In this article, we review the recent progress that has been made in the field of Lewis-acid catalysis of carbon carbon-bond-forming reactions in aqueous solution. Since water hampers the hard hard interactions between the catalyst and the reactant, it often complicates catalysis. However, once coordination has taken place, water can have beneficial effects on rates and selectivities of Lewis acid catalysed Diels Alder reactions, aldol reactions, allylation reactions, Barbier and Mannich type reactions as well as Michael additions.
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In mijn vorige blog schreef ik dat ik "groene chemie" niet zo'n goede term vind. Dit bericht borduurt daar enigszins op voort en is mijn persoonlijke kritische noot bij de transitie naar een groene(re) economie die momenteel in volle gang is.
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The catalytic oxidation of potato starch by [MnIV2 (μ-O)3(tmtacn)2][H2O](CH3COO)2 (Mncat, with tmtacn =1,4,7-trimethyl-1,4,7-triazacyclononane) with H2O2, was recently introduced as a promising alternative to ubiquitous sodium hypochlorite (NaOCl). Here, we report an in-depth investigation into interactions of the catalyst with the starch granule. Pitted starches obtained by pre-treatment with high-frequency ultrasound (HFUS) were shown to result in a uniquely homogeneous oxidation. To study this further, fractionation of oxidised potato starch was done which showed a preference for the oxidation of smaller granules with a higher relative surface area. This result was corroborated by chemical surface gelatinisation of fractionated granules. These studies showed that the inside of the granules was oxidised, but that Mncat had a moderate preference for oxidation of the periphery. Together, these results allow for a better understanding of oxidation of starch by Mncat and how it differs from NaOCl oxidation making further optimisation of the process possible.
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Michael additions of α-nitroesters with enones and α,β-unsaturated aldehydes result in quantitative conversions to the corresponding 1,4-adducts by performing the reactions in water in the presence of ytterbium triflate as water-tolerant Lewis acid.
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The invention relates to the use of modified starch obtainable by treating amylose containing starch in aqueous medium with an enzyme from the group of the α-1,4-α-1,4-glucosyl transferases (EC 2.4.1.25) or an enzyme the activity of which corresponds to that of enzymes from the group just mentioned, as an agent for forming a thermoreversible gel. The invention also relates to products in the form of a thermoreversible gel having as gel-forming substance a modified starch as defined. The invention further relates to the use of a modified starch as defined in the form of an aqueous solution.
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Competitive advantage is probably the most popular business concept today (Mooney, 2007). This article aims to investigate critically the discourse on competitive advantage, as expressed by business literature, by locating its meanings in the public higher education sector. This research reveals that people working within the HEIs have given broader and more diversified meanings to this concept, which are partly due to the message received from external environment, and partly because of the influence of professional settings in which they function. By studying these diversified meanings, 13 elements are identified in constructing the competitive advantages of higher education institutions. Furthermore, the importance of each element is rated and ranked which enables us to assess the quantitative significance. The clarification of this container concept “competitive advantage” leads to the conclusion that the business way of defining of competitive advantage should be critically reviewed and verified in the context of public higher education sector, because the competition in the public education market is different from the normal market competition defined by the business literature.
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