Publications
177 results found
Newton OJ, Hellgardt K, Richardson J, et al., 2023, ‘Homeopathic’ palladium catalysis? The observation of distinct kinetic regimes in a ligandless Heck reaction at (ultra-)low catalyst loadings, Journal of Catalysis, Vol: 424, Pages: 29-38, ISSN: 0021-9517
The catalytic behaviour of ‘ligandless’ palladium(II) acetate in the Heck arylation reaction of iodobenzene with methyl acrylate is examined at (ultra-)low catalyst loadings using in situ spectroscopy. The study reveals two distinctive kinetic regimes with distinct Pd orders. A simplified microkinetic model revealed the presence of at least two kinetically competent catalysts, represented by a monomeric (Pd1) and dimeric (Pd2) species. The relative catalytic activity and deactivation rates for both species can also be estimated from the experimental results. This work provides direct kinetic evidence that a higher-order Pd species can be more active than a monomeric species, and the key role played by catalyst deactivation, particularly at higher catalyst loadings. This implies that lowering the catalyst loading may be an effective strategy to combat catalyst deactivation without necessarily incurring significant deterioration in reaction rate.
Horvath-Gerber F, Kuok Mimi Hii K, Holtze C, et al., 2023, Mass Transport of Diazomethane across Teflon AF2400 Membrane for Scale-Up Development, Organic Process Research and Development, Vol: 27, Pages: 899-909, ISSN: 1083-6160
Diazomethane is an attractive C1 building block in organic chemistry, but its hazardous nature presents scale-up challenges to this date. The use of a Teflon AF2400 membrane, most commonly in a tube-in-tube reactor setup, is the current state-of-the-art methodology for inherently safer laboratory-scale generation, separation, and consumption of anhydrous diazomethane. For the successful scale-up of this membrane process, the key mass transfer coefficient of the AF2400 membrane, its permeability for diazomethane, was investigated. We report in this contribution a novel methodology to determine diazomethane permeability for the rational scale-up of membrane processes for the safe handling of diazomethane. Missing physical properties of diazomethane were established, and the full mass balance of in situ-generated diazomethane within the tube-in-tube reactor was experimentally validated. A numerical model of the membrane reactor system in combination with experimental data yielded a permeability value of 414 barrer. This result enables scale-up development of the laboratory membrane reactor toward production-scale systems.
Takle MJ, Deadman BJ, Hellgardt K, et al., 2023, A Flash Thermal Racemization Protocol for the Chemoenzymatic Dynamic Kinetic Resolution and Stereoinversion of Chiral Amines, ACS Catalysis, Pages: 10541-10546
A highly practical and effective ‘Flash Thermal Racemization’ (FTR) protocol was developed in continuous flow, without needing a base or a H donor. This can be integrated with an enzyme to enable the chemoenzymatic kinetic resolution of primary amines to be achieved in a more atom-efficient manner without additives. An unprecedented space-time yield of up to 1362 μmol mL-1 h-1 can be achieved for the dynamic kinetic resolution of 1-aminoindane, which is at least 10 times more productive than previously reported, and up to 1700-fold more productive when the Pd catalyst loading is taken into account. With a slight modification, the flow reactor system can also be used to convert an optically active amine to its opposite enantiomer.
Schrecker L, Dickhaut J, Holtze C, et al., 2023, An efficient multiparameter method for the collection of chemical reaction data via ‘one-pot’ transient flow, Reaction Chemistry and Engineering
The advent of transient flow methods has increased the efficiency and diversity of reaction data collected through the collection of data series in a wider reaction space, beyond traditionally temporal series. Thus far, these methods have been limited to studying continuous reaction parameters. In this work, transient flow is combined with “one-pot” chemistry (OP-TF) to efficiently collect diverse reaction data on a continuous-discrete multiparameter space, exemplified with the aromatic Claisen rearrangement. Six independent substrates were studied simultaneously, producing data on temperature and substituent effects in a single experiment, extending into the supercritical phase. This data allowed us to extract thermodynamic information and predict kinetic parameters for other substrates accurately, thus allowing synthetic feasibility of a substrate to be assessed a priori.
Li AY, Pedersen A, Feng J, et al., 2022, From haemoglobin to single-site hydrogenation catalyst, Green Chemistry, Vol: 24, Pages: 7574-7583, ISSN: 1463-9262
Iron-based single-site catalysts hold immense potential for achieving highly selective chemical processes, with the added advantage of iron being an earth-abundant metal. They are widely explored in electrocatalysis for oxygen reduction and display promising catalytic activity for organic transformations. In particular, FeNx@C catalysts are active for the reduction of nitroarene into aromatic amines. Yet, they are difficult to mass-produce, and most preparation methods fail to avoid single site aggregation. Here we prepared FeNx@C catalysts from bio-derived compounds, xylose and haemoglobin, in a simple two-step process. Since haemoglobin naturally contains FeNx single-sites, we successfully repurposed them into hydrogenation catalytic centers and avoided their aggregation during the preparation of the material. Their single-site nature was demonstrated by aberration-corrected transmission electron microscopy and X-ray absorption techniques. They were shown to be active for transfer hydrogenation of nitroarenes into anilines, with excellent substrate selectivity and recyclability, as demonstrated by the preserved yield across seven catalytic cycles. We also showed that FeNx@C could be used to prepare 2-phenylbenzimidazole through a reduction/condensation tandem. Our work shows for the first time the viability of biomass precursors to prepare Fe single-site hydrogenation catalysts.
Schrecker L, Dickhaut J, Holtze C, et al., 2022, Discovery of unexpectedly complex reaction pathways for the Knorr pyrazole synthesis via transient flow, REACTION CHEMISTRY & ENGINEERING, Vol: 8, Pages: 41-46, ISSN: 2058-9883
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- Citations: 1
Stark RT, Pye D, Chen W, et al., 2022, Assessing a sustainable manufacturing route to lapatinib, Reaction Chemistry and Engineering, Vol: 7, Pages: 2420-2426, ISSN: 2058-9883
A synthetic route to an anti-cancer drug, lapatinib, was devised to support the development of a sustainable manufacturing process in South Africa. Quantitative metrics were employed to evaluate the sustainability of the key steps of the reaction.
Colberg J, Hii KKM, Koenig SG, 2022, Importance of green and sustainable chemistry in the chemical industry a joint virtual issue between ACS sustainable chemistry & engineering and organic process research & development, Organic Process Research and Development, ISSN: 1083-6160
Colberg J, Hii KKM, Koenig SG, 2022, Importance of Green and Sustainable Chemistry in the Chemical Industry A joint virtual issue between ACS Sustainable Chemistry & Engineering and Organic Process Research & Development, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, ISSN: 2168-0485
Deadman BJ, Gian S, Lee VEY, et al., 2022, On-demand, in situ, generation of ammonium caroate (peroxymonosulfate) for the dihydroxylation of alkenes to vicinal diols, Green Chemistry, Vol: 24, Pages: 5570-5578, ISSN: 1463-9262
Using the dihydroxylation of alkenes as a benchmark, the reactivities of fresh and aged solutions of (NH4)2S2O8 (electrochemically generated) were compared to commercially-procured peroxydisulfate and Oxone®. The study revealed that peroxymonosulfate (Caro’s acid, PMS) is the active oxidant in such reactions. Using complementary redox colorimetry and in situ IR spectroscopy to monitor the oxidants, the competitive decomposition of peroxydisulfate in an acidic solution into PMS and H2O2 can be quantified for the first time. The new insight enabled the design and implementation of both batch and flow processes to maximise the concentration of active PMS oxidant. The utility of these oxidants for organic synthesis is demonstrated by the dihydroxylation of eight styrenes and seven alkyl alkenes, where the ammonium PMS solutions performed better than Oxone® (counterion effect). Last but not least, a non-chromatographic method for isolating and purifying the water-soluble diol product was developed.
Cannon AS, Carrier DJ, Engelberth AS, et al., 2022, Women in Green Chemistry and Engineering: Agents of Change Toward the Achievement of a Sustainable Future, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 10, Pages: 2859-2862, ISSN: 2168-0485
Allen DT, Licence P, Subramaniam B, et al., 2022, Building Pathways to a Sustainable Planet, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 10, Pages: 1-2, ISSN: 2168-0485
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- Citations: 1
Allen DT, Carrier DJ, Chen J, et al., 2021, Expectations for Perspectives in ACS Sustainable Chemistry & Engineering, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 9, Pages: 16528-16530, ISSN: 2168-0485
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- Citations: 1
Wang S, Panayides J-L, Riley D, et al., 2021, Rapid formation of 2-lithio-1-(triphenylmethyl)imidazole and substitution reactions in flow, Reaction Chemistry and Engineering, Vol: 6, Pages: 2018-2023, ISSN: 2058-9883
The functionalisation of imidazoles is a necessary step in the formation of many active pharmaceutical intermediates. Herein, we report a flow chemistry approach for the rapid and efficient formation of 2-lithio-1-(triphenylmethyl)imidazole at ambient temperature and its reaction with a range of electrophiles, achieving modest to high yields (40–94%) in short reaction times (<1 min). The method is amenable to the scale-up of this highly reactive lithio-imidazole intermediate.
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
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- Citations: 22
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
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- Citations: 1
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
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- Citations: 1
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
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- Citations: 7
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
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- Citations: 1
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 %.
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