Mild and efficient synthesis and base-promoted rearrangement of novel isoxazolo[4,5-b]pyridines.

An efficient method for the synthesis of isoxazolo[4,5-b]pyridines has been developed on the basis of readily available 2-chloro-3-nitropyridines via the intramolecular nucleophilic substitution of the nitro group as a key step. The previously unknown base-promoted Boulton-Katritzky rearrangement of isoxazolo[4,5-b]pyridine-3-carbaldehyde arylhydrazones into 3-hydroxy-2-(2-aryl[1,2,3]triazol-4-yl)pyridines was observed.

Prediction of control temperature and emergency temperature of monadic/binary aromatic nitro compounds by quantitative structure-property relationship: correlation study of self-accelerating decomposition temperature in thermal hazard assessment.

CONTEXT: The thermal hazard of reactions caused by the structural instability of aromatic nitro compounds is a major concern in the field of chemical process safety and one of the main causes of major thermal runaway (TR) accidents such as fire and explosion. Among them, the self-accelerating decomposition temperature (SADT), as an important parameter, has been widely used to evaluate the thermal hazards of aromatic nitro compounds in actual storage and transportation processes. However, the control temperature (CT) and emergency temperature (ET), which depend on and are associated with SADT, have been rarely reported in previous studies. In this work, multiple linear regression (MLR) and artificial neural network (ANN) models for CT and ET were constructed based on the molecular descriptors corresponding to the stable structures of 27 monadic/binary aromatic nitro compounds, combined with advanced adiabatic accelerating calorimetric experiments and quantitative structure-property relationship (QSPR). The optimal subset of descriptors with significant contributions was screened out while the fit, predictive ability, and robustness of the four types of models were evaluated with internal and external validation parameters, and finally, two types of parameters (R2 and ARE) were selected as the main indicators for a comprehensive comparative analysis. The results show that the four models fit the experimental data well. During this period, the accuracy of ANN models is slightly higher than that of MLR models, and the QSPR models under the two modes (linear and nonlinear) are more inclined toward ET in prediction ability. Based on simplifying the calculation process and realizing rapid parameter prediction, this study is expected to provide technical support for engineering applications such as safe operation, safe storage and transportation of substances, and emergency response in the chemical industry. METHODS: In this work, we tested and calculated the thermal safety parameters of 27 monadic/binary aromatic nitro compounds by ARC and AKTS and further used the PubChem database and Gaussian 09 software program to obtain and optimize their corresponding molecular structures. The geometric optimization process adopts DFT on the B3LYP level and the 6-31 + G(d, p) basis set, while the same functional and basis set was used for vibration analysis. The OpenBabel toolbox and ChemDES platform were used for transformation coding and descriptor calculation. Finally, IBM SPSS Statistics 24 and MATLAB software were used to construct MLR models and ANN models, respectively.

Straightforward and Efficient Protocol for the Synthesis of Pyrazolo [4,3-b]pyridines and Indazoles.

An efficient method for the synthesis of pyrazolo [4,3-b]pyridines has been developed on the basis of readily available 2-chloro-3-nitropyridines via a sequence of SNAr and modified Japp-Klingemann reactions. The method offers a number of advantages including utilization of stable arenediazonium tosylates, operational simplicity as well as combining the azo-coupling, deacylation and pyrazole ring annulation steps in a one-pot manner. An unusual rearrangement (C-N-migration of the acetyl group) was observed and a plausible mechanism was proposed based on the isolated intermediates and NMR experiments. In addition, the developed protocol was successfully applied to the synthesis of 1-arylindazoles combining the Japp-Klingemann reaction and cyclization of the resulting hydrazone as a one-pot procedure.

The Combined Effect of Ambient Conditions and Diluting Salt on the Degradation of Picric Acid: An In Situ DRIFT Study.

An unexpected promoting effect of KBr, used as a diluting salt, on the degradation of picric acid (PA) was observed during in situ diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy experiments performed here under accelerated ageing conditions-at 80 °C and under an inert or oxidative atmosphere. While the formation of potassium picrate was excluded, this promoting effect-which is undesired as it masks the possible effects of test conditions on the ageing process of the material-was assumed to favor a first step of the decomposition mechanism of PA, which involves the inter- or intramolecular transfer of hydrogen to the nitro group, and possibly proceeds up to the formation of an amino group. An alternative diluting salt, ZnSe, which is much less commonly used in infrared spectroscopy than KBr, was then proposed in order to avoid misleading interpretation of the results. ZnSe was found to act as a truly inert diluting salt, preventing the promoting effect of KBr. The much more chemically inert nature (towards PA) of ZnSe compared to KBr was also confirmed, at much higher temperatures than DRIFT experiments, by dynamic differential scanning calorimetry (DSC) runs carried out on pure PA (i.e., PA without salt) and PA/salt (ZnSe or KBr) solid mixtures.

Catecholic alkaloid sulfonates and aromatic nitro compounds from Portulaca oleracea and screening of their anti-inflammatory and anti-microbial activities.

Acidic compounds were enriched from a water decoction of Portulaca oleracea using 717 anion exchange resin column chromatography. A total of 22 compounds including 9 catecholamine derivatives, of which six were rare sulfonic acid derivatives, and 9 nitro derivatives, were further isolated through various column chromatographic methods, and their structures were elucidated by interpreting their spectroscopic data and ECD calculations. Among them, 16 compounds were isolated from P. oleracea for the first time, 8 of which were undescribed compounds and four compounds were natural products. Pharmacological screening indicated that cis-3-(3-nitro-4-hydroxyphenyl)-methyl acrylate exhibited anti-inflammatory activity, measured as inhibition of nitric oxide production in LPS-stimulated RAW264.7 macrophage cells, with an EC50 value of 18.0 µM, The compounds showed only weak anti-microbial activity with (2R)-(+)-2-chloro-3-(3-nitro-4-hydroxyphenyl)-propionic acid methyl ester inhibiting Candida albicans with a MIC of 256 µg/mL, and 3-methoxy-4,5-dinitrophenol inhibiting Shigella sonnei with a MIC of 512 µg/mL.

Carbon quantum dots @ Pd-SnS2 nanocomposite: The role of CQDs @ Pd nanoclusters in enhancing photocatalytic reduction of aromatic nitro compounds.

2D layered SnS2 is one of the most popular semiconductor photocatalysts. However, its performance on photocatalytic reduction of aromatic nitro compounds is unsatisfactory, due to charge carrier recombination and weak adsorption of active hydrogen from the hydrolysis of NaBH4. Herein, we have prepared CQDs @ Pd nanoclusters with Pd nanoparticles below 5 nm through an in-situ reducing Pd(Ⅱ) with CQDs containing some oxygen-containing groups at first. CQDs @ Pd-SnS2 is achieved through a strong interaction of sulfur ions bonding on nanometric Pd surface. The composite shows a stable and efficient visible-light-driven catalytic reduction of aromatic nitro compounds in H2O and NaBH4. Under 40 min visible light irradiation, the conversion rate of 4-NP attains 99.7% on CQDs @ Pd-SnS2. The first order reaction rate constant is 0.0332 min-1, 586.5, 202.4 and 31.9 times that on SnS2, CQDs-SnS2 and Pd-SnS2 in the condition of 20 mg·L-1 4-NP and excess NaBH4, respectively. The significant enhancement is ascribed to CQDs @ Pd promoting the charge carrier separation on SnS2 and increasing the adsorption of active hydrogen from the hydrolysis of NaBH4.

Copper nanoparticles on graphene support: an efficient photocatalyst for coupling of nitroaromatics in visible light.

Copper is a low-cost plasmonic metal. Efficient photocatalysts of copper nanoparticles on graphene support are successfully developed for controllably catalyzing the coupling reactions of aromatic nitro compounds to the corresponding azoxy or azo compounds under visible-light irradiation. The coupling of nitrobenzene produces azoxybenzene with a yield of 90 % at 60 °C, but azobenzene with a yield of 96 % at 90 °C. When irradiated with natural sunlight (mean light intensity of 0.044 W cm(-2) ) at about 35 °C, 70 % of the nitrobenzene is converted and 57 % of the product is azobenzene. The electrons of the copper nanoparticles gain the energy of the incident light through a localized surface plasmon resonance effect and photoexcitation of the bound electrons. The excited energetic electrons at the surface of the copper nanoparticles facilitate the cleavage of the NO bonds in the aromatic nitro compounds. Hence, the catalyzed coupling reaction can proceed under light irradiation and moderate conditions. This study provides a green photocatalytic route for the production of azo compounds and highlights a potential application for graphene.