Journal of Chemical Sciences最新文献

Thiols are ubiquitous compounds found in almost all spheres of life, viz: from simple matter to complex human body. It has widespread applications in diverse domains such as pharmaceuticals, materials, agricultural science, fire science, laser science, catalytic systems, reagent systems, and industry. Although all sulphur compounds encompass one or the other significant properties. However, thiols containing –SH bond are vital as they act as starting substrates for many chemical reactions, are directly present in the biological systems, are abundantly found in natural products, and exhibit profound chemical and biotechnological properties. For example, the –SH group can be easily manipulated to a range of other potent functionalities such as –S–S, –SO₂Cl₂, –SOCH₃, –SOCl₂, –SONH₂, –Cl, –NH₂, –OH, etc. In this view, this review focuses on reporting detailed synthetic methodologies giving access to thiols (–SH). For interesting reading, it has been categorised as follows: (i) via isothiouronium salts; (ii) catalytic preparation of thiols using H₂S; (iii) using silanethiol/disilathiane; (iv) using thiolacetic acid/thioacetates; (v) from xanthates; (vi) reaction of sodium thiocyanate; (vii) using sodium trithiocarbonates; (viii) using Lawesson’s reagent; (ix) using phosphorus decasulfide; (x) enzymatic method; and the rest of a methods are classified under miscellaneous section.

Graphical abstract

Synthetic methodologies to form terminal –SH bonds using various reagent systems, viz; (i) isothiouronium salts; (ii) catalytic preparation using H₂S; (iii) silanethiol/disilathiane; (iv) thiolacetic acid/thioacetates; (v) xanthates; (vi) reaction of sodium thiocyanate; (vii) sodium trithiocarbonates; (viii) Lawesson’s reagent; (ix) phosphorus decasulfide and (x) few enzymatic methods.

Among the various Schiff bases, those containing 2,4-diaminotoluene as a primary amine and 2-hydroxy-4-methoxybenzaldehyde as a carbonyl compound are new and deserve special attention because their logical spectral properties find application in analytical chemistry as a smart probe. The new Schiff base has been synthesized to its pure crystalline form. It is characterized by single-crystal XRD, FT-IR, NMR, TGA, and mass spectrometry. We have studied the spectral properties of the Schiff base and its aluminium adduct by UV-vis and fluorescence spectroscopy and rationalized them by computational analysis. The Job's plot and mass spectrometry indicate the 1:1 binding ratio between the ligand and the Al³⁺ ion. The suitable binding constant value (8.329×10³ M^–1) leads to the development of Al³⁺ sensation by the Schiff base. The sensor has an appreciably low limit of detection value of 7.638×10^–9(M), i.e., 0.00163 ppm for Al³⁺. The logical behaviour of the probe (NAND-type molecular logic gate with two inputs, Al³⁺ and EDTA) leads to the development of a renewable aluminium testing kit.

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The synthesis of poly(4-vinylbenzyl-g-β-butyrolactone) (poly(VB-g-BL)) graft copolymer was carried out by “click” chemistry of terminal azido poly(4-vinylbenzyl chloride) (PVB-N₃) and terminal propargyl poly(β-butyrolactone) (β-BL-propargyl). For this purpose, poly(4-vinylbenzyl chloride) (poly-4-VBC) was obtained using 4-vinylbenzyl chloride and 2,2′-azobis(2-methylpropionitrile) by free-radical polymerization. PVB-N₃ was synthesized using sodium azide and poly-4-VBC. β-BL-propargyl was obtained by the reaction of β-butyrolactone monomer with propargyl alcohol via ring-opening polymerization. The graft copolymer was also synthesized via “click” chemistry, employing PVB-N₃ and β-BL-propargyl. The products were thoroughly characterized by GPC, FT-IR, SEM, and ¹H-NMR. DSC and TGA were used to track the graft copolymer’s thermal characteristics. Thermal and spectroscopic measurements verified that the reactions were effectively completed.

Graphical abstract

Poly(4-vinylbenzyl chloride) was obtained by free-radical polymerization. Terminal azido poly(4-vinylbenzyl chloride) was synthesized using sodium azide and poly(4-vinylbenzyl chloride). Terminal propargyl poly(β-butyrolactone) was obtained by β-butyrolactone and propargyl alcohol via ring-opening polymerization. Poly(4-vinylbenzyl-g-β-butyrolactone) graft copolymer was synthesized by “click” chemistry. Thermal and spectroscopic measurements verified that the reactions were completed.

Hydrophobic surface modification is an emerging concept for electrochemical gas-phase reactions like nitrogen reduction reaction to ammonia as the restricted surface wettability helps to surpass the competitive hydrogen evolution reaction. However, the extensive studies on this strategy lack a discussion on the influence of substrates on the stability of the hydrophobic coating. The present work summarizes a case study on the substrate-dependent electrochemical behaviour of the alkanethiol-coated flattened Cu foil and porous dendritic Cu foam surfaces. NRR studies reveal that the porous dendritic architecture with electrified tips and the hydrophobic coating-induced gas diffusion layer proved to be beneficial for NRR activity in Cu foam-SH. However, for a prolonged experimental hour, the flattened surface of the Cu foil could better hold the hydrophobic coating. The results corresponded with water contact angle as well as double layer capacitance measurements and a detailed X-ray photoelectron spectroscopy study. It is supposed that the prolonged exposure to applied potential alters the polarization of the Cu dendritic tips and weakens the Cu–S bond, loosening the alkanethiol layer over Cu foam.

Graphical abstract

Hydrophobic Cu substrates facilitate electrochemical nitrogen reduction reactions owing to the better N₂ diffusion and trapping underneath the hydrophobic coating. While the NRR activity gets accelerated at the electrified dendritic tips of Cu foam, the steady hydrophobic layer over the flattened Cu foil surface ascertains long-term use of the material.

For relatively newer developments such as Li–S battery, polysulphide shuttle effect, volume expansion, and low conductivity of sulphur have been the main hurdles in the path towards its commercialisation. To get rid of the polysulphide shuttle effect, we looked at the binder material of the cathode component. An attempt at keeping up with the capacity while making components sustainable led us to explore a protein-based biopolymer, zein. The carbonyl-rich binder helped to glue the components together while the long chain of amino acids aided in preserving the performance. The UV-visible spectroscopy technique verified the adsorption of polysulphides by zein and activated carbon. The carbon host used for this study possessed a high Bruner Emmet Teller (BET) surface area of around 1900 m² g^–1, which helped to load higher amounts of sulphur, as revealed by thermogravimetric analysis. Owing to a porous host, the volume expansion effect could also be buffered to maintain the performance as observed through stability studies. The cycling study of zein binder containing cathode showed an enhanced performance of around 100 mAh g^–1 throughout the 250 cycles compared to the PVDF binder containing cathode.

Catalysts based on KL-zeolite exchanged with alkali metal ions (Rb⁺ and Cs⁺) were studied for conversion of ethanol to oligomerization through the Guerbet reaction pathway. The catalysts were characterized by techniques such as ICP-AES, FESEM-EDX, N₂-adsorption-desorption, and CO₂-TPD to assess their physio-chemical properties. Effects of operating parameters, namely reaction temperature, pressure, and feed flow rate on catalytic activity for the conversion of ethanol to n-butanol were examined. Furthermore, influence of alkali metal loading on KL-zeolite was explored. Substantial ethanol conversion (42.6%) and n-butanol yield (13.9%) were achieved at 450°C and 30 kg/cm² after a 6 h reaction employing Cs-KL zeolite catalyst. Observations indicated that the butanol selectivity is highest among the reported literature. Additionally, this catalyst has exhibited low deactivation rate attributable to coke formation. Spent catalysts were studied for XRD and DTG/TGA analysis. Present investigation establishes that KL-zeolite, particularly when modified with alkali metal ions, proves to be an efficient catalyst for the Guerbet conversion of ethanol, highlighting its potential for ethanol upgrading.

Efficient and durable non-precious cathode catalysts are needed at this hour for the development of fuel cells and metal-air batteries. The instability of one of the well-studied non-precious catalysts, Fe–N–C, in acidic electrolytes and its inferior bifunctional electrocatalytic activity in alkaline electrolytes, shifts the attention towards other electrocatalysts based on Ni and Co. Herein, we demonstrate the synthesis of nitrogen and transition metal (M=Co, Ni) co-doped mesoporous carbon (Co/Ni–N–mC) catalysts for bifunctional oxygen electrocatalysis. The synthetic approach involves the thermal annealing-induced transformation of the graphitic carbon nitride (g–C₃N₄) to nitrogen-doped graphitic mesoporous carbon (N–mC). The Co–N–mC catalyst has superior bifunctional oxygen electrocatalytic activity. It promotes the 4-electron pathway for the reduction of oxygen to water and is highly durable in alkaline electrolyte. The bifunctional activity is evaluated in terms of the potential gap (ΔE). The small ΔE for Co–N–mC makes it suitable for metal-air batteries. The rechargeable zinc-air battery is fabricated with Co–N–mC and it delivers a specific capacity of 718 mAh g⁻¹_Zn and a power density of 122.2 mW/cm² with long-time charge-discharge cycling stability for 100 h. The synergistic effect between metal nanoparticles and nitrogen-doped carbon matrix, as well as the post-synthetic surface engineering-induced morphological changes, account for the enhanced activity.

Graphical abstract

The transformation of supramolecular aggregate-derived metal-doped graphitic carbon nitride to electrocatalytically highly active nitrogen-doped mesoporous carbon and its electrocatalytic performance for aqueous rechargeable zinc-air battery is demonstrated.

In this work, we present the CO oxidation by molecular and atomic oxygen on the Cu₃ site of the Cu₁₉ cluster employing the density functional theory (DFT)-PW91PW91/[LANL2DZ, 6-31G(d)] level. The computed results demonstrate that the O atom, O₂, and CO molecule adsorptions on the copper cluster are all chemical. For the CO oxidation by O₂ molecules that leads to the formation of C–O bonds and the dissociation of O–O bonds, the Langmuir–Hinshelwood (LH) mechanism is preferred. On the other hand, the Eley–Rideal (ER) mechanism is slightly favored by the oxidation of CO by atomic oxygen. According to the intrinsic reaction coordinate (IRC) calculation, the activation energy for CO oxidation is 4.02 kcal/mol for molecular oxygen and 3.17 kcal/mol for atomic oxygen. Therefore, molecular and atomic oxygen are very reactive for CO oxidation on the Cu₁₉ cluster. To check the applicability of the global hardness response (GHR) profile satisfying the maximum hardness principle along the IRC in the metal cluster reactions, the GHR profile for the oxidation reaction of CO with molecular oxygen and atomic oxygen was computed. The results indicate that this meets the principle of maximum hardness, effectively showcasing the use of DFT methods to analyze the global hardness profile using frontier molecular orbital energy in the context of metal cluster reaction pathways.

Graphical abstract

The CO oxidation by molecular and atomic oxygen on the Cu₃ site of the Cu₁₉ cluster employing the density functional theory has been studied. The results show that the CO oxidation by atomic oxygen slightly favors the Eley–Rideal (ER) mechanism, while the CO oxidation by molecular oxygen prefers the Langmuir–Hinshelwood (LH) mechanism. Both molecular and atomic oxygen are very reactive for CO oxidation. Furthermore, the global hardness profile along the intrinsic reaction coordinate follows the maximum hardness principle.

This paper discusses synthesizing green, recyclable, heterogeneous nickel–chromium oxide (NiCr₂O₄) catalyst and its application in solvent-free, room-temperature Knoevenagel condensation reaction. Nickel–chromium oxides (Ni–Cr oxides) were prepared using the coprecipitation method in various proportions, such as 2:1, 1:1, and 1:2 ratios. The synthesized catalysts were characterized using X-ray diffraction, SEM-EDX, and BET-surface area analysis. The synthesized catalysts were employed as heterogeneous catalysts in the Knoevenagel condensation model reaction of 4-chlorobenzaldehyde and malononitrile under room temperature, solvent-free grinding reaction conditions, and the results were compared. This paper will discuss the most suitable catalyst and its possible mechanism.