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J.C.W. thanks EaStCHEM for financial support and D.P.C. thanks the US National Science Foundation. Computational support was provided through the EaStCHEM Research Computing Facility. The boron-centered radicals derived from alkenyl N-heterocyclic carbene (NHC)-boranes bearing ester substituents were recently found to ring close in 5-endo mode by addition to the oxygen atoms of the ester substituents. The inference from this was that NHC-boryl radicals might add intermolecularly to carbonyl-containing substrates. Several different NHC-boryl radicals were generated by H-atom abstraction from NHC-ligated trihydroborates. Electron paramagnetic resonance (EPR) spectroscopy proved that these did indeed add to the oxygen atoms of diaryl ketones with production of the corresponding bora-ketyl radicals. The same unusual regioselectivity of addition was observed with monoaryl ketones, but no bora-ketyls were observed with dialkyl ketones. Similarly, no bora-ketyl adduct radicals were observed with esters, even esters of benzoic acid. EPR spectroscopic evidence suggested that NHC-boryl radicals were also added to the O-atoms of aromatic aldehydes. Amine-boryl and phosphine-boryl radicals were also observed to add to the O-atom of benzophenone with production of the corresponding ketyl radicals. Postprint

J.C.W. thanks EaStCHEM for financial support, and D.P.C. thanks the US National Science Foundation. Computational support was provided through the EaStCHEM Research Computing Facility. Radical H atom abstraction from a set of N-heterocyclic carbene (NHC) complexes of alkenylboranes bearing two tert-butyl ester substituents was studied by EPR spectroscopy. The initial boraallyl radical intermediates rapidly ring closed onto the O atoms of their distal ester groups in 5-endo mode to yield 1,2-oxaborole radicals. Unexpectedly, two structural varieties of these radicals were identified from their EPR spectra. These proved to be two stable rotamers, in which the carbonyl group of the tert-butyl ester was oriented toward and away from the NHC ring. These rotamers were akin to the s-trans and s-cis rotamers of α,β-unsaturated carbonyl compounds. Their stability was attributed to the quasi-allylic interaction of their unpaired electrons with the carbonyl units of their adjacent ester groups. EPR spectroscopic evidence for two rotamers of the analogous methyl ester containing NHC-oxaborole radicals was also obtained. An improved synthetic procedure for preparing rare NHC-boralactones was developed involving treatment of the alkenyl NHC-boranes with AIBN and tert-dodecanethiol. Postprint

The concept behind the research described in this article was that of marrying the 'soft' methods of radical generation with the effectiveness and flexibility of nucleophile/electrophile synthetic procedures. Classic studies with pulse radiolysis and laser flash photolysis had shown that free radicals could be more acidic than their closed shell counterparts. QM computations harmonised with this and helped to define which radical centres and which structural types were most effective. Radicals based on the sulfonic acid moiety and on the Meldrum's acid moiety (2,2-dimethyl-1,3-dioxane-4,6-dione) were found to be extreme examples in the superacid class. The ethyne unit could be used as a very effective spacer between the radical centre and the site of proton donation. The key factor in promoting acidity was understood to be the thermodynamic stabilisation of the conjugate anion-radicals released on deprotonation. Solvation played a key part in promoting this and theoretical microhydration studies provided notable support. A corollary was that heterolytic dissociations of free radicals to yield either electrophiles or nucleophiles were also enhanced relative to non-radical models. The most effective radical types for spontaneous releases of both these types of reagents were identified. Ethyne units were again effective as spacers. The enhancement of release of phosphate anions by adjacent radical centres was an important special case. Reactive oxygen species and also diradicals from endiyne antibiotics generate C4'-deoxyribose radicals from nucleotides. Radicals of these types spontaneously release phosphate and triphosphate and this is a contributor to DNA and RNA strand breaks.

This article reviews the excited-state quenching, pro-vitamin A activity and anticarcinogenicity of carotenes and xanthophylls in relation to their chemical structures. Excited-state quenching improved with the length of the conjugated chain structure. Pro-vitamin A activity was dependent on the presence of at least one beta-ionyl ring structure. The effectiveness of carotenoids as antioxidants depended on their ability to trap peroxyl radicals with production of resonance-stabilized carotenyl radicals. The products identified from oxidations of carotenes and xanthophylls with molecular oxygen and other oxidizing agents are presented. The free radical-mediated mechanisms that have been proposed to account for the different classes of products are reviewed.

J.C.W. thanks EaStCHEM for financial support. Radical centers close to protons are known to enhance their dissociation. Investigation of the generality of this radical enhanced deprotonation (RED-shift) phenomenon, and the kinds of structures in which it operates, are reported. The pKas for sulfinic, sulfonic, pentan-2,4-dione, and Meldrum's acid species, with adjacent radicals centered on C-, N-, and O atoms, were computed by a DFT method from free energies of deprotonation. All series showed significant RED-shifts that increased with the electronegativity of the radical center. The hugely negative pKa obtained for a Meldrum's acid with an alkoxyl radical substituent showed it to belong to the superacid class. The ethyne unit was found to be uniquely effective at enhancing acidity and conducting RED-shifts through chains up to and beyond 20 atoms. These connector units enable a radical center to alter the pKa of a spatially remote acidic group. RED-shifted species were characterized by conjugate radical anions displaying site exchange of spin with electronic charge. Postprint

A fast, convenient and user-friendly modelling tool was used to model biochemical and physico-chemical processes in the collection system. With this new tool two case studies were investigated with different scopes and purposes: one with a focus on the integrated modelling of sewer and wastewater treatment plants (WWTP) and the other aiming at a large-scale sewer network. Scenario analysis was carried out under different chemical dosing strategies. The work proves that processes in sewers can cause a significant impact on a downstream WWTP, and the wastewater treatment process can be better managed and optimized with the help of sewer-WWTP integrated modelling. The tool can also identify hotspots of key indicators like total dissolved sulfide in a large-scale collection system. It is suggested that investigating the network from a wider perspective can help target key issues and regions.

This work was financially supported by the EPSRC and COST action CM1302 SIPs. Here, we highlight the ability of peri-substitution chemistry to promote a series of unique P–P/P–As coupling reactions, which proceed with concomitant C–H bond formation. This dealkanative reactivity represents an interesting and unexpected expansion to the established family of main-group dehydrocoupling reactions. These transformations are exceptionally clean, proceeding essentially quantitatively at relatively low temperatures (70–140 °C), with 100% diastereoselectivity in the products. The reaction appears to be radical in nature, with the addition of small quantities of a radical initiator (azobisisobutyronitrile) increasing the rate dramatically, as well as altering the apparent order of reaction. DFT calculations suggest that the reaction involves dissociation of a phosphorus centred radical (stabilised by the peri-backbone) to the P–P coupled product and a free propyl radical, which carries the chain. This unusual reaction demonstrates the powerful effect that geometric constraints, in this case a rigid scaffold, can have on the reactivity of main group species; an area of research that is gaining increasing prominence in recent years. Postprint Postprint

J.C.W. thanks EaStCHEM for financial support. T.R.M. and D.P.C. thank the US National Science Foundation for grant CHE-1660927. Three-member ring boracyclopropanes (boriranes) with N-heterocyclic carbene substituents were prepared by a recently discovered route. H atoms were selectively abstracted from the boron atoms by t-butoxyl radicals and this enabled boriranyl radicals to be detected and characterized by EPR spectroscopy for the first time. Their EPR parameters indicated they had planar π-character. From competition experiments, the rate constant for H atom abstraction was determined and found to be about 2 orders of magnitude less than for NHC-boranes. The B–H BDE of an NHC-borirane was estimated to be about 95 kcal mol–1. Postprint

J.C.W. thanks EaStCHEM for financial support. Comparison of accepted pKa values of bicarbonate, carboxyl, and hydroperoxyl radicals, with those of models having the unpaired electron replaced by H atoms, implied the acidity of the radicals was greatly increased. A Density Functional Theory computational method of estimating pKas was developed and applied to a set of radicals designed to probe the phenomenon of radical-enhanced deprotonation (RED-shift) and its underlying causes. Comparison of the computed pKa values of 12 acid radicals to those of the corresponding model acids confirmed the intensified acidity of the title radicals and also pin-pointed the carboxy-ethynyl (HO2CC≡C•) and the carboxy-aminyl (HO2CNH•) radicals as having enhanced acidity. The underlying cause was found to be extensive charge distribution away from the anionic O atoms of the conjugate radical anions, coupled with spin density displaced toward these O atoms. Ethyne spacers, between the radical and carboxylate centers, transmitted the effect extremely efficiently such that measurable enhancement was detectable up to at least six alkyne units. The bicyclo[1.1.1]pent-1-yl-3-carboxylic acid radical also displayed enhanced acidity, but additional cage units drastically attenuated the effect. Nitroxide radicals with suitably situated carboxylic acid substituents also exhibited enhanced acidity. Several families of potentially persistent radicals with enhanced acidity were identified. Postprint

5- to 6-member ring enlargements of 3-oxa-2-silacyclopentylmethyl to 4-oxa-3-silacyclohexyl radicals were investigated by EPR spectroscopy and QM computations of model indano-oxasilacyclopentane and oxasilinanyl compounds. Both experimental and computational evidence favored a mechanism via a concerted 1,2-migration of the "tethered" Si-group. Thus, the "forbidden" 1,2-Si-group migration from carbon to carbon becomes allowed when the Si-group is "tethered". The EPR data from 3-oxa-2-silacyclopentylmethyl radicals disclosed ground state conformations having semioccupied p-orbitals close to antiperiplanar with respect to their β-Si-C bonds, but indicated Si-hyperconjugation (β-silicon effect) was insignificant in radicals. Kinetic data was obtained by the steady state EPR method for ring enlargement of indano-3-oxa-2-silacyclopentylmethyl radicals. The scope of the novel rearrangement in terms of other ring types and sizes, as well as the analogous 1,2-migration of "tethered" C-centered groups, was explored computationally.

J.C.W. thanks EaStCHEM for financial support. Experimental and computational results have shown that deprotonation was enhanced for precursors containing radical centers (RED-shift). An examination of whether the inverse heterolytic dissociations that release nucleophiles instead of electrophiles could also be stimulated by suitably sited radicals is reported in this paper. A DFT method was employed to assess the free energies of heterolytic dissociations releasing C-centered and O-centered nucleophiles. In most instances a radical adjacent to the incipient positive charge in the precursors led to significant enhancement of heterolytic dissociation, but inhibition was found in some cases. Greater enhancements were obtained with C-centered rather than O-centered radicals. Exergonic dissociations for both O- and C-centered nucleophiles could be achieved with fluorenylmethyl- and cyclohepta-2,4,6-trienylmethyl-containing precursors. Heterolytic phosphate release from ribose and deoxyribose nucleotide C4' radicals was also found to be enhanced. This provided supporting evidence of the importance of these radicals in DNA and RNA strand breaking. The effect of ethyne, ethene, and phenyl spacer units between the radical center and the incipient positive charge was examined. Evidence was obtained that the key factor promoting heterolytic dissociation was the resonance stabilization of the coreleased radical-cations. Postprint

In this study, sludge generated from chemically enhanced treatment of primary influent was treated to recover the ferric coagulant, which was reused to coagulate fresh primary influent. The treatment process used to recover the ferric coagulant consisted of acidification and mixing of the chemically – enhanced primary sludge, followed by final separation using centrifugation to recover the coagulant. Although, they performed equally well, sulphuric acid was chosen over hydrochloric acid for the maximum recovery of the coagulant occurring at an optimal pH 1.5. A chemical equilibrium model describing iron-SO4-2 and iron-Cl- chemistry at various pH predicted the formation of complexes like jarosite, which reduced the recovery of iron. With fresh ferric chloride, 90% total suspended solids (TSS), 77% total phosphorous (TP), 70% soluble phosphorous (sP), 62% chemical oxygen demand (COD), and 18% total nitrogen (TN) were removed from primary effluent. With the recovered coagulant, there was a decrease in the TSS, COD and TN removal efficiencies and a corresponding approximately 10% increase in their concentration in the primary effluent. A significant increase in phosphorous concentration occurred due to recycling of the coagulant, which was precipitated as struvite at the end of the second cycle. A preliminary operational cost analysis conducted on the recovery process shows the increased cost of acidification can be offset by the reduction in costs of fresh coagulant, dewatering and sludge disposal.

J.C.W. thanks EaStCHEM for financial support, and D.P.C. thanks the U.S. National Science Foundation. Computational support was provided through the EaStCHEM Research Computing Facility. EPR studies of radical hydrogen abstraction reactions of N-heterocyclic carbene (NHC) complexes of alkenylboranes bearing two ester substituents revealed not the expected boraallyl radicals but instead isomeric 1,2-oaxborole radicals. Such radicals are new, and DFT calculations show that they arise from the initially formed boraallyl radicals by a rapid, exothermic 5-endo cyclization. These spectroscopic and computational discoveries prompted a series of preparative experiments that provided access to a novel family of robust NHC-boralactones. A one-pot procedure was developed to access the boralactones directly from an NHC-borane (NHC-BH3) and dimethyl acetylenedicarboxylate. Postprint

The study investigates how water chemistry evolves as ephemeral stream runoff is formed through the interaction of sediments and precipitation in the Amargosa Desert region and by analogy other desert regions. In this study, thirty lysimeters were installed in the major arroyos in the Amargosa Desert to capture runoff water. The sampling process included sediment, precipitation, and runoff water chemistry. Innovative and low cost methods were used to measure the chemical composition of the resulting runoff and examined some of the important processes affecting the runoff chemistry. Results of the analytical and statistical analyses indicate that runoff salinity is low as a result of net salt accumulation in sediments. Chemical behavior between precipitation and runoff is classified as leached (TDS, alkalinity, Ca, Mg, K, Na, Ba, Cs, Li, Sr, Fe, Ni), nutrient (Br, As, SO 4 2 − , PO 4 3 − , NO 3 − , Rb, B, Cu, Zn, V), scavenged (U, F), and conservative (Al, Mo, Mn). Bromide behaves as a nutrient meaning the chloride/bromide ratio, a common tracer of groundwater sources, is not conservative. Runoff chloride, sulfate, and sodium are predominantly associated with concentrations of the same ions in sediment. Trace elements are more closely associated with precipitation chemistry.

Heterogeneous semiconductor photoredox catalysis (SCPC), particularly with TiO2, is evolving to provide radically new synthetic applications. In this review we describe how photoactivated SCPCs can either (i) interact with a precursor that donates an electron to the semiconductor thus generating a radical cation; or (ii) interact with an acceptor precursor that picks up an electron with production of a radical anion. The radical cations of appropriate donors convert to neutral radicals usually by loss of a proton. The most efficient donors for synthetic purposes contain adjacent functional groups such that the neutral radicals are resonance stabilized. Thus, ET from allylic alkenes and enol ethers generated allyl type radicals that reacted with 1,2-diazine or imine co-reactants to yield functionalized hydrazones or benzylanilines. SCPC with tertiary amines enabled electron-deficient alkenes to be alkylated and furoquinolinones to be accessed. Primary amines on their own led to self-reactions involving C–N coupling and, with terminal diamines, cyclic amines were produced. Carboxylic acids were particularly fruitful affording C-centered radicals that alkylated alkenes and took part in tandem addition cyclizations producing chromenopyrroles; decarboxylative homo-dimerizations were also observed. Acceptors initially yielding radical anions included nitroaromatics and aromatic iodides. The latter led to hydrodehalogenations and cyclizations with suitable precursors. Reductive SCPC also enabled electron-deficient alkenes and aromatic aldehydes to be hydrogenated without the need for hydrogen gas.

The scope and limitations of a photoinitiated N- to C-sulfonyl migration process within a range of dihydropyridinones is assessed. This sulfonyl transfer proceeds without erosion of either diastereo- or enantiocontrol, and is general across a range of N-sulfonyl substituents (SO

Estimation of groundwater flowpaths and effective recharge was performed in the vicinity of Amargosa Desert, Nevada, USA, using multivariate statistical methods (MSMs) and a simple elevation-dependent chloride mass-balance method modified by estimating a minimum effective recharge elevation (MERE). MSMs were applied to major ion data to explain the relationships among different groundwater chemical species, define hydrochemical facies needed to determine groundwater flowpaths and evolution, and identify the influence of surface and geologic features on groundwater. For each defined watershed, an average groundwater chloride concentration is used and the chloride deposition rate is assessed in the subject watersheds over all land elevations above the estimated MERE by assuming two constant spatial and temporal concentrations of chloride in precipitation which is a function of elevation. The MERE for the Amargosa Desert was appraised as 1200 m above mean sea level (m-amsl), based upon the elevation of the orifice of Cane Spring (1237 m-amsl), one of the lowest elevation, permanent springs, on the Nevada National Security Site. This minimum elevation is the cutoff altitude for our calculations at which precipitation is considered to make a significant contribution to recharge. Elevation-dependent precipitation was evaluated relating elevation data from the online mapping software ACME Labs Mapper 2.1 and precipitation data from the PRISM Climate Group’s PRISM. These analyses provide further insight into the hydrology of the region and demonstrate the strong impact surface and geologic features can have on surface water infiltration and groundwater in arid regions. Specifically, evidence is presented of past focused recharge around the ephemeral Fortymile Wash and interaction between geologic faults and groundwater infiltration and flowpaths. In addition, groundwater flow, based upon water chemistry, appears to be segmented by major faults. Groundwater recharge in the vicinity of the Amargosa Desert has been estimated around 15,280 acre-ft/year.

Stormwater along ephemeral arroyos and areal infiltration in nearby boreholes were studied in the Amargosa Desert Region of Southern Nevada, USA. Chemical composition of ephemeral stream runoff was measured at elevations below where areal infiltration generally occurs in arid environments using lysimeters designed for this study. Borehole cuttings from several wells were evaluated in terms of chloride migration. Analysis of the borehole data indicates that net areal infiltration has been insignificant for the past 10 000+ years. This is associated with an environment where chloride and other soluble salts accumulate in shallow sediments and potentially in runoff waters. Measured storm events during the 4-year study period were small and localized but sufficient to produce surface runoff, at least near the lysimeters. Composition of storm runoff captured by the lysimeters was found to be a combination of the water chemistry types found in precipitation and from leaching tests of near-surface sediments. All major cations and bicarbonate increased relative to chloride when precipitation interacted with sediments to form ephemeral stream runoff. The changes were consistent with calculated saturation indices. Despite the long-term accumulation of chloride in soils and deep sediments caused by complete evapotranspiration of infiltrating precipitation, runoff waters were characterized by low chloride and total dissolved solids. This study presents a limitation of the chloride mass-balance method, as chloride and water migration were disassociated from each other in the study area. Copyright © 2014 John Wiley & Sons, Ltd.

The authors thank the EPSRC for funding (Grant EP/I003479/1) and the EPSRC National Mass Spectrometry Service, Swansea. A mild procedure for the reduction of electron-deficient alkenes and carbonyl compounds is described. UVA irradiations of substituted maleimides with dispersions of titania (Aeroxide P25) in methanol/acetonitrile (1:9) solvent under dry anoxic conditions led to hydrogenation and production of the corresponding succinimides. Aromatic and heteroaromatic aldehydes were reduced to primary alcohols in similar titania photocatalyzed reactions. A mechanism is proposed which involves two proton-coupled electron transfers to the substrates at the titania surface. Publisher PDF

A passive rainwater harvesting technique was used to design a sustainable landscape for a residential lot located in the desert. The design was adapted to the Desert Southwest region of the United States based on thirty years of daily historical climate data including precipitation and reference evapotranspiration (ET0). Four cities including El Paso, TX, Albuquerque, NM, Phoenix, AZ, and Pahrump, NV, were selected to represent the area. The residential lot was broken up into micro-watersheds reflecting the runoff of water from each separate portion of the house roof, driveway, and lawn area. The paper explains in detail the design steps for one of the micro-watersheds where water retention and infiltration structures were distributed throughout the soil area to capture stormwater runoff close to its source. A passive rainwater capture landscape was obtained by using the stormwater captured in the infiltration structures and stored in the surrounding soil. Native vegetation (shrubs and trees) will use this water exclusively for growth. These plants will not require watering once their root establishment period has passed, except in extreme droughts. Meanwhile, stormwater discharge from the lot will decrease and the groundwater recharge will increase. Results indicate that the current urban water budget can be made sustainable by replacing watering of landscape by municipal water with harvested stormwater. This results in a relatively lush and shady environment even in desert climates. The success is an artifact of the tendency of urban watersheds to increase the volume of stormwater relative to pre-development conditions.

This work was funded by EPSRC Grant Numbers: EP/I003479/1, EP/I003800/2. The paper was made open accees through RCUK block grant funds. Suitably functionalised carboxylic acids undergo a previously unknown photoredox reaction when irradiated with UVA in the presence of maleimide. Maleimide was found to synergistically act as a radical generating photoxidant and as a radical acceptor, negating the need for an extrinsic photoredox catalyst. Modest to excellent yields of the product chromenopyrroledione, thiochromenopyrroledione and pyrroloquinolinedione derivatives were obtained in thirteen preparative photolyses. In situ NMR spectroscopy was used to study each reaction. Reactant decay and product build-up were monitored, enabling reaction profiles to be plotted. A plausible mechanism, whereby photo-excited maleimide acts as an oxidant to generate a radical ion pair, has been postulated and is supported by UV/Vis. spectroscopy and DFT computations. The radical-cation reactive intermediates were also characterised in solution by EPR spectroscopy. Publisher PDF

Photochemical reactions employing TiO and carboxylic acids under dry anaerobic conditions led to several types of C-C bond-forming processes with electron-deficient alkenes. The efficiency of alkylation varied appreciably with substituents in the carboxylic acids. The reactions of aryloxyacetic acids with maleimides resulted in a cascade process in which a pyrrolochromene derivative accompanied the alkylated succinimide. The selectivity for one or other of these products could be tuned to some extent by employing the photoredox catalyst under different conditions. Aryloxyacetic acids adapted for intramolecular ring closures by inclusion of 2-alkenyl, 2-aryl, or 2-oximinyl functionality reacted rather poorly. Profiles of reactant consumption and product formation for these systems were obtained by an in situ NMR monitoring technique. An array of different catalyst forms were tested for efficiency and ease of use. The proposed mechanism, involving hole capture at the TiO surface by the carboxylates followed by CO loss, was supported by EPR spectroscopic evidence of the intermediates. Deuterium labeling indicated that the titania likely donates protons from surface hydroxyl groups as well as supplying electrons and holes, thus acting as both a catalyst and a reaction partner. Publisher PDF

Funding: The authors thank the EPSRC (grant EP/I003479/1) & EaStCHEM for funding, the EPSRC UK National Electron Paramagnetic Resonance Service at the University of Manchester and the EPSRC National Mass Spectrometry Service, Swansea. Sensitised photolyses of ethoxycarbonyl oximes of aromatic and heteroaromatic ketones yielded iminyl radicals which were characterised by EPR spectrscopy. Iminyls with suitably placed arene or heteroarene acceptors underwent cyclisations yielding phenanthridine type products from ortho-additions. For benzofuran and benzothiophene acceptors, spiro-cyclisation predominated at low temperatures but thermodynamic control ensured ortho-products, benzofuro- or benzothieno-isoquinolines, formed at higher temperatures. Estimates by steady state kinetic EPR established that iminyl radical cyclisations onto aromatics took place about an order of magnitule more slowly than prototypical C-centred radicals. Cyclisation energetics were investigated by DFT computations which gave insights into factors influencing the two cyclisation modes. Publisher PDF

A set of oxime carbamates, having N-alkyl- and N,N-dialkyl-substituents, was prepared via carbonyldiimidazole intermediates. It was shown by EPR spectroscopy that they underwent clean homolysis of their NO bonds on UV photolysis. During photolysis of acetophenone O-allylcarbamoyl oxime the corresponding oxazolidin-2-onylmethyl radical was detected by EPR spectroscopy, providing the first evidence that N-mono-substituted carbamoyloxyl radicals can hold their structural integrity. N,N-Di-substituted carbamoyloxyl radicals dissociated rapidly at the lowest accessible temperatures. Above room temperature both types of oxime carbamate acted as selective new precursors for aminyl and iminyl radicals. Rate parameters were measured for 5-exo-cyclization of N-benzyl-N-pent-4-enylaminyl radicals; the rate constant was smaller than for C-centered and O-centered analogs. Oxime carbamates derived from the volatile diethylamine afforded aryl-iminyl radicals that proved convenient for phenanthridine preparations. Publisher PDF

INTRODUCTION Hydraulic fracturing occurs when high pressure fluids primarily consisting of water and sand are pumped at high pressure into subsurface formations, typically shale that contains natural gas and/or oil. The high pressure fluid causes the rock to fracture. The new fractures increase the surface area of the shale and better interconnect previously existing fractures, allowing more natural gas and/or oil to be pumped from the formation. Modern hydraulic fracturing, referred to as “fracking,” is an evolving technology that largely began after 2000 and has significantly increased natural gas production in the United States in the past five years with corresponding decreases in natural gas prices. The revolution in hydraulic fracturing has been made possible by technological advancements in directional drilling. In the past, wells were drilled vertically and sometimes passed only briefly into the producing formation. Shale is a sedimentary rock that is initially formed underwater as a horizontal la...

Knitting: Recently Antonchick and Manna described a unique annulation that knits together three acetophenones to construct cyclopropanes. The cascade is mediated by organocopper and free radical species, and amounts to the first known [1+1+1] cyclotrimerization. It works well for ketones having electron-deficient or electron-rich substituents in their aryl rings. DTBP=di-tert-butylperoxide.

John C. Walton and Raphael C. Mordi acknowledge the financial support of EaStCHEM. Canthaxanthin is a carotenoid that lacks pro-vitamin A activity but is known to have antioxidant activity. The products of its oxidation in oxygen were found to be mainly substituted apo-carotenals and apo-carotenones. The product profile resembles that obtained in the oxidation of β-carotene, except that with canthaxanthin these products are the 4-oxo-β-apo-carotenals and 4-oxo-β-apo-carotenones. Epoxides and diepoxides were clearly identified from β-carotene oxidation but in contrast, with canthaxanthin, apart from 5,6-epoxy-canthaxanthin, which was detected at the early stage of oxidation and minor quantities of 5,6-epoxy-β-ionone and 5,6-epoxy-4-oxo-β-apo-11-carotenal, no other epoxides were detected. The identities of these products lead us to suggest that the mechanism of canthaxanthin oxidation bears significant similarity to that of β-carotene. Postprint

The author thanks EaStCHEM for financial support. Recently Antonchick and Manna described a unique annulation that knits together three acetophenones to construct cyclopropanes. The cascade is mediated by organo-copper and free radical species and amounts to the first known [1+1+1] cyclotrimerization. It works well for ketones having electron-deficient or electron-rich substituents in their aryl rings. Postprint

Heterogeneous semiconductor photoredox catalysis (SCPC), particularly with TiO2, is evolving to provide radically new synthetic applications. In this review we describe how photoactivated SCPCs can either (i) interact with a precursor that donates an electron to the semiconductor thus generating a radical cation; or (ii) interact with an acceptor precursor that picks up an electron with production of a radical anion. The radical cations of appropriate donors convert to neutral radicals usually by loss of a proton. The most efficient donors for synthetic purposes contain adjacent functional groups such that the neutral radicals are resonance stabilized. Thus, ET from allylic alkenes and enol ethers generated allyl type radicals that reacted with 1,2-diazine or imine co-reactants to yield functionalized hydrazones or benzylanilines. SCPC with tertiary amines enabled electron-deficient alkenes to be alkylated and furoquinolinones to be accessed. Primary amines on their own led to self-reactions involving C–N coupling and, with terminal diamines, cyclic amines were produced. Carboxylic acids were particularly fruitful affording C-centered radicals that alkylated alkenes and took part in tandem addition cyclizations producing chromenopyrroles; decarboxylative homo-dimerizations were also observed. Acceptors initially yielding radical anions included nitroaromatics and aromatic iodides. The latter led to hydrodehalogenations and cyclizations with suitable precursors. Reductive SCPC also enabled electron-deficient alkenes and aromatic aldehydes to be hydrogenated without the need for hydrogen gas.

The adoption of pulsed electric field technologies is currently limited by the lack of application-specific knowledge as well as the availability of reliable and validated full-scale reactors. In this paper, the progress made towards the design, optimization and scale-up of the OpenCEL TM technology applied to high-flow, heterogeneous matrices are illustrated. Specific challenges included engineering systems capable of sustained long-term operation in harsh environments operating with complex non-Newtonian fluids. The paper also describes the importance of adopting standard operating procedures for evaluating and validating equipment performance. Robust experimentation coupled with numerical model was also instrumental in guiding the optimization of the reactor chamber in a way that mass and energy transport could simultaneously be taken into account.

Under dry, anaerobic conditions, TiO(2) photocatalysis of carboxylic acid precursors resulted in carbon-carbon bond-forming processes. High yields of dimers were obtained from TiO(2) treatment of carboxylic acids alone. On inclusion of electron-deficient alkenes, efficient alkylations were achieved with methoxymethyl and phenoxymethyl radicals. In reactions with maleic anhydride or maleimides, phenoxyacetic acid produced chromenedione derivatives in addition to adducts. These photocatalytic reactions are simple and cheap to perform, and the TiO(2) is easily removed by filtration. The anaerobic photocatalysis strategy offers a range of synthetic possibilities.

Applications of microwave (MW)-assistance to radical-mediated organic preparations and procedures are reviewed. Radical additions and cyclisations onto a wide range of acceptors benefited from the technique, as did organic halide reductions by tin hydrides and numerous cascade and sequential processes. Reaction times of chain processes initiated by AIBN were, in several cases, reduced to a few minutes. Regioselectivity in radical additions and ring closures was normally maintained under MW conditions, although stereoselectivities were usually poorer. MW methods have been developed for generation of C-, N-, O-, S- and P-centred radicals. As a result of this a notable number and diversity of heterocycles have been accessed. MW-methods have opened up several new and innocuous alternatives to toxic organotin reagents. Alkoxyamines smoothly release C-centred radicals and oxime ethers provide a variety of iminyl radicals on MW heating. In addition, several types of organo-element and organometallic precursors have yielded novel C-centred and hetero-radicals. To date applications of MW-assistance to homolytic processes are comparatively limited, but it is clear the alliance of the two holds a lot of promise.

In this study, the hydrogeochemical program PHREEQC was used to determine the chemical speciation and mineral saturation indices (SIs) of groundwater in the vicinity of the proposed high-level nuclear waste repository at Yucca Mountain, Nevada (USA). In turn, these data were used to interpret the origin and recharge mode of groundwater, to elucidate the mechanisms of flow and transport, and to determine potential sources of groundwater contamination. PHREEQC was run to determine aqueous dissolved species and minerals that would be in equilibrium with the study area’s groundwater. Selected major ions, associated SI, F− and Ca/Na ion exchange were then examined using the multivariate statistical methods of principal component factor analysis and k-means cluster analysis. Analysis of dissolved ion concentrations, SIs, and Ca/Na ion exchange allows simultaneous consideration of arithmetic (raw concentrations) and logarithmic (SI, ion exchange) variables that describe the hydrochemical system and, therefore, can provide further insight into the system’s behavior. The analysis indicates that the dominant processes and reactions responsible for the hydrochemical evolution in the system are (1) evaporative concentration prior to infiltration, (2) carbonate equilibrium, (3) silicate weathering reactions, (4) limited mixing with saline water, (5) dissolution/precipitation of calcite, dolomite and fluorite, and (6) ion exchange. Principal component factor analysis and k-means cluster analysis of factor scores allow the reduction of dimensions describing the system and the identification of hydrogeochemical facies and the processes that defined and govern their evolution. Statistical analysis results indicate that the northern, west face and southern Yucca Mountain groundwater is fresh water with low concentrations of Ca2+, Mg2+, Cl−, Ca2+/(Na+)2, and CaF2. The Fortymile Wash groundwater is dilute. The carbonate signature is shown in the Ash Meadows and Death Valley waters with high fluorite SI. Finally, the Crater Flat, Stripped Hills, and Skeleton Hills are dominated by Ca/Na ion exchange, Mg and Ca. The hydrochemical and statistical analyses showed three main groundwater signatures or hydrochemical processes indicating groundwater evolution, potential flowpaths, and recharge areas. The flowpaths are the trace of the Amargosa River, the trace of Fortymile Wash, and its convergence with the Amargosa River. This appears to represent not just a groundwater flow path, but traces of surface runoff infiltration as well.

In this paper we shed some light on the safety of unsaturated zone nuclear geological repositories in the long run by examining the effect of physical and chemical processes that take place inside a partially failed nuclear waste container. Our analysis addresses the safety of the proposed nuclear repository at Yucca Mountain, which is intended to store high-level nuclear waste. Our study is independent of the US Department of Energy (DOE) analysis, which involves a number of complex computer codes and assumptions, and relies on the performance of an engineered barrier system. Our safety analysis could be applied in general to any geological repository designed to be in an unsaturated zone, since it is based on the geology, unsaturated zone location, and a key characteristic of the waste, heat production. This analysis shows that the radionuclide release from a partially failed waste container, stored in an unsaturated zone geological repository, is likely to be gradual and long delayed.

A new conceptual model for release rate of radionuclides from the proposed repository for high level nuclear waste located at Yucca Mountain, Nevada is developed. The model predicts that heat generated from radioactive decay combined with the unsaturated environment will lead to an inward flow system that, under many relevant conditions, will slow the release of and sometimes sequester radionuclides at locations of higher heat release and lower water percolation. The amount of protection will be greatest for more concentrated waste forms such as spent fuel and less for glass waste forms. The redistribution and concentration of the radionuclides is anticipated to significantly delay radionuclide release and create a tendency towards gradual release over time that is independent of localized penetrations of metallic barriers.

A wide range of biologically active compounds contain the quinazoline ring system. A new free-radical-based method of making functionalized quinazolines is described, which relies on microwave-promoted reactions of O-phenyl oximes with aldehydes. A small set of 2-aminoaryl alkanone O-phenyl oximes was prepared and shown to produce dihydroquinazolines when mixed with an aldehyde in toluene and subjected to microwave heating. When ZnCl(2) was included in the reaction mixture, fully aromatic quinazolines were produced in high yields by a rapid and convenient process. The method worked well with alkyl, aryl, and heterocyclic aldehydes and for a variety of substituents in the benzenic part of the molecule. Similar reactions employing ketones instead of aldehydes were less efficient. Although some dihydroquinazolines did form, they were accompanied by several byproducts. Surprisingly, in each case, one of the byproducts was a quinoline derivative, and a plausible mechanism to account for this rearrangement is proposed.