Solvent-free Reaction Conditions Research Articles

Metal-free regioselective construction of 2-aryl-substituted quinolines via Aza-Henry (Nitro-Mannich) reactions under neat conditions

A new and practical synthetic approach to construct 2-aryl-quinoline derivatives has been described through the sequential Aza-Henry (Nitro-Mannich) reaction using readily available 2,3-dihydro-1H-inden-5-amines, aldehydes and nitroalkanes under one-pot solvent-free reaction conditions using TsOH·H2O as the sustainable catalyst. In this regioselective approach, we described a cascade that proceeds through a sequential imine formation/Aza-Henry reaction/cyclization/denitration/rearrangement followed by oxidative aromatization to afford diverse 2-aryl-quinolines. This approach features large substrate scope, good functional group tolerance, mild reaction conditions and excellent yields with gram scale synthetic utility.

Novel Methodologies for Chemical Activation in Organic Synthesis under Solvent-Free Reaction Conditions.

One central challenge for XXI century chemists is the development of sustainable processes that do not represent a risk either to humanity or to the environment. In this regard, the search for more efficient and clean alternatives to achieve the chemical activation of molecules involved in chemical transformations has played a prominent role in recent years. The use of microwave or UV-Vis light irradiation, and mechanochemical activation is already widespread in many laboratories. Nevertheless, an additional condition to achieve “green” processes comes from the point of view of so-called atom economy. The removal of solvents from chemical reactions generally leads to cleaner, more efficient and more economical processes. This review presents several illustrative applications of the use of sustainable protocols in the synthesis of organic compounds under solvent-free reaction conditions.

N-Iodosuccinimide as a Precatalyst for Direct Cross-Coupling of Alcohols with C-Nucleophiles under Solvent-Free Reaction Conditions

C–C bond formation is one of the most important implements in synthetic organic chemistry. In pursuit of effective synthetic routes functioning under greener pathways to achieve direct C–C bond formation, we report N-iodosuccinimide (NIS) as the most effective precatalyst among the N-halosuccinimides (NXSs) for the direct cross-coupling of benzyl alcohols with C-nucleophiles under solvent-free reaction conditions (SFRC). The protocol is metal-free, and air- and water-tolerant, providing a large-scale synthesis with almost quantitative yields.

CO2 cycloaddition to epichlorohydrin over an aluminum fumarate metal-organic framework synthesized by a sonochemical route

Aluminum fumarate was tested as a catalyst for CO 2 cycloaddition to epichlorohydrin under solvent-free reaction conditions. This material was synthesized hydrothermally via a sonochemical route (Al fumarate-(S)), which exhibited a higher catalytic activity than Al fumarate synthesized by a conventional method owing to the higher number of Lewis acid sites formed in Al fumarate-(S). The CO 2 uptake of Al fumarate-(S) was high: approximately 269 mg g −1 at 25 °C and 10 bar. High conversion (96%) of epichlorohydrin with excellent selectivity (97%) to cyclic carbonate was obtained at 50 °C and 10 bar CO 2 after 6 h of reaction. The kinetic analysis of the reaction confirmed an approximately 1st order dependence on the epichlorohydrin concentration and CO 2 pressure with an activation energy of approximately 39 kJ mol −1 . The recovered Al fumarate-(S) catalyst, however, showed a steady decline in catalytic activity during the recycling runs, as reported for other metal-organic framework catalysts. The deactivation was monitored by N 2 adsorption-desorption isotherms and spectroscopic analyses. • The aluminum fumarate metal-organic framework was synthesized via a sonochemical route. • It showed higher amounts of Lewis acid sites and more active for CO 2 cycloaddition than the one conventionally prepared. • A reaction mechanism for CO 2 cycloaddition to epichlorohydrin was proposed.

Synthesis of Nano ZnO: A Catalyst for N-formylation of Aromatic Amines and Biodiesel Application

Background: Zinc oxide nanoparticles prepared from an easy, eco-friendly and cost-effective green combustion technique using an extract of turmeric root has been an immense attractive nanomaterial that is used widely in light emitting display systems, piezoeletricity, electric conductivity, and biological applications. The prepared samples were characterized for their structural and morphological study using various analytical techniques. Results: Crystallite size was calculated by both XRD as well as UV-visible absorption measurements and Crystallite size was found to be 14-36 nm. An equation was developed with the aid of an effective mass model (Brus 1986) to calculate the size of the particle as a function of the peak absorbance wavelength. The energy bandgap of the synthesized sample calculated to be in the range of 4.74 - 5.0 eV by UV-Vis spectra confirms the quantum confinement. ZnO nanocatalyst is used for the synthesis of biodiesel from garcinia gummigutta seed oil has been studied. The environmental friendly procedure was carried for the formylation of amines under solvent-free reaction condition and simple work-up giving pure products with prompt recyclability behavior are the main features of the reaction. Conclusion: In this work, ZnO NPs were synthesised using turmeric root extract as a fuel via green combustion method. It is an environmentally friendly, easy as well as cost-effective method for the synthesis of nanoparticles. ZnO NPs were examined through various equipments such as PXRD, UV-Vis, FTIR, and SEM studies. XRD study show the hexagonal wurtzite structure. it is a good catalyst for the synthesis of biodiesel from the pongamiapinnata oil. It also serves as a catalyst for the Nformylation reactions, which involves the clean procedure under milder reaction conditions with an excellent yield of the desired products

A green and chemoselective synthesis of coumarins via Pechmann condensation using recoverable heterogeneous catalyst (Au@pSiO2)

Nano Au@porous SiO2 as a heterogeneous catalyst was prepared and characterized by Fourier transform infrared, X‐ray powder diffraction, transmission electron microscopy, thermogravimetric analysis and inductively coupled plasma–atomic emission spectroscopy techniques and then used as an efficient catalyst in the condensation of various phenols with ethyl acetoacetate for the preparation of coumarin derivatives through the Pechmann reaction. The combined merits of chemoselective and solvent free reaction conditions and the recyclability of the nanostructured catalyst make the condensation a safe operation, with low pollution, rapid access to products and simple workup.

Simple and solvent free practical procedure for chalcones: An expeditious, mild and greener approach

An extremely simple, expeditious and greener synthetic method for a variety of chalcone derivatives (3) under mild and solvent free reaction conditions has been developed. The present protocol discloses the use of p-toluenesulfonic acid (p-TSA) as a solid phase organocatalyst which accelerates the Claisen–Schmidt condensation reaction dramatically under mild conditions. Various aryl aldehydes (1) were treated with differently substituted aryl ketones (2) in the presence of p-TSA at 50–60 ​°C to yield the desired products in a very short period of reaction time. Mild reaction conditions, clean reaction media, expulsion of hazardous solvents, simple work-up, exclusive formation of products in high yields without side products, and easy purification are advantages of the present methodology.

Sulfonated Magnetic Nanoparticles as Recyclable Catalyst for Facile One-Pot Green Synthesis of 3,4-Dihydro-2H-indazolo[1,2-b]phthalazine-1,6,11(13H)-trione Derivatives

Sulfonated magnetic nanoparticles (SO3H-Fe3O4@SiO2 MNPs) have been explored as an efficient, cost-effective, and recyclable nanocatalyst for the facile synthesis of 3,4-dihydro-2H-indazolo[1,2-b]phthalazin-1,6,11(13H)-triones through a one-pot three-component reaction between aldehydes, dimedone, and phthalhydrazide under mild and green (solvent-free) conditions. Simple separation of the catalyst using an external magnet, efficient recyclability of the developed magnetic nanocatalyst up to five fresh runs without significant loss in its catalytic activity, excellent yields of the designed reactions (88 to 98%), low reaction times as well as solvent-free and facial reaction condition are some advantages of the present procedure that qualified the fabricated magnetic nanocatalyst for industrial applications.

Functional hexanuclear Y(III) cluster-based MOFs supported Pd(II) single site catalysts for aerobic selective oxidation of styrene

Oxidation of styrene is one of the significant reactions in organic synthesis. In this work, a serious of PdCl2 moiety-decorated Y6-MOFs adopting post-synthetic strategy were fabricated as applicable single-site catalysts for oxidation of styrene. Specifically, the functional organic linker, H2bpydc (2,2′-bipyridine-5,5′-dicarboxylic acid), was first incorporated quantitatively into Y6 clusters-based MOF, [(CH3)2NH2]2[Y6(μ3-OH)8(bpdc)6] (bpdc = 4,4′-biphenyl dicarboxylic acid) via post-synthetic ligand exchange. Then post-synthetic Pd(II) metalation was performed to enhance the density of isolated single sites. The obtained Pd(II)-Y-bpydcx/bpdc1-x can be used as highly efficient heterogeneous single-site catalysts to promote selective oxidative cleavage of styrene to benzaldehyde using O2 as a oxidant under solvent-free and mild reaction conditions (1 atm and 80 °C). Importantly, when using Pd(II)-Y-bpydc0.8/bpdc0.2 (0.024 mmol Pd) as catalyst, the high conversion of styrene and the selectivity for benzaldehyde can reach 88.7 % and 82.2 %, respectively.

A Three-Dimensional Cu(II)-MOF with Lewis acid−base dual functional sites for Chemical Fixation of CO2 via Cyclic Carbonate Synthesis

A 3D porous Cu(II)-MOF (1), having Lewis acid−base dual-functional sites, has been utilized, whose frameworks have two types of 1D channels decorated with both axially water-bound metal sites and weak base, i.e., tertiary amine groups in the crystallographic c-axis. Upon activation under a high vacuum at 120 °C, the axial water molecule is removed and affords a solvent-free and unsaturated Lewis acidic Cu(II) containing framework (1′). The piperazine functionalities from the linkers enhance the selective adsorption of CO2 which, in turn, facilitate the further interaction with the open Cu(II) metal centres, leading to catalytic chemical fixation of CO2 into five-membered cyclic carbonates, in the presence of epoxides and co-catalyst TBAB, under mild and solvent-free reaction conditions. The significance of dual functionalization and the synergy with TBAB on adeptly catalyzed CO2 fixation are explored using several epoxides, and substantial conversion is achieved. Moreover, the catalyst 1′ displays satisfactory stability and easy recyclability for five consecutive cycles without any appreciable loss in its catalytic activity. The results are compared with various MOFs based catalysts at the closest reaction conditions and, based on literature and experimental inferences, a possible mechanism of chemical fixation of CO2 with epoxide catalyzed by 1′ has been proposed.

Solvent-Free Environmentally Benign Approach for the Selective Olefin Epoxidation Catalyzed by Mn(III)-Immobilized Mesoporous Nanoarchitectonics.

Immobilization of transition metal complexes at the surface of 2D-hexagonal functionalized SBA-15 material is one of the promising strategies in designing an efficient catalytic system for the olefin epoxidation reaction. Here we have immobilized Mn(III) on the Schiff-base anchore 2D-hexagonally ordered functionalised mesoporous SBA-15 material. Powder X-ray diffraction (PXRD), N₂-sorption and high resolution transmission electron microscopic (HRTEM) studies of the resulting SBA-15-SB-Mn material suggested 2D-hexagonally ordered porous nanostructure and X-ray photoelectron spectroscopy (XPS) analysis suggested the presence of surface bound Mn(III) species in this nanomaterial. This mesoporous material showed excellent performance in the selective catalytic oxidation of various alkenes to the corresponding epoxides in the presence of tert-butyl hydroperoxide (TBHP, 70% aqueous solution) as oxidant under solvent-free mild reaction conditions together with high recycling efficiency.

N-Halosuccinimides as Precatalysts for C-, N-, O-, and X-Nucleophilic Substitution Reactions of Alcohols under Mild Reaction Conditions

N-halosuccinimides (chloro, bromo, and iodo, respectively) were introduced, tested, and applied as efficient and non-metal precatalysts for C-, N-, O-, and X-nucleophilic substitution reactions of alcohols under solvent-free reaction conditions (SFRC) or under high substrate concentration reaction conditions (HCRC) efficiently and selectively, into the corresponding products.

MIL-101(Cr) for CO2 Conversion into Cyclic Carbonates, Under Solvent and Co-Catalyst Free Mild Reaction Conditions

Mild reaction conditions (nearly room temperature and atmospheric CO2 pressure) for the cycloaddition of CO2 with epoxides to produce cyclic carbonates were investigated applying MIL-101(Cr) as a catalyst. The MIL-101 catalyst contains strong acid sites, which promote the ring-opening of the epoxide substrate. Moreover, the high surface area, enabling the adsorption of more CO2 (substrate), combined with a large pore size of the catalyst is essential for the catalytic performance. Additionally, epoxide substrates bearing electron-withdrawing substituents or having a low boiling point demonstrated an excellent conversion towards the cyclic carbonates. MIL-101(Cr) for the cycloaddition of carbon dioxide with epoxides is demonstrated to be a robust and stable catalyst able to be re-used at least five times without loss in activity.

Solvent-free synthesis of 1-amidoalkyl-2-naphthols using magnetic nanoparticle-supported 2-(((4-(1-iminoethyl)phenyl)imino)methyl)phenol Cu (II) or Zn (II) Schiff base complexes

Two magnetic nanoparticle-supported 2-(((4-(1-iminoethyl)phenyl)imino)methyl)phenols were successfully synthesized, characterized, and applied in the one-pot three-component reaction of substituted benzaldehydes, 2-naphthol, and amides for synthesis of 1-amidoalkyl-2-naphthols. These three-component processes occurred under solvent-free reaction conditions at 80 °C. The magnetically recoverable supported Schiff base metal catalysts can be reused several times in the model reaction. The synthesized catalysts are also easily separated from the reaction mixture by applying an external magnet. This procedure offers the advantages of simple, operational procedure as well as no use of hazardous organic solvents.

Microwave-Assisted Synthesis of Some Indole and Isoniazid Derivatives as Antitubercular Agents and Molecular Docking Study

An efficient and expeditious microwave-assisted synthesis of isoniazid derivatives from various indole-3-carbaldehydes, phenols, and isoniazid via Betti’s reaction under one pot, solvent-free, and green reaction conditions is described. The same compounds were also prepared by conventional method. Relatively short reaction time and good yields make the proposed protocol highly significant. The structures of the newly synthesized compounds were confirmed by spectral and analytical data. The synthesized compounds were evaluated for their potential in vitro antitubercular activity against M. tuberculosis H37Rv strain using Alamar Blue assay. Some of the tested compounds were found to be highly active against M. tuberculosis H37Rv with minimum inhibitory concentrations of 3.12, 6.25, and 12.5 µg/mL, while the others showed a moderate activity. Docking of the potent compounds inside the active site of the target enzyme mycobacterial enoyl reductase (InhA) (FabI ENR, PDB code 4TZK) was performed in order to interpret the results.

A Facile, Efficient and Solvent-Free Titanium (IV) Ethoxide Catalysed Knoevenagel Condensation of Aldehydes and Active Methylenes

: Titanium ethoxide has been employed as a novel and efficient reagent for the Knoevenagel condensation of aldehydes with active methylenes such as diethyl malonate and ethyl cyanoacetate under solvent free conditions to afford substituted olefins in high to excellent yields. The reaction is suitable for a variety of aromatic, aliphatic and heteroaromatic aldehydes with various active methylenes. Parallel to this, microwave irradiation has been utilized to achieve improved reaction rates and enhanced yields. Herein, we illustrated a convenient method for the preparation of α,β-unsaturated compounds using both conventional and microwave irradiation methods. An efficient and solvent free Knoevenagel condensation between aldehydes and active methylenes was developed using titanium ethoxide. The procedure proved to be successful with a wide range of substrates such as aromatic, aliphatic and heterocyclic aldehydes and various active methylenes to afford substituted olefins. The reaction was also carried out under microwave irradiation to accomplish the corresponding olefins with improved reaction rates, yields and cleaner reaction profiles.We have developed an efficient and novel methodology for the synthesis of olefinic compounds by Knoevenagel condensation under solvent-free conditions using titanium ethoxide, for the first time, as a reagent as well as a solvent. This method is appropriate for the synthesis of a variety of aromatic aldehydes containing various electron-donating and withdrawing groups, aliphatic and heteroaromatic aldehydes. The significant advantages offered by this methodology could be applied to various active methylenes in order to offer the corresponding Knoevenagel products. Thus, we believe that this method delivers high conversions, cleaner reaction profiles under solvent-free reaction conditions and shorter reaction times, all of which make it a very useful and attractive approach for the preparation of a wide range of substituted olefins.

NaAlO2‐Promoted Mesoporous Catalysts for Room temperature Knoevenagel Condensation Reaction

AbstractMesoporous solid base catalysts are essential candidates for green and sustainable catalytic processes. In this work, novel mesoporous solid base catalysts was synthesized by promoting mesoporous supports with sodium aluminate (NaAlO2). The prepared catalysts are characterized using a wide variety of molecular and solid‐state techniques to determine their structural and textural properties. The catalysts texture was strongly affected by the promotion of sodium aluminate. The nature of the support and the sodium aluminate loading are shown to play a crucial role on the total basicity. In turn, these NaAlO2‐containing mesoporous materials showed high catalytic activity for Knoevenagel condensation under solvent free reaction conditions. The catalysts are truly heterogeneous without leaching any active sites and also showed good reusability.

Eco-friendly heteropoly acid supported on natural clay for the synthesis of calix[4]resorcinarene derivatives

The catalytic activity of green catalyst heteropoly-11-tungsto-1-vanadophosphoric acid, H4[PVW11O40] (HPV) supported on activated natural clay (HPVAC) has been tested towards the synthesis of calix[4]resorcinarene under solvent-free condition. It is a one-pot multi-component condensation reaction of four moles of aromatic aldehydes with four moles of resorcinol. The advantages of the protocol, solvent-free heterogeneous reaction condition, simple workup procedure, short reaction time, high yield of products and reusability of the catalyst make this method to declare as green approach for synthesis of calix[4]resorcinarene.

An efficient protocol for synthesis of novel polyheterocyclic chromeno pyrimido[1,2-b]indazolone derivatives using [Et3NH][HSO4] as a reusable catalyst under solvent-free conditions

A convenient and highly efficient method for the synthesis of novel polyheterocyclic chromeno pyrimido[1,2-b]indazolone derivatives via a three-component condensation of 1H-indazol-3-amine, aldehydes and 4-hydroxycoumarin catalyzed by Bronsted acid ionic liquid [Et3NH][HSO4] under solvent-free reaction conditions is presented. This ionic liquid is air and water stable and easy to prepare from amine and acid. The main advantages of this protocol includes short reaction time, excellent yield, easy work-up, operational simplicity, a wide range of functional group tolerance and column chromatography-free method. The catalyst can be recovered and reused for at least four runs without any significant impact on the product yields.

Synthesis of a new chiral organocatalyst derived from (S)-proline containing a 1,2,4-triazolyl moiety and its application in the asymmetric aldol reaction. Importance of one molecule of water generated in situ

A simple and efficient preparation of a novel chiral derivative of (S)-proline containing a 1,2,4-triazolyl moiety is described. The high-yielding synthetic protocol includes the use of microwave irradiation to afford new chiral pyrrolidine derivatives in high yield. Our triazolyl-containing heterocycle was evaluated as organocatalyst (10 mol% load, under neat reaction conditions) in the enantioselective aldol reaction between four different types of ketones and a variety of aryl aldehydes. Good results in terms of enantioselectivity and chemical yield were observed under solvent-free reaction conditions and in the absence of any additive. Evidence is provided for the involvement of the water molecule generated upon enamine formation in the transition state of the aldol reaction.