Agro-Waste Extract Based Solvents: Emergence of Novel Green Solvent for the Design of Sustainable Processes in Catalysis and Organic Chemistry

Palladium nanoparticle catalyzed synthesis of indoles via intramolecular Heck cyclisation

A system utilizing palladium(II)-PEG has been devised for the intramolecular Heck cyclization of N-vinyl and N-allyl-2-haloanilines. The synthesis of a variety of indoles, including 2,3-diester substituted ones and 3-methyl indoles, has been accomplished using this catalytic system. The N-vinyl starting materials are obtained by the aza-Michael addition of 2-haloanilines with alkynecarboxylate esters, which, upon cyclization, yield ester-substituted indoles. Conversely, N-allyl-2-haloanilines yield 3-methylated indoles as the major products. The high activity of the system is owed to the in situ generation of Pd nanoparticles.

Nanostructural Design of ZnO Using an Agro-Waste Extract for a Sustainable Process and Its Photocatalytic Activity

The use of agro-waste extracts (AWEs) as a sustainable medium for developing cost-effective and ecologically friendly nanomaterials has piqued the interest of current researchers. Herein, waste extracts from papaya barks, banana peels, thumba plants, and snail shells were used for synthesizing ZnO nanostructures via a hydrothermal method, followed by calcination at 400 °C. The crystallinity and pure wurtzite phase formation of ZnO nanostructures were confirmed via X-ray diffraction. ZnO nanostructures with various morphologies such as tight sheet-like, spherical, porous sheet-like, and bracket-shaped, comprising small interconnected particles with a highly catalytically active exposed (0001) facet, were observed via field emission scanning electron microscopy and transmission electron microscopy. The formation mechanism of the various morphologies of the ZnO nanostructures was proposed. Ultraviolet-visible spectra showed different absorption band edges of ZnO nanostructures with a bandgap in the range of 3.17-3.27 eV. Photoluminescence studies showed the presence of various defect states such as oxygen and zinc vacancies and oxygen and zinc interstitials on ZnO nanostructures, which are usually observed in traditionally prepared ZnO. The photocatalytic activity of ZnO nanostructures was evaluated under direct sunlight using rhodamine B (RhB) and Congo red (CR) dyes as probe pollutants. Furthermore, prepared ZnO nanostructures could potentially adsorb anionic dyes (e.g., CR) in the absence of light. Superoxide and hydroxide radicals played a vital role in the photocatalytic activity of ZnO. The photocatalyst could be reused for up to three cycles, indicating its stability. Therefore, this study reports the diverse use of AWEs as cost-effective media for nanomaterial synthesis.

Synthesis, characterization, and photocatalytic activity of ZnO nanoparticles using water extract of waste coconut husk

The present work reports the use of natural alkaline extract from coconut husk ash as a precipitating agent for metal oxide nanoparticles synthesis. The abundance of K₂O and K₂CO₃ in it makes the extract highly basic and could be the alternative source of basic media in the laboratory. In this study, highly photoactive zinc oxide nanoparticles have been synthesized using water extract of waste coconut husk ash in a green approach which is considered as replacement of homogeneous base like NaOH and KOH. The formation of zinc oxide nanoparticles at different pH of the solution of coconut husk ash was confirmed through powder XRD, BET, SEM-EDX, UV-Vis, FTIR, and photoluminescence spectroscopy. The photocatalytic performance of the samples was evaluated through the degradation of methylene blue (MB) and methyl orange (MO) under solar irradiation which undergo degradation around 97% and 68% within 120 min, respectively. The high photocatalytic activity and rate constant could be attributed to the large surface area due to small particle size that could provide quicker photon absorption and reduction of charge carrier recombination. This current work introduces a new method to reduce energy consumption for the synthesis of highly photoactive low-cost zinc oxide nanoparticles.

Dual Functionality of Choline Hydroxide for the Dakin Reaction

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A facile synthetic approach to Dakin oxidation utilizing green conditions was demonstrated. A combination of hydrogen peroxide and aqueous choline hydroxide in cooperation with various hydroxyl aryl aldehydes and ketones was used to provide the corresponding dihydric aromatic compounds. The whole procedure was conducted at ambient temperature in an aerobic environment. The scope of ChOH/H2O2 platform was also investigated, showing that the reactivity of the present platform was highly dependent on the position of the hydroxy group of the aromatic ring.

Synthesis of bioactive scaffolds catalyzed by agro-waste-based solvent medium

The backbone of synthetic organic chemistry is the formation of carbon–carbon and carbon–heteroatom bonds. Scientists are actively working to develop new methods of bond-forming reactions because it is one of the most useful tools for the development of structurally diverse molecular entities. On the other hand, scientists are constantly discovering chemical processes to make them more sustainable in order to avoid the ever-increasing chemical emission associated with hazards to the environment. Thus, the development of greener catalytic reactions demonstrated a massive uptick in the ability to carry out carbon–carbon and carbon–heteroatom bond-forming reactions under environmentally friendly and simple reaction conditions. Various approaches are demonstrated, namely, solvent-free, microwave irradiation, ionic liquids, ball milling, ultrasound, one-pot, and aqueous-mediated methods under green chemistry protocol. Agro-waste is the postharvest part or agricultural residues derived from various agricultural activities, which has diverse scope and applications. The use of this agro-waste is an eco-friendly and cost-effective process of waste management. Appropriate and optimal utilization of these waste by-products is one of the major challenges in the present days. The recent trend around the globe is to transform waste into wealth concepts to achieve various applications. Agro-waste-derived ashes and extracted medium are successfully studied recently as a heterogeneous- or homogenous-based catalyst in various organic transformations. Agro-waste-derived catalysts are easily available, cost-effective, simple to prepare, nontoxic, easy to handle, biodegradable, and more environmentally benign. This article focuses more on a few instances of agro-waste-based homogeneous and heterogeneous organic synthesis, especially those used in the construction of bioactive molecule synthesis via C–C and C–X bond formation reactions are discussed. The compiled literature in this article is based on keywords used in the search engine on “agro-waste-based catalyst for organic transformations”, and review articles published on this topic, future scope, and summary are discussed.

Water extract of red mud: an efficient and renewable medium for environmentally benign synthesis of 2-amino-4H-chromenes

In this study, an efficient and convenient domino Michael addition/intramolecular cyclization protocol is presented for the synthesis of biologically relevant 2-amino-4H-chromenes in short reaction times using water extract of red mud (WERM) at room temperature. Red mud is generated abundantly as wastes in aluminum industries and this is the first report to utilize WERM as an effective and renewable medium in organic synthesis. As the precursor material is a waste, the present method is environmentally benign and economical. The final 2-amino-4H-chromenes were obtained in high yields by simple precipitation and subsequent washing by aqueous ethanol which eliminates the chromatographic separation. The present method is tolerated by electronically diverse functional groups and also applicable for large-scale synthesis. Moreover, WERM was recovered from the reaction medium and reused for several cycles without significant loss of reactivity.

Agro-waste sourced catalyst as an eco-friendly and sustainable approach for Knoevenagel condensation reaction

Background:

The present work describes an eco-friendly and sustainable approach for the Knoevenagel condensation of an aromatic aldehyde with ethyl cyanoacetate, and salicylaldehyde with Meldrum acid for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin (2-oxo-2H-1-benzopyran) derivatives, respectively. The reaction performed under greener catalytic media Water Extract of Watermelon Fruit Peel Ash (WEWFPA) is an eco-friendly protocol derived from the agro-waste feedstock. Various protocols have been reported for the synthesis of Knoevenagel condensation reaction using a hazardous catalyst or/and solvent found toxic to the environment, reaction time longer, poor yield, and required purification of the final product. The present method provides several added advantages of being completely greener, economic, giving high yield, inexpensive catalyst, and the final product isolated in pure form with good yield.

Objective:

The objective of the study was to develop a green methodology for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives.

Results:

The agro-waste based catalyst developed avoids the use of external inorganic/organic base, additives, and solvent-free synthesis of Knoevenagel condensation of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives under rt and microwave irradiation, respectively described. The microwave irradiation condition requires less time for the completion of the reaction and also gave better yield isolation

Methods:

We have demonstrated WEWFPA as a greener homogenous agro-waste is employed under rt stirring and microwave irradiation for the economic synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives. The developed method was found robust, non-hazardous and solvent-free with simple work-up gave target product.

Conclusion:

In conclusion, we have established an efficient, simple, agro-waste based catalytic approach for the synthesis of ethylbenzylidenecyanoacetate and 3-carboxy coumarin derivatives employing WEWFPA as an efficient catalyst under rt stirring and microwave synthesis, respectively. The method is a greener, economical and eco-friendly approach for the synthesis of Knoevenagel condensation products. The advantages of the present approach are solvent-free, no external metal, chemical base free, short reaction time and isolated product in good to excellent yields. The catalyst is agro-waste derived, which has abundant in natural sources, thus making the present approach a greener one.

Ultrasound-Promoted Sustainable Synthesis and Antimicrobial Evaluation of 2-Aryl Benzimidazoles Catalyzed by BPAE at Room Temperature

Background:

Present-day chemists are more interested in developing and using green chemistry protocol for various organic transformations, which employ natural feedstock extracts, and solvent-free, and greener catalysts; they are well known for their non-hazardous nature and have replaced many organic and inorganic based catalysts. In literature, the reported homogenous catalytic approaches have been employed for various bioactive heterocycle syntheses, which follow the green chemistry principle established for various organic transformations catalyzed by WERSA, BFE, WEPPA, WEMFSA, WEMPA, and Eichhorniacrassipes. Among them, 2-aryl benzimidazole derivatives have emerged as prominent molecules with a wide variety of applications in biological and material science.

Methods:

The agro-waste sourced from the banana peel is utilized for the preparation of BPAE catalyst, which is employed for the synthesis of 2-aryl benzimidazole derivatives under ultrasound waves at room temperature.

Results:

Here, 2-Aryl benzimidazoles synthesized through the reaction of a substituted o-phenylene diamine with substituted benzoyl chloride catalyzed by BPAE under ultrasound waves at room temperature are described. Furthermore, catalyst BPAE is characterized by flame emission spectrometry, SEM-EDX, and XRD techniques.

Conclusion:

The present work established an eco-friendly, sustainable and novel approach for the synthesis of 2-aryl benzimidazoles using natural feedstock BPAE. The major merits of BPAE include its use as an agro-waste-derived catalyst. It is also highly abundant, inexpensive, yields faster reactions, has a simple workup, and does not require the use of column chromatography.

Biomass waste-derived recyclable heterogeneous catalyst for aqueous aldol reaction and depolymerization of PET waste

Eco-friendly biomass waste-derived recyclable heterogeneous catalyst for aldol reaction in water and for methanolysis of PET waste.

Green strategies for transition metal-catalyzed C–H activation in molecular syntheses

Sustainable strategies for the activation of inert C–H bonds towards improved resource-economy.

Glycolysis of Poly(Ethylene Terephthalate) Using Biomass-Waste Derived Recyclable Heterogeneous Catalyst

Plastic production has increased by almost 200-fold annually from 2 million metric tons per year in 1950s to 359 million metric tons in 2018. With this rapidly increasing production, plastic pollution has become one of the most demanding environmental issues and tremendous efforts have been initiated by the research community for its disposal. In this present study, we reported for the first time, a biomass-waste-derived heterogeneous catalyst prepared from waste orange peel for the depolymerisation of poly(ethylene terephthalate) (PET) to its monomer, bis(2-hydroxyethyl terephthalate) (BHET). The prepared orange peel ash (OPA) catalyst was well-characterised using techniques such as IR, inductively coupled plasma (ICP)-OES (Optical Emission Spectrometry), XRD, X-ray fluorescence (XRF), SEM, energy-dispersive X-ray spectroscopy (EDX), TEM, BET (Brunauer-Emmett-Teller) and TGA. The catalyst was found to be composed of basic sites, high surface area, and a notable type-IV N₂ adsorption–desorption isotherm indicating the mesoporous nature of the catalyst, which might have eventually enhanced the rate of the reaction as well as the yield of the product. The catalyst completely depolymerises PET within 90 min, producing 79% of recrystallised BHET. The ability of reusing the catalysts for 5 consecutive runs without significant depreciation in the catalytic activity and its eco- and environmental-friendliness endorses this protocol as a greener route for PET recycling.

Suzuki-Miyaura cross coupling is not an informative reaction to demonstrate the performance of new solvents

The development and study of new solvents has become important due to a proliferation of regulations preventing or limiting the use of many conventional solvents. In this work, the suitability of the Suzuki-Miyaura reaction to demonstrate the usefulness of new solvents was evaluated, including Cyrene™, dimethyl isosorbide, ethyl lactate, 2-methyltetrahydrofuran (2-MeTHF), propylene carbonate, and γ-valerolactone (GVL). It was found that the cross coupling is often unaffected by the choice of solvent, and therefore the Suzuki-Miyaura reaction provides limited information regarding the usefulness of any particular solvent for organic synthesis.

Chemical Analysis of Traditional Food Additive Dokhora Khar Derived from Water Hyacinth (Eichhornia crassipes)

Background:

Dhokora khar (solid alkali), derived from water hyacinth (Eichhornia crassipes) is used by the people of Assam as a traditional food additive and as an antacid. It is usually prepared from the aqueous extract of water hyacinth ash. It is very popular in lower Assam particularly in the district of Barpeta and nearby areas. Apart from its use as a food additive in preparing palatable dishes, it is also used for the cure of ailments arising from stomach acidity and indigestion. In rural Assam, this khar finds applications as a natural fertilizer as well as a cleansing agent.

Methods:

Standard chemical and spectral procedures have been used to confirm the presence of acid and basic radicals. SEM-EDX, Atomic Absorption Spectrometry and Flame Photometry were used for information on chemical constituents.

Results:

Standard chemical and spectral procedures have been used to confirm the presence of acid and basic radicals. SEM-EDX, Atomic Absorption Spectrometry and Flame Photometry were used for information on chemical constituents.

Conclusion:

The investigation suggests that dokhora khar consists of a mixture of carbonates, chlorides, sulfates and phosphates of various metals such as K, Mg, Ca, Na, Fe, Mn, Zn, Cu, etc. Some of these metals such as Fe, Co, Mn, Ni, Cu, Zn, Cr, etc., are essential nutrients. Hence the results establish that the consumption of this traditional food additive by the natives of Assam provides health benefits.

Trash to Treasure: Eco-Friendly and Practical Synthesis of Amides by Nitriles Hydrolysis in WEPPA

The hydration of nitriles to amides in a water extract of pomelo peel ash (WEPPA) was realized with moderate to excellent yields without using external transition metals, bases or organic solvents. This reaction features a broad substrate scope, wide functional group tolerance, prominent chemoselectivity, and good reusability. Notably, a magnification experiment in this bio-based solvent at 100 mmol further demonstrated its practicability.

WEPA: a bio-derived medium for added base, π-acid and ligand free Ullmann coupling of aryl halides using Pd(OAc)2

A bio-derived sustainable medium based on water extract of pomegranate ash (WEPA) has, for the first time, been developed for the homocoupling of aryl halides under palladium-assistance. Avoiding the requirement of an external base, ligand and π-acid, the use of the proposed renewable medium offers remarkable attributes like wide substrate scope, good to nearly quantitative yields of biphenyls with exceptional chemoselectivity and scale up viability.