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Dirhodium tetraacetate catalyzed reaction of α-diazo-β-keto-carboxylates and -phosphonates with arenecarboxamides gives 2-aryloxazole-4-carboxylates and 4-phosphonates by carbene N-H insertion and cyclodehydration. In stark contrast, dirhodium tetrakis(heptafluorobutyramide) catalysis results in a dramatic change of regioselectivity to give oxazole-5-carboxylates and 5-phosphonates. α-Diazo-β-ketosulfones behave similarly and give 5-sulfonyloxazoles upon dirhodium tetrakis(heptafluorobutyramide) catalyzed reaction with carboxamides. The analogous reactions of thiocarboxamides give the corresponding thiazole-5-carboxylates, -phosphonates, and -sulfones. [ABSTRACT FROM AUTHOR]

SiO 2 aerogels have attracted extensive attention due to their unique structural characteristics, which exhibit many special properties, especially good optical transparency. As far as we know, the sol-gel stage during the synthesis of aerogel plays an important role in the construction of the gel skeleton. In this study, we adjusted the amount of silicon source and catalyst to explore the best scheme for preparing highly transparent SiO 2 aerogels, and further clarify the effects of both on the properties of SiO 2 aerogels. Results indicated that the pore size distribution was between 10 and 20 nm, the thermal conductivity was between 0.0135 and 0.021 W/(m·K), and the transmittance reached 97.78% at 800 nm of the aerogels, better than most studies. Therefore, it has the potential to be used in aerogel glass for thermal insulation.

In this work, three-dimensional numerical simulations with a simplified reaction mechanism are conducted to investigate the effect of implementing a perforated plate in an ammonia-fueled micro-power systems on the NO x emission behavior. Detailed analyses on 1) the perforated plate hole dimensionless width w, dimensionless location l as well as the material property are performed. Results show that with an optimized perforated plate implemented, the NO emission is reduced by up to 73.3 % compared to those in the absence of perforated plates. The decrease is mainly due to the formation of a recirculation zone with a low flame temperature. Increasing w is shown to play a positive role in minimizing the NO generation, while l leads to a reverse trend resulting from the size variation of the recirculation zone. In contrast, the plate material has a negligible effect on NO x emissions. It is also shown that the pressure loss P loss is varied non-monotonically with l, but monotonically with w and the NH 3 volumetric flow rate. Furthermore, the conjugate heat transfer between the plate and combustion products has a certain impact on P loss . The present work shed lights on reducing NO x emissions by implementing a well-designed perforated plate for practical micro-power systems., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A simple, new three-step sequence for the conversion of hydrazides into pyridines is reported in which the key steps are N-H insertion by a copper carbene intermediate derived from alpha-diazo-beta-ketoesters into the hydrazide, reaction with ammonium acetate to give 1,2,4-triazines, followed by Diels-Alder reaction with norbornadiene.