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N-Heterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
Additional versatility and complexity have also been introduced to the hydroamination reaction by one-pot multistep reaction sequences [122–126]. Alkyne hydroamination results in imines which act as good targets for further functionalization as they are prone to hydrolysis. In fact, the imines are isolated and characterized after hydrolysis with hydrogen chloride or SiO2. Synthetically useful reductions employ hydrogen/palladium/carbon, lithium aluminium hydride, or NaBH3CN/zinc chloride. Yet, sequential hydroamination/hydrosilylation reactions, utilizing metal as catalysts in both processes, are more elegant. This reaction is performed using Ir [127], Ti [128] and rare-earth metal catalysts (Scheme 38) [41].
Methods of extracting silica and silicon from agricultural waste ashes and application of the produced silicon in solar cells: a mini-review
Published in International Journal of Sustainable Engineering, 2021
Fortunate Farirai, Maxwell Ozonoh, Thomas Chinedu Aniokete, Orevaoghene Eterigho-Ikelegbe, Mathew Mupa, Benson Zeyi, Michael Olawale Daramola
Production of SiNPs takes on the solution phase synthesis which received plausible efforts (JR Heath 1992). The starting materials were silicon halides. These were systematically reduced by sodium naphthalenide (Baldwin et al. 2002; Heath 1992; Zou et al. 2006), lithium naphthalenide (Kornowski et al. 1993), lithium aluminium hydride (Hapala et al. 2013; Sudeep, Page, and Emrick 2008) or zinc salts (Bley and Kauzlarich 1996) These reactions were carried out in a variety of surfactant solvent environments resulting in small-sized, free-standing SiNPs which were hydrogen capped (Hapala et al. 2013; Wilcoxon, Samara, and Provencio 1999). Recently, Chang and Sun 2014 used allyltrichlorosilane as both the surfactant and the functionalization reagent and silicon tetrachloride in a ratio of 1:3, to explore a simple approach to the synthesis of morphology-controlled hexagonal silicon nanocrystals modified with allyl in the range of 20–50 nm.
Synthesis, structure and reactivity of some chiral benzylthio alcohols, 1,3-oxathiolanes and their S-oxides
Published in Journal of Sulfur Chemistry, 2020
R. Alan Aitken, Philip Lightfoot, Andrew W. Thomas
In order to access the full range of target benzylthio alcohols B we adopted the more direct approach of initial nucleophilic displacement using sodium benzylthiolate (Scheme 2). Thus the bromo acids 1–3 afforded the benzylthio acids 8–10 in good yield. Of these three compounds, only 9 has been previously reported [6] and it showed good agreement with literature NMR data although, as noted in the experimental section, there is a slight error in the literature interpretation. The three acids were then readily esterified to give the benzylthio esters 11–13 in almost quantitative yield. Again two of these three compounds are previously unknown and only compound 11 is briefly mentioned in the literature [7] with no characterization data. The final reduction to the target benzylthio alcohols 7, 14, and 15 was achieved in high yield with lithium aluminium hydride in diethyl ether. Of these three compounds, the valine-derived example 14 has been reported by Evans [8] and used to form mixed P/S ligands for palladium catalysis. In his study, installation of an additional stereocentre adjacent to OH was followed by reaction with Ar2PCl to give a phosphinite much as suggested in Figure 1. Importantly however, our optical rotation value for 14 is roughly half that reported by Evans and also for the isoleucine derived compounds 10, 13 and 15 with a second and presumably invariant stereocentre present, diastereomeric mixtures were evident by NMR, thus pointing to a degree of racemization, most likely at the stage of the initial sodium benzylthiolate substitution. Clearly this problem would need to be addressed for effective implementation of the strategy outlined in Figure 1. However, in the mean time, progress in this direction was halted by the discovery that treatment of the benzylthio alcohols 7, 14 and 15 with sodium hydride followed by diethyl chlorophosphite gave not the expected phosphites F but rather the isomeric chlorides G formed via an intermediate thiiranium salt (Scheme 3). This will be described in detail elsewhere.
Unwise Relationships and an Unsound Valence Theory: The Chemical Career of Robert Fergus Hunter (1904–1963)
Published in Ambix, 2021
William H. Brock, Michael Jewess
Hunter stayed only a year at Manchester, where he took up his colleague Donald H. Hey's interest in free radicals and published work with Charles Bawn on the “trimethylene biradical.”80 At the same time, Hunter's interests underwent a dramatic turn towards biochemistry, probably because Heilbron and his co-workers had turned their attention to the synthesis of vitamin A. In 1937 Hunter seized the opportunity of working as a research biochemist at the London School of Hygiene & Tropical Medicine in its new headquarters opposite Senate House in London's Bloomsbury quarter. There he began research on the structure of vitamin A and its derivatives. With the expansion of biochemistry, perhaps he hoped there would be the chance of a chair in the subject? However, within a year he was head-hunted by Lever Brothers at Port Sunlight to become a Senior Organic Research Chemist and Section Manager, a post he retained until 1946.81 At Port Sunlight Hunter took up more extensive research on vitamins and published work on the structure of vitamin A and the palm-oil carotenoids.82 His work was now published in the Biochemical Journal as well as in JCS. He was to write the section on the carotenoid group for Ernest Rodd's huge reference work, The Chemistry of Carbon Compounds, in 1953.83 His final years from 1946 were spent as Research Manager for Bakelite Ltd in Tyseley, Birmingham, where he took up the subject of phenol-formaldehyde resins.84 In the 1950s he synthesised 2, 4, 6-trishydroxymethylphenol and confirmed its hitherto suspected presence in many phenolic resins. The synthesis involved the reduction of the triethyl ester of hydroxytrimesic acid using the new reducing agent, lithium aluminium hydride.85 Together with various junior collaborators, Hunter also prepared a huge number of polymers called “Novolaks” (i.e. linear, branched and bridged phenolic nuclei linked by methylene groups), as well as exploring the possibility of making useful resins from polymerising acetylene and allyl derivatives. His last publication appeared in 1959, suggesting that he either gave up personal research work for an administrative role, or took early retirement because of illness.86