Browsing by Author "Dhananjay Yadav"

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Access to Fully Substituted Thiazoles and 2,3-Dihydrothiazoles via Copper-Catalyzed [4 + 1] Heterocyclization of α-(N-Hydroxy/aryl)imino-β-oxodithioesters with α-Diazocarbonyls
(American Chemical Society, 2017) Abhijeet Srivastava; Gaurav Shukla; Dhananjay Yadav; Maya Shankar Singh
An efficient chemoselective practical route to fully substituted thiazoles and 2,3-dihydrothiazoles has been devised by [4 + 1] heterocyclization of α-(N-hydroxy/aryl)imino-β-oxodithioesters with in situ generated Cu-carbenoids of diazocarbonyls. The α-(N-hydroxy/aryl)imino-β-oxodithioesters are readily accessible by the reaction of β-oxodithioesters with nitrous acid/nitrosoarenes. The overall transformation involves sequential N-O/C-N bonds cleavage followed by cascade C-N/C-S bonds formation in one-pot. This new strategy allows full control over the introduction of various sensitive functional groups at different positions of the thiazole ring, broadening the arsenal of synthetic methods to obtain such scaffolds. © 2017 American Chemical Society.
Access to Nitrones from Amines via Electrocatalysis at Room Temperature
(John Wiley and Sons Inc, 2022) Gaurav Shukla; Dhananjay Yadav; Saurabh Singh; Maya Shankar Singh
A self-enabled electrooxidative protocol for the synthesis of nitrones from bench stable amines has been developed under constant current electrolysis at room temperature, rendering metal and external oxidant-free protocol in an alkaline medium. The electrocatalysis steps of reported strategy involve anodic oxidation of benzyl amines followed by cathodic reduction of nitro-functional group in an undivided cell affording functional nitrones. The robustness of the electrocatalysis was reflected by tolerant substrate scope, oxidant-free conditions, and an operationally friendly procedure. Moreover, the cyclic voltammetry and control experiment studies also support the electrochemical process in alkaline medium. (Figure presented.). © 2022 Wiley-VCH GmbH.
Analytical and numerical examinations on the stability investigation of Casson nanofluid flow in a permeable layer controlled by vertical throughflow
(Emerald Publishing, 2024) A.M. Mohamad; Dhananjay Yadav; Mukesh Kumar Awasthi; Ravi Ragoju; Krishnendu Bhattacharyya; Amit Mahajan
Purpose: The purpose of the study is to analytically as well as numerically investigate the weight of throughflow on the onset of Casson nanofluid layer in a permeable matrix. This study examines both the marginal and over stable kind of convective movement in the system. Design/methodology/approach: A double-phase model is used for Casson nanofluid, which integrates the impacts of thermophoresis and Brownian wave, whereas for flow in the porous matrix the altered Darcy model is occupied under the statement that nanoparticle flux is disappear on the boundaries. The resultant eigenvalue problem is resolved analytically as well as numerically with the help of Galerkin process with the Casson nanofluid Rayleigh–Darcy number as the eigenvalue. Findings: The findings revealed that the throughflow factor postpones the arrival of convective flow and reduces the extent of convective cells, whereas the Casson factor, the Casson nanoparticle Rayleigh–Darcy number and the reformed diffusivity ratio promote convective motion and also decrease the extent of convective cells. Originality/value: Controlling the convective movement in heat transfer systems that generate high heat flux is a real mechanical challenge. The proposed framework proved that the use of throughflow is one of the most important ways to control the convective movement in Casson nanofluid. To the best of the authors’ knowledge, no inspection has been established in the literature that studies the outcome of throughflow on the Casson nanofluid convective flow in a porous medium layer. However, the convective flow of Casson nanofluid finds many applications in improving heat transmission and energy efficiency in a range of thermal systems, such as the cooling of heat-generating elements in electronic devices, heat exchangers, pharmaceutical practices and hybrid-powered engines, where throughflow can play a significant role in controlling the convective motion. © 2024, Emerald Publishing Limited.
Analytical and numerical examinations on the stability investigation of Casson nanofluid flow in a permeable layer controlled by vertical throughflow
(Emerald Publishing, 2025) Abdul M. Mohamad; Dhananjay Yadav; Mukesh Kumar Awasthi; Ragoju Ravi; Krishnendu Bhattacharyya; Amit Mahajan
Purpose – The purpose of the study is to analytically as well as numerically investigate the weight of throughflow on the onset of Casson nanofluid layer in a permeable matrix. This study examines both the marginal and over stable kind of convective movement in the system. Design/methodology/approach – A double-phase model is used for Casson nanofluid, which integrates the impacts of thermophoresis and Brownian wave, whereas for flow in the porous matrix the altered Darcy model is occupied under the statement that nanoparticle flux is disappear on the boundaries. The resultant eigenvalue problem is resolved analytically as well as numerically with the help of Galerkin process with the Casson nanofluid Rayleigh–Darcy number as the eigenvalue. Findings – The findings revealed that the throughflow factor postpones the arrival of convective flow and reduces the extent of convective cells, whereas the Casson factor, the Casson nanoparticle Rayleigh–Darcy number and the reformed diffusivity ratio promote convective motion and also decrease the extent of convective cells. Originality/value – Controlling the convective movement in heat transfer systems that generate high heat flux is a real mechanical challenge. The proposed framework proved that the use of throughflow is one of the most important ways to control the convective movement in Casson nanofluid. To the best of the authors’ knowledge, no inspection has been established in the literature that studies the outcome of throughflow on the Casson nanofluid convective flow in a porous medium layer. However, the convective flow of Casson nanofluid finds many applications in improving heat transmission and energy efficiency in a range of thermal systems, such as the cooling of heat-generating elements in electronic devices, heat exchangers, pharmaceutical practices and hybrid-powered engines, where throughflow can play a significant role in controlling the convective motion. © 2024 Emerald Publishing Limited
Brønsted acid-catalyzed metal-free one-pot synthesis of benzimidazoles via [4+1] heteroannulation of ortho-phenylenediamines with β-oxodithioesters
(Arkat, 2017) Abhijeet Srivastava; Gaurav Shukla; Dhananjay Yadav; Maya Shankar Singh
An operationally simple and user-friendly one-pot domino protocol for the synthesis of 2-aryl/hetaryl benzimidazoles has been devised from easily available and inexpensive 1,2-phenylenediamines and β-oxodithioesters. The strategic [4+1] heteroannulation initiated by Bronsted acid PTSA relies on remarkable domino sequence of condensation, cyclization, and elimination. The current approach enables N-H/N-H functionalization under solventless and metal-free conditions leading to diverse benzimidazoles. The reactions proceeded smoothly affording the desired products in good to excellent yields, exhibiting gram-scale ability and broad functional groups tolerance. Notably, the approach is highly chemo- and regioselective. © 2018 ARKAT USA, Inc.
Buoyancy driven non-Newtonian Prandtl-Eyring nanofluid flow in Darcy-Forchheimer porous medium over inclined non-linear expanding sheet with double stratification
(Taylor and Francis Ltd., 2022) Ajeet Kumar Verma; Krishnendu Bhattacharyya; Sohita Rajput; Mani Shankar Mandal; Ali J. Chamkha; Dhananjay Yadav
In the existence of mixed convection and double stratification, the 2D, viscous, incompressible, steady, laminar boundary layer flow of Prandtl-Eyring nanofluid over the inclined non-linear expanding sheet in Darcy-Forchheimer porous medium is scrutinized. To analyze the impacts of Brownian motion and thermophoretic force on diffusion of nanoparticles Buongiorno model has been utilized. Flow governing equations are non-linear, higher order, coupled PDEs with no slip boundary condition, which are transforming into coupled, non-linear, higher order ODEs via suitable transformations. Obtained ODEs are solved using MATLAB bvp4c function. The impacts of flow governing parameters on flow associated distributions are acknowledged through graphs. In limiting sense, to check the credibility of numerical method, present results are compared with previously published data. The analysis reveals that fluid velocity displays an enhancement with first Prandtl-Eyring parameter α and a diminution with second Prandtl-Eyring parameter β. Whereas, due to presence of both stratifications (thermal and solutal) there is a decline in fluid velocity. Also, nanofluid temperature is augmented with Forchheimer number (Formula presented.) and inclination angle γ, whereas it declines with α and thermal stratification parameter (Formula presented.). Nanoparticle concentration escalates with γ, whereas it drops with concentration stratification parameter (Formula presented.). For larger thermophoresis parameter Nt, the nanoparticle concentration achieves higher level than its initial value in mid-region of boundary layer, while near surface it assumes lower value. The surface drag-force elevates with β and Nt. Whereas surface cooling rate enhances with (Formula presented.) and it weakens with (Formula presented.). © 2022 Informa UK Limited, trading as Taylor & Francis Group.
Chemical Reaction and Internal Heating Effects on the Double Diffusive Convection in Porous Membrane Enclosures Soaked with Maxwell Fluid
(MDPI, 2022) Dhananjay Yadav; Maimouna Al-Siyabi; Mukesh Kumar Awasthi; Salma Al-Nadhairi; Amna Al-Rahbi; Maryam Al-Subhi; Ravi Ragoju; Krishnendu Bhattacharyya
In this paper, the joint impact of the interior heating and chemical reaction on the double diffusive convective flow in porous membrane enclosures soaked by a non-Newtonian Maxwell fluid is investigated applying linear and nonlinear stability techniques. The porous enclosures are square, slender and rectangular. Using the linear stability analysis, the expression for the critical thermal Rayleigh–Darcy number, above which the convective movement occurs, is derived analytically in terms of associated physical parameters. A nonlinear stability examination reliant on the Fourier double series is executed to calculate the convective heat and mass transports of the arrangement. It is observed that the pattern of convective activity is oscillatory only in the occurrence of a relaxation parameter and the threshold value of the relaxation parameter for the occurrence of the oscillatory pattern depends on the other physical parameters. The onset of convective instability accelerates with the increasing chemical reacting parameter, the interior heating parameter, the solute Rayleigh–Darcy number, the Lewis number, the Vadasz number, and the relaxation parameter, while it delays with the heat capacity ratio. The convective heat and mass transfers increase with the solute Rayleigh– Darcy number, the Vadasz number, the relaxation parameter, and the aspect ratio (for rectangular enclosure), while it decreases with the heat capacity ratio and the aspect ratio (for slender enclosure). Additionally, the convective heat transfer enhances with the interior heating parameter, while the convective mass transfer enhances with the chemical reacting parameter and the Lewis number. The effects of Vadasz number, heat capacity ratio, and relaxation parameter are witnessed only on the oscillatory pattern of convection and unsteady convective heat and mass transfers. Further, some existing literature results are compared with the current findings. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
Chemoselective one-pot access to benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones via copper-catalyzed oxidative [3 + 2] annulation of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols
(Elsevier Ltd, 2018) Dhananjay Yadav; Gaurav Shukla; Monish A. Ansari; Abhijeet Srivastava; Maya Shankar Singh
An operationally simple and efficient one-pot method for the synthesis of 1-aroyl (or alkanoyl)-2-thioalkyl-3-aryl (or alkyl)-3H-benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones has been devised by copper-catalyzed cross-coupling of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols in open air for the first time. The key to the success of this transformation is the room temperature oxidation of α-/β-naphthol to 1,2-naphthoquinone as a reactive species, which undergoes formal [3 + 2] annulation with α-oxoketene N,S-acetals/β-ketothioamides via cascade sequence of Michael addition/tautomerization/oxidation/cyclization/aromatization reactions, enabling addition of a pyrrole/thiophene ring onto naphthoquinone moiety. Further, benzo[e]indole-4,5-diones were transformed to pentacyclic fused phenazine derivatives under solvent-free conditions. Based on our experimental outcomes, a tentative mechanistic rationale for this chemoselective protocol is proposed, which is well validated and supported by the control experiments. © 2018 Elsevier Ltd
Comparison between graphene-water and graphene oxide-water nanofluid flows over exponential shrinking sheet in porous medium: Dual solutions and stability analysis
(Elsevier B.V., 2022) Ajeet Kumar Verma; Sohita Rajput; Krishnendu Bhattacharyya; Ali J. Chamkha; Dhananjay Yadav
To achieve ultra-high cooling rate requirement of modern-day industries the combined use of nanofluid and porous medium in several engineering and industrial processes provides excellent outcomes. In present analysis, the comparison between the flows of Gr-w and GO-w nanofluids over exponential shrinking sheet inside porous medium is investigated. Governing coupled PDEs are changed into ODEs by appropriate transformations which are solved numerically with the help of shooting method with RK4; and obtained dual solutions of Darcy flow for certain enforced mass suction exist and consequently, a stability analysis is performed to test physical stability of both solutions which proves physical stability of upper solution branch and instability of lower solution branch. The impacts of several physical parameters are presented in graphical modes along with a tabular comparison. The study reveals that Gr-w nanofluid delays the boundary layer flow separation more in comparison with GO-w nanofluid and hence, the requirement of mass suction for existence of Gr-w nanofluid flow is of lower amount. Also, consideration of porous material as flow medium defers the separation phenomenon. The rise of surface-drag force is witnessed for porous medium and mass suction and it is relatively larger for Gr-w nanofluid than GO-w nanofluid in case of upper branch solution and the surface cooling rate is larger for Gr-w nanofluid in comparison with GO-w nanofluid. © 2022
Convective flow of ethylene glycol-silver Jeffery nanofluid in a Hele-Shaw cell with an influence of external magnetic field
(John Wiley and Sons Ltd, 2023) Dhananjay Yadav; Sara Al-Balushi; Mukesh Kumar Awasthi; Taif Al-Hadi; Raya Al-Abri; Jawhara Al-Wahaibi; Fatan Al-Nasseri; Sara Al-Siyabi; Ravi Ragoju; Krishnendu Bhattacharyya
This effort investigates the arrival of magnetothermal convection of ethylene glycol-silver Jeffrey nanofluid in a Hele-Shaw cell utilizing the linear stability concept. The model practiced for the Jeffrey nanofluid includes the impacts of Brownian movement and thermophoresis. The norms for both marginal and overstable modes of convections are developed analytically. The impact of magnetic Chandrasekhar number (Figure presented.), magnetic Prandtl number (Figure presented.), Jeffrey parameter (Figure presented.), Hele-Shaw number (Figure presented.), and a variety of nanofluid parameters such as the volumetric fraction of nanoparticles (Figure presented.), nanoparticle Rayleigh number (Figure presented.), adjusted diffusive ratio (Figure presented.), and Lewis number (Figure presented.) on the beginning of convective motion are investigated, and results are illustrated graphically. It is observed that the overstable approach of convection is probable below the certain threshold estimate of the magnetic Prandtl number (Figure presented.). This threshold estimate of the magnetic Prandtl number (Figure presented.) upturns with a rise in the rate of (Figure presented.), (Figure presented.), and (Figure presented.), while it drops with a surge in the nanofluid parameters. The system was found to be more stable by decreasing the Hele-Shaw number (Figure presented.), the Jeffery parameter (Figure presented.), and nanofluid parameters, while it was unstable by decreasing the magnetic Chandrasekhar number (Figure presented.) and the magnetic Prandtl number (Figure presented.). © 2023 Curtin University and John Wiley & Sons Ltd.
Copper(II)-Catalyzed [3+2] Annulation of Thioamides with AIBN: Facile Access to Highly Functionalized Thiazolidin-4-ones
(Georg Thieme Verlag, 2022) Pragya Pali; Dhananjay Yadav; Gaurav Shukla; Maya Shankar Singh
An efficient and versatile copper-catalyzed intermolecular radical [3+2] annulation of thioamides with azobisisobutyronitrile (AIBN) is described. This two-component copper(II)-catalyzed transformation is achieved in one pot via cascade formation of C-S/C-N bonds through cyclization of an in situ generated N,S-acetal intermediate derived from a?-ketothioamide. This operationally simple method allows direct access to synthetically demanding thiazolidin-4-ones in good to excellent yields containing diverse functional groups of different electronic and steric nature. The readily available reaction partners, the avoidance of expensive/toxic reagents and a gram-scale synthesis are additional attributes of this strategy. AIBN plays a dual role as a radical initiator and an unusual source of a two-carbon coupling partner. Notably, the products possess Z stereochemistry with regard to the exocyclic C=C double bond at position 2 of the thiazolidine ring. © 2021. Thieme. All rights reserved.
Copper-Catalyzed One-Pot Cross-Dehydrogenative Thienannulation: Chemoselective Access to Naphtho[2,1-b]thiophene-4,5-diones and Subsequent Transformation to Benzo[a]thieno[3,2-c]phenazines
(American Chemical Society, 2018) Gaurav Shukla; Abhijeet Srivastava; Dhananjay Yadav; Maya Shankar Singh
A facile, cost-effective, and highly efficient copper-catalyzed, TEMPO-mediated straightforward synthesis of 2,3-disubstituted naphtho[2,1-b]thiophene-4,5-diones has been achieved via cross-dehydrogenative thienannulation. The reaction proceeded via in situ generated naphthalene-1,2-diones by dearomatization of β-naphthols, followed by oxidative heteroannulation with α-enolic dithioesters chemoselectively in an open flask. Further, the naphtho[2,1-b]thiophene-4,5-diones undergo l-proline-catalyzed cross-dehydrative coupling with ortho-phenylenediamine enabling pentacyclic benzo[a]thieno[3,2-c]phenazines in good yields under solvent-free conditions. A mechanistic rationale for this cascade reaction sequence is well supported by the control experiments. © 2018 American Chemical Society.
Double diffusive convective motion in a reactive porous medium layer saturated by a non-Newtonian Kuvshiniski fluid
(American Institute of Physics Inc., 2022) Dhananjay Yadav; Mukesh Kumar Awasthi; M. Al-Siyabi; S. Al-Nadhairi; A. Al-Rahbi; M. Al-Subhi; Ravi Ragoju; Krishnendu Bhattacharyya
The impact of chemical reactions on the double-diffusive convective motion in a non-Newtonian viscoelastic fluid (Kuvshiniski type) saturated porous layer is examined applying both linear and nonlinear stability techniques. The Darcy model that includes the Kuvshiniski type viscoelastic effect of viscoelastic fluid and the Boussinesq estimation is employed as the momentum equation. The conditions for the occurrence of the stationary and oscillatory style of convective motions are determined by applying linear stability theory in terms of a critical thermal Rayleigh-Darcy number. Using the weakly nonlinear stability analysis, the convective heat and mass transfers are calculated. It is observed that the occurrence of oscillatory convection is possible only if the value of the solute Rayleigh-Darcy number is negative and also depends on other involved physical parameters. With rising values of the Kuvshiniski parameter and the heat capacity ratio, the range of the solute Rayleigh-Darcy number in which oscillatory convection is privileged diminishes, whereas it grows with the chemical reacting parameter and the Lewis number. The critical thermal Rayleigh-Darcy number at which the convective motion occurs increased nearly 3% with a 15% increase in the value of the Kuvshiniski parameter. Furthermore, the convective heat and mass transfers are reduced by growing the Kuvshiniski parameter and the heat capacity ratio, while both are enhanced by increasing the thermal Rayleigh-Darcy number and the solute Rayleigh-Darcy number. © 2022 Author(s).
Evaluation and comparison of stress distribution around periodontally compromised mobile teeth splinted with different materials: Three-dimensional finite element analysis
(Wolters Kluwer Medknow Publications, 2019) Farhan Durrani; Arpit Galohda; Sanjay Rai; Nishant Singh; Rati Verma; Dhananjay Yadav; S.M. Karthickraj
Background: Progressive attachment loss around the teeth because of periodontal disease can result in increased tooth mobility. This adversely affects patient's comfort, function, and esthetics. Periodontal splinting helps in accomplishing stability by redistributing the functional and parafunctional forces. There are various materials that have been used for periodontal splinting. Fiber-reinforced composite, composite resin, and metal-reinforced composite are often used as splinting materials for periodontally compromised teeth. In our study, a comparison was done among these materials for their ability to distribute the stresses at different bone levels in mobile lower incisors splinted together with canines. Materials and Methods: Five patients of age group 25-50 years with Grade 2 and 3 mobile incisors having 40% or more bone loss and firm canines with optimal bone support were selected. From the computed tomography scan of each patient, three models were developed demonstrating splinting of mandibular incisors and canines with metal-reinforced composite, fiber-reinforced composite, and composite resin. So in total, 15 models were developed and each one of them was subjected to vertical and transverse loads of 150 N. Pattern of stress distribution was observed in these models using three-dimensional finite element analysis. Results: After splinting, the stress on the canine increased when bone levels around incisors decreased while stress on incisors reduced. Conclusion: Tested splinting materials were successful in stress distribution, and metal-reinforced composite was found to be better than the other splinting materials. © 2019 Indian Journal of Dental Research.
Impact of temperature-reliant thermal conductivity and viscosity variations on the convection of Jeffrey fluid in a rotating cellular porous layer
(Royal Society Publishing, 2024) Dhananjay Yadav; Mukesh Kumar Awasthi; Ravi Ragoju; Krishnendu Bhattacharyya; Raghunath Kodi; Mohammad Hassan; Junye Wang
In this analysis, the collective impact of temperature-dependent thermal conductivity and viscosity variations on the convective instability of a Jeffrey fluid in a rotating layer of cellular porous material is examined using an improved Jeffrey–Darcy model. This study has significant implications for cellular foams made from plastics, ceramics and metals, in which radiative heat transmission can be taken as a diffusion practice. Utilizing the linear stability concept and Galerkin method, approximate analytical and numerical solutions accurate to one decimal place are offered. The analysis reveals that the effect of the thermal conductivity variation factor and the rotation factor is to postpone the convective wave, whereas the viscosity variation factor and the Jeffrey factor have a dual effect in the form of rotation. The range of the convective cell is reduced with cumulating thermal conductivity variation factor, viscosity variation factor, Jeffrey factor and rotation factor. In the absence of rotation, the range of the convective cell is not dependent on the Jeffrey factor or the viscosity variation factor. Furthermore, the outcomes are matched with the existing literature for the specific case of this investigation. © 2024 The Author(s). Published by the Royal Society. All rights reserved.
Impact of viscous dissipation, throughflow and rotation on the thermal convective instability of Jeffrey fluid in a porous medium layer
(Elsevier Ltd, 2025) Dhananjay Yadav; Mukesh Kumar Awasthi; Ragoju Ravi; Krishnendu Bhattacharyya; Amit Mahajan; Junye Wang
In this analysis, the collective effects of rotation, viscous dissipation and vertical throughflow on the onset of convective movement in Jeffrey fluid saturated permeable layer is studied. The improved Darcy model is applied to depict the rheological performance of Jeffrey fluid flow in porous medium. The approximate analytical solution with overall error 0.4 % and numerical solution accurate to one decimal place are presented using the Galerkin process. The analysis reveals that the convective motion concentrates in the top layer if it occurred with sufficiently high value of the Darcy–Eckert number. The rotation factor and the Péclet number postponement the onset of convective drive while, the Gebhart number quicken it weakly. In the occurrence of rotation, the Jeffrey factor displays dual impact on the coming of convective movement. The magnitude of the convection cell declines with increasing the rotation factor, the Jeffrey factor and the Péclet number, while it decreases with enhancing the Gebhart number. It is also found that in the lack of rotation, the Jeffrey factor has no impression on the extent of the convective cell, whereas in the nonexistence of the Péclet number, the Gebhart number has no impact on the arrival of convective drive as well as on the magnitude of the convective cells. © 2024 Elsevier Masson SAS
Insight into the relationship between non-linear mixed convection and thermal radiation: The case of Newtonian fluid flow due to non-linear stretching
(KeAi Communications Co., 2023) Amit Kumar Pandey; Krishnendu Bhattacharyya; Anil Kumar Gautam; Sohita Rajput; Mani Shankar Mandal; Ali J. Chamkha; Dhananjay Yadav
The current research focuses the light on the characterization of buoyancy-driven non-linear mixed convection and non-linear radiation in a Newtonian flow over a non-linearly stretching vertical sheet, and this type of flow has useful applications in many industrial processes, such as the paper and pulp industry, polymer industry, electronic device cooling, solar collectors, gas turbine plants, and nuclear power. Using appropriate transformations, governing PDEs for non-linear mixed convection are reduced to higher-order non-linear ODEs and those are numerically solved. Along with tabular presentations of computed results, the graphical representations are generated to elucidate the effects of involved parameters on convection transport properties and their inter-relations. It demonstrates that flow velocity increases near the surface and decreases away from the surface as the non-linear convection parameter increases. Furthermore, increments in the thermal buoyancy, temperature ratio and non-linear radiation parameters result in the boost of velocity. The temperature decreases as linear and non-linear buoyancy-related parameters (non-linear convection and thermal buoyancy parameters) are of higher levels. In contrast, the temperature rises with two non-linear thermal radiation-related parameters (thermal ratio and non-linear radiation parameters). For greater values of the non-linear stretching related parameter, a lower velocity and a higher temperature are witnessed. The non-linear convection, thermal buoyancy, thermal ratio and non-linear radiation parameters contribute toward the reduction of the magnitude of surface-drag force and growth of the surface cooling rate. But, with the non-linearity in surface stretching there are significant percentage hikes of surface-drag force magnitude and surface cooling rate. © 2022 The Authors
Linear and nonlinear investigations of the impact of chemical reaction on the thermohaline convection in a permeable layer saturated with Casson fluid
(American Institute of Physics Inc., 2024) Dhananjay Yadav; Sanjith Bharatharajan Nair; Mukesh Kumar Awasthi; Ravi Ragoju; Krishnendu Bhattacharyya
In this effort, the consequence of chemical reaction on the thermohaline convection in a permeable layer containing Casson fluid is inspected utilizing both linear and nonlinear stability procedures. To model the momentum equation, the Casson fluid version of Darcy's law is utilized. Applying the linear stability concept, the situation for the start of stationary and oscillatory pattern of convective motion is obtained, whereas the convective heat and mass transferences are determined using nonlinear stability theory. It is found that the oscillatory type of convective flow is probable only if the evaluation of the solutal Rayleigh-Darcy number is less than zero. The effect of the chemical reacting factor, the Casson factor, the Lewis number, and the solutal Rayleigh-Darcy number is to hurry the start of convection toward both stationary and oscillatory styles of convection and also surge the size of the convective cells. The convective heat and mass transfers enhance with increasing the Casson factor, the solutal and thermal Rayleigh-Darcy numbers while both decrease with enhancing the heat capacity quotient. The effect of chemical reacting factor is to increase the mass transmission in the system, while it has no effect on the heat transmission. It is also noted that the convective heat and mass transfers in the system enhance nearly 5.4% and 3.8%, respectively, with a 50% increase in the value of Casson factor. © 2024 Author(s).
Metal- and Catalyst-Free One-Pot Cascade Coupling of α-Enolic Dithioesters with in situ Generated 4-Chloro-3-formylcoumarin: Access to Thioxothiopyrano[3,2-c]chromen-5(2H)-ones
(Wiley-VCH Verlag, 2020) Dhananjay Yadav; Monish A. Ansari; Mitilesh Kumar; Maya Shankar Singh
An efficient and viable one-pot protocol for the synthesis of a specific class of 2-thioxothiopyrano[3,2-c] chromen-5(2H)-ones has been devised by the cross-coupling of 4-hydroxycoumarin and α-enolic dithioesters under metal- and additive-free conditions in open air. The reaction proceeds via in situ generation of 4-chloro-3-formylcoumarin followed by consecutive Michael-type addition/intramolecular cyclization/ elimination cascade, enabling the creation of thiopyran-2-thione ring over coumarin framework through successive formation of C−C and C−S bonds. Remarkably, the benign conditions, atom-economy, and quantifying forbearance of a wide horizon of functional groups are added characteristics to this strategy. (Figure presented.). © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Metal-Free One-Pot Annulative Coupling of 2-Hydroxybenzaldehydes with β-Ketothioamides: Access to Diverse 2-Arylimino-2 H-Chromenes
(American Chemical Society, 2022) Pragya Pali; Dhananjay Yadav; Subash C. Sahoo; Maya Shankar Singh
A concise and practical one-pot sustainable approach for expedient synthesis of 2-arylimino-2H-chromenes by two-component cascade [4 + 2] annulative coupling of easily available 2-hydroxybenzaldehydes with β-ketothioamides has been developed in good yields for the first time. Remarkably, metal- and additive-free conditions, use of simple K2CO3as a mild base, open atmosphere, exclusive regioselectivity, step/atom economy, nonhazardous reagents, and easy purification are added characteristics to the strategy. This annulative protocol will not only provide an efficient method to access diverse chromene scaffolds, but also enrich the research domain of β-ketothioamides. © 2022 American Chemical Society. All rights reserved.