A Convenient Synthesis Of 2-Methyl-5-(Methylthio)Benzothiazole

A convenient and efficient four step synthesis of 2-methyl-5-(methylthio)benzothiazole is presented.     

Solvent-Free C-Benzoylation and N-Benzoylation Reactions Using Microwave Heating

An ecofriendly and efficient microwave-irradiated solvent-free benzoylation method was developed. The procedure for C-benzoylation used 50 mol% AlCl₃ as a Lewis acid catalyst at 130 °C and was completed in 10 min. The isolated yield was between 71% and 100%. N-benzoylation was conducted in a catalyst-free environment at 130 °C in 10 min. The isolated yield was between 80% and 100%.

A Silyliumylidene Cation Stabilized by an Amidinate Ligand and 4‐Dimethylaminopyridine

The synthesis and reactivity of a silyliumylidene cation stabilized by an amidinate ligand and 4‐dimethylaminopyridine (DMAP) are described. The reaction of the amidinate silicon(I) dimer [ L Si:]₂ ( 1 ; L =PhC(NtBu)₂) with one equivalent of N‐trimethylsilyl‐4‐dimethylaminopyridinium triflate [4‐NMe₂C₅H₄NSiMe₃]OTf and two equivalents of DMAP in THF afforded [ L Si(DMAP)]OTf ( 2 ). The ambiphilic character of 2 is demonstrated from its reactivity. Treatment of 2 with 1 in THF afforded the disilylenylsilylium triflate [ L′ ₂( L )Si]OTf ( 3 ; L′ = L Si:) with the displacement of DMAP. The reaction of 2 with [K{HB(iBu)₃}] and elemental sulfur in THF afforded the silylsilylene [ L SiSi(H){(NtBu)₂C(H)Ph}] ( 4 ) and the base‐stabilized silanethionium triflate [ L Si(S)DMAP]OTf ( 5 ), respectively. Compounds 2 , 3 , and 5 have been characterized by X‐ray crystallography.     

From Nongelating to Gelating: Synthesis and Structural Self‐Assembling Property Relationships of a Homologous Series of Oligo(amide–triazole)s

A homologous series of oligo(amide–triazole)s (OAT) [ OAT‐CO₂H‐2 n and OAT‐COPrg‐(2 n +1) ] with an increasing number of primary amide (CONH) and triazole hydrogen‐bonding functionalities was prepared by an iterative synthetic procedure. It was found that their self‐assembly and thermoreversible gelation strength had a strong correlation to the number of hydrogen‐bonding moieties in the oligomers. There also existed a threshold value of the number of CONH units, above which all the oligomers became organogelators. Hence, oligomers with ≤4 CONH units are devoid of intermolecular hydrogen bonding and also non‐organogelating, whereas those that contain >4 CONH units show intermolecular association and organogelating properties. For the organogelators, the T_gel value increases monotonically with increasing number of CONH units. On the basis of FTIR measurements, both the CONH and triazole C? H groups were involved in the hydrogen‐bonding process. A mixed xerogel that consisted of a 1:1 weight ratio of two oligomers of different lengths ( OAT‐CO₂H‐6 and OAT‐CO₂H‐12 ) was found to show microphase segregation according to differential scanning calorimetry, thus indicating that oligomers that bear a different number of hydrogen‐bonding units exhibited self‐sorting to maximize the extent of intermolecular hydrogen bonding in the xerogel state.     

Purity assessment for avoparcin

Well-characterized pure-substance reference materials for the use as calibrants are essential to establish the metrological traceability of the results of chemical measurements. Normally, the characterization of this type of reference material is conducted through a thorough purity assessment of the compound concerned. For this reason, studies on purity assessment, especially for neat organic compounds, continues as an important part of work being undertaken by metrological institutions around the world. Among others, the need for certified pure reference standards continues to increase for residues analysis in foods, particularly for those compounds which have been banned for food safety reasons, but their residues in foods are still monitored under food surveillance program in many countries. In this respect, avoparcin serves as a very good example where testing laboratories have difficulties in obtaining traceable and comparable results on determination of avoparcin in food matrix samples due, in part, to the unavailability of certified pure-substance reference material as calibrant. In this study, it was attempted to assess the purity of a commercially available test material of avoparcin using the mass balance approach. The objective of this paper is to share the difficulties encountered during the course of purity assessment and how they were addressed. As expected, the most challenging part of work was to identify and estimate the amount of unknown impurities, both organic and inorganic-related ones, given the chemical structure and properties of avoparcin. For instance, avoparcin exists in two forms in the test material, i.e., α- and β-avoparcin, and they were found to be susceptible to hydrolysis under certain conditions.     

Influence of Substitutional Defects in ZIF-8 Membranes on Reverse Osmosis Desalination: A Molecular Dynamics Study

In this study, molecular dynamics simulation is used to investigate the effects of water-based substitutional defects in zeolitic imidazolate frameworks (ZIF)-8 membranes on their reverse osmosis (RO) desalination performance. ZIF-8 unit cells containing up to three defect sites are used to construct the membranes. These substitutional defects can either be Zn defects or linker defects. The RO desalination performance of the membranes is assessed in terms of the water flux and ion rejection rate. The effects of defects on the interactions between the ZIF-8 membranes and NaCl are investigated and explained with respect to the radial distribution function (RDF) and ion density distribution. The results show that ion adsorption on the membranes occurs at either the nitrogen atoms or the defect sites. Complete NaCl rejection can be achieved by introducing defects to change the size of the pores. It has also been discovered that the presence of linker defects increases membrane hydrophilicity. Overall, molecular dynamics simulations have been used in this study to show that water-based substitutional defects in a ZIF-8 structure reduce the water flux and influence its hydrophilicity and ion adsorption performance, which is useful in predicting the type and number of defect sites per unit cell required for RO applications. Of the seven ZIF-8 structures tested, pristine ZIF-8 exhibits the best RO desalination performance.     

Shear zones and wall slip in the capillary flow of concentrated colloidal suspensions

We image the flow of a nearly random close packed, hard-sphere colloidal suspension (a "paste") in a square capillary using confocal microscopy. The flow consists of a "plug" in the center while shear occurs localized adjacent to the channel walls, reminiscent of yield-stress fluid behavior. However, the observed scaling of the velocity profiles with the flow rate strongly contrasts yield-stress fluid predictions. Instead, the velocity profiles can be captured by a theory of stress fluctuations originally developed for chute flow of dry granular media. We verified this both for smooth and rough walls.     

Time-dependent discrete road network design with both tactical and strategic decisions

This paper aims to model and investigate the discrete urban road network design problem, using a multi-objective time-dependent decision-making approach. Given a base network made up with two-way links, candidate link expansion projects, and candidate link construction projects, the problem determines the optimal combination of one-way and two-way links, the optimal selection of capacity expansion projects, and the optimal lane allocations on two-way links over a dual time scale. The problem considers both the total travel time and the total CO emissions as the two objective function measures. The problem is modelled using a time-dependent approach that considers a planning horizon of multiple years and both morning and evening peaks. Under this approach, the model allows determining the sequence of link construction, the expansion projects over a predetermined planning horizon, the configuration of street orientations, and the lane allocations for morning and evening peaks in each year of the planning horizon. This model is formulated as a mixed-integer programming problem with mathematical equilibrium constraints. In this regard, two multi-objective metaheuristics, including a modified non-dominated sorting genetic algorithm (NSGA-II) and a multi-objective B-cell algorithm, are proposed to solve the above-mentioned problem. Computational results for various test networks are also presented in this paper.     

Gold‐Catalyzed Cycloisomerization of 1,6,8‐Dienyne Carbonates and Esters to cis‐Cyclohepta‐4,8‐diene‐Fused Pyrrolidines

A synthetic approach that provides access to cis‐cyclohepta‐4,8‐diene‐fused pyrrolidines efficiently through Au^I‐catalyzed cycloisomerization of 1,6,8‐dienyne carbonates and esters at a low catalyst loading of 2 mol % is reported. Starting carbonates and esters with a pendant alkyl group on the terminal alkenyl carbon center were found to favor tandem 1,2‐acyloxy migration/cyclopropanation followed by Cope rearrangement of the resulting cis‐3‐azabicyclo[3.1.0]hexane intermediate. On the other hand, substrates containing a terminal diene or starting materials in which the distal alkene moiety bears a phenyl substituent were observed to undergo competitive but reversible 1,3‐acyloxy migration prior to the nitrogen‐containing bicyclic ring formation. The delineated reaction mechanism also provides experimental evidence for the reversible interconversion between the oft‐proposed organogold intermediates obtained in this step of the tandem process.