Browsing by Author "Mal, S.S."

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A Liquid Derivative of Phosphotungstic Acid as Catalyst for Benzyl Alcohol Oxidation in Water: Facile Separation and Stability of Benzaldehyde at Room Temperature†
(Wiley-Blackwell, 2017) Bhattacharjee, R.R.; Thangamani, S.; Mal, S.S.
Polyetheramines belong to a class of green di-block copolymer with ethylene oxide and propylene oxide moieties along with terminal amine functionality. The polymers are biocompatible and show temperature dependant phase separation properties. Herein, we report the effect of a polyetheramine (Jeffamine®) on the catalytic properties of a well studied polyoxometalate catalysts, phosphotungstic acid (PTA). The catalytic reaction chosen for the test is the hydrogen peroxide-mediated oxidation of benzyl alcohol (BzOH). Modification of PTA with Jeffamine® (PTA-Jeffamine®) resulted in a solvent-less liquid-like material accessible to a wide range of solvents. The PTA-Jeffamine® catalyst was observed to enhance the conversion of BzOH compared to that of pristine PTA and facilitated easy separation of benzaldehyde (BzH) and catalyst from reaction mixture. Stability of synthesized BzH was studied with gas chromatography attached with mass spectrometry (GC-MS). Synthesis of the catalyst is cost-effective and scalable due to easy availability of the individual components and nature of the synthetic protocol. UV-visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FE-SEM) were used to characterize the catalyst. Surface tension experiment, FE-SEM, ICP-MS and controlled experiments were performed to understand the effect of Jeffamine® in the catalytic process. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
A scalable and high-yielding synthesis of 2-(2-furyl)-1,3-dioxolane from biomass derived furfural and ethylene glycol using heteropoly acids as green catalyst
(Chemical Publishing Co., 2019) Tiwari, R.; Mal, S.S.; Dutta, S.
In present work, Keggin-type commercial heteropoly acids have been employed as efficient solid acid catalysts in the acetalization of biomass-derived furfural with ethylene glycol. The reaction was optimized on parameters such as the type and loading of catalyst, duration of reaction and the relative ratio of reagents. The reaction was scaled up and the cyclic acetal 2-(furan-2-yl)-1,3-dioxolane was isolated in 92 % yield within 4 h using only 2 wt % of phosphotungstic acid in refluxing benzene. © 2019 Chemical Publishing Co.. All rights reserved.
Activated carbon- supported Vanado-nickelate (IV) based hybrid materials for energy application
(Elsevier Ltd, 2021) Maity, S.; BM, N.; Kella, T.; Shee, D.; Das, P.P.; Mal, S.S.
The rapid development of supercapacitor (SC) technology leads to increased demand for nanofabrication of novel and effective electroactive hybrid materials for next-generation energy storage devices. Herein, nickel tetradecavanadate, K2H5[NiV14O40](NiV14), is doped into porous activated carbon (AC), for the first time, in different wt.% in order to investigate the homogeneous loading of the inorganic metal-oxide component on the AC matrix. The resulting complex, AC-NiV14, is found to have possessed an enhanced electrochemical characteristic (for both symmetric and asymmetric SC cell), which operates at a significantly higher potential of 1.2 V. The combination of the double-layer capacitance (EDLC) and the redox-active polyoxometalate cluster leads to an intrinsic increase in specific capacitance (capacity) (from 45.3 Fg?1 (54.4 Cg?1) for AC to 316 Fg?1 (379.2 Cg?1) for 15 wt.% AC-NiV14 at a current density of 1 Ag?1). It was also observed that there is an increase of 20% in the operating voltage compared to conventional AC supercapacitors with acidic aqueous electrolytes. Firstly, symmetric supercapacitor's electrochemical performances of various wt.% of NiV14 composition were studied in acidic aqueous electrolyte (0.5 M H2SO4) solution. We observed that the 15 wt.% of AC-NiV14 hybrid electrode showed remarkable specific energy value (~63.2 Wh kg?1) compared with pristine AC and NiV14 electrodes, separately. Besides, the asymmetric layout (AC//AC-NiV14) increased the potential window up to 1.5 V and enhanced the specific energy and power values (90.1 Whkg?1 and 2400 Wkg?1, respectively), with 98% coulombic efficiency. Meanwhile, the AC-NiV14//NiV14 asymmetric cell possesses a specific capacitance (capacity) of 375 Fg?1 (450 Cg?1) with a maximum power of 3140 Wkg?1 at the high current density of 2 Ag?1. © 2021 Elsevier Ltd
Advanced Microscopic Visualization for Structural Characterization of Cellulose Extracted from Saccharum Spontaneum (Kohua Bon) of Assam, India
(Optica Publishing Group (formerly OSA), 2021) Chakraborty, I.; Kalita, R.D.; Singh, P.; Banik, S.; Govindaraju, I.; Mal, S.S.; Zhuo, G.-Y.; Mahato, K.K.; Mazumder, N.
Alpha, microcrystalline and nanocrystalline cellulose were sequentially extracted from stems and leaves of Saccharum spontaneum and were subjected to morphological and structural characterization using advanced microscopy techniques, including Scanning electron microscopy and nonlinear optical microscopy. Â© Optica Publishing Group 2021, Â© 2021 The Author (s)
An insight into microscopy and analytical techniques for morphological, structural, chemical, and thermal characterization of cellulose
(John Wiley and Sons Inc, 2022) Chakraborty, I.; Rongpipi, S.; Govindaraju, I.; Rakesh, B.; Mal, S.S.; Gomez, E.W.; Gomez, E.D.; Kalita, R.D.; Nath, Y.; Mazumder, N.
Cellulose obtained from plants is a bio-polysaccharide and the most abundant organic polymer on earth that has immense household and industrial applications. Hence, the characterization of cellulose is important for determining its appropriate applications. In this article, we review the characterization of cellulose morphology, surface topography using microscopic techniques including optical microscopy, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Other physicochemical characteristics like crystallinity, chemical composition, and thermal properties are studied using techniques including X-ray diffraction, Fourier transform infrared, Raman spectroscopy, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. This review may contribute to the development of using cellulose as a low-cost raw material with anticipated physicochemical properties. Highlights: Morphology and surface topography of cellulose structure is characterized using microscopy techniques including optical microscopy, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Analytical techniques used for physicochemical characterization of cellulose include X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. © 2022 Wiley Periodicals LLC.
An Insight into the Gelatinization Properties Influencing the Modified Starches Used in Food Industry: A review
(Springer, 2022) Chakraborty, I.; N, P.; Mal, S.S.; Paul, U.C.; Rahman, M.H.; Mazumder, N.
Native starch is subjected to various forms of modification to improve its structural, mechanical, and thermal properties for wider applications in the food industry. Physical, chemical, and dual modifications have a substantial effect on the gelatinization properties of starch. Consequently, this review explores and compares the different methods of starch modification applicable in the food industry and their effect on the gelatinization properties such as onset temperature (To), peak gelatinization temperature (Tp), end set temperature (Tc), and gelatinization enthalpy (ΔH), studied using differential scanning calorimetry (DSC). Chemical modifications including acetylation and acid hydrolysis decrease the gelatinization temperature of starch whereas cross-linking and oxidation result in increased gelatinization temperatures. Common physical modifications such as heat moisture treatment and annealing also increase the gelatinization temperature. The gelatinization properties of modified starch can be applied for the improvement of food products such as ready-to-eat, easily heated or frozen food, or food products with longer shelf life. © 2022, The Author(s).
Assessment of biocompatibility for citric acid crosslinked starch elastomeric films in cell culture applications
(Nature Research, 2025) Pooja, N.; Ahmed, N.Y.; Mal, S.S.; Bharath, P.A.S.; Zhuo, G.-Y.; Noothalapati, H.; Managuli, V.; Mazumder, N.
This study investigates the synthesis of potato starch elastomers reinforced with silicon dioxide (SiO2) and citric acid as a crosslinking agent to enhance their mechanical and barrier properties. Surface morphology analysis using optical microscopy revealed that pure potato starch films had uneven surfaces. However, higher SiO2 concentrations increased roughness, while citric acid crosslinked films displayed smoother surfaces overall. Water vapor transmission rates (WVTR) indicated that native starch films were highly hydrophilic, while SiO2 incorporation and citric acid crosslinking significantly reduced WVTR of 17% (30% lower than native film), enhancing the barrier properties. Tensile strength testing revealed that citric acid crosslinking increased the tensile strength by 25%, while SiO2 further reinforced the films but decreased elasticity by 15%. SiO2 had little impact on degradation rates, while citric acid crosslinking delayed microbial growth, extending film longevity by 20%. Biocompatibility assays using SiHa, HT-29, and HEK 293 cell lines revealed that the films had varying degrees of cell confluency. Films with both SiO2 and citric acid showed improved confluency (20% higher) compared to films containing only SiO2. However, citric acid alone resulted in the highest confluency (95% viability), suggesting its significant role in biocompatibility. This eco-friendly approach demonstrates substantial advancements in film properties, offering potential applications in diverse biomedical industries. © The Author(s) 2025.
Biocompatiblity of potato starch-based elastomer films for cell culture
(Optical Society of America, 2023) Ahmed, N.Y.; Pooja, N.; Mal, S.S.; Mazumder, N.
Novel biodegradable elastomers based on potato starch are synthesized and utilized as cell substrates. The elastomers were characterized in terms of their functional properties. To assess the suitability of th e synthesized elastomers for biomedical applications, studies on cell adhesion and cell viability were carried out. Â© Optica Publishing Group 2023, Â© 2023 The Author(s)
Carbon Nanotube-Supported Vanadium Substituted Phospho-Molybdate Nanohybrid for Supercapacitor Applications
(John Wiley and Sons Inc, 2025) Biradar, B.R.; Swetha, M.T.; Thathron, N.; Puniyanikkottil, M.A.; Hanchate, A.; Das, P.P.; Mal, S.S.
Owing to the depletion of conventional energy sources, our civilization is slowly transitioning to renewables. Therefore, designing effective energy storage systems is one of the most pressing technical demands. The quest for improved energy and power densities in energy storage devices, particularly those with long cycle life, has pushed the investigation of novel materials intended to build effective supercapacitors. In this work, nanohybrid materials are synthesized using a hydrothermal technique by mixing carbon nanotubes and a polyoxometalate cluster, H4[PVMo11O40].xH2O. Henceforth, this complex is acronymed as CNT-PVMo11. Further, electrochemical analysis of CNT-PVMo11 nanohybrid is carried out to examine various characteristics of the supercapacitor cell made with this nanohybrid. The cyclic voltammetry confirms the diffusive-dominant charge-storage process, quantifying a 72.83% diffusion mechanism at a scan rate of 1 mV s?1. The galvanostatic charge–discharge analysis of CNT-PVMo11 nanohybrid material showed a specific capacitance of 229.35 F g?1 with energy and power densities of 31.85 Wh kg?1 and 2000 W kg?1, respectively, at 1 A g?1 current density. The electrode material also shows 90% capacitance retention even after 6000 cycles at 8 A g?1 current density, indicating the material's remarkable stability. The high specific capacitance, excellent energy density, and impressive cycling stability of the hybrid material make it a promising candidate for next-generation supercapacitor electrodes. © 2025 Wiley-VCH GmbH.
Catalytic Synthesis of Xanthene and Unprecedented Evolution of Naphthopyrans Using Heteropoly Acid-Tantalum(V) Oxide Hybrid Composite as Promoter
(John Wiley and Sons Inc, 2025) Mahapatra, J.; Dastidar, S.G.; Jagankar, D.; Roy, N.; Sharma, J.; Mukherjee, A.; Maity, C.; Panda, T.K.; Mal, S.S.
Xanthene derivatives are prepared by using tantalum(V) oxide (Ta2O5)-supported heteropoly acid (HPA), Keggin 12-phosphotungstic acid (PTA)-based heterogeneous catalyst PTA@Ta2O5 under neat conditions. The composite is prepared by the wetness impregnation method and is characterized by various techniques. Under optimized conditions, xanthenes are synthesized with prominent yields in remarkably short reaction times. The green chemistry metrics are appraised for the xanthene reaction. Surprisingly, a few novel naphthopyran derivatives are isolated instead of the conventional xanthene derivatives when cinnamaldehyde analogous are introduced under the same reaction protocol. Unprecedented naphtho[2,1-b]pyran-type derivatives of 3m, 3n, and 3o are isolated, depending on the specific substituted cinnamaldehyde used, and interestingly, the nature of the substituent in cinnamaldehyde decides the different reaction pathways leading to the formation of respective pyrans. Diverse possible mechanisms are encountered with the PTA@Ta2O5 catalyst based on the respective transformations. The solid-state structures of xanthenes and naphthopyrans are thoroughly investigated. Furthermore, some derivatives are studied in vitro to assess their antimicrobial activity, and the findings are compared with those of reference standard antibiotics. © 2025 Wiley-VCH GmbH.
Catalytically controlled formation of coumarin-based hydrogelator enables colorimetric ferrous ion detection in sol and hydrogel
(Nature Research, 2025) Das, N.; Mandal, S.; Mal, S.S.; Bose, S.; Maity, C.
In-situ generation of a hydrogelator from non-assembling precursors offers an effective strategy for preparing supramolecular hydrogel materials with precise spatiotemporal control. These hydrogels hold broad potential for applications ranging from theranostics to chemical sensing. Herein, we report a method for the in-situ formation of a coumarin-based supramolecular hydrogelator by simply mixing aqueous solutions of two non-assembling precursors under ambient conditions. The formation of the hydrogelator, its subsequent self-assembly into a hydrogel network, and the resulting material properties can all be modulated via acid catalysis. The hydrogelator exhibits excellent selectivity toward Fe(II) ions, providing a distinct colorimetric response with a linear correlation and a notable detection limit. Additionally, the hydrogel material can be easily applied to disposable paper strips, enabling convenient and portable detection of Fe(II) ions. This system demonstrates strong potential for addressing key challenges in Fe(II) ion sensing in both aqueous environments and self-assembled hydrogel states. (Figure presented.) © The Author(s) 2025.
Characterization of PtIV-containing polyoxometalates by high-resolution solid-state 195Pt and 51V NMR spectroscopy
(Royal Society of Chemistry, 2016) Dugar, S.; Izarova, N.V.; Mal, S.S.; Fu, R.; Joo, H.-C.; Lee, U.; Dalal, N.S.; Pope, M.T.; Jameson, G.B.; Kortz, U.
We report on the feasibility of applying high-resolution solid-state 195Pt MAS NMR spectroscopy for several PtIV-containing polyoxotungstates, and of 195Pt as well as 51V for a PtIV-containing polyoxovanadate. This method is particularly useful for polyanions which are unstable in solution and/or poorly soluble, as well as for systems exhibiting crystallographic disorder of Pt and W sites. We also report solution 195Pt and 183W NMR spectra of hexatungstoplatinate(iv) [H3PtW6O24]5- for the first time. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2016.
Comparative analysis of biopolymer films derived from corn and potato starch with insights into morphological, structural and thermal properties
(Springer Nature, 2024) Pooja, N.; Banik, S.; Chakraborty, I.; Sudeeksha, H.C.; Mal, S.S.; Srisungsitthisunti, P.; Patil, A.; Mahato, K.K.; Mazumder, N.
Starch biopolymer films were prepared using the solvent casting method involving acetic acid hydrolysis and glycerol plasticization. This process facilitated a more uniform distribution of plasticizers within the starch matrix, enhancing the films' flexibility. Fourier-transform infrared (FTIR) and Raman spectroscopy confirmed the formation of ester linkages and structural changes in the biopolymer films, attributed to glycerol integration. The optimal formulation comprised 6% starch, 6.8% acetic acid, and 6.8% glycerol. X-ray diffraction (XRD) analysis revealed a reduction in crystallinity of the starch during film formation, enhancing flexibility. Second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy indicated that potato starch films had higher crystallinity compared to corn starch films. Thermal analysis via differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that potato starch films exhibited lower gelatinization temperatures and higher thermal stability compared to corn starch films. Functional characterization demonstrated that higher starch content decreased water solubility and water vapor transmission rate, while increasing starch content improved the film's structural integrity. The films were hydrophilic, with static water contact angles indicating moderate wettability. Degradation studies showed that the films were stable in neutral and basic conditions but degraded under acidic conditions over time. The results suggest that potato starch films, with optimized glycerol and acetic acid content, offer improved flexibility, thermal stability, and structural integrity compared to corn starch films. Their performance in various conditions highlights their potential for specific applications, particularly where moisture and environmental stability are critical. © The Author(s) 2024.
Dependence of the 0.5 × (2e2/h) conductance plateau on the aspect ratio of InAs quantum point contacts with in-plane side gates
(American Institute of Physics Inc. subs@aip.org, 2017) Das, P.P.; Jones, A.; Cahay, M.; Kalita, S.; Mal, S.S.; Sterin, N.S.; Yadunath, T.R.; Advaitha, M.; Herbert, S.T.
The observation of a 0.5 × (2e2/h) conductance plateau in asymmetrically biased quantum point contacts (QPCs) with in-plane side gates (SGs) has been attributed to the onset of spin-polarized current through these structures. For InAs QPCs with the same width but a longer channel length, there is roughly a fourfold increase in the range of common sweep voltage applied to the SGs over which the 0.5 × (2e2/h) plateau is observed when the QPC aspect ratio (ratio of length over the width of the narrow portion of the structure) is increased by a factor 3. Non-equilibrium Green's function simulations indicate that the increase in the size of the 0.5 × (2e2/h) plateau is due to an increased importance, over a larger range of common sweep voltage, of the effects of electron-electron interactions in QPC devices with a larger aspect ratio. The use of asymmetrically biased QPCs with in-plane SGs and large aspect ratio could therefore pave the way to build robust spin injectors and detectors for the successful implementation of spin field effect transistors. © 2017 Author(s).
Development of a cholesterol biosensor and energy storage system based on polypyrrole coated polyoxometalate
(Elsevier Ltd, 2025) Biradar, B.R.; Thathron, N.; Hanchate, A.; Das, P.P.; Mal, S.S.
Designing sustainable and environmentally acceptable multifunctional electrode materials is vital for various purposes, such as energy storage and healthcare. The redox property of polyoxometalates is attractive for different electrochemistry fields, such as sensors, energy storage, catalysis, etc. In this study, potassium 9-tungsto-2-molybdo-1-vanadosilicate K5[?-SiMo2VW9O40].10H2O (hereafter acronym as SiMo2VW9) embedded on polypyrrole (PPy), which acts as a nanohybrid, was synthesized for supercapacitor and biosensor applications. The electrochemical analysis for both applications was carried out using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The PPy-SiMo2VW9 nanohybrid showed the highest specific capacitance of 174.5 F g?1 with power and energy densities of 799.94 W kg?1 and 15.51 Wh kg?1, respectively, at 0.5 M H2SO4 electrolytic medium. The nanohybrid showed the diffusion-dominant charge storage mechanism with 92.24 % at a 5 mV s?1 scan rate, which refers to the battery-type material. Furthermore, electrochemical sensing for cholesterol was also carried out using the cyclic voltammetry approach in the range of 0.03–0.58 mM cholesterol concentration. The PPy-SiMo2VW9 nanohybrid showed a sensitivity of 7.97 mAm M cm?2 with limit-of-detection (LOD) and limit-of-quantification (LOQ) of 0.06 and 0.2 mM, respectively. The outcomes show that PPy-SiMo2VW9 nanohybrid material is promising in sensing and supercapacitor studies. © 2025 Elsevier B.V.
Dual oxygen reservoir model for nonpolar resistive switching in nickel tetradecavanadate based molecular switch
(Elsevier B.V., 2025) Thathron, N.; Biradar, B.R.; Pandey, S.K.; Mal, S.S.; Das, P.P.
The data explosion and computing limitations of traditional computer systems have led researchers to find alternate data storage devices. Resistive random access memory devices have been accepted as a promising candidate to meet the growing demand for multi-bit memory storage and unconventional computing applications. In this report, we provide a comprehensive mechanistic insight into the multistate nonpolar resistive switching in nickel-embedded polyoxovanadate molecules, K2H5[NiV14O40] based memory device having the architecture Al/K2H5[NiV14O40]/ITO. Such molecular cluster belongs to a larger group of polyoxometalate family. The formation and rupture of multiple conductive filaments made up of oxygen vacancies and their lateral widening with different compliance currents allow the device to exhibit multiple resistance states. The resistance states are likely to be modulated by the multiple redox reactions of Ni and V centers of the active switching layer. The coexistence of two unipolar and two bipolar modes of resistive switching suggests that the device can be modeled as having a dual oxygen reservoir structure where both thermochemical and electrochemical mechanisms of filament theory for resistive switching coexist in the same memory cell. The observation of quantized steps in the conductance plot confirms the conductive filament based resistive switching. The enhancement and reduction in conductance with the increase in the number of pulses can mimic the potentiation and depression in biological synapses. This promises that the polyoxometalate based resistive switching devices can connect memory with neuromorphic applications. © 2025 Elsevier B.V.
Dual-functional phosphomolybdic acid–polypyrrole–ionic liquid nanocomposites for energy storage and hydrogen evolution: experimental and theoretical studies
(Royal Society of Chemistry, 2025) Anees, M.P.K.; Iniyan, S.; Pratap Singh, C.; Murugavel, M.; Krishnamurty, S.; Mal, S.S.
Recent advancements in pseudocapacitive materials for energy storage and catalytic activities highlight the benefits of incorporating nanostructured active materials. This study investigates the modification of polypyrrole (PPy) surfaces using polyoxometalate H4[PVMo11O40].xH2O (PVMo11) combined with ionic liquids hexadecyltrimethylammonium chloride (CTAC) and 1-benzyl-3-methylimidazolium chloride (BMI). Among various synthesized nanocomposites, PVMo11-BMI-PPy demonstrated superior electrochemical properties in a 0.25 M H2SO4 aqueous electrolyte, achieving a remarkable specific capacitance of 400 F g?1, an energy density of 49.5 W h kg?1 and a power density of 906 W kg?1 at a current density of 1 A g?1. It achieves a capacitive contribution of 94.5% at 10 mV s?1 with an impressive cyclic retention rate of 91.1% and a coulombic efficiency of 98.9% after 10?000 GCD cycles. Additionally, PVMo11-BMI-PPy exhibited outstanding electrocatalytic activity for hydrogen evolution reaction (HER), achieving the highest catalytic activity of 19 mV at a current density of 10 mA cm?2, outperforming the benchmark Pt catalyst. Its superior performance is underscored by a high TOF of 6.91 × 10?7 s?1 and excellent long-term stability in 0.5 M H2SO4 over 24 hours. It is a promising candidate for bifunctional activities such as energy storage and catalytic applications. Additionally, density functional theory (DFT) studies were conducted to gain insights into the enhanced performance of PVMo11-BMI-PPy. The thermodynamic and electronic characteristics indicate that the V site of PVMo11-BMI-PPy offers the most efficient and balanced catalytic environment for hydrogen evolution reaction (HER) compared with all other sites examined. These theoretical findings align well with experimental observations, demonstrating superior HER activity of the PVMo11-BMI-PPy catalyst, thereby confirming the computational predictions. This journal is © The Royal Society of Chemistry, 2026
Efficient and Scalable Production of Alkyl Levulinates from Cellulose-Derived Levulinic Acid Using Heteropolyacid Catalysts
(Wiley-Blackwell info@wiley.com, 2019) Onkarappa, S.B.; Javoor, M.; Mal, S.S.; Dutta, S.
This work reports a straightforward and scalable synthesis of a series of alkyl levulinates from cellulose-derived levulinic acid and alkyl alcohols using commercially available heteropolyacid catalysts under homegenous conditions. The reaction was optimized on parameters such as temperature, molar ratio of reagents, type and loading of catalyst. The solvent-free reactions afforded alkyl levulinates in high isolated yields (>85%) using only slight excess of alcohols and 10 wt% of catalyst at 120 °C in 6 h. Further, the catalysts were successfully recycled for three consecutive cycles without significant loss in activity. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Efficient Preparation of Alkyl Benzoates by Heteropolyacid-Catalysed Esterification of Benzoic Acid under Solvent-Free Condition
(Wiley-Blackwell, 2019) Tiwari, R.; Rahman, A.; Bhat, N.S.; Onkarappa, S.B.; Mal, S.S.; Dutta, S.
This study reports a high-yielding, solvent-free, and scalable synthesis of alkyl benzoates from benzoic acid and its derivatives using heteropolyacids (HPA) as efficient and recyclable acid catalysts. The alkyl benzoates were obtained in excellent isolated yields (>85%) within 4 h at 120 °C using 1.5 equivalent of the alcohol reagent and only 0.4 mol% of the phosphotungstic acid (PTA) catalyst. The PTA catalyst was conveniently recovered and reused for three consecutive cycles without significant loss in mass or activity. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Efficient Preparation of the Esters of Biomass-Derived Isohexides by Base-Catalyzed Transesterification under Solvent-Free Conditions
(American Chemical Society, 2023) Bhat, N.S.; Vinod, N.; Tarafder, K.; Nayak, M.K.; Jana, A.; Mal, S.S.; Dutta, S.
The monoesters and diesters of glucose-derived isosorbide (IS) have potential applications as sustainable dispersants, surfactants, emulsifiers, monomer units for polymers, and plasticizers. This work reports a solvent-free, high-yielding, and scalable pathway for producing the monoesters and diesters of IS by a transesterification reaction using K2CO3 as an efficient, inexpensive, and recyclable base catalyst. In the case of monoesters, the selectivity toward the exo-monoester of IS was found higher than that toward the endo-monoester. The methodology was successfully extended to synthesize the monoesters and diesters of isomannide and isoidide. The gram-scale preparation of alkyl, vinyl, and aryl esters of isohexides was optimized on the reaction temperature, duration, equivalence of the ester reagent, and catalyst loading. Under optimized conditions (50 mol % K2CO3, 180 °C, 6 h), various aryl and alkyl esters of the isohexides were isolated in satisfactory yields. The unsymmetrical diesters of the isohexides were conveniently synthesized by stepwise transesterification. © 2023 American Chemical Society.