163 results found
Debecker DP, Hii KKM, Moores A, et al., 2021, Shaping Effective Practices for Incorporating Sustainability Assessment in Manuscripts Submitted to ACS Sustainable Chemistry & Engineering: Catalysis and Catalytic Processes, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 9, Pages: 4936-4940, ISSN: 2168-0485
Subramaniam B, Allen D, Hii KKM, et al., 2021, Lab to Market: Where the Rubber Meets the Road for Sustainable Chemical Technologies, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 9, Pages: 2987-2989, ISSN: 2168-0485
Allen DT, Carrier DJ, Chen J, et al., 2020, Remembering Professor, Academician, and Editor Lina Zhang, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 8, Pages: 16385-16385, ISSN: 2168-0485
Allen DT, Carrier J, Chen J, et al., 2020, Expectations for Manuscripts in ACS Sustainable Chemistry & Engineering: Scope Summary and Call for Creativity, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 8, Pages: 16046-16047, ISSN: 2168-0485
Allen DT, Carrier DJ, Chen J, et al., 2020, The Changing Structure of Scientific Communication: Expanding the Nature of Letters Submissions to ACS Sustainable Chemistry & Engineering, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 8, Pages: 8469-8470, ISSN: 2168-0485
Hii KK, Mulligan C, Parker J, 2020, Revisiting the mechanism of the Fujiwara-Moritani reaction, Reaction Chemistry and Engineering, Vol: 5, Pages: 1104-1111, ISSN: 2058-9883
The Fujiwara–Moritani reaction between p-methylacetanilide and n-butyl acrylate, catalysed by Pd(OAc)2 in the presence of toluenesulfonic acid and benzoquinone, was (re-)investigated using reaction calorimetry and complementary spectroscopic methods. The (most) active catalyst was identified and the catalytic turnover rate was found to be independent of all stoichiometric reagents. Catalyst regeneration and deactivation pathways are discussed.
Hii KKM, Moores A, Pradeep T, et al., 2020, Expectations for manuscripts on catalysis in ACS sustainable chemistry & engineering, ACS Sustainable Chemistry and Engineering, Vol: 8, Pages: 4995-4996, ISSN: 2168-0485
Checchia S, Mulligan CJ, Emerich H, et al., 2020, Pd-LaFeO3 catalysts in aqueous ethanol: Pd reduction, leaching, and structural transformations in the presence of a base, ACS Catalysis, Vol: 10, Pages: 3933-3944, ISSN: 2155-5435
The reactive behavior of three catalysts based on Pd-loaded LaFeO3 was investigated in terms of the reducibility of Pd and its propensity to leaching into the liquid phase in flowing solutions prototypical of C–C coupling catalysis in a continuous flow reactor cell. In situ quick extended X-ray absorption fine structure spectroscopy showed that Pd remains stable and nonreducible in the flowing ethanol/water solvent mixture under heating to 353 K. However, ex situ transmission electron microscopy, high-energy X-ray diffraction, and fluorescence yield Fe K-edge X-ray absorption near-edge structure show that the addition of a significant amount of base (K2CO3, 0.1 M) results in the structural degradation of the perovskite support as well as the mobilization of Pd along the sample bed that is dependent on the structure and crystallite size of the perovskite. The results are discussed in terms of the use of perovskite-type oxides in various areas of research where they are placed in contact with liquid phases of variable temperature and elevated pH.
Allen DT, Carrier DJ, Chen J, et al., 2020, The evolution of ACS sustainable chemistry & engineering, ACS Sustainable Chemistry and Engineering, Vol: 8, Pages: 1-1, ISSN: 2168-0485
Newton M, Ferri D, Mulligan C, et al., 2019, In situ study of metal leaching from Pd/Al2O3 induced by K2CO3, Catalysis Science and Technology, Vol: 10, Pages: 466-474, ISSN: 2044-4753
In situ time- and spatially-resolved Quick Extended X-ray Absorption Fine Structure Spectroscopy (QEXAFS) was deployed to study the leaching of Pd from a heterogeneous catalyst caused by K2CO3 temporally and spatially.
Bourne RA, Hii KKM, Reizman BJ, 2019, Introduction to Synthesis 4.0: towards an internet of chemistry, REACTION CHEMISTRY & ENGINEERING, Vol: 4, Pages: 1504-1505, ISSN: 2058-9883
Mulligan C, Bagale S, Newton O, et al., 2019, Peracetic acid: An atom-economical reagent for Pd-catalyzed acetoxylation of C-H bonds, ACS Sustainable Chemistry and Engineering, Vol: 7, Pages: 1611-1615, ISSN: 2168-0485
Peracetic acid can be used universally as a source of acetate and an oxidant for the selective acetoxylation of C–H bonds in compounds containing ortho-directing groups, catalyzed by Pd(OAc)2. Compared to previous procedures, where persulfates and PhI(OAc)2 were used, the new protocol provides significant improvements in atom efficiency, product yield, substrate scope, cost, scalability, and environmental impact.
Wong VHL, Hii KK, 2018, 3 Silver-Catalyzed Cyclizations, Silver Catalysis in Organic Synthesis, Pages: 85-181, ISBN: 9783527342815
Roberts F, Richard C, Zemichael F, et al., 2018, Base-free, tunable, Au-catalyzed oxidative esterification of alcohols in continuous flow, Reaction Chemistry and Engineering, Vol: 3, Pages: 942-948, ISSN: 2058-9883
Under continuous flow conditions, hydrogen peroxide oxidizes primary alcohols (cinnamyl alcohol, decenol, decanol and benzyl alcohol) in methanol over Au/TiO2, without the need for added base. While the allylic alcohols afforded conjugated aldehydes, aliphatic and benzylic alcohols afforded acids or esters. Selectivity for either product can be achieved by adjusting the reaction parameters. Kinetic studies revealed that the formation of the easter is faster than that of the acid, due to a greater pre-organization (larger ln A) attributed to the more favourable formation of the hemiacetal intermediate.
Hii KM, hellgardt, barreiro, et al., 2018, Spatial, temporal and quantitative assessment of catalyst leaching in continuous flow, Catalysis Today, Vol: 308, Pages: 64-70, ISSN: 0920-5861
Catalyst leaching is a major impediment to the development of commercially-viable processes conducted in a liquid-phase. To date, there is no reliable technique that can accurately identify the extent and dynamics of the leaching process in a quantitative manner. In this work, a tandem flow-reactor system has been developed, which allowed us to distinguish between surface-catalyzed reactions from those occurring in solution by comparing%conversion at the exit of each reactor (S1, S2) corresponding to predominance of heterogeneous/homogeneous reactions (spatial) and two different residence times (temporal). A multiscale model is subsequently established to quantify the two types of reaction rate and simulate the catalyst leaching from a cross-coupling catalyst, PdEncat™ 30; including: (1) a multi-particle sizes model for catalyst scale; and (2) a dispersion model for reactor scale. The results show that catalyst leaching occurs via more than one process, and that the homogeneous Pd-catalyst (leached from the immobilized catalyst and dissolved in the flow) dominates the reaction and possesses a much higher activity than the heterogeneous (immobilized) Pd-catalyst. Additionally, the change of leached Pd stream inside reactors can be predicted along with the axial direction and the reaction time through the reactor-scale dispersion model.
Bystron T, Horbenko A, Syslova K, et al., 2018, 2-Iodoxybenzoic acid synthesis by oxidation of 2-Iodobenzoic acid at a Boron-doped diamond anode, ChemElectroChem, Vol: 5, Pages: 1002-1005, ISSN: 2196-0216
For the first time, the electrochemical synthesis of 2-iodoxybenzoic acid (IBX), a benign, well-established, popular and highly selective oxidising agent, is described. The objective of the work was to investigate the possibility of generating IBX electrochemically in aqueous solutions by using boron-doped diamond anodes. In 0.2 M H2SO4 aqueous solution, 2-iodobenzoic acid (IBA) was found to be oxidised at potentials >1.6 V vs. SCE, initially to 2-iodosobenzoic acid (IsBA), which was oxidised to IBX at potentials >1.8 V vs. SCE. Reductions of IBX to IsBA and IsBA to IBA occurred at similar potentials of ca. −0.7 V vs. SCE. The voltammetry results were confirmed by performing a series of batch electrolyses at different electrode potentials. Thus, depending on the electrode potential chosen, IBA can be oxidised anodically either to IsBA or IBX with 100 % overall selectivity. The only side-reaction was O2 generation, but charge yields did not decrease below 55 % even at conversions >95 %.
Keung Leung AY, Hellgardt K, Leung A, et al., 2018, Catalysis in flow: nickel-catalyzed synthesis of primary amines from alcohols and NH3, ACS Sustainable Chemistry and Engineering, Vol: 6, Pages: 5479-5484, ISSN: 2168-0485
A highly selective synthesis of primary amines from alcohols and NH3 was achieved on using a commercially available Ni catalyst, without adding H2. Using a continuous flow reaction platform, the amination of aliphatic alcohols can be achieved in good yields and selectivities, as the accumulation of water byproduct can be removed. Competitive formation of the nitrile side-product was suppressed when the catalyst was prereduced. Modes of catalyst deactivation were also briefly examined.
Luo M, Zhang JC, Pang WM, et al., 2017, Erratum to: One-step multicomponent synthesis of chiral oxazolinyl-zinc complexes, Chemistry Central Journal, Vol: 11, ISSN: 1752-153X
Luo M, Zhang JC, Pang WM, et al., 2017, One-step multicomponent synthesis of chiral oxazolinyl-zinc complexes, CHEMISTRY CENTRAL JOURNAL, Vol: 11, ISSN: 1752-153X
BackgroundTypically, oxazolinyl metal complexes are synthesized in two steps, where the free ligand is prepared by the condensation reaction between a functionalized nitrile and an amino alcohol in the presence of a Lewis or Brønsted acid catalyst, followed by a further reaction with metal salts to obtain the corresponding metal complexes. Very often, the yield afforded by the two-step procedure is not high, and very few oxazolinyl zinc complexes have been prepared by this route. Given that metal-oxazoline complexes often contain Lewis acidic metals, it is conceivable that the two steps may be telescoped.ResultsA series of novel chiral organozinc complexes 1–15 were assembled in a single step, All crystalline compounds were fully characterized, including the report of 15 X-ray crystal structures, including a wide structural diversity.ConclusionsA series of novel chiral organozinc complexes were assembled in a single step, from nitriles, chiral D/L amino alcohols, and a stoichiometric amount of ZnCl2, with moderate to high yields (20–90%).
Hii KM, Newton MA, Nicholls R, et al., 2017, Effect of retained chlorine in ENCAT™ 30 catalysts on the development of encapsulated Pd: insights from in situ Pd K, L3 and Cl K-edge XAS, Catalysis, Structure & Reactivity, Vol: 3, Pages: 149-156, ISSN: 2055-074X
In situ X-ray absorption spectroscopy (XAS) and Pd K, LIII, and Cl K-edges shows that Cl can be present in significant amounts in ENCAT™ 30 catalysts and that it can severely retard Pd nanoparticle (NP) development in flowing solvents. We also show that whilst polymeric encapsulation protects the Pd against solvent induced agglomeration of Pd nanoparticles the evidence suggests it does not prevent the formation PdHx through reaction with the aqeous ethanol solvent, and that, as received, ENCAT™ 30 NP catalysts are not, for the most part, comprised of nanoparticulate Pd0 irrespective of the presence of Cl.
Deadman BJ, Hellgardt K, Hii KM, 2017, A colorimetric method for rapid and selective quantification ofperoxodisulfate, peroxomonosulfate and hydrogen peroxide, Reaction Chemistry and Engineering, Vol: 2, Pages: 462-466, ISSN: 2058-9883
Redox colorimetric tests have been devised for the rapid analysis of the individual components of aqueous mixtures of peroxodisulfate, peroxomonosulfate and hydrogen peroxide; providing a convenient and selective method for the determination of these industrially relevant oxidants, which are known to inter-convert in solution.
Hii KM, Loponova KN, Deadman BJ, et al., 2017, Controlled multiphase oxidations for continuous manufacturing of fine chemicals, Chemical Engineering Journal, Vol: 329, Pages: 220-230, ISSN: 0300-9467
The feasibility of an integrated continuous biphasic oxidation process was studied, incorporating (i) electrochemical generation of an oxidant, (ii) membrane emulsification and an Oscillatory Flow Reactor (OFR) to facilitate mass-transfer in a biphasic reaction system and (iii) product extraction to enable regeneration of the oxidant. The biphasic, organic solvent-free dihydroxylation of styrene by ammonium peroxodisulfate solutions (including electrochemically generated peroxodisulfate) was investigated as a model reaction, both in batch and in an OFR. Heating of peroxodisulfate in a strongly acidic solution was demonstrated to be essential to generate the active oxidant (Caro’s acid). Membrane emulsification allowed mass-transfer limitations to be overcome, reducing the time scale of styrene oxidation from several hours in a conventional stirred tank reactor to less than 50 min in a dispersion cell. The influence of droplet size on overall reaction rate in emulsions was studied in detail using fast image capturing technology. Generation of unstable emulsions was also demonstrated during the oxidation in OFR and product yields >70% were obtained. However, the high-frequency/high-displacement oscillations necessary for generation of fine droplets violated the plug flow regime. Membrane emulsification was successfully integrated with the OFR to perform biphasic oxidations. It was possible to operate the OFR/cross-flow membrane assembly in plug flow regime at some oscillatory conditions with comparable overall oxidation rates. No mass-transfer limitations were observed for droplets <60 μm. Finally, the continuous post-reaction separation was demonstrated in a single OFR extraction unit to enable continuous regeneration of the oxidant.
Brazier JB, Newton MA, Barreiro EM, et al., 2017, Solvent–dependent nuclearity, geometry and catalytic activity of [(SPhos)Pd(Ph)Cl]2, Dalton Transactions, Vol: 46, Pages: 7223-7231, ISSN: 1477-9226
The nuclearity and structures of the palladium complex [(SPhos)Pd(Ph]Cl]2 in the solid and solution states are revisited, using a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, NMR spectroscopy, mass spectrometry, DFT calculations and trapping experiments. The complex was tested for its catalytic activity in the coupling reaction between chlorobenzene and n-hexylamine, where different deactivation behaviour were observed in toluene, 1,4-dioxane and DMF.
Hii KM, Brazier JB, 2017, Effects of Cl on the reduction of supported PdO in ethanol/water mixtures, Catalysis, Structure & Reactivity, Vol: 3, Pages: 54-62, ISSN: 2055-074X
The reduction of γ-Al2O3-supported PdO in flowing aqueous ethanol was investigated. Quick EXAFS (QEXAFS) performed at the Pd K-edge reveals that the presence of Cl can have a profound effect on the reduction process. At low loadings of Pd (1 wt-%), the size dependency of the process is inverted, compared to Cl-free samples. The extent of reduction was found to be dependent on loading/particles size. It is shown, using in situ QEXAFS at the Cl K- and Pd L3-edges, that residual Cl is not removed by the flowing solvent mixture, even at an elevated temperature of 350 K. The origins of these behaviours are discussed in terms of the differing effects that Cl may have when bonded to oxidic or reduced metal centres and the results were compared to earlier observations made on the effects of Cl on commercial polyurea encapsulated Pd ENCAT™ NP 30 catalysts.
Hii KM, Brazier JB, Hellgardt K, 2017, Catalysis in flow: O2 effect on the catalytic activity of Ru(OH)x/Al2O3 during the aerobic oxidation of an alcohol, Reaction Chemistry and Engineering, Vol: 2, Pages: 60-67, ISSN: 2058-9883
Changes in the turnover frequency (TOF) of Ru(OH)x/γ-Al2O3 during aerobic oxidation of benzyl alcohol in a plug flow differential reactor were monitored online using an inline FTIR instrument over extended periods of time (up to 72 h). A new equation for catalyst deactivation is derived, to account for the different lengths of time the catalyst is exposed to the reactants (benzyl alcohol and O2). Catalyst activity and stability are dependent on the amount of O2 in the system; catalyst deactivation can be attributed to two simultaneous processes: a fast and reversible inhibition by the benzoic acid side product and a slower and irreversible loss of catalytic sites due to reduction of Ru. At steady state, the reaction rate is zero-order in benzyl alcohol and partial positive order in O2. Finally, the suitability of a packed-bed (integral) reactor for the reaction is discussed.
Hellgardt K, Mimi Hii KK, 2017, Continuous flow technologies in the development of “green” organic reactions and processes, Advanced Green Chemistry: Part 1: Greener Organic Reactions and Processes, Pages: 257-284, ISBN: 9789813228108
Newton MA, Brazier JB, Barreiro EM, et al., 2016, Restructuring of supported Pd by green solvents: an operando Quick EXAFS (QEXAFS) study and implications for the derivation of structure-function relationships in Pd catalysis, Catalysis Science & Technology, Vol: 6, Pages: 8525-8531, ISSN: 2044-4753
Transmission electron microscopy (TEM) is commonly used as an ex-situ technique to determine structural changes by comparing images of catalyst particles before and after a reaction. This requires the use of an alcoholic solvent to disperse the particles on a grid. In this work, we will show that Pd catalysts can be transformed during the procedure, by using EXAFS to determine the structure of Pd catalysts in different environments (as dry or wet samples). Supported palladium nanoparticles exposed to aqueous ethanolic solution (50% w/v) are transformed to a common, reduced, and hydrogen-contaminated state, irrespective of their initial habit or support. Catalysts comprised of nanosize PdO are reduced at ca. 350 K, whereas samples comprised of very small (ca. ≤ 10 atoms) Pd particles react with the solvent at just above room temperature and agglomerating with considerable loss of dispersion. As such any potential benefits to catalysis sought through the synthesis of very highly dispersed metallic Pd supported upon a range of inorganic dispersants will be rapidly erased through the action of such solvents.
Wong VH, Vummaleti SV, Cavallo L, et al., 2016, Corrigendum: Synthesis, Structure and Catalytic Activity of NHC-AgI Carboxylate Complexes., Chemistry - A European Journal, Vol: 22, Pages: 17888-17888, ISSN: 0947-6539
Hii KM, Hellgardt K, Gavriilidis A, et al., 2016, Aerobic oxidations in flow: opportunities for the fine chemicals and pharmaceuticals industries, Reaction Chemistry & Engineering, Vol: 1, Pages: 595-612, ISSN: 2058-9883
Molecular oxygen is without doubt the greenest oxidant for redox reactions, yet aerobic oxidation is one of the most challenging to perform with good chemoselectivity, particularly on an industrial scale. This collaborative review (between teams of chemists and chemical engineers) describes the current scientific and operational hurdles that prevent the utilisation of these reactions for the production of speciality chemicals and active pharmaceutical ingredients (APIs). The safety aspects of these reactions are discussed, followed by an overview of (continuous flow) reactors suitable for aerobic oxidation reactions that can be applied on scale. Some examples of how these reactions are currently performed in the industrial laboratory (in batch and in flow) are presented, with particular focus on the scale-up strategy. Last but not least, further challenges and future perspectives are presented in the concluding remarks.
Xia C, White AJ, Hii KK, 2016, Synthesis of isoindolinones by Pd-catalyzed coupling between N-methoxybenzamide and styrene derivatives, Journal of Organic Chemistry, Vol: 81, Pages: 7931-7938, ISSN: 1520-6904
An atom-economical protocol for a tandem process involving Fujiwara-Moritani-aza-Wacker reactions has been developed for the Pd-catalyzed coupling between N-methoxy benzamide with styrene derivatives. The generality of the methodology was demonstrated by the synthesis of a library of twenty-five 3-benzylidene isoindolinones in moderate to good yields. A further twenty-two 3-benzyl derivatives were obtained by telescoping the process with a catalytic hydrogenation reaction.
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