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Mn promotion in FT can direct products between oxygenates and paraffins. A simple in situ treatment forms MnTiO3 while an ex situ support is demonstrated with the benefits of Mn inclusion while controlling activity and inhibiting alcohol selectivity.

A proxy-based high-throughput experimental approach was used to explore the stability and activity of Co-based Fischer-Tropsch Synthesis catalysts with different promoters on a variety of supports. The protocol is based on XRD estimation of the active phase polymorph, particle size and ratio of crystalline phases of Co to support. Sequential sample libraries enabled exploration of four Co loadings with five different promoters on six support materials. Catalysts stable to aging in syngas, i.e. displaying minimal change of particle size or active phase concentration, were evaluated under industrial conditions. This procedure identified SiC as a support that confers catalyst stability and that a combination of Ru and Hf promotes the stabilisation of hcp Co. Unsupported bulk samples of Co with appropriate amounts of Ru and Hf revealed that the formation of hcp Co is independent of the support. The hcp Co-containing catalyst afforded the highest catalytic activity and C5+ selectivity amongst the samples tested in this study, confirming the effectiveness of the proxy-based high-throughput method.

In situ TEM gas-cell imaging and spectroscopy with in situ XRD have been applied to reveal morphological changes in NiFe2O4@Co3O4 core–shell nanoparticles in hydrogen. The core–shell structure is retained upon reduction under mild conditions (180 °C for 1 h), resulting in a partially reduced shell. The core–shell structure was retained after exposing these reduced NiFe2O4@Co3O4 core–shell nanoparticles to Fischer–Tropsch conditions at 230 °C and 20 bar. Slightly harsher reduction (230 °C, 2 h) resulted in restructuring of the NiFe2O4@Co3O4 core–shell nanoparticles to form cobalt islands in addition to partially reduced NiFe2O4. NiFe2O4 underwent further transformation upon exposure to Fischer–Tropsch conditions, resulting in the formation of iron carbide and nickel/iron–nickel alloy. The turnover frequency in the Fischer–Tropsch synthesis over NiFe2O4@Co3O4 core–shell nanoparticles reduced in hydrogen at 180 °C for 1 h was estimated to be less than 0.02 s–1 (cobalt-time yield of 8.40 μmol.g-1.s–1) with a C5+ selectivity of 38 C-%. The low turnover frequency under these conditions in relation to the turnover frequency obtained with unsupported cobalt is attributed to the strain in the catalytically active cobalt.

Sasol Ltd., the University of Glasgow and EPSRC [award reference EP/P505534/1.] are thanked for the provision of postgraduate studentship (ALD). The STFC Rutherford Appleton Laboratory is thanked for access to neutron beam facilities [RB 1520269/1610413]. Diamond Light Source is thanked for time on B18 beamline through the Catalysis Hub BAG application (SP15151 and rapid access beamtime SP18431). The Royal Society is thanked for the provision of an Industry Fellowship (PBW). The technique of inelastic neutron scattering (INS) is used to investigate how hydrogen is partitioned within a series of Na and S promoted iron-based Fischer-Tropsch-to-olefin catalysts. Two reaction test regimes are examined. First, reaction testing at elevated temperature and pressure demonstrate how Na/S additions enhance short chain olefin selectivity and reduce methane formation under industrially relevant reaction conditions. For a fixed level of Na incorporation (2000 ppm), sulfur concentrations of ≤ 100 ppm result in only a modest improvement in olefin selectivity. However, for sulfur values of ≥ 100 ppm there is a noticeable and systematic increase in C2-C4 olefin selectivity; rising from ∼30.0 % to 35.2% at 250 ppm. Second, using ambient pressure CO hydrogenation as a test reaction in INS and micro-reactor configurations, catalyst samples are further analysed by TPR, TPO, XRD and S K-edge XANES. INS shows the formation of a hydrocarbonaceous overlayer to be significantly attenuated by the presence of the promoters, with increasing S levels significantly reducing the intensity of the sp2 and sp3 hybridised ν(C-H) modes of the overlayer, albeit to differing degrees. A probable role for how this combination of promoters is perturbing the form of the hydrocarbonaceous overlayer to subsequently moderate the product distribution is considered. Publisher PDF

NiFe2O4@Co3O4 and ZnFe2O4@Co3O4 core-shell nanoparticles were synthesized and reduced to be used as catalysts for the Fischer-Tropsch synthesis. The as-synthesized materials were determined to have an incomplete Co3O4 shell around the ferrite core with a maximum thickness of 3 nm. Using in-situ TEM, it was shown that reduction of these core-shell nanoparticles in pure hydrogen at 230 °C and 250 °C, respectively, resulted in the formation of small cobalt islands on the ferrite surface. Catalytic testing of the core-shell materials, NiFe2O4@Co3O4 and ZnFe2O4@Co3O4, after reduction showed a cobalt-time yield of 13.64 μmolCO·gCo−1·s−1 and 4.27 μmolCO·gCo−1·s−1 and a C5+ selectivity of 47 C-% and 68 C-%, respectively. The observed difference in cobalt-time yield and selectivity between NiFe2O4@Co3O4 and ZnFe2O4@Co3O4 core-shell nanoparticles was ascribed to a combination of effects that arose from the morphological and compositional changes that occurred after reduction and under Fischer-Tropsch synthesis conditions.

The synthesis of four new bulky bidentate phosphines that possess both tert-butyl and trifluoromethylphenyl substituents is described. Symmetric ligands were readily obtained by alkylation of phosphidoboranes of the type Li[P(BH(3))(tBu)(Ar)] with dihaloalkanes. Non-symmetric ligands were prepared from a new stable precursor, tBu(2)P(BH(3))(CH(2))(3)Br, that should prove useful for other ligand syntheses. Palladium(II) complexes of the four new ligands were prepared and were characterised by spectroscopic methods, microanalysis and X-ray crystallography. The new [PdCl(2)(L)] complexes were evaluated as catalysts for the hydroxycarbonylation of styrene and found to give unprecedented regioselectivity and yields for a diphosphine-based catalyst. A study on promoter effects reveals that the presence of acid and chloride is necessary to achieve such selectivities. It has been proposed in the literature that such conditions result in a new pathway in which styrene is converted into 2-phenethyl chloride, with the latter being the real substrate in the reaction. However, a deuterium labelling study seems to rule out this mechanism, at least under the conditions used herein.

Aldol condensation between phenylacetates and benzaldehydes affords 2,3-diaryl-3-hydroxypropanoates which serve as common precursors to both the first racemic trans-pterocarpan and enantiopure cis- and trans-6a-hydroxypterocarpans.

Epoxidation of a series of poly-oxygenated chalcones with urea-hydrogen peroxide complex in THF in the presence of DBU and poly-( l )- or -( d )-leucine, followed by TBTH/AIBN catalysed ring opening, afforded β-hydroxydihydrochalcones in moderate to high enantiomeric excess and yield. This represents the first stereoselective route towards this group of flavonoids. Epoxidation of a series of poly-oxygenated chalcones with urea-hydrogen peroxide complex in THF in the presence of DBU andpoly-(L)-or-(D)-leucine, followed by TBTH/AIBN catalysed ring opening, afforded β-hydroxydihydrochalcones in moderate to high enantiomeric excess and yield. This represents the first stereoselective access to this group of flavonoids Download : Download full-size image

The disproportionation of dicobalt octacarbonyl induced by the free carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and the X-ray characterization of the cyclohexane solvate of the resulting cobalt carbonyl N-heterocyclic carbene salt, [Co(CO)3(IMes)2]+[Co(CO)4] -·1/4C6H12, is reported. The crystal structure represents the first example of a [Co(CO)3(L)2][Co(CO)4] disproportionate salt reported to date.

Dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) and silver tetrafluoroborate (AgBF 4 ) activate the C 4 S bond in the 4-thioethers of flavan-3-ols toward carbon nucleophiles to permit formation of the interflavanyl bond in procyanidins under neutral conditions.

Epoxidation of a series of poly-oxygenated chalcones with urea-hydrogen peroxide complex in THF in the presence of DBU and poly-( l )- or -( d )-leucine, followed by TBTH/AIBN catalysed ringopening, afforded β-hydroxydihydrochalcones in moderate to high enantiomeric excess and yield.

Epoxidation of a series of poly-oxygenated chalcones with H2O2 in the presence of poly-α-aminoacids yielded chiral aromatic oxygenated oxiranes in moderate to high optical yields. Lewis acid-catalysed phenylmethanethiol ringopening of the epoxide functionality and subsequent formation of the pyranone heterocycle, afforded trans- and cis-dihydroflavonols in moderate to high enantiomeric excess and yield.

Asymmetric dihidroxylation of (E)-1-(3,4-dimethoxyphenyl)-3-(2-methoxy-methyl-4,6-dimethoxy-phenyl)-propene with AD-mix-α or AD-mix-β in the presence of methanesulfonamide, followed by acid catalysed cyclization, afforded the four catechin diastereomers in high enantiomeric excesses and yields. © 1997 Published by Elsevier Science Ltd.

Asymmetric dihydroxylation of a series of polyoxygenated 1,3-diarylpropenes with AD-mix-α or AD-mix-β in the presence of methanesulfonamide and subsequent acid-catalysed cyclization, affords for the first time synthetic access to trans- and cis-flavan-3-ol derivatives, essentially enantiopure and in good yield.

The purpose of this contribution is to analyse and explain the South African HRH case, its historical evolution, and post-apartheid reform initiatives aimed at addressing deficiencies and shortfalls. HRH in South Africa not only mirrors the nature and diversity of challenges globally, but also the strategies pursued by countries to address these challenges. Although South Africa has strongly developed health professions, large numbers of professional and mid-level workers, and also well-established training institutions, it is experiencing serious workforce shortages and access constraints. This results from the unequal distribution of health workers between the well-resourced private sector over the poorly-resourced public sector, as well as from distributional disparities between urban and rural areas. During colonial and apartheid times, disparities were aggravated by policies of racial segregation and exclusion, remnants of which are today still visible in health-professional backlogs, unequal provincial HRH distribution, and differential access to health services for specific race and class groups. Since 1994, South Africa’s transition to democracy deeply transformed the health system, health professions and HRH establishments. The introduction of free-health policies, the district health system and the prioritisation of PHC ensured more equal distribution of the workforce, as well as greater access to services for deprived groups. However, the HIV/AIDS epidemic brought about huge demands for care and massive patient loads in the public-sector. The emigration of health professionals to developed countries and to the private sector also undermines the strength and effectiveness of the public health sector. For the poor, access to care thus remains constrained and in perpetual shortfall. The post-1994 government has introduced several HRH-specific strategies to recruit, distribute, motivate and retain health professionals to strengthen the public sector and to expand access and coverage. Of great significance among these is the NHI Plan that aims to bridge the structural divide and to redistribute material and human resources more equally. Its success largely hinges on HRH and the balanced deployment of the national workforce. Low- and middle-income countries have much to learn from South African HRH experiences. In turn, South Africa has much to learn from other countries, as this case study shows.

Asymmetric dihydroxylation of a series of poly-O-methoxymethyl-1,3-diarylpropenes with AD-mix-α or AD-mix-β and subsequent acid-catalyzed cyclization of the intermediate syn-diols permits the first synthetic access to all four diastereoisomers of free phenolic flavan-3-ols in high enantiomeric excess and yield.

Aldol condensation between phenylacetates and benzaldehydes affords 2,3-diaryl-3-hydroxypropanoates which serve as common precursors to both the first racemic trans-pterocarpan and enantiopure cis- and trans-6a-hydroxypterocarpans.

Some new bulky fluorinated diphosphines have been prepared and converted to palladium dichloride complexes that have been found to give increased regioselectivity and activity over other Pd–diphosphine systems when used as catalysts for hydroxycarbonylation of styrene.

The first example of a catalyst utilising a sulfur-based ligand [MeC(CH2SBu)3] for the selective hydrogenation of dimethyl oxalate to methyl glycolate is reported.

Recent years have witnessed considerable development toward an understanding of the intricate principles governing the chemistry of oligomeric proanthocyanidins. These developments were initiated by the growing realization of the industrial importance of the proanthocyanidins, which is based upon their interactions with key molecules in the biological domain. Despite the surprisingly limited array of carbon-carbon and carbon-oxygen bonds in the heterocycles of proanthocyanidin oligomers, a rich variety of ingenious protocols aimed at manuevering these bonds in a controlled mode has emerged over the past 10–15 years. These studies blend with the heavy focus on the formation and rupture of the interflavanyl bond(s), which played such a decisive role in the structural elucidation of proanthocyanidin oligomers during the seventies and early eighties. Methodologies to chemically exploit the heterocyclic bonds are highly relevant to progress in the chemistry of these important and intriguing biomolecules and constitute the subject of this review.

The oligo- and polymeric proanthocyanidins represent a major group of phenolic constituents in woody and some herbaceous plants.1,2 These compounds usually originate by coupling at C(4) (C-ring) of an electrophilic flavanyl unit, generated from a flavan-4-ol1 or a flavan-3,4-diol3 (the chain extender units), to a nucleophilic flavanyl moiety, often a flavan-3-ol1,3 (the chain terminating unit). Recent developments were initiated by the numerous industrial applications and by the growing realization that the oligo- and polymeric proanthocyanidins may be credited for the profound health-promoting properties of tea, fruit juices, and red wine. This is mainly due to their in vitro radical scavenging4 or antioxidant5 biological properties, while the polyflavanoids in red wine have recently been implicated in protection against cardiovascular disorders,6 e.g. the “French paradox”.7–9 The realization that many of these effects are closely associated with the intramolecular interactions of the proanthocyanidins with other biomolecules has triggered a substantial research effort towards understanding the chemical dynamics of this complex group of natural products. The most relevant results emanating from these studies constitute the subject of this review. The nomenclature delineated in reference 1 will be consistently used.

The beneficial role of flavonoids in general and of the proanthocyanidins in particular to mankind is increasingly being recognized. In addition to the multitude of industrial applications, the oligo- and polymeric proanthocyanidins are now also credited for the profound health-promoting effects of tea, fruit juices, and red wine. This is mainly due to their in vitro antioxidant or radical scavenging properties, while the polyflavonoids in red wine have recently been implicated in protection against cardiovascular disorders, e.g., the “French paradox”. These observations highlight the need for synthetic access to enantiopure flavonoid monomeric precursors exhibiting the aromatic oxygenation pattern of the constituent flavanyl units of the naturally occurring proanthocyanidins, hence paving the route to synthesize a representative series of these important biomolecules. This review accordingly focuses on methodologies aimed at the stereoselective syntheses of the different sets of the four diastereomers of both the dihydroflavonols and fiavan-3-ols exhibiting characteristic “natural product” phenolic oxygenation patterns.

CD data of all four diastereoisomers of the permethylaryl ether 3- O-acetyl derivatives of a series of flavan-3-ols permit assignment of the absolute configuration at the stereocentres of the heterocyclic ring.

Asymmetric dihydroxylation of a series of poly- O-methoxymethyl-1,3-diarylpropenes with AD-mix-α or AD-mix-β and subsequent acid-catalyzed cyclization of the intermediate syn-diols permits the first synthetic access to all four diastereoisomers of free phenolic flavan-3-ols in high enantiomeric excess and yield.

Epoxidation of a series of polyoxygenated chalcones with H2O2 in the presence of poly(α-amino acid) catalysts, followed by Lewis acid-catalysed phenylmethanethiol ring-opening and cyclization, afforded trans- and cis-dihydroflavonols in moderate to high enantiomeric excess and yield.