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We performed a systematic investigation of the conditions causing or preventing self-ignition of spent palladium on a carbon catalyst after hydrogenation reactions. The solvent used for hydrogenati...

Grindelia squarrosa, known as gumweed, is a shrub that grows in arid lands in North America with up to 8% biocrude (or bio-oil) content that can be extracted by using a common solvent extraction method. This solvent-extracted biocrude (SEB) has nearly 24 wt% oxygen, which is not suitable for direct combustion as a bio-oil or biodiesel. In this study, supercritical water (SCW) upgrading is used to reduce the oxygen of the SEB and increase the fuel value by creating lighter oil fractions. Treatment for 30 min reduces the oxygen content from 24.1 ± 1.6 (for raw SEB) to 7.2 ± 0.7%, 7.1 ± 0.4%, and 6.9 ± 0.6% at 380, 400, and 420 °C respectively. The addition of palladium on carbon (Pd/C) catalyst at 400 °C further reduces the oxygen content to 4.8 ± 0.7%. This removal in oxygen content is shown in the reduction of carboxylic acid compounds in the oils. Without having to use hydrogen, such as with the traditional hydrodeoxygenation process, the SCW upgrading has rather high energy yields for the oils which all have higher heating values between 41.0 and 42.8 MJ kg−1 (with no significant effect of temperature or catalyst). Treatment at 400 °C had the highest energy yield at 76.4 ± 1.7%, and treatment with the Pd/C catalyst at 400 °C had the lowest at 61.4 ± 2.8%. These energy yields, higher heating values, and low oxygen contents show that SCW can effectively be used to convert gumweed-derived SEB into a valuable bio-oil.

A previously developed and industrially feasible process for selective, Pd-mediated, liquid-phase heterogeneous catalytic hydrogenation of nitriles to primary amines was extended to the reduction of 3-phenylpropionitrile (PPN) to 3-phenylpropylamine (PPA). PPN, which belongs to the homologous series of benzonitrile (BN) and benzyl cyanide (BC), was hydrogenated under mild reaction conditions (30–80 °C, 6 bar), over Pd/C, in two immiscible solvents (dichloromethane/water) and using acidic additives (NaH2PO4 and H2SO4). Although relatively high conversion (76%) was achieved, the selectivity to PPA (26%) and its isolated yield (20%) were lesser than those in the case of the hydrogenation of BN or BC reported earlier. However, the purity of PPA was >99% without using any purification method. Quantum chemical calculations using a density functional theory (DFT) method were performed to compare the adsorption interactions of the different imine intermediates on palladium, as well as to clarify the differences observed in the primary amine selectivity. PPA is a valuable intermediate for the synthesis of carboxypeptidase B enzyme inhibitors, antimuscarinic drugs, or potential anticancer agents in the pharmaceutical industry.

Direct C(sp2)–H bond functionalization of indoles with arylboronic acids is achieved using palladium supported on carbon as a reusable heterogeneous catalyst in the presence of an oxidant under mild conditions. The current protocol formed exclusive C-2 selective products without the aid of any ligand or directing group. The catalyst is reusable for up to four catalytic cycles with the retention of catalytic efficiency.

The 2-vinylbenzoic acids have wide applications in the field of polymer chemistry and are key precursors for the synthesis of important bioactive molecules. Herein, an ortho-halogen-induced deoxygenative approach for the generation of 2-vinylbenzoic acids from alkyl aryl ketones by palladium catalysis is discovered and explored. This approach requires no base or stoichiometric additives and can be carried out through a simple one-step process. Furthermore, the present reaction is scalable up to one-gram scale. The commercially available palladium on carbon (5 wt%) was used as a heterogeneous catalyst and showed excellent recyclability (

The Pd/C-catalyzed reactions, including reduction reactions and cross-coupling reactions, play an irreplaceable role in modern organic synthesis. Compared to the homogeneous palladium catalyst system, the heterogeneous Pd/C catalyst system offers an alternative protocol that has particular advantages and applications. Herein, a review on Pd/C-catalyzed reactions is presented. Both the advances in Pd/C-catalyzed methodologies and the application of Pd/C-catalysis in total synthesis are covered in this review.

Effective preparation of olivacine and ellipticine via late-stage D-ring cyclization is described. Key features of the synthetic routes include trifluoroacetic acid-mediated formation of a lactone that is fused to a tetrahydrocarbazole derivative and its one-pot two-step ring opening and aromatization mediated by para-toluenesulfonic acid and palladium on carbon, respectively.

A batch catalytic slurry reactor system was used to study the hydrodeoxygenation (HDO) of pyrolysis oil model compounds at high conversions and conditions similar to petroleum hydrotreatment reactors. The lignin fraction of pyrolysis oil was represented in this study by anisole, m-cresol and phenol, both individually and blended in pairs. Experiments were run from 250 °C to 350 °C using platinum on alumina (Pt/Al2O3) or palladium on carbon (Pd/C) in a Parr reactor at 50 bar. The Pt/Al2O3 catalysts exhibited ring saturation, demethylation and hydrodeoxygenation, with temperature-dependent pathway shifts. Tests with blended pairs yielded no secondary reactions but competitive adsorption for catalyst active sites was observed. Tests with Pd/C showed ring saturation followed by methanol abstraction. Rate constants and adsorption parameters were fitted to a Langmuir-Hinshelwood model for each catalyst and compound. Arrhenius relationships for those rate constants and surface adsorption parameters were then calculated. When used in a slurry reactor model with catalyst-specific reaction data, the product composition, hydrogen consumption, and energy requirements are well predicted for a known feed and set of reactor conditions.

An efficient deracemization method for conversion of the racemate to the desirable (R)-enantiomer of Praziquantel has been developed by coupling incompatible racemization and crystallization processes. By a library approach, a derivative that crystallizes as a conglomerate has been identified. Racemization occurs via reversible hydrogenation over a palladium on carbon (Pd/C) packed column at 130 0C, whereas deracemization is achieved by alternating crystal growth/dissolution steps with temperature cycling between 5-15 0C. These incompatible processes are combined by means of a flow system resulting in complete deracemization of the solid phase to the desired (R)-enantiomer (98 % ee ). Such an unprecedented deracemization by a decoupled crystallization/racemization approach can readily be turned into a practical process and opens new opportunities for the development of essential enantiomerically pure building blocks that require harsh methods for racemization.

We report insights into our observations of the wide variability in quality of palladium catalyst from different suppliers, finding the fundamental differences can be rationalized through a combination of XRD, XPS, and TEM analysis, offering the possibility to predict a catalysts performance prior to the use of valuable synthetic material and save time consuming efforts to identify high quality palladium on carbon catalysts. The synthetic glycan accessed in this study will allow further steps towards the development of semisynthetic vaccines against cryptococcal infections.

A practical and efficient method for scavenging palladium leached into the reaction mixture using thiol-modified dual-pore silica beads has been developed. Reducing the level of metal contamination, especially palladium, in pharmaceutical and bioactive compounds and fine chemicals to below the regulatory value is quite important for the quality assurance of industrial products. We have evaluated the performance of dual-pore silica beads as a palladium scavenger by investigating their ability to eliminate the divalent palladium ions in dilute palladium(II) acetate in methanol (5 and 50 ppm) and ethyl acetate (5 ppm) solutions. The ability of the dual-pore silica beads to eliminate the palladium species leached from a 10% palladium on carbon (Pd/C) catalyst during the ligand- and copper-free 10% Pd/C-catalyzed Sonogashira-type coupling reaction was also investigated. The thiol-modified dual-pore silica beads exhibit a more rapid and effective elimination ability toward leached palladium species in the react...

Compounds such as 3, the product of a palladium[0]-catalyzed Ullmann cross-coupling of o-iodonitrobenzene and 2-iodocyclohex-2-en-1-one, undergo complementary modes of reductive cyclization depending upon the conditions employed. Thus, on treatment with hydrogen in the presence of palladium on carbon, the tetrahydrocarbazole 4 is formed, while reaction of the same substrate (3) with TiCl3 in acetone affords the 1,2,3,9-tetrahydro-4H-carbazol-4-one 6.

In the present work we developed a practical, faster, and more sustainable way to prepare conjugated materials, derived from poly-p-phenylenes (PPPs), using 10% palladium on carbon as catalyst and distilled water as solvent under microwave heating for 3 h. The oligomers were also prepared by the classical Suzuki reaction to enable a comparison of results. All materials were characterized by nuclear magnetic resonance (NMR), infrared (IR), absorption and emission analysis, gel permeation chromatography (GPC), and thermogravimetric analysis. The polymers prepared by the alternative method were obtained in higher yields than the polymers produced by the classical Suzuki reaction. In addition, characterization data showed no significant differences in terms of molecular structures and luminescent properties between the polymers synthesized through the different protocols. Therefore, the alternative method developed was considered appropriated for the synthesis of PPPs derivatives.

A series of phenolic bio-oil components were selectively hydrodearomatized by palladium on carbon into the corresponding ketones or alcohols in excellent yields using polymethylhydrosiloxane and wa ...

This protocol describes an electrochemical synthesis of 1,2-diazides from alkenes. Organic azides are highly versatile intermediates for synthetic chemistry, materials, and biological applications. 1,2-Diazides are commonly reduced to form 1,2-diamines, which are prevalent structural motifs in bioactive natural products, therapeutic agents, and molecular catalysts. The electrochemical formation of 1,2-diazides involves the anodic generation of an azidyl radical from sodium azide, followed by two successive additions of this N-centered radical to the alkene, and is assisted by a Mn catalyst. The electrosynthesis of 1,2-diazides can be carried out using various experimental setups comprising custom-made or commercially available reaction vessels and a direct-current power supply. Readily accessible electrode materials can be used, including carbon (made from reticulated vitreous carbon and pencil lead), nickel foam, and platinum foil. This protocol is also demonstrated using ElectraSyn, a standardized electrochemistry kit. Compared with conventional synthetic approaches, electrochemistry allows for the precise control of the anodic potential input, eliminates the need for stoichiometric and often indiscriminate oxidants, and minimizes the generation of wasteful byproducts. As such, our electrocatalytic synthesis exhibits various advantages over existing methods for alkene diamination, including sustainability, operational simplicity, substrate generality, and exceptional functional-group compatibility. The resultant 1,2-diazides can be smoothly reduced to 1,2-diamines in a single step with high chemoselectivity. To exemplify this, we include a procedure for catalytic hydrogenation using palladium on carbon. This protocol, therefore, constitutes a general approach to accessing 1,2-diazides and 1,2-diamines from alkenes.

Dihydronepetalactone (DHN) is a safe and effective topical insect repellent,(5,6,8) comparable in efficacy to that of N,N-diethyl-m-toluamide (DEET). The latter is the most commonly used active ingredient, found in many commercial insect repellents for a broad range of biting insects. DHN can be produced by hydrogenating nepetalactone (NL), which is the primary ingredient of the essential oil obtained from the renewably sourced catmint plant, Nepeta cataria. Optimizing the hydrogenation reaction to produce DHN from catmint oil is a key economic driver for the process. Prior to the study described here, Six Sigma methodologies were used to select palladium on carbon (5% Pd/C) as the catalyst of choice. The hydrogenation step was studied as a function of critical process variables and the composition of the oil. As described in this article, a robust, two-step hydrogenation process was developed to maximize the yield of the desired DHNs from treated catmint oil. It was observed that the composition of the c...

Transition metal-catalyzed dehydrogenation is a clean oxidation method requiring no additional oxidants. We have accomplished a heterogeneous Pd/C-catalyzed aqueous dehydrogenation of 1,4-cyclohexadienes and cyclohexenes to give the corresponding highly-functionalized arenes. Furthermore, various arenes could be efficiently constructed in a one-pot manner via a Diels–Alder reaction and the following dehydrogenation.

In the presence of either Pd/C or Pt/C, 4-alkoxybenzyl alcohols, 4-alkoxy-phenylalkyl alcohols and cinnamyl alcohols undergo liquid etherification to bis(4-alkoxybenzyl) ethers, bis[(4-alkoxybenzyl)alkyl] ethers and bis(cin-namyl) ethers at temperatures of 100°C - 135°C. In a number of cases, Pt/C and Pd/C as catalysts, also when they are doped with Ru, show distinct differences when the reactions run in air, with an oxidative dehydrogenation of the alcohols as side-reaction, yielding the corresponding ketones and aldehydes as by-products. Also, the reactivity of fluorinated phenylalkenols under these conditions has been investigated. Furthermore, the immobilization of alkyl aryl ethers on silica within a column with passage of hexane as solvent was found to lead to the formation and elution of styrenes from the column in fair yield.

Reaction of methyl-2-(2-formylphenyl)acetate with primary amines in a reductive amination/cyclisation process resulted in N-substituted 1,4-dihydro-3(2H)-isoquinolinones. With H 2NCH 2R sodium borohyride is a suitable reductant (11 examples), but H 2NCHR 1R 2 required a transfer hydrogenation using ammonium formate catalysed by palladium on carbon (9 examples). 4-Substituted-1,4-dihydro-3(2H)-isoquinolinones were synthesised by deprotonation (n-butyllithium) and addition of R 3CH 2Br (12 examples with R 3 = alkyl, Ar, CH[dbnd]CH 2, C[tbnd]CH). Modest diastereoselectivity was achieved with 1,4-dihydro-3(2H)-isoquinolinones derived from H 2NCHMeR 2 [R 2 = (η 5-C 5H 4)Co(η 4-C 4Ph 4) - max. dr = 1.9: 1], but use of H 2NCHMeFc (Fc = ferrocenyl) provided a new method of 1,4-dihydro-3(2H)-isoquinolinone N-deprotection with formic acid.

Hydrogen has attracted much attention as one of the most promising chemical fuel candidates because of its zero emission during consumption. In order to solve the freezing problem of water based hydrolysis process, herein, the Pd/C as an efficient and stable catalyst for the methanolysis, ethanolysis, propanolysis and butanolysis of B2pin2 for the generation of hydrogen has been first developed. The large kinetic isotope effect (KIE) of kH/kD = 5.0, D2 formation from CD3OD and in situ tandem reaction have confirmed that alcohol is the only hydrogen source. Interestingly, the order of Ea of these alcohols in H2 evolution is MeOH (methanol, 29.57 kJ/mol) EtOH > PrOH > nBuOH).

A facile direct deposition approach for the preparation of recyclable Pd/C catalysts simply by stirring a solution of Pd2dba3 with a suitable carbon material was evaluated. An extraordinary rapid catalyst preparation procedure (< 5 min) under mild conditions and its excellent performance in cross-coupling and hydrogenation reactions were demonstrated. The key point for catalyst design was to directly deposit Pd(0) centers onto highly accessible surface area and to avoid ill-defined Pd(II)/Pd(0) states.

In the presence of palladium on carbon (Pd/C) as a catalyst, hydrogenation of aliphatic nitriles in cyclohexane efficiently proceeded at 25-60 °C under ordinary hydrogen gas pressure to afford the corresponding tertiary amines. However, the use of rhodium on carbon (Rh/C) led to the highly selective generation of secondary amines. Hydrogenation of aromatic nitriles and cyclohexanecarbonitrile selectively produced secondary amines in the presence of either Pd/C or Rh/C.

Nucleophilic substitution in nitroarenes to form biaryl ethers is of fundamental importance in organic synthesis. Under non-catalytic conditions, this can occur when a highly activated nitroarenes are used, or the nucleophile is activated by strong stoichiometric base. We have established a new method, using ligand-free palladium on carbon (Pd/C) catalyst, for the cross-coupling of activated nitroarenes with relatively non-nucleophilic phenol derivatives, including naphthol, in the absence of harsh bases. Control experiments, hot-filtration, three-phase test and ICP-AES analysis reveals that the catalysis proceeds via a usual oxidative addition step of nitroarene to Pd/C and releases active palladium particles having an extremely high catalytic activity. DFT calculations were made to realize the origin of selectivity of activated nitroarenes.

The catalytic hydrogenation of cardanol was studied in a stirred three-phase-slurry reactor using palladium on carbon, often referred to as the Pd/C catalyst (5% loading of palladium is supported on activated carbon powder). The effects of various process parameters were examined. The kinetics of hydrogenation, which proceeds through three parallel–series reactions, was investigated. The reaction was observed to be of first order with respect to both hydrogen and cardanol. A simple second-order series reaction model was well fitted to the experimental data. Also, the Langmuir–Hinshelwood–Hougen–Watson approach was used to interpret the possible mechanistic behaviour of the reaction. It was observed that the reaction follows dual site, competitive and dissociative type of adsorption of hydrogen. Surface reaction of the adsorbed reactants was identified as the overall rate controlling step. Various rate constants and adsorption equilibrium constants for the different steps were also estimated. Different thermodynamic parameters associated with these constants were obtained to assess their physical significance. Also, these constants were evaluated statistically using the F-test and t-test.

Palladium nanomaterials have attracted great attention on the development of electrocatalysts for fuel cells. Herein, we depicted a novel strategy in the synthesis of palladium nanoparticles with superior electrocatalytic activity. The new approach, based on the self-assembly of bacitracin biotemplate and palladium salt for the preparation of bacitracin-palladium nanoparticles (Bac-PdNPs), was simple, low-cost, and green. The complex, composed by a series of spherical Bac-PdNPs with a diameter of 70 nm, exhibited a chain-liked morphology in TEM and a face-centered cubic crystal structure in X-Ray diffraction and selected area electron diffraction. The palladium nanoparticles were mono-dispersed and stable in aqueous solution as shown in TEM and zeta potential. Most importantly, compared to the commercial palladium on carbon (Pd/C) catalyst (8.02 m 2 g −1 ), the Bac-PdNPs showed a larger electrochemically active surface area (47.57 m 2 g −1 ), which endowed the products an excellent electrocatalytic activity for ethanol oxidation in alkaline medium. The strategy in synthesis of Bac-PdNPs via biotemplate approach might light up new ideas in anode catalysts for direct ethanol fuel cells.

We have demonstrated a direct arylation polycondensation of 3,4-ethylenedioxythiophene with 2,7-dibromo-9,9-dioctylfluorene using palladium on carbon (Pd/C) as a catalyst. Pd/C is a low-cost solid-supported palladium catalyst, giving one of the effective catalytic systems for direct arylation. The Pd/C-catalyzed direct arylation polycondensation with acetic acid/potassium carbonate in N,N-dimethylacetamide furnished a high molecular weight π-conjugated alternating copolymer of EDOT-fluorene (Mn = 89,300, Mw/Mn = 3.27) in high yield. The polycondensation of EDOT with various dibromoarenes was also achieved, giving EDOT-carbazole, EDOT-dialylamine, and EDOT-bithiophene polymers. Optical and electrochemical properties of the polymers were also discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

This work describes the synthesis and characterization of a new class of oxamic acid derivatives containing pyrazole and isoxazole as substituents to investigate their ability to form hydrogen bonds aiming at applying them in crystal engineering and molecular self-recognition. In this respect, we report a new synthesis of 2-(4-nitrophenyl)-1,3-propanedial (1) in high yield using SOCl2 as a chlorinating agent. The new oxamic esters 4-(1H-pyrazol-4-yl)phenylene-N-(ethyloxamate) (2d) and 4-(1,2-oxazol-4-yl)phenylene-N-(ethyloxamate) (3d) were prepared from 1. The synthetic route consists of the cyclisation of 1 either with hydrazine to afford 4-(-aminophenyl)-1H-pyrazole (2a) or with hydroxylamine to obtain the isoxazole-based molecule 4-(4-nitrophenyl)-1,2-oxazole (3a). The reduction of 2a and 3a was carried out in an acidic/tin solution to yield 4-(4-ammoniophenyl)-1H-pyrazol-2-ium trichlorostannate(II) chloride monohydrate (2b) and 4-(4-ammoniophenyl)-1,2-oxazole hexachlorostannate(IV) (3b). Basic extraction of 3b provided 4-(4-aminophenyl)-1,2-oxazole (3c). The reduction of 2a to 4-(4-aminophenyl)-1H-pyrazole (2c) was achieved by means of hydrazine associated with supported palladium on carbon. The condensation of 2c and 3c with ethyl chlorooxoacetate delivers oxamic esters 2d and 3d. In n-tetrabutylammonium hydroxide solution 2d is fully hydrolyzed, obtaining the n-tetrabutylammonium salt of 4-(1H-pyrazole-4-yl)phenylene-N-oxamate as a hemihydrate (2e). The low stability of isoxazole molecules in basic solutions was proved by crystallizing the n-tetrabutylammonium salt of 1-cyano-1-(4-nitrophenyl)-2-oxoethanide (3f) (obtained by cleavage of 3d with n-Bu4NOH) and preparing its conjugated acid 2-(4-nitrophenyl-3-oxopropanenitrile (3e). The structures of 2b, 3b, 3d and 2e were solved by single crystal X-ray diffraction techniques. The analysis of their crystal packing reveals hydrogen bond features compatible for all compounds as well as some differences depending on the pH of the crystallization solution and the presence or absence of the oxamate group due to the increase of hydrogen bond donors and acceptors.

The α-alkylation of ketones with alcohols represents a green strategy for the formation of crucial carbon–carbon bonds since it only produces water as byproduct. In terms of reaction mechanism, the evidence for homogeneous catalysis supports a catalytic hydrogen-borrowing pathway; however, the reaction mechanism has not been investigated for heterogeneous Pd/C catalysts. Here, we report an improved method for α-alkylation of ketones with alcohols using commercially available Pd/C, ubiquitous in organic synthesis labs, as catalyst. The reaction conditions are mild compared to state-of-the-art for both homo- and heterogeneous catalysts, and the developed conditions produces quantitative yields for most ketones and alcohols. A hot filtration experiment and recycling of the catalyst supports the heterogeneous nature of catalysis. Importantly, the reaction mechanism is studied for the first time by a combination of stoichiometric experiments and kinetic analyses by in-situ IR (React-IR).

An efficient and convenient one-pot procedure for the stereoselective catalytic synthesis of ring-substituted [amino(phenyl)methyl]phosphonates has been developed. The enantioselective hydrogenation of easily available diisopropyl (Z)-[aryl(phenylhydrazono)methyl]phosphonates using palladium(II) acetate as a precatalyst, (R)-2,2′-bis(diphenylphosphino)-5,5′-dichloro-6,6′-dimethoxy-1,1′-biphenyl [(R)-Cl–MeO-BIPHEP] as a ligand, and (1S)-(+)-10-camphorsulfonic acid as an activator in a mixture of 2,2,2-trifluoroethanol and methylene chloride at ambient temperature results in the formation of corresponding [aryl(2-phenylhydrazino)methyl]phosphonates. The subsequent cleavage of the N−N bond has been accomplished with molecular hydrogen after the addition of palladium on carbon and methanol into crude reaction mixture to afford the optically active [amino(aryl)methyl]phosphonates. The method is operationally simple and provides an appreciable enantioselectivity up to 98 % ee.

The modification of benzylic quaternary, tertiary, and secondary carbon centers through palladium-catalyzed hydrogenolysis of C(sp3)–C(sp3) σ bonds is presented. When benzyl Meldrum's acid derivatives bearing quaternary benzylic centers are treated under mild hydrogenolysis conditions – palladium on carbon and atmospheric pressure of hydrogen – aromatics substituted with tertiary benzylic centers and Meldrum's acid are obtained with good to excellent yield. Analogously, substrates containing tertiary or secondary benzylic centers yield aromatics substituted with secondary benzylic centers or toluene derivatives, respectively. Furthermore, this strategy is used for the high yielding synthesis of diarylmethanes. The scope of the reductive dealkylation reaction is explored and the limitations with respect to steric and electronic factors are determined. A mechanistic analysis of the reaction is described that consisted of deuterium labelling experiments and hydrogenolysis of enantioenriched derivatives. The investigation shows that the C(sp3)–C(sp3) σ bond-cleaving events occur through a hybrid SN1/SN2 mechanism, in which the palladium center displaces a carbon-based leaving group, namely Meldrum's acid, with inversion of configuration, followed by reductive elimination of palladium to furnish a C−H bond.

10% Palladium on carbon (10% Pd/C) successfully catalyzed the intramolecular C−H amination of various N-mesylated 2-aminobiphenyls in the presence of a catalytic amount of pyridine N-oxide in heated dimethyl sulfoxide (DMSO) under an oxygen atmosphere to afford the corresponding N-mesylcarbazoles. The reaction would proceed via a single-electron transfer process based on its significant suppression by the addition of a single-electron scavenger, tetracyanoquinodimethane (TCNQ), and the substituents on the aromatic rings of the substrate have an insignificant effect on the reaction progress.

The combination of commercially available palladium on carbon (Pd/C) with 1,1,3,3-tetramethyldisiloxane (TMDS) was found to be an effective catalyst system for the production of tertiary amines by deoxygenative silane-reduction of carboxamides. Facile removal of both the metallic species and silane residues can be achieved by simple extraction, and the recovered Pd/C was reusable. Other palladium complexes and salts, Pd2(dba)3(CHCl3) [dba = dibenzylideneacetone], Pd(OAc)2, and PdCl2, were also effective for the reduction of tertiary carboxamides with TMDS. Detailed mechanistic studies of the present Pd/C–TMDS system revealed that the catalytically active species is the soluble palladium colloids leached from the palladium particles on the carbon support by treating with TMDS, and carboxamides, amine products, and TMDS act as a stabilizer for the generated palladium species in solution.

A trickle bed reactor (TBR) was used to study different process parameters upon hydrogen peroxide direct synthesis. The catalysts used were commercial palladium on active carbon. The influence of pressure (1.75–25 barg), temperature (5–60°C), liquid flow rate (2–13.8 ml·min-1), gas flow rate (3.4–58.5 ml·min-1), catalyst amount (90–540 mg), Pd percentage on the support (5% wt., 10% wt. and 30% wt. Pd/C) as well as promoter concentrations (0.0005–0.001 m) were all varied as process parameters to better understand the behaviour of the system. By contrast, the gas phase molar composition of the feed (4:20:76=H2:O2:CO2) was kept constant. The strong influence between liquid flow rate, gas flow rate and catalyst amount were identified as the key parameters to tune the reaction, and related to the activity of the catalyst. In essence, these parameters must be carefully tuned to control the hydrogen consumption. The maximum productivity (289 μmol H2O2·min-1) and yield (83.8%) were obtained when a diluted bed of 30% Pd/C was applied. The H2O2 hydrogenation was studied in order to understand its role in the H2O2 direct synthesis reaction network. The hydrogenation reaction mechanism and the role of NaBr were identified thanks to the experiment proposed in the present work. Consequently, understanding the whole reaction mechanism from the process conditions studied led to a deeper understanding of all of the phenomena involved in the H2O2 direct synthesis.

A dehydrogenative oxygenation of C(sp2)H bonds with intramolecular phenolic hydroxy groups has been developed, which provides a straightforward and concise access to structurally diversely benzofurans from ortho-alkenylphenols. The reaction is catalyzed by palladium on carbon (Pd/C) without any oxidants and sacrificing hydrogen acceptors.

We have demonstrated a palladium on carbon-catalyzed approach to regioselectively alter the cleavage sites of the C-C bonds of cinnamaldehyde derivatives by a slight change in the reaction conditions in isopropanol under an O2 atmosphere. Styrene derivatives could be selectively formed by the addition of Na2CO3 in association with the dissociation of carbon monoxide, while benzaldehyde derivatives were generated by the addition of CuCl and morpholine instead of Na2CO3.

An atom economical and catalytic route for the synthesis of aryl- and alkyl-substituted secondary amines has been developed. Using a bis(amidate)bis(amido)titanium(IV) precatalyst, the hydroamination of terminal alkynes with a range of amines results in the selective formation of the anti-Markovnikov product. The crude enamine/imine mixtures are effectively hydrogenated using palladium on carbon (Pd/C) and H2 to afford the corresponding secondary amine in excellent yields. Simple work-up procedures allow for the isolation of pure compounds while avoiding purification via column chromatography.

Heterogenous hydrogenations of high value chemicals are a widely used class of reaction that potentially benefit from the advantages continuous processing possesses. Trickle bed reactors offer a viable alternative to batch manufacture, however further understanding of the interplay between hydrogen mass transfer and catalytic reaction is required to facilitate the uptake of such technologies. To isolate the transport processes, the hydrogenation of styrene was conducted with a single 1% palladium on carbon pellet immobilized within glass beads with a liquid feed either hydrogen saturated or hydrogen free and the liquid flow rate was varied. The transfer rate of hydrogen was found to be significantly affected by the hydrogen content in the feed. The observations are well described by a new model in which the pellet film is treated as a plug flow reactor, with mass transfer from the gas phase to the film modelled as diffusion through a stagnant film, and mass transfer from the film to the catalyst surface and the subsequent reaction modelled as resistances in series. Our findings indicate that the provision of inert mass transfer area to saturate the fluid with hydrogen can significantly increase the productivity per unit mass of catalyst. In addition, by controlling the ratio of catalytic and inert surface the hydrogen concentration close to the catalyst surface can be tuned. This could be utilised to adjust both the activity and selectivity of the system and therefore, give trickle bed reactors an advantage in chemical manufacturing processes.

A highly efficient liquid-phase hydrogenation reaction using a recyclable palladium on carbon (Pd/C) catalyst has been used for the transformation of naringin to its corresponding dihydrochalcone. The effects of various solvents on the hydrogenation process were studied, with water being identified as the optimal solvent. The analysis also revealed that sodium hydroxide (NaOH) can accumulate on the surface of the Pd/C catalyst in alcoholic solvents, leading to its inactivation. The higher solubility of NaOH in water implies that it remains in solution and does not accumulate on the Pd/C catalyst surface, ensuring the catalytic activity and stability.

A library of positional isomers of d-glucose ( O-1- O-6) as ligands and their 11 light-active ruthenium conjugates has been synthesized. A protecting group strategy without the necessity of using palladium on carbon for the modification for the 2- O and 4- O position allows for the incorporation of sulfur donor atoms as ligands for transition metal complexes.

Herein, we report the use of γ-valerolactone as a new biomass-derived reaction medium for microwave assisted organic synthesis. The interaction of this solvent with microwaves and its heating profile under microwave irradiation has been fully characterized for the first time, demonstrating its stability and the applicability in microwave assisted Pd/C catalysed reactions avoiding the arcing phenomena frequently observed in these conditions. The use of γ-valerolactone demonstrated to be compatible with aliphatic and aromatic amines in the hydrogen transfer Pd/C mediated synthesis of benzimidazoles. ispartof: SCIENTIFIC REPORTS vol:8 issue:1 ispartof: location:England status: published

Palladium was impregnated on carbon particles with various structures using 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF6]) to synthesize a catalyst for hexafluoropropylene hydrogenation. Under the identical reaction conditions (1 bar and 120 °C), the catalyst with mesoporosity (pore size > 500 nm) showed higher than 80% reactant conversion. However, the conversion over the catalyst possessed small pore size was very low. Moreover, the catalyst prepared with ionic liquids was more stable than without ionic liquids.

Application of a trickle bed reactor (TBR) renders a very compact solution to carry out direct synthesis of hydrogen peroxide in water over a carbon supported palladium. The laboratory scale reactor was filled with silica particles (50–70 mesh) physically mixed with 37.5 to 75 mg of 5%Pd/C particles. The reaction conditions applied were 15 °C, 15–28 barg, 0.5 to 6 mL min −1 of liquid and 4.0–4.5 mL min −1 of gas flowrate (86.7/11/2.23 mol% of CO 2 /O 2 /H 2 ). Thus, we demonstrated that the ratio between H 2 and Pd is one of the key factors to achieve optimized, higher yields of hydrogen peroxide. Consequently, low H 2 concentrations lead to low productivities. One of the least studied parameters, addressed here, is the ratio between the bed filling (SiO 2 ) and the catalyst; i.e. the active catalytic species dilution effect. In short, it was found that when the amount of Pd was reduced below 0.094 mg Pd cm −3 SiO 2 the highest productivity of H 2 O 2 could be achieved. The selectivity obtained were between 5.3 and 38.0%, respectively, corresponding to turn-over-frequencies (TOF) ranging from 65 to 921 mmol H 2 O 2 gPd −1 h −1 .

A modified palladium on carbon (Pd/C) catalyzed hydrogenolysis method for the removal of the phenolic-OH group in phenolic alkaloids as the 1-phenyl-1H-tetrazol-5-yl derivative by the addition of magnesium metal or ammonium acetate in acetic acid is described. Five different types of isoquinoline alkaloids, i.e., phenanthrene alkaloid, aporphine, pavine, protoberberine, and 1-benzyltetrahydroisoquinoline, were used as reactants. The results indicate that the addition of either magnesium metal or ammonium acetate has the advantage of decreasing the amount of Pd/C and the accelerating reaction rate over the simple Pd/C-catalyzed hydrogenolysis, thus it is practical for larger-scale preparation of de-phenolated alkaloids for pharmacological study.

The catalytic dehydrogenation of alcohols to carbonyl products is a green sustainable oxidation with no production of waste except for hydrogen, which can be an energy source. Additionally, a reusable heterogeneous catalyst is valuable from the viewpoint of process chemistry and water is a green solvent. We have accomplished the palladium on carbon (Pd/C)-catalyzed dehydrogenation of primary alcohols to carboxylic acids in water under a mildly reduced pressure (800 hPa). The reduced pressure can be easily controlled by the vacuum controller of the rotary evaporator to remove the excess of generated hydrogen, which causes the reduction (reverse reaction) of aldehydes to alcohols (starting materials) and other undesirable side reactions. The present method is applicable to the reaction of various aliphatic and benzylic alcohols to the corresponding carboxylic acids, and the Pd/C could be reused at least 5 times.

A convenient method for the deuteration of organic substrates using deuterated hypophosphite as the deuterium source was investigated. Transfer deuteration of organic substrates, such as aromatic halides, alkenes, alkynes, epoxides, and O-benzyl derivatives, in the presence of palladium on carbon in deuterium oxide proceeded efficiently to give the corresponding deuterated products in excellent yields with high deuterium contents.

The continuous flow Suzuki-Miyaura reaction between various haloarenes and arylboronic acids was successfully achieved within only ca. 20 s during the single-pass through a cartridge filled with palladium on carbon (Pd/C). No palladium leaching was observed in the collected reaction solution by atomic absorption spectrometry (detection limit: 1 ppm).

This work reports the synthesis of polyamides using an efficient, ligand free and Pd/C-catalyzed protocol. Various polyamides can be synthesized by carbonylation polycondensation reaction of aromatic diiodides, diamines and carbon monoxide using Pd/C as a heterogeneous and recyclable catalyst. Variation in inherent viscosities observed with the structure of diamine component. Notably this synthetic route does not require any ligand and give high yield of the polyamides. Catalyst Pd/C can be recovered easily and was characterized using XPS analysis. The catalyst was recycled five times without substantial loss in activity.