Current Green Chemistry (v.3, #2)

Meet Our Editorial Board Member by M.R. Jayapal (119-119).

Ionic Liquid in Multicomponent Reactions: A Brief Review by Lennine R. Melo, Wender A. Silva (120-132).
Chemistry today is focused on the development of most effective reactions and methodologies that should be used in more sustainable and eco-friendly conditions. The ionic liquids are recognized for their ability to form clusters and enhance properties of certain catalysts. Attempts to connect the advantages of catalysis in ionic liquids (IL) with multicomponent reaction (MCR) are found. Multicomponent Reactions (MCRs) offer many advantages, and due to there ability to quickly create molecular diversity and molecular complexity allowing the generation of compounds containing essentially all atoms of reactants, they have become an important new way of synthesizing bioactive products. Methods: The main results reported from 2012 until the present day are summarized in this review about catalysis in ionic liquids (IL) with multicomponent reaction (MCR). Results: Several research groups are highlighted in catalysis study in ionic liquids to further enhance the results of possibilities within the universe of multicomponent reactions, showing his versatility in synthesizing complex systems with high convergence and good yields. Conclusion: A wide range of multicomponent reaction in ionic liquid showed in this review confirms that this area of science stands out for presenting general methods and mild and environmentally friendly conditions.

Sample Treatment in Organic Compound Determination: A Green Chemistry Perspective by Noemí M. Fernández, Ana M. Coto-García, Raquel Gonzalo-Lumbreras, Jon Sanz-Landaluze, Concepción Pérez-Conde, Carmen Cámara (133-144).
Background: Analysis of organic compounds in several complex matrices is a growing need and great efforts have been made to achieve analytical characteristics for their quantification or identification in small samples. Sample treatment in terms of time spent, and the use of large amounts of solvents, generating considerable amounts of wastes are the most limiting aspects of an analytical method.
Methods: Here, we review the features of different extraction and cleaning techniques for organic compound determination from a green chemistry perspective.
Results: The large number of techniques discussed in this review implies a great advance in comparison to conventional extraction techniques in terms of solvent consumption, extraction time or automation. The current trend of miniaturization of the extraction process is a viable alternative from a Green Chemistry perspective. Miniaturization involves reduction of amounts of organic solvents and wastes, and also the contamination risk or analyte losses. Thus, automation of the whole analytical process is facilitated. Final decision regarding the extraction technique to choose in each analysis will depend on the type of compounds to be determined, the type of sample or matrix and their concentration. Combination of microextraction techniques with novel extractants or new sorbents will open the door either to improve current extraction techniques or to develop new ones aiming to diminish environmental damage and enabling the automation of the process.

Allylic Amination via Acid Catalyzed Leaving Group Activation by Marija Skvorcova, Aigars Jirgensons (145-159).
Background: Allylic amination via acid catalyzed activation of a leaving group is promoted by non-expensive and low toxicity Lewis acid and Bronsted acid catalysts to give valuable allyl amine derivatives. In many cases, non-toxic byproducts such as water or acetic acid are generated. Moreover catalysts that perform the reactions in water as a solvent and the use of recyclable catalysts have been developed.
Methods: Peer-reviewed research literature methods on allylic amination via acid catalyzed activation were compiled using data bases such as Sci-Finder and Scopus.
Results: The mini-review summarizes the most important methods for allylic amination via acid catalyzed activation of a leaving group in the recent decade. These are divide in two main groups - Lewis acid and Bronsted acid catalysed reactions.
Conclusion: Allylic amination via acid catalyzed activation of a leaving group meet criteria of the green chemistry paradigm which has motivated method development for this type of reaction in recent years.

Background: Synthesis of heterocyclic compounds containing the isoxazole structural unit is important, as many of these compounds and their derivatives show biological activity. The use of green solvents in organic synthesis is an area of extensive research and several green solvents like water, ionic liquids, polyethylene glycol and some bio based solvents have been reported in the literature. The current paper discusses the synthesis of a series of arylmethylidene isoxazolone derivatives by a one pot three component condensation reaction between ethyl acetoacetate, hydroxylamine hydrochloride and aromatic aldehydes, in the presence of cerium chloride heptahydrate, a mild water tolerant Lewis acid as a catalyst and 70% ethyl lactate as the solvent.
Methods: Several isoxazolone derivatives were synthesized by the developed protocol and they were characterized by m.p., IR, 1H NMR, CMR, HRMS and comparison with reported data.
Results: Good to moderate yields of the desired isoxazolone derivatives were obtained with aldehydes having electron releasing substituents as well as pi excessive heterocycles. In addition, as compared to previous reports, the reaction yields the desired product in moderate yields with halo substituted aldehydes as well.
Conclusion: We have developed a protocol with easy workup for the facile synthesis of isoxazol- 5(4H)- ones using cerium chloride heptahydrate in 70% ethyl lactate which is a biodegradable solvent. The reaction is carried out at room temperature and the catalyst and solvent are recyclable up to three times without appreciable loss in activity.

In this study, silica sodium carbonate (SSC) as an eco-friendly solid recyclable Bronsted base and highly efficient catalyst has been successfully applied to green and promoted selective synthesis of benzylpyrazolocoumarins in aqueous medium. Using this solid Bronsted catalyst has some advantages in the synthesis of benzylpyrazolocoumarins including obtaining excellent yields of products, short reaction times, green and safety protocol, easy to handle, and capability of catalyst to recycle. By this achievement some interesting potential biological active compounds were obtained via a green procedure.
Methods: A green and highly efficient protocol for the catalytic synthesis of benzylpyrazolocoumarins by the use of SSC as an eco-friendly and recyclable Bronsted base is introduced.
Results: Some potential biologically active benzylpyrazolocoumarins were efficiently synthesized via a green Domino reaction. To examine generality of the reaction, a wide range of both electron-rich and electron-poor aryl aldehydes were applied. The efficiency of catalyst on the reaction progress with other acidic and basic catalysts were studied and compared with each other. Also, the capability of the catalyst to reuse was evaluated that the results showed SSC can be reused upto five times without remarkable miss of activity.
Conclusion: The SSC showed that could successfully catalyze alternative Knoevenagel condensations and Michael addition reactions. Furthermore, by this achievement some important potential biologically active products were efficiently synthesized in a green procedure.

Background: Water becomes much less polar with increasing temperature, and thus, the solubility of organics in subcritical water is dramatically enhanced. This allows efficient extraction of organic compounds using subcritical water as the extraction fluid while eliminating the use of hazardous organic solvents. Another recently developed separation technique, high temperature liquid chromatography (HTLC), offers several advantages including shorter separation time, better separation efficiency, and reduced quantity of organic modifiers required for the mobile phase.
Methods: In this study, a greener separation approach, the on-line coupling of subcritical water extraction (SBWE) with high temperature liquid chromatography was investigated. The extracted analytes were collected in a short trapping column during subcritical water extraction. Then the HTLC mobile phase was arranged to pass through the trapping column, sweeping the collected analytes, and delivering them into the HTLC separation column.
Results: This on-line SBWE-HTLC system was tested using three very different classes of analytes: BTX (benzene, toluene, and p-xylene), phenols, and benzoic acid derivatives. The extraction matrices were spiked sand and Isatis indigotica roots to mimic soil and medicinal herb samples. The recoveries obtained by SBWE-HTLC are comparable to those obtained by SBWE-HPLC developed previously.
Conclusion: The results of our study reveal that this new SBWE-HTLC coupling technique is as efficient and reliable as the SBWE-HPLC coupling approach. Since organic solvents are eliminated during the subcritical water extraction step and significantly reduced in the high temperature liquid chromatography step, this is an attractive greener separation technique.

Enantioselective Tsuji-Trost Reactions in Low Toxicity Ionic Liquids by Mukund Ghavre, Brid Quilty, Nicholas Gathergood (181-189).
Background: Low toxicity ionic liquids (ILs) have shown a wide range of applications in material chemistry, synthetic chemistry, and green chemistry. They can be considered as 'green' alternatives to the conventional solvents, as their unique properties can offer additional benefits. In our previous reports, we have shown that such ILs can be used as reaction media in hydrogenation, carbonyl-ene reactions, and Bronsted acid catalyzed reactions.
Methods: Low toxicity ILs are prepared by a short synthesis. The palladium based catalyst bearing an asymmetric ligand is immobilized in these ILs. This 'green' catalytic system is employed for enantioselective Tsuji-Trost reactions. For comparison, several reactions are run in conventional solvents.
Results: The reactions in ILs provide good to excellent enantiomeric excess, however, low yields are obtained compared to the conventional solvents. The catalytic system is recyclable.
Conclusion: Conventional solvent (DMSO) is proved to be superior to our ILs, however, the results in our ILs are an improvement over [bmim] ILs. The low yields are attributed to high viscosity of the ILs, and we propose can be resolved by tuning the viscosity of the IL by anion exchange.