Analysis on typical characteristics and causes of coal mine gas explosion accidents in China.

Large-scale coal mine gas explosion (CMGE) accidents have occurred occasionally and exerted a devastating effect on society. Therefore, it is essential to systematically identify the characteristics and association rules of causes of CMGE accidents through analysis on large-scale CMGE accident reports. In this study, 298 large-scale CMGE accidents in China from 2000 to 2021 were taken as the data sample, and mathematical statistical methods were adopted to analyze their general characteristics, coupling cross characteristics, and characteristics of gas accumulation and ignition sources. Moreover, the text mining technology and the Apriori algorithm were used for exploring the formation mechanism of CMGE accidents, during which 46 main causal factors were identified and 59 strong association rules were obtained. Furthermore, an accident causation network was constructed based on the co-occurrence matrix. The key causal items and sets of CMGE accidents were clarified through network centrality analysis. According to the research results, electrical equipment failure, cable short circuit, mine lamp misfire, hot-line work, and blasting spark are the key ignition sources of CMGE. Fan failure, airflow short circuit, and local ventilation fan damage are the main causes of gas accumulation. Besides, the confidence levels of two association rules of "static spark-fan failure" and "blasting spark-airflow short circuit" are higher than 70%, indicating that they are the two dominant risk-coupling paths of gas explosions. In addition, six causes appear frequently in the shortest risk paths of gas explosion and are closely related to other causes, i.e., fan failure, local ventilation fan damage, static sparks, electrical equipment failure, self-heating ignition, and friction impact sparks. This study provides a new perspective on identifying causes of accidents and their complex association mechanisms from accident report data for practical guidance in risk assessment and accident prevention.

Exploring the Effect of Low-Temperature Oxidation on the Petrophysical Characteristics of Coal.

Low-temperature oxidation leads to the accumulation of heat in coal, and it is an important trigger for coal spontaneous combustion (CSC). The oxidation effects induce irreversible damage in the pore and fracture structures of coal, which provide a way for the infiltration of oxygen. In this work, the evolution of pores and cracks of coal in the progress of low-temperature oxidation is researched based on nitrogen adsorption, scanning electron microscopy (SEM), and ultrasonic testing. The results show that the oxidation effect increases microporous structures and promotes the development of mesopores and macropores in coal. Besides, as the temperature increases, the oxidation effect becomes more significant, while the pore morphology has not changed significantly yet. Meanwhile, the oxidation effect causes coal particles to block or collapse in the macropores, and the plugging degree increases with increasing temperature.

Divergent and Selective Light Alkene Cross-Coupling.

Light olefins are abundantly manufactured in the petroleum industry and thus represent ideal starting materials for modern chemical synthesis. Selective and divergent transformations of feedstock light olefins to value-added chemicals are highly sought-after but remain challenging. Herein we report an exceptionally regioselective carbonickelation of light alkenes followed by in situ trapping with three types of nucleophiles, namely a reductant, base, or Grignard reagent. This protocol enables efficient 1,2-hydrofunctionalization, dicarbofunctionalization, and branched-selective Heck-type cross-coupling of light alkenes with aryl and alkenyl reagents to streamline access to diverse alkyl arenes and complex alkenes. Harnessing bulky N-heterocyclic carbene ligands with acenaphthyl backbones for nickel catalysts is crucial to attain high reactivity and selectivity. This strategy provides a rare, modular, and divergent platform for upgrading feedstock alkenes and is expected to find broad applications in medicinal chemistry and industrial processes.

Research on gas emission quantity prediction model based on EDA-IGA.

In order to accurately predict the possible gas emission quantity in coal mines, it is proposed to use the multi-thread calculation of the Immune Genetic Algorithm (IGA) and injection of vaccines to improve the accuracy of prediction and combine the Estimation of Distribution Algorithm (EDA) to the distribution probability of excellent populations. Calculating, and selecting excellent populations for iteration, optimize the population generation process of the Immune Genetic Algorithm, so that the population quality is continuously optimized and improved, and the optimal solution is obtained, thereby establishing a gas emission quantity prediction model based on the Immune Genetic Algorithm and Estimation of Distribution Algorithm. Using the 9136 mining face with gas emission hazards in a coal mine from Shandong Province in China as the prediction object, the absolute gas emission quantity is used to scale the gas emission quantity, and it is found that the model can accurately predict the gas emission quantity, which is consistent with the on-site emission unanimous. In the prediction comparison with IGA, it is found that the accuracy of the prediction results has increased by 9.51%, and the number of iterations to achieve the required goal has been reduced by 67%, indicating that the EDA has a better role in optimizing the population update process such as genetic selection of the IGA. Comparing the prediction results of other models, it is found that the prediction accuracy of the EDA-IGA is 94.93%, which is the highest prediction accuracy, indicating that this prediction model can be used as a new method for the prediction of coal mine gas emission. Accurately predicting the gas emission quantity can provide guidance for safe mining in coal mines. The gas emission quantity can also be used as a safety indicator to reduce the possibility of coal mine accidents, ensure the personal safety of coal miners and reduce economic losses in coal mines.

Unsymmetric N-heterocyclic carbene ligand enabled nickel-catalysed arylation of bulky primary and secondary amines.

The arylation of sterically hindered amines represents one of the long-standing challenges in synthetic chemistry. Herein, we report a highly efficient Ni-catalysed arylation of sterically hindered primary and secondary amines with aryl chlorides or phenol derivatives enabled by an unsymmetric N-heterocyclic carbene (NHC) ligand. The protocol provides general, efficient, and scalable access to various sterically demanding anilines in excellent yields under mild conditions. A wide range of functional groups and heterocycles are compatible (>50 examples), including those present in biologically relevant molecules. Computational studies suggest that the unsymmetric bulky and flexible NHC ligand was critical to balance the oxidative addition and reductive elimination elementary steps, thus promoting this challenging transformation.

Dynamic kinetic asymmetric arylation and alkenylation of ketones.

Despite the importance of enantioenriched alcohols in medicinal chemistry, total synthesis, and materials science, the efficient and selective construction of enantioenriched tertiary alcohols bearing two contiguous stereocenters has remained a substantial challenge. We report a platform for their preparation through the enantioconvergent, nickel-catalyzed addition of organoboronates to racemic, nonactivated ketones. We prepared several important classes of α,ß-chiral tertiary alcohols in a single step with high levels of diastereo- and enantioselectivity through a dynamic kinetic asymmetric addition of aryl and alkenyl nucleophiles. We applied this protocol to modify several profen drugs and to rapidly synthesize biologically relevant molecules. We expect this nickel-catalyzed, base-free ketone racemization process to be a widely applicable strategy for the development of dynamic kinetic processes.

Enantio- and Regioselective Ni-Catalyzed para-C-H Alkylation of Pyridines with Styrenes via Intermolecular Hydroarylation.

Direct asymmetric functionalization of the pyridyl C-H bond represents a longstanding challenge in organic chemistry. We herein describe the first enantioselective para-C-H activation of pyridines through the use of a Ni-Al bimetallic catalyst system and N-heterocyclic carbene (NHC) ligand for intermolecular hydroarylation of styrenes. The reaction procceds in high to excellent enantioselectivities (up to 98.5:1.5 er) and high site-selectivities for both styrene and pyridine components (up to >98:2). Consequently, a broad range of enantioenriched 1,1-diarylalkanes containing pyridine moieties could be prepared in a single step with 100% atom economy. Computational studies supported a mechanism involving a ligand-to-ligand H-transfer (LLHT) and reductive elimination sequence, with LLHT being the rate- and enantioselectivity-determining step. DFT studies indicate that the π-π stacking interaction between the NHC aryl fragment and trans-styrenes is critical for high reactivity and enantiocontrol.

Instantaneous discharge characteristics and its methane ignition mechanism of coal mine rock damage.

The goaf is the main site of gas explosions in coal mines. A large number of accidents indicate that the occurrence of gas explosion in the goaf is related to the deformation and fracture of the goaf roof. An experimental system was constructed to study the instantaneous discharge characteristics and its ignition mechanism caused by rock damage. The research results reveal that different rocks produce avalanche-like dust clouds ejected outward during the fracture process, and the generation process takes an extremely short time. This dust cloud is not caused by rock fragments heated to incandescence because of friction. The electric sparks produced in the process of rock rupture and the appearance of instantaneous discharge are related not only to the quartz content of the rock, but also to the compressive strength of the rock. The piezoelectric effect of the rock becomes the key factor for the strength or the generation of an electric spark. The instantaneous discharge leaded to the collision of high-energy electrons released during the fracture process with air molecules, ionising, and breaking down the air. When the surrounding medium is gas air within the explosion limit, ionisation is formed and causes gas explosions.

Enantioselective Ni/N-Heterocyclic Carbene-Catalyzed Redox-Economical Coupling of Aldehydes, Alkynes, and Enones for Rapid Construction of Acyclic All-Carbon Quaternary Stereocenters.

Acyclic quaternary carbon stereocenters exist widely in natural products and bioactive molecules, but their enantioselective construction remains a prominent challenge. In particular, multicomponent enantioselective couplings of simple precursors to acyclic all-carbon quaternary stereocenters are very rare. We describe herein an N-heterocyclic carbene (NHC)-Ni catalyzed redox-economical three-component reaction of aldehydes, alkynes, and enones that proceeds in a highly chemo-, regio-, and enantioselective manner. A wide variety of valuable acyclic α-quaternary chiral ketones were synthesized in a single step with 100% atom economy. This reaction proceeds through the formation of a transient cyclic enolate followed by an aldol reaction/ring-opening sequence. The strategy is expected to inspire new and efficient approaches to generate other acyclic quaternary stereocenters.

Enantioconvergent Arylation of Racemic Secondary Alcohols to Chiral Tertiary Alcohols Enabled by Nickel/N-Heterocyclic Carbene Catalysis.

The direct upgrading reaction of simple and readily available achiral alcohols via C-H functionalization is an ideal strategy to prepare value-added chiral higher alcohols. Herein, we disclose the first enantioconvergent upgrading reaction of simple racemic secondary alcohols to enantioenriched tertiary alcohols. An N-heterocyclic carbene (NHC)-nickel catalyst was leveraged to enable this highly efficient formal asymmetric alcohol α-C-H arylation via a dehydrogenation using phenyl triflate as a mild oxidant followed by asymmetric addition of arylboronic esters to the transient ketones. Mechanistic studies and control experiments were conducted to reveal the possible reasons for the exceptional control over chemo- and enantioselectivity.

Low-Temperature Nickel-Catalyzed C-N Cross-Coupling via Kinetic Resolution Enabled by a Bulky and Flexible Chiral N-Heterocyclic Carbene Ligand.

The transition-metal-catalyzed C-N cross-coupling has revolutionized the construction of amines. Despite the innovations of multiple generations of ligands to modulate the reactivity of the metal center, ligands for the low-temperature enantioselective amination of aryl halides remain a coveted target of catalyst engineering. Designs that promote one elementary reaction often create bottlenecks at other steps. We here report an unprecedented low-temperature (as low as -50 °C), enantioselective Ni-catalyzed C-N cross-coupling of aryl chlorides with sterically hindered secondary amines via a kinetic resolution process (s factor up to >300). A bulky yet flexible chiral N-heterocyclic carbene (NHC) ligand is leveraged to drive both oxidative addition and reductive elimination with low barriers and control the enantioselectivity. Computational studies indicate that the rotations of multiple σ-bonds on the C2 -symmetric chiral ligand adapt to the changing needs of catalytic processes. We expect this design would be widely applicable to diverse transition states to achieve other challenging metal-catalyzed asymmetric cross-coupling reactions.

Regio- and Trans-Selective Ni-Catalyzed Coupling of Butadiene, Carbonyls, and Arylboronic Acids to Homoallylic Alcohols under Base-Free Conditions.

We herein report a Ni-catalyzed three-component coupling of 1,3-butadiene, carbonyl compounds, and arylboronic acids as a general synthetic approach to 1,4-disubstituted homoallylic alcohols, an important class of compounds, which have previously not been straightforward to access. The reaction occurs efficiently using a Ni(cod)2 catalyst without any external base and ligand at ambient temperature and allows a highly regioselective and trans-selective 1,4-dicarbofunctionalization of feedstock butadiene in a single operation. This simple and practical protocol could apply to a comprehensive scope of substrates. The neutral conditions show extraordinary tolerance for even highly base-sensitive functional groups.

Research on the prediction of dangerous goods accidents during highway transportation based on the ARMA model.

The COVID-19 epidemic has caused a lack of data on highway transportation accidents involving dangerous goods in China in the first quarter of 2020, and this lack of data has seriously affected research on highway transportation accidents involving dangerous goods. This study strives to compensate for this lack to a certain extent and reduce the impact of missing data on research of dangerous goods transportation accidents. Data pertaining to 2340 dangerous goods accidents in the process of highway transportation in China from 2013 to 2019 are obtained with webpage crawling software. In this paper, the number of monthly highway transportation accidents involving dangerous goods from 2013 to 2019 is determined, and the time series of transportation accidents and an autoregressive moving average (ARMA) prediction model are established. The prediction accuracy of the model is evaluated based on the actual number of dangerous goods highway transportation accidents in China from 2017 to 2019. The results indicate that the mean absolute percentage error (MAPE) between the actual and predicted values of dangerous goods highway transportation accidents from 2017 to 2019 is 0.147, 0.315 and 0.29. Therefore, the model meets the prediction accuracy requirements. Then, the prediction model is applied to predict the number of dangerous goods transportation accidents in the first quarter of 2020 in China. Twenty-two accidents are predicted in January, 23 accidents in February and 27 accidents in March. The results provide a reference for the study of dangerous goods transportation accidents and the formulation of accident prevention and emergency measures.

Fast Enantio- and Chemoselective Arylation of Ketones with Organoboronic Esters Enabled by Nickel/N-Heterocyclic Carbene Catalysis.

A general, efficient, highly enantio- and chemoselective N-heterocyclic carbene (NHC)/Ni-catalyzed addition of readily available and stable arylboronic esters to ketones is reported. This protocol provides unexpectedly fast access (usually 10 min) to various chiral tertiary alcohols with exceptionally broad substrate scope and excellent functional group tolerance (76 examples, up to 98 % ee). This process is orthogonal to other known Ni-mediated Suzuki-Miyaura couplings, as it tolerates aryl chlorides, fluorides, ethers, esters, amides, nitriles, and alkyl chlorides. The reaction is applied to late-stage modifications of various densely functionalized medicinally relevant molecules. Preliminary mechanistic studies suggest that a rare enantioselective η2 -coordinating activation of ketone carbonyls is involved. This cross-coupling-like mechanism is expected to enable other challenging transformations of ketones.

A Bulky Chiral N-Heterocyclic Carbene Palladium Catalyst Enables Highly Enantioselective Suzuki-Miyaura Cross-Coupling Reactions for the Synthesis of Biaryl Atropisomers.

Axially chiral biaryl scaffolds are essential structural units in chemistry. The asymmetric Pd-catalyzed Suzuki-Miyaura cross-coupling reaction has been widely recognized as one of the most practical methods for constructing atropisomers of biaryls. However, longstanding challenges remain in this field. For example, substrate scope is often narrow and specialized, functional groups and heterocycles can lead to reduced reactivity and selectivity, bulky ortho-substituents are usually needed, and reported methods are generally inapplicable to tetra-ortho-substituted biaryls. We have developed an unprecedented highly enantioselective N-heterocyclic carbene (NHC)-Pd catalyzed Suzuki-Miyaura cross-coupling reaction for the synthesis of atropisomeric biaryls. These reactions enable efficient coupling of aryl halides (Br, Cl) or aryl triflates with various types of aryl boron compounds (B(OH)2, Bpin, Bneo, BF3K), tolerate a remarkably broad scope of functional groups and heterocycles (>41 examples), employ low loading of catalyst (0.2-2 mol %), and proceed under mild conditions. The protocol provided general and efficient access to various atropisomeric biaryls and heterobiaryls in excellent enantioselectivities (up to 99% ee) with no need of using bulky ortho-substituted substrates and was effective for the synthesis of tetra-ortho-substituent biaryls. Moreover, the method was successfully applied to the diastereo- and enantioselective synthesis of atropisomeric ternaphthalenes. Critical to the success of the reaction is the development and application of an extremely bulky C2-symmetric chiral NHC, (R,R,R,R)-DTB-SIPE, as the ligand for palladium. To the best of our knowledge, this is the first highly enantioselective (>90% ee) example of a chiral NHC-metal-catalyzed C(sp2)-C(sp2) cross-coupling reaction.

Nickel/NHC-Catalyzed Asymmetric C-H Alkylation of Fluoroarenes with Alkenes: Synthesis of Enantioenriched Fluorotetralins.

Chiral polyfluoroarene derivatives are an important scaffold in chemistry. An unprecedented enantioselective C-H alkylation of polyfluoroarenes with alkenes is described. The reaction employs bulky chiral N-heterocyclic carbene (NHC) ligands for nickel catalysts to enable exclusive activation of C-H bonds over C-F bonds and complete endo-selective C-H annulation and excellent enantioselectivity. A wide variety of chiral fluorotetralins, compounds otherwise difficultly accessed but serve as important bioisosteric analogs of both tetralin and heterocycle units for drug design, are expediently synthesized from easily available substrates. To our knowledge, this is the first example of catalytic enantioselective C-H functionalization of polyfluoroarenes.

Base-catalysed reductive relay hydroboration of allylic alcohols with pinacolborane to form alkylboronic esters.

An unprecedented base-catalysed reductive relay hydroboration of allylic alcohols is described. Commercially available nBuLi was found to be a robust transition metal-free initiator for this protocol, affording various boronic esters in high yield and selectivity. Mechanistically, this methodology involves a one-pot three-step successive process (dehydrocoupling/allylic hydride substitution/anti-Markovnikov hydroboration).

Regio- and Enantioselective C-H Cyclization of Pyridines with Alkenes Enabled by a Nickel/N-Heterocyclic Carbene Catalysis.

Annulated pyridines are ubiquitous scaffolds in many bioactive molecules. A highly regio- and enantioselective Ni(0)-catalyzed endo-selective C-H cyclization of pyridines with alkenes has been developed. An unprecedented enantioselective C-H activation at pyridyl 3- or 4-positions was enabled by bulky chiral N-heterocyclic carbene ligands. This protocol provides expedient access to a series of optically active 5,6,7,8-tetrahydroquinolines and 5,6,7,8-tetrahydroisoquinolines, compounds otherwise accessed with difficulty, in moderate to high yields (up to 99% yield) and enantioselectivities (up to 99% ee). To our knowledge, this is the first example of enantioselective C-H cyclization of pyridines to chiral annulated products.

Enhanced Electrochemical Properties of Zr4+-doped Li1.20[Mn0.52Ni0.20Co0.08]O2 Cathode Material for Lithium-ion Battery at Elevated Temperature.

The typical co-precipitation method was adopted to synthesized the Li-excess Li1.20[Mn0.52-xZr x Ni0.20Co0.08]O2 (x = 0, 0.01, 0.02, 0.03) series cathode materials. The influences of Zr4+ doping modification on the microstructure and micromorphology of Li1.20[Mn0.52Ni0.20Co0.08]O2 cathode materials were studied intensively by the combinations of XRD, SEM, LPS and XPS. Besides, after the doping modification with zirconium ions, Li1.20[Mn0.52Ni0.20Co0.08]O2 cathode demonstrated the lower cation mixing, superior cycling performance and higher rate capacities. Among the four cathode materials, the Li1.20[Mn0.50Zr0.02Ni0.20Co0.08]O2 exhibited the prime electrochemical properties with a capacity retention of 88.7% (201.0 mAh g-1) after 100 cycles at 45 °C and a discharge capacity of 114.7 mAh g-1 at 2 C rate. The EIS results showed that the Zr4+ doping modification can relieve the thickening of SEI films on the surface of cathode and accelerate the Li+ diffusion rate during the charge and discharge process.