Over recent years, in-depth understanding of the mechanism of oxidative N-heterocyclic carbene (
NHC
) catalyzed reactions in the presence of a mild oxidant and the structure of key radical ...intermediates have been considered as an important challenge in organic chemistry. Furthermore, the role of using a mixture of bases with different strengths is unclear in
NHC
-catalyzed reactions. In this paper, the detailed competing oxidative mechanisms, origin of stereoselectivity, and role of the
NHC
-organocatalyst in the
NHC
-catalyzed reactions of dioxindoles with enals were studied using the density functional theory method. In addition, the roles of newly produced Brønsted acids of the applied bases,
i.e.
DBU·H
+
and
DABCO·H
+
, are examined. The computational results indicated that the oxidation of the Breslow intermediate by nitrobenzene (
NB
) occurs first through a hydrogen atom transfer (HAT) pathway from the Breslow intermediate, and then it is oxidized into acyl azolium by single electron transfer (SET). We found that the energy barrier of the proton transfer processes is remarkably reduced by the conjugated Brønsted acid of the weaker base in the solution. Further, the calculated results revealed that the
NHC
catalyst has different behavior before and after the oxidation of the Breslow intermediate in these reactions. Before oxidation, the nucleophilicity of
R1
increased by adding
R1
to
NHC
, while, after the oxidation process, the electrophilicity of
R1
increases, and as a result the product of oxidation, α, β unsaturated acyl azolium, acts as an electrophile. This mechanistic study paves the way for the rational design of oxidative
NHC
-catalyzed reactions.
In-depth understanding of the mechanism of N-heterocyclic carbene catalyzed reactions in the presence of a mild oxidant is considered.
ABSTRACTThis paper addresses the challenge of quality characteristics that follow an exponential distribution, which can significantly impact decision-making in various fields. Existing approaches ...rely on approximations to convert exponential distributions to normal distributions, upon which control charts are constructed. However, such conversions introduce errors that can lead to incorrect outcomes, particularly for highly sensitive characteristics. To address this limitation, we propose the development of control charts specifically designed for exponential characteristics, without relying on approximations. Our objective is to introduce four different schemes for constructing these control charts: a statistical scheme, an economic scheme, an economic-statistical scheme combined with Taguchi’s loss function, and an economic-statistical scheme without the application of a loss function. To determine optimal design parameter values for each scheme, we employ the artificial bee colony algorithm. Additionally, we conduct a sensitivity analysis to investigate the impact of design parameters on each proposed design. To illustrate the practical implementation of these control charts, we provide a numerical example that demonstrates their effectiveness. By addressing the limitations of existing approaches and offering novel control chart designs, this paper contributes to enhancing decision-making accuracy and reliability in scenarios involving exponentially distributed quality characteristics.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A simple, inexpensive, environmentally friendly and efficient route for the synthesis of benzimidazole and formamidine derivatives by the reaction of O-phenylenediamines or amines with orthoesters ...using hexafluoroisopropanol as a solvent/catalyst is described.
Display omitted
•CuI was supported on magnetically separable mixed-ligand system based on carboxamide and bis(N-heterocyclic thione) donors.•The catalyst was characterized using FT-IR, XRD, SEM, EDX, ...TEM, TGA, VSM and ICP-OES analyses.•The catalyst exhibited high activity for one-pot synthesis of imidazo1,2-apyridines using TBAB/glycerol DES.•Both catalyst and solvent are able to recycle and reuse several times.
A Cu-incorporated nanocatalyst has been developed by immobilizing copper iodide on a magnetically retrievable mixed-donor ligand system, containing carboxamide, imidazolidine-2-thione and imidazole-2-thione donor groups and characterized by various analysis techniques such as FT-IR, XRD, FE-SEM, EDX elemental mapping, TEM, ICP-OES, TGA, and VSM. The versatility of the synthesized nanocatalyst has been demonstrated for the one-pot synthesis of imidazo1,2-apyridine derivatives via three-component reaction of 2-aminopyridines, aldehydes and alkynes using tetrabutyl ammonium bromide/glycerol (TBAB/glycerol) deep eutectic mixture as a sustainable medium. The nanocatalyst has exhibited high activity and stability under the reaction conditions with a negligible copper leaching, which can be due to the effective coordination interaction between the oxygen atom of carbonyl group as well as the sulfur atoms of thiocarbonyl groups in the supported ligand with copper iodide. The catalyst system can be readily recovered and successfully reused at least five times. Eco-friendly conditions, solvent recoverability, higher TON, wide functional group tolerance and lower E factor (0.2) are some other merits of the present work.
•A simple novel strategy for direct oxidation of organic halides and alcohols to aldehyde and its derivatives.•Taking advantage of ionic liquids as a safe oxidant.•Utilizing ionic liquids as oxidant ...and solvent simultaneously for the oxidation reaction.
Choline nitrate is prepared by the anion exchange of choline chloride and sodium nitrate. Also, choline chloride gives a low melting point mixture in the presence of aluminum nitrate. The use of choline nitrate as a safe and environmentally friendly solvent and reactant provides an efficient procedure, simple and mild for oxidizing alcohols and organic halides to aldehydes. Aldehydes using choline nitrate and trimethylsilyl chloride mixture as a selective oxidant and without using catalysts were synthesized from alcohols and the relevant halides. Benzyl chloride in the presence of choline nitrate and trimethylsilyl chloride at 70 °C produced the corresponding aldehyde product with 87% efficiency, while benzyl alcohol at 50 °C with 90% efficiency performed this conversion.The prepared aldehyde is easily separated from the reaction medium by vacuum distillation or extraction by organic solvent without the need for further purification.
Display omitted
Hepatitis B virus (HBV) infection is a worldwide public health problem. In this paper, we study the dynamics of hepatitis B virus (HBV) infection which can be controlled by vaccination as well as ...treatment. Initially we consider constant controls for both vaccination and treatment. In the constant controls case, by determining the basic reproduction number, we study the existence and stability of the disease-free and endemic steady-state solutions of the model. Next, we take the controls as time and formulate the appropriate optimal control problem and obtain the optimal control strategy to minimize both the number of infectious humans and the associated costs. Finally at the end numerical simulation results show that optimal combination of vaccination and treatment is the most effective way to control hepatitis B virus infection.
Nowadays, recognizing the current situation and forecasting the desired status of spatial analysis of infrastructures regarding security and defense considerations is of great importance. Besides, ...the use of approaches such as futures studies and its simultaneous application with GIS has the most fundamental contribution to the field of decision-making and appropriate planning method in studies on the spatial defense planning. Accordingly, this paper aims to evaluate the spatial distribution of regional infrastructures in the northeast of Iran using a passive defense approach. In this regard, a descriptive-analytical research methodology, library-documentary studies, and statistical surveys were used in the model framework along with software (Mic Mac and Scenario Wizard) and system analysis (GIS) to achieve the research objective. The statistical population of the study was defined in two human and spatial scales. The entire geographical space of Khorasan Razavi province made the spatial scale. On the human scale, 40 experts (n = 15) and elites (n = 25) in the field of this study were selected as the statistical sample using a purposive non-random model. It is noteworthy that all of the subjects had the required scientific and executive knowledge. According to the total research indicators, the vulnerable zones of the study area could be distinguished into five categories of areas with very high (7.33%), high (16.52%), moderate (29.78%), low (16.94%), and very low (29.4%) vulnerability. Also, according to the results, the density and dispersion patterns of the study area infrastructures were concentrated, clustered, and randomly self-clustered, respectively. In the meantime, factors such as legal, policy, and institutional infrastructure criteria were identified as key drivers influencing the spatial distribution of the province infrastructures. Therefore, it is possible to realize the future models in three scenarios of high desirability (green status), acceptable (yellow status), and crisis (red status). Finally, the paper concludes with some suggestions to increase the desirability of infrastructures in Khorasan Razavi province.
Spatial futures studies; Passive defense; Regional infrastructure; Regional development.
A new mild and chemoselective method for mono‐N‐protection of amines and amine derivatives as tert‐butoxycarbonyl derivatives is reported. The reaction proceeds with lithium perchlorate (20 mol %) ...and pyrocarbonates, and shows general applicability. The catalytic action of LiClO4 is specific for the activation of Boc2O, thus acid‐sensitive functionalities of the starting materials remain unchanged in the protection process. This procedure works well for sterically hindered primary amine as well as electron‐deficient primary arylamines, primary and secondary amino alcohols, α‐amino acid esters, hydroxylamines, hydrazines and sulfonamides.
Brucellosis and Crimean Congo Hemorrhagic Fever (CCHF) are both common zoonoses that may co-occur in similar epidemiological conditions, e.g., among young livestock breeders, veterinarians, and ...farmers in rural areas. Transmission of Brucella bacteria is through ingestion of contaminated dairy products, while CCHF virus infection occurs via infective tick bite or exposure of damaged skin and mucosa to the tissues and blood of viremic animals. Brucellosis occurs almost in all seasons, while CCHF is of lower incidence in the cold seasons due to decreased activity of tick vectors. CCHF mimics brucellosis and vice versa, mainly when the latter manifests severe thrombocytopenia and hemorrhage. Occasionally, the two illnesses present similar clinical features and laboratory results, e.g., fever, muscle aches, increased liver enzymes, and thrombocytopenia. This article discusses the similar clinical, epidemiological and laboratory aspects of the two diseases and warns physicians to avoid the inappropriate use of drugs such as ribavirin, which is dangerous in patients with kidney failure and pregnancy.
Since the data about this phenomenon is binary, meaning the presence or absence of an event, so it applied the binary logistic regression model for the binary response variable in which the dependent ...variable is either equal to one for the occurrence of the event or zero for the absence of the event. The research aims to use this model to obtain the most important factors affecting cancerous tumors. The study included cancerous tumor data from the Ministry of Health and the Tumor Teaching Hospital, The statistical program (SPSS). The conclusions showed that the logistic regression model is suitable for testing the data and does not suffer from the problem of multilinearity. As well as six factors affecting cancer diseases (Smoking, chronic diseases, family history, weight, height, and marital status), but sex does not have a significant effect on cancerous diseases, according to the sample drawn.
PDF
