123 research outputs found
Et3SiH + KOtBu provide multiple reactive intermediates that compete in the reactions and rearrangements of benzylnitriles and indolenines
The combination of potassium tert-butoxide and triethylsilane is unusual because it generates multiple different types of reactive intermediates simultaneously that provide access to (i) silyl radical reactions, (ii) hydrogen atom transfer reactions to closed shell molecules and to radicals, (iii) electron transfer reductions and (iv) hydride ion chemistry, giving scope for unprecedented outcomes. Until now, reactions with this reagent pair have generally been explained by reference to one of the intermediates, but we now highlight the interplay and competition between them
A practical and general amidation method from isocyanates enabled by flow technology
The addition of carbon nucleophiles to isocyanates represents a conceptually flexible and efficient approach to the preparation of amides. This general synthetic strategy has, however, been relatively underutilized, due to narrow substrate tolerance, and the requirement for less favourable reaction conditions. Herein, we disclose a highâyielding, mass efficient, and scalable method with appreciable functional group tolerance for the formation of amides by reaction of Grignard reagents with isocyanates. Through the application of flow chemistry, and the use of subâstoichiometric amounts of CuBr2, this process has been developed to encompass a broad range of substrates, including reactants found to be incompatible with previously published protocols
The impact of COVID-19 public health restrictions on particulate matter pollution measured by a validated low-cost sensor network in Oxford, UK
Emergency responses to the COVID-19 pandemic led to major changes in travel behaviours and economic activities with arising impacts upon urban air quality. To date, these air quality changes associated with lockdown measures have typically been assessed using limited city-level regulatory monitoring data, however, low-cost air quality sensors provide capabilities to assess changes across multiple locations at higher spatial-temporal resolution, thereby generating insights relevant for future air quality interventions. The aim of this study was to utilise high-spatial resolution air quality information utilising data arising from a validated (using a random forest field calibration) network of 15 low-cost air quality sensors within Oxford, UK to monitor the impacts of multiple COVID-19 public heath restrictions upon particulate matter concentrations (PM10, PM2.5) from January 2020 to September 2021. Measurements of PM10 and PM2.5 particle size fractions both within and between site locations are compared to a pre-pandemic related public health restrictions baseline. While average peak concentrations of PM10 and PM2.5 were reduced by 9â10 ÎŒg/m3 below typical peak levels experienced in recent years, mean daily PM10 and PM2.5 concentrations were only âŒ1 ÎŒg/m3 lower and there was marked temporal (as restrictions were added and removed) and spatial variability (across the 15-sensor network) in these observations. Across the 15-sensor network we observed a small local impact from traffic related emission sources upon particle concentrations near traffic-oriented sensors with higher average and peak concentrations as well as greater dynamic range, compared to more intermediate and background orientated sensor locations. The greater dynamic range in concentrations is indicative of exposure to more variable emission sources, such as road transport emissions. Our findings highlight the great potential for low-cost sensor technology to identify highly localised changes in pollutant concentrations as a consequence of changes in behaviour (in this case influenced by COVID-19 restrictions), generating insights into non-traffic contributions to PM emissions in this setting. It is evident that additional non-traffic related measures would be required in Oxford to reduce the PM10 and levels to within WHO health-based guidelines and to achieve compliance with PM2.5 targets developed under the Environment Act 2021
New reductive rearrangement of N-Arylindoles triggered by the Grubbs-Stoltz reagent Et3SiH/KOtBu
N-Arylindoles are transformed into dihydroacridines in a new type of rearrangement, through heating with triethylsilane and potassium tert-butoxide. Studies indicate that the pathway involves (i) the formation of indole radical anions followed by fragmentation of the indole C2-N bond, and (ii) a ring-closing reaction that follows a potassium-ion dependent hydrogen atom transfer step. Unexpected behaviors of âradical-trapâ substrates prove very helpful in framing the proposed mechanis
A detailed study of irradiation requirements towards an efficient photochemical WohlâZiegler procedure in flow
A platform has been developed to enable standardization of light sources, allowing consistent scaleâup from highâthroughput screening in batch to flow, using the same pseudoâmonochromatic light source. The impact of wavelength and light intensity on a photochemical reaction was evaluated within this platform using the WohlâZiegler benzylic bromination of 4âmethylâ3â(trifluoromethyl)benzonitrile with Nâbromosuccinimide as a model system. It was found that only 40â% of the maximum light intensity was required while still maintaining reaction rate, allowing more reliable temperature control and lower energy consumption. The optimized reaction conditions were subsequently applied to a range of synthetically relevant (hetero)aromatic compounds under continuous conditions, exploring the scope of the process within a mild and scalable procedure
An unfolding signifier: London's Baltic Exchange in Tallinn
In the summer of 2007 an unusual cargo arrived at Muuga and Paldiski harbors outside Tallinn. It consisted of nearly 50 containers holding over 1,000 tons of building material ranging from marble columns, staircases and fireplaces, to sculpted allegorical figures, wooden paneling and old-fashioned telephone booths. They were once part of the Baltic Exchange in the City of London. Soon they will become facets of the landscape of Tallinn. The following article charts this remarkable story and deploys this fragmented monument to analyze three issues relating to the Estonian capital: the relocation of the âBronze Soldierâ, the demolition of the Sakala Culture Center, and Tallinnâs future role as European Cultural Capital in 2011
Aerial wetting contact angle measurement using confocal microscopy
A method is presented in which the wetting contact angle of a sessile drop is acquired aerially using confocal techniques to measure the radius and the height of a droplet deposited on a planar surface. The repeatability of this method is typically less than 0.25°, and often less than 0.1°, for droplet diameters less than 1âmm. To evaluate accuracy of this method, an instrument uncertainty budget is developed, which predicts a combined uncertainty of 0.91° for a 1âmm diameter water droplet with a contact angle of 110°. For droplets having diameters less than 1âmm and contact angles between 15° and 160°, these droplets approach spherical shape and their contact angles can be computed analytically with less than 1% error. For larger droplets, gravitational deformation needs to be considered
A study of the reactivity of cyclic aminomethylammonium mannich salts
A novel method for the preparation of aminoalkylaminomethyl products was developed utilising novel Mannich-type salts featuring a R 2NCH 2NR 3 + moiety. This methodology showed good nucleophile scope and was successfully employed in reactions under basic, acidic, and neutral conditions. A wide range of diamine products was successfully synthesised, including a neuropeptide Y antagonist
An exhibition of work by the Victorian tapestry workshop
An exhibition of work by the Victorian tapestry workshop
Fine Arts Gallery, University Centre, Churchill Ave., Sandy Bay 24 April - 10 Ma
Mantle heat drives hydrothermal fluids responsible for carbonate-hosted base metal deposits: evidence from 3He/4He of ore fluids in the Irish Pb-Zn ore district
There is little consensus on whether carbonate-hosted base metal deposits, such as
the world-class Irish Zn+Pb ore field, formed in collisional or extensional tectonic
settings. Helium isotopes have been analysed in ore fluids trapped in sulphides
samples from the major base metal deposits of the Irish Zn-Pb ore field in order to
quantify the involvement of mantle-derived volatiles, that require melting to be realised,
as well as test prevailing models for the genesis of the ore fields. 3He/4He ratios
range up to 0.2 Ra, indicating that a small but clear mantle helium contribution is
present in the mineralising fluids trapped in galena and marcasite. Sulfides from ore
deposits with the highest fluid inclusion temperatures (~200°C) also have the highest
3He/4He (> 0.15 Ra). Similar 3He/4He are recorded in fluids from modern continental
regions that are undergoing active extension. By analogy we consider that the
hydrothermal fluids responsible for the carbonate-hosted Irish base metal
mineralization circulated in thinned continental crust, undergoing extension, and
demonstrates that enhanced mantle heat flow is ultimately responsible for driving fluid
convection
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