Asymmetric benzylic C(sp3)−H acylation via dual nickel and photoredox catalysis

Asymmetric C(sp3)−H functionalization is a persistent challenge in organic synthesis. Here, we report an asymmetric benzylic C−H acylation of alkylarenes employing carboxylic acids as acyl surrogates for the synthesis of α-aryl ketones via nickel and photoredox dual catalysis. This mild yet straightforward protocol transforms a diverse array of feedstock carboxylic acids and simple alkyl benzenes into highly valuable α-aryl ketones with high enantioselectivities. The utility of this method is showcased in the gram-scale synthesis and late-stage modification of medicinally relevant molecules. Mechanistic studies suggest a photocatalytically generated bromine radical can perform benzylic C−H cleavage to activate alkylarenes as nucleophilic coupling partners which can then engage in a nickel-catalyzed asymmetric acyl cross-coupling reaction. This bromine-radical-mediated C−H activation strategy can be also applied to the enantioselective coupling of alkylarenes with chloroformate for the synthesis of chiral α-aryl esters.

Preparation of Core–Shell Silica Microspheres with Controllable Shell Thickness for Fast High Performance Liquid Chromatography Separation of Alkyl Benzenes and Intact Proteins

As it is difficult to prevent secondary nucleation and agglomeration during the preparation of core–shell silica microspheres, these issues have been successfully resolved in this study using template-dissolution-induced redeposition. The non-porous particles are transformed into core–shell silica microspheres (CSSMs) in the presence of cetyltrimethylammonium bromide and octyltrimethylammonium bromide under basic conditions. The shell thickness and pore sizes of the CSSMs are controlled by adjusting the etching time and molar ratio of the template, respectively. The CSSMs are modified using octadecyltrimethylammonium chloride to separate the mixture of alkyl benzenes, and a high column separation efficiency is achieved within two minutes. The CSSMs are used for the separation and analysis of proteins and the digests of bovine serum albumin. The chromatographic column packed with core–shell particles affords a significantly higher separation efficiency than the commercial column. Therefore, as a chromatographic stationary phase, these core–shell particles can potentially be used for the fast separation of proteins, small solutes, and complex samples.

Impact of Aromatic Structures and Content in Formulated Fuel for Jet Engine Applications on Particulate Matter Emissions

Fuel formulation with the particular selection of fuel components is a promising approach that offers the reduction of harmful emissions without altering the combustion system performance. Each fuel component has its own combustion characteristics and hence contribution to emissions. Aromatic is one of the main components of fossil-based fuels and has a strong correlation with the formation of particulate matter (PM) emissions. Besides, aromatics presence in fuel is essential for the compatibility of fuel with the combustion system and maintaining the energy density of the fuel. In this regard, a Rolls-Royce combustor rig was used to test 16 aromatics blended with jet fuels in three different proportions. Moreover, a novel approach of flame luminosity imaging is employed to measure the PM emissions through the soot propensity profile. The results show that PM emissions increase with the proportional increase of aromatics. The di- and cyclo-aromatics produced significantly higher PM emissions compared to alkyl-benzenes. 3-Isopropylcumene tends to lowest PM formation and thus is a consideration as a selection of aromatic type in future fuels for lower PM emissions. Furthermore, it was also observed that PM number concentration measured by the extractive method with DMS 500 instrument correlates well with imaging methods for all the tested fuels. The present study provides information on particular selection of aromatic for future fuel development.

Rate coefficients for reactions of OH with aromatic and aliphatic volatile organic compounds determined by the multivariate relative rate technique

The multivariate relative rate method was applied to a range of volatile organic compound (VOC) reactions with OH. This previously published method (Shaw et al., 2018) was improved to increase the sensitivity towards more slowly reacting VOCs, broadening the range of compounds which can be examined. A total of 35 room temperature relative rate coefficients were determined, eight of which have not previously been reported. Five of the new reaction rate coefficients were for large alkyl substituted mono-aromatic species recently identified in urban air masses, likely with large ozone production potentials. The new results (with kOH (296 K) values in units of 10−12 cm3 molec.−1 s−1) were n-butylbenzene, 11 (±4); n-pentylbenzene, 7 (±2); 1,2-diethylbenzene, 14 (±4); 1,3-diethylbenzene, 22 (±4); and 1,4-diethylbenzene, 16 (±4). Interestingly, whilst results for smaller VOCs agreed well with available structure–activity relationship (SAR) calculations, the larger alkyl benzenes were found to be less reactive than the SAR prediction, indicating that our understanding of the oxidation chemistry of these compounds is still limited. kOH (296 K) rate coefficients (in units of 10−12 cm3 molec.−1 s−1) for reactions of three large alkanes with OH were also determined for the first time: 2-methylheptane, 9.1 (±0.3); 2-methylnonane, 11.0 (±0.3); and ethylcyclohexane, 14.4 (±0.3), all in reasonable agreement with SAR predictions. Rate coefficients for the 27 previously studied OH + VOC reactions agreed well with available literature values, lending confidence to the application of this method for the rapid and efficient simultaneous study of gas-phase reaction kinetics.

Factors influencing volatile organic compounds in Canadian homes

Volatile organic compounds, several of which may impact health, have many possible indoor sources. To further investigate this, we tested the association between indoor concentrations of 47 passively collected volatile organic compounds and both home characteristics and occupant behaviours in a Canadian population-based sample of 3454 participants. Homes with smokers were excluded from analysis. Homes with a door connecting to an attached garage had greater concentrations of hexanal, benzaldehyde, all the measured alkyl benzenes and ketones, most of the simple hydrocarbons and terpenes. Major home renovations within the past month were associated with higher concentrations of most or all of the volatile organic compounds in the categories of alcohols, alkyl benzenes, ketones, simple hydrocarbons and terpenes. Using paints and stains within the past week were associated with an increase in concentrations of the majority of alcohols, alkyl benzenes and simple hydrocarbons. Several building characteristics and occupant’s behaviours appear to increase exposure to volatile organic compounds. Modification of these factors is generally under the control of the occupant(s), suggesting that education could result in reduced indoor volatile organic compound exposure in the Canadian population.

Chemical Variation and Implications on Repellency Activity of Tephrosia vogelii (Hook f.) Essential Oils Against Sitophilus zeamais Motschulsky

The aim of this research is to characterize the variation in the chemical composition of Tephrosia vogelii essential oils from different locations and to investigate the repellency of essential oils against Sitophilus zeamais. Chemical variability in the components of T. vogelii essential oils from eastern Uganda was identified using principal component analysis (PCA) and agglomerative hierarchical clustering (AHC). Based on the profiles of the compounds of the farnesene family, three chemotypes were found: farnesol (chemotype 1), springene (β-springene and α-springene) and β-farnesene were all distinctive in chemotype 2 and a mixed variety of farnesol and springene. In the three cases, alkyl benzenes (o-xylene, m-xylene and ethylbenzene) were significant components in the oil. The compounds 1,4-dihydroxy-p-menth-2-ene, 6,10-dimethyl-5,9-undecadien-2-one, and 3,4-dimethyl-3-cyclohexen-1-carboxaldehyde were other prominent constituents. The yields of the essential oils did not vary significantly, however the chemical composition varied with harvesting time during the rainy and dry seasons. In choice repellency tests, chemotype 1 and chemotype 2 were more active against Sitophilus zeamais than the mixed chemotype. Farnesol was found to be effective only at a higher concentration as a repellent against S. zeamais. We therefore hypothesize that farnesol is a key player in this and we demonstrated the weak repellency of this compound. However, further study that aims to optimize and standardize the varieties and harvesting period is needed for recommendation to smallhold farmers.

Rate coefficients for reactions of OH with aromatic and aliphatic volatile organic compounds determined by the Multivariate Relative Rate Technique

The multivariate relative rate method was applied to a range of volatile organic compounds (VOC) reactions with OH. This previously published method (Shaw et al., 2018b) was improved to increase the sensitivity towards slower reacting VOC, broadening the range of compounds which can be examined. A total of thirty-five room temperature relative rate coefficients were determined; eight of which have not previously been reported. Five of the new reaction rate coefficients were for large alkyl substituted monoaromatic species recently identified in urban air masses, likely with large ozone production potentials. The new results (with kOH (296 K) values in units of 10–12 cm3 molecule−1 s−1) were: n-butylbenzene, 11 (± 4); n-pentylbenzene, 7 (± 2); 1,2-diethylbenzene, 14 (± 4); 1,3-diethylbenzene, 22 (± 4) and 1,4-diethylbenzene, 16 (± 4). Interestingly, whilst results for smaller VOC agreed well with available structure activity relationship (SAR) calculations, the larger alkyl benzenes were found to be less reactive than the SAR prediction, indicating that our understanding of the oxidation chemistry of these compounds is still limited. kOH (296 K) rate coefficients (in units of 10–12 cm3 molecule−1 s−1) for reactions of three large alkanes with OH were also determined for the first time: 2-methylheptane, 9.1 (± 0.3); 2-methylnonane, 11.0 (± 0.3) and ethylcyclohexane, 14.4 (± 0.3), all in reasonable agreement with SAR predictions. Rate coefficients for the twenty-seven previously studied OH + VOC reactions agreed well with available literature values, lending confidence to the application of this method for the rapid and efficient simultaneous study of gas-phase reaction kinetics.

Catalytic oxidation of alcohols and alkyl benzenes to carbonyls using Fe3O4@SiO2@(TEMPO)-co-(Chlorophyll-CoIII) as a bi-functional, self-co-oxidant nanocatalyst

A new magnetically recyclable bi-functional self-co-oxidant based on a copolymer of TEMPO and chlorophyll has been developed for aerobic and selective oxidation of alcohols and alkyl benzenes.