Efficient thioacetalisation of carbonyl compounds

The thioacetalisation of a variety of heterocyclic, aromatic, and aliphatic carbonyl compounds (1 mmol) with ethane-1,2-dithiol (1 mmol) using silica sulphuric acid (SSA) is presented as an efficient heterogeneous catalyst under mild and solvent-free conditions at 60°C. The thioacetals were formed within a short reaction time (1–34 min) and isolated with 90–98 % yield following an extractive procedure and chromatography on silica gel. The competitive protection reaction between aldehyde and ketone with ethane-1,2-dithiol afforded the protected derivatives of benzaldehyde and acetophenone with 92 % and 8 % yields, respectively, indicating some selectivity.     

Trichloroisocyanuric Acid (TCCA) and N-Chlorosuccinimide (NCS) as Efficient Reagents for the Direct Oxidative Conversion of Thiols and Disulfides to Sulfonyl Chlorides

Abstract

Trichloroisocyanuric acid (TCCA) and N-chlorosuccinimide (NCS) were found to be mild and efficient reagents for the direct oxidative conversion of sulfur compounds to the corresponding arenesulfonyl chlorides in good-to-excellent yields through the oxidative chlorination. The overall process is simple and practical, and it provides convenient access to a variety of aryl or heteroarylsulfonyl chlorides. The mild reaction conditions and the broad substrate scope render this method attractive and complementary to existing syntheses of aryl or heteroarylsulfonyl chlorides.     

Kinetics and Mechanistic Study of Acetaminophen‐Captopril Interaction by Electrochemical Methods

In this work kinetics parameters and electrochemical mechanism for electrooxidation of acetaminophen in the absence and presence of captopril in a condition close to acetaminophen natural oxidation pathway was investigated. The electrooxidation of acetaminophen in the presence of captopril was investigated by voltammetry and coulometry methods. The results of this work show that acetaminophen is oxidized to its respective p‐quinoneimine. The quinoneimine attacked by captopril, forms thioether. The proposed electrochemical mechanism is ECEC. The estimated value for homogeneous rate constant k_obs is 3.1×10⁴±155 M^?1s^?1 and k_f/k_b is 1.6×10⁸±8.0×10⁵.     

Single‐wall Boron Nitride Nanotube with Various Diameters under the Influence of Electric Field,A Computational Investigation

Structural and electrical response of the (4, 0), (5, 0) and (6, 0) zigzag model of single‐walled boron nitride nanotube (BNNT) with H‐terminated at the open ended, have been investigated under the external electric field (EF) with intensities 0–1.6 × 10^?2 a.u. using the DFT B3LYP/6‐31G* level of theory. Results of this study show that with increasing BNNTs diameter, the HOMO‐LUMO gap (HLG) values increase, and with increasing the EF intensity, the HLG values decrease. In both cases with increasing EF intensity and the BNNT diameters, the electric dipole moment is increased significantly. Also the calculated natural bond orbital (NBO) atomic charges on the atoms of the BNNT show that the separation of the center of the positive and the center of the negative electric charges of the boron nitride nanotubes are increases in both case. We have found that the properties of the BNNTs are dependent on their diameters and can be tuned by applied electric fields intensity.     

The Impact of Organoclay on the Physical and Mechanical Properties of Epoxy-Clay Nanocomposite Coatings

Nanocomposite coatings have recently been of interest because of their superior technical, environmental and economical advantages. Some new solvent free nanocomposite coatings were formulated using epoxy resin and montmorillonie (MMt) nanoclay. The organomodified MMt was well dispersed and partially exfoliated in the epoxy resin. The dispersion process comprised high-shear mixing and ultrasonication. The structure of the resultant coatings was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses. The effect of the clay content on the physical and mechanical properties of the resultant coatings, such as abrasion and impact resistance, hardness, and flexibility were measured and compared with unmodified coatings. The introduction of organoclay up to 4 wt% in coating systems resulted in improvement in the physical and mechanical properties such as hardness (micro and König) and abrasion resistance. Also an increment of up to 3 wt% of organoclay leads to an increase in the impact resistance and flexibility of resultant coating films. On the other hand, flexibility and impact resistance of the coatings containing more than 3 wt% of clay was decreased. The main reason for these observations was agglomeration of the clay particles for high clay-loading compositions.     

Kinetic Study of the Oxidation of Catechols in the Presence of Some Aza‐crown Ethers by Digital Simulation of Cyclic Voltammograms

The electrochemical oxidation of catechols ( 1 ) have been studied in the presence of diaza‐18‐crown‐6 (DA18C6) ( 3a ), diaza‐15‐crown‐5 (DA15C5) ( 3b ), and aza‐15‐crown‐5 (A15C5) ( 3c ) as nucleophiles in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate the participation of electrochemically generated o‐benzoquinones ( 2 ) in Michael‐type reaction with aza‐crown ethers ( 3 ) to form the corresponding new o‐benzoquinone‐aza‐crown ether adducts ( 5 ). Based on ECE mechanism, the observed homogeneous rate constants (k_obs) of the reaction of o‐bezoquinones ( 2 ) with aza‐crown ethers ( 3 ) were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. The calculated observed homogeneous rate constants (k_obs) was found to vary in the order DA18C6>DA15C5>A15C5.     

First principle electric field response of single-walled boron nitride nanotube: a case study of zigzag (4,0) model

Structural and electrical responses of the (4,0) zigzag model of single-walled boron nitride (BN) nanotube (NT) (with edges terminated by H atoms) have been investigated under the external electric fields (parallel and transverse) with strengths 0−2.0 × 10⁻² a.u. using DFT-B3LYP/6-31G* method. Calculated electric dipole moment shows a significant change in the presence of the parallel and perpendicular external electric fields which result in much stronger interactions at higher electric field strengths. Natural bond orbital (NBO) atomic charges analysis shows that the separation of the center of the positive and the center of the negative electric charges of (4,0) zigzag BNNT increase with increase the applied parallel and transverse electric field strengths. The applied fields change the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies and decrease the HOMO–LUMO gap (HLG) values. The calculated electronic spatial extent (ESE) showed small changes of <0.63% and <1.53% over the entire range of the applied parallel and perpendicular electric field strengths, respectively. Results of this study indicate that the properties of BNNTs can be controlled by applying the proper external electric field. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Electrochemical oxidaton of N,N-dialkyl-p-phenylenediamines in the presence of arylsulfinic acids. An efficient method for the synthesis of new sulfonamide derivatives

Electrochemical oxidation of N,N-dialkyl-p-phenylenediamines have been studied in the presence of arylsulfinic acids as nucleophiles in aqueous solutions. The results indicate that the electrochemically generated quinone-imines participate in Michael type addition reaction with arylsulfinic acids and via an EC mechanism convert to the corresponding new sulfonamide derivatives. In this work, an efficient and one-pot electrochemical method for the synthesis of new sulfonamide derivatives in aqueous solution is reported.     

Oxidative Aromatization of 1,3,5‐Trisubstituted 4,5‐Dihydro‐1H‐Pyrazoles Efficiently by Tetrabromine‐1,3,5,7‐Tetrazatricyclo[3.3.1.13,7]Decane Complex,Br4‐Tatcd,as a Novel Reagent both Under Microwave Irradiation and at Room Temperature

Oxidation of 1,3,5‐trisubstituted 4,5‐dihydro‐1H‐pyrazoles to the corresponding pyrazoles has been achieved by utilizing tetrabromine‐1,3,5,7‐tetrazatricyclo[3.3.1.1^3,7]decane complex, Br₄‐TATCD, in glacial acetic acid under microwave irradiation and conventional thermal condition at room temperature with excellent yields.     

Activity and selectivity of Ni nanoclusters in the selective hydrogenation of acetylene: A computational investigation

In this work, the Ni_n (n = 2–10) nanoclusters were investigated to design new catalysts for the selective hydrogenation of acetylene. Our results show that among the Ni_n nanoclusters, the Ni₆ nanocluster can be used as a catalyst in the reactions of hydrogenation. In the presence of the Ni₆ nanocluster, the E_a of the forward step in the reaction of conversion of vinyl to ethylene was 21.21 kJ/mol lower than that of the reverse step in the reaction of conversion of acetylene to vinyl. Also, the E_a of the forward step in the reaction of conversion of ethyl to ethane was 96.59 kJ/mol higher than that of the reverse step in the reaction of conversion of ethylene to ethyl. According to the obtained results, the Ni₆ nanocluster can selectively act in the hydrogenation of a mixture of acetylene and ethylene.