorone and cinnamaldehyde as model substrates using manganese oxide octahedral molecular sieve (OMS‐2) based catalysts. For the first time, OMS‐2 has been shown to be an efficient and selective hydrogenation catalyst. High selectivities for either the CC or CO double bond at ≈100 % conversion were achieved by using OMS‐2 and platinum supported on OMS‐2 catalysts. Density functional theory (DFT) calculations showed that the dissociation of H2 on OMS‐2 was water assisted and occurred on the surface Mn of OMS‐2(0 0 1) that had been modified by an adsorbed H2O molecule. The theoretically calculated activation barrier was in good agreement with the experimentally determined value for the hydrogenation reactions, indicating that H2 dissociation on OMS‐2 is likely to be the rate‐determining step. A significant increase in the rate of reaction was observed in the presence of Pt as a result of the enhancement of H2 dissociative adsorption and subsequent reaction on the Pt or spillover of the hydrogen to the OMS‐2 support. The relative adsorption strengths of ketoisophorone and cinnamaldehyde on the OMS‐2 support compared with the Pt were found to determine the product selectivity.

Facile in situ synthesis of nanofluids based on ionic liquids and copper oxide clusters and nanoparticles

Two stable nanofluids comprising of mixed valent copper(I,II) oxide clusters (<1 nm) suspended in 1-butyl-3-methylimidazolium acetate, [C(4)mim][OAc], and copper(II) oxide nanoparticles (<50 nm) suspended in trioctyl(dodecyl)phosphonium acetate, [P(8 8 8 12)][OAc], were synthesised in a facile one-pot reaction from solutions of copper(II) acetate hydrate in the corresponding ionic liquids. Formation of the nanostructures was studied using (13)C NMR spectroscopy and differential scanning calorimetry (DSC). From a solution of Cu(OAc)(2) in 1-ethyl-3-methylimidazolium acetate, [C(2)mim][OAc], crystals were obtained that revealed the structure of [C(2)mim][Cu(3)(OAc)(5)(OH)(2)(H(2)O)]·H(2)O, indicating the formation of copper hydroxo-clusters in the course of the reaction. Synthesised nanostructures were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Physical properties of the prepared IL-nanofluids were examined using IR and UV-VIS spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and densitometry.

The First Continuous Flow Hydrogenation of Amides to Amines

Amines are a versatile class of compounds with applications ranging from dyes, solvents and detergents to the pharmaceutical industry. Amine functionalities are often introduced by initial amide formation followed by a reduction step using reducing agents such as LiAlH4 or boranes. These reducing agents are, however, hazardous and difficult to handle, particularly on large scale, and their use often involves complex and wasteful workup procedures. Thus, routes to selective and environmentally benign amide reduction are sought after, and for this reason, the American Chemical Society Green Chemistry Institute (GCI) and members of the Pharmaceutical Round Table have shortlisted amide hydrogenation as one of their three most desirable reactions for development. Although a number of successful amide reductions through catalytic hydrosilylation have been reported, catalytic hydrogenation represents a promising alternative, as water is generated as the only by-product. The groups of Saito, Milstein, and Bergens reported homogeneously catalysed hydrogenation of amides, but in all cases, the reduction proceeds either through C N bond cleavage to give amines and alcohols or through monohydrogenation to give hemiaminals. We recently reported the first successful homogeneous Ru-based catalyst capable of selectively hydrogenating amides to amines without C N bond cleavage, even in the presence of aromatic ring systems. The scope of this reaction is, however, currently limited to substrates containing a phenyl ring directly attached to the N atom and to primary amides. A number of bimetallic heterogeneous hydrogenation catalysts have been reported by the groups of Fuchikami and Whyman to give good conversions of amides into amines, but they generally require fairly harsh operating conditions. More recently, promising bimetallic graphite-supported Pd–Re and TiO2-supported Pt–Re based catalysts capable of promoting amide hydrogenations under mild reaction conditions were reported independently by the groups of Breit and Hardacre. Although the use of a heterogeneous catalyst for amide hydrogenation is currently limited to nonaromatic substrates owing to the complication of unwanted ring hydrogenation, the ease of catalyst separation associated with such systems is a great advantage to their implementation in continuous flow systems for industrial applications. Herein, we report the first selective catalytic hydrogenation of amides to amines in continuous flow by using a bimetallic TiO2-supported Pt–Re-based catalyst. [10] The air-stable 4 % Pt–4 % Re/TiO2 catalyst employed in this study was first reported by some of us to be catalytically active towards amide hydrogenation. A range of bimetallic Pt–Rebased catalysts supported on CeZrO4, TiO2 and Al2O3 were tested for the selective hydrogenation of N-methylpyrrolidin-2one to N-methylpyrrolidine in hexane under an atmosphere of hydrogen (20 bar, 1 bar = 100 kPa) at 120 8C. Under these conditions, 4 % Pt–4 % Re/TiO2 displayed the highest activity and gave almost full conversion after 24 h. For this system, the nature of the solvent was shown to play an important role, and the rate of the reaction was found to decrease in the order: hexane> tetrahydrofuran diethyl ether>methanol> methyl tert-butyl ether. To assess the performance of this catalyst under continuous flow conditions, we developed a versatile flow reactor. The reactor is vertical with an upwards flow and has the facility to flow liquids, gases and CO2 simultaneously through the vertical-packed bed reactor containing the catalyst. The flowing stream is then decompressed, and the products are collected free from the catalyst and other impurities apart from side products, solvent, and unreacted substrates. A schematic of the reactor is shown in Figure 1. Prior to testing 4 % Pt–4 % Re/TiO2 in continuous flow, the catalyst was tested in batch mode with an aromatic substrate to determine the tolerance of this catalyst towards arene functionalities. Acetanilide, a substrate that performed very well with the homogeneous [Ru(acac)3]/triphos [acac = acetylacetonate, triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane] system (Table 1, entry 1), was used as a test substrate. Acetanilide (5 mmol) in hexane was heated at 120 8C in the presence of 4 % Pt–4 % Re/TiO2 (1.6 mol % in metal) under an atmosphere of hydrogen (20 bar, RT) for 16 h (Table 1, entry 4). Although this resulted in hydrogenation of 36 % of the amide functionality, ring hydrogenation occurred for both the final amine as well as the remaining substrate to give a mixture of N-cyclohexyl-N-ethylamine (2) and N-cyclohexylacetamide (3) as the final products (Scheme 1). In addition, minor amounts of N-cyclohexylamine (4) and ethanol (5) were produced as a result of C N bond cleavage. [a] Dr. J. Coetzee, Prof. Dr. D. J. Cole-Hamilton EastChem, School of Chemistry, North Haugh University of St. Andrews St. Andrews, Fife KY16 9ST, Scotland (United Kingdom) Fax: (+ 44) 0-1334-463808 E-mail : djc@st-andrews.ac.uk [b] Dr. H. G. Manyar, Prof. Dr. C. Hardacre CenTACat, School of Chemistry and Chemical Engineering Queen’s University Stranmillis Road, Belfast BT9 5AG, Northern Ireland (United Kingdom) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201300431.

Evaluation of Pt and Re oxidation state in a pressurized reactor: Difference in reduction between gas and liquid phase

Determination of metal oxidation state under relevant working conditions is crucial to understand catalytic behaviour. The reduction behaviour of Pt and Re was evaluated simultaneously as a function of support and solvent in a pressurized reactor (autoclave). The bimetallic catalysts are used in selective hydrogenation of carboxylic acids and amides. Gas phase reduction reduced the metals more efficiently, in particular Pt.

The green catalytic oxidation of alcohols in water by using highly efficient manganosilicate molecular sieves

An efficient and green catalytic protocol for the oxidation of alcohols to the corresponding aldehydes is the need of industry and is continuously being sought for. This report describes the use of manganosilicate molecular sieves as an efficient heterogeneous catalyst in aqueous conditions using the peroxodisulfate ions as the oxidising agent. The advantageous feature of this oxidation methodology is the efficiency and selectivity with which it oxidizes the heterocyclic and aliphatic alcohols. The other interesting facet of this communication is the synthesis of manganosilicate molecular sieves by a facile complexing procedure leading to the uniform mesoporous cubic structure devoid of extra-framework bulk manganese oxide species.

Structure and dynamics of aqueous 2-propanol: a THz-TDS, NMR and neutron diffraction study

Aqueous liquid mixtures, in particular, those involving amphiphilic species, play an important role in many physical, chemical and biological processes. Of particular interest are alcohol/water mixtures; however, the structural dynamics of such systems are still not fully understood. Herein, a combination of terahertz time-domain spectroscopy (THz-TDS) and NMR relaxation time analysis has been applied to investigate 2-propanol/water mixtures across the entire composition range; while neutron diffraction studies have been carried out at two specific concentrations. Excellent agreement is seen between the techniques with a maximum in both the relative absorption coefficient and the activation energy to molecular motion occurring at ∼90 mol% H2O. Furthermore, this is the same value at which well-established excess thermodynamic functions exhibit a maximum/minimum. Additionally, both neutron diffraction and THz-TDS have been used to provide estimates of the size of the hydration shell around 2-propanol in solution. Both methods determine that between 4 and 5 H2O molecules per 2-propanol are found in the 2-propanol/water clusters at 90 mol% H2O. Based on the acquired data, a description of the structure of 2-propanol/water across the composition range is presented.

Neutron Scattering of Aromatic and Aliphatic Liquids.

Abstract Organic solvents, such as cyclohexane, cyclohexene, methylcyclohexane, benzene and toluene, are widely used as both reagents and solvents in industrial processes. Despite the ubiquity of these liquids, the local structures that govern the chemical properties have not been studied extensively. Herein, we report neutron diffraction measurements on liquid cyclohexane, cyclohexene, methylcyclohexane, benzene and toluene at 298 K to obtain a detailed description of the local structure in these compounds. The radial distribution functions of the centres of the molecules, as well as the partial distribution functions for the double bond for cyclohexene and methyl group for methylcyclohexane and toluene have been calculated. Additionally, probability density functions and angular radial distribution functions were extracted to provide a full description of the local structure within the chosen liquids. Structural motifs are discussed and compared for all liquids, referring specifically to the functional group and aromaticity present in the different liquids.