Current Green Chemistry - Volume 4, Issue 2, 2017

Background: High-pressure chemistry offers the possibility to have faster and cleaner transformations thus addressing most of the green chemistry principles. Among the devices recently developed, Q-tube is worth mentioning since it is cheap, easy to handle, safe and highly versatile. Methods: The most recent and interesting results obtained using such technique are reviewed in this study. Results: Examples of the Q-tube assisted reactions in organic synthesis are presented in a critical manner making where possible, a comparison with conventional heating strategies and unconventional energy source such as microwave or ultrasounds assisted synthesis. The application of Q-tube pressure reactor in biofuels manufacture is also discussed. Conclusion: The literature survey clearly revealed that Q-tube is a valid tool in organic synthesis.

Background: Industrial technologies (included energy production, environmental technolgies etc.) are equally straining after the introduction and broadening of green technologies, innovating and applying humane and health promoting/protecting procedures and technologies. There are also eminent trends of greening” in food processing and production technologies however it is hard to believe to produce high quality and healthy food products without application of safe and strictly controlled food additives. Methods: This paper highlights the three main functions of additives which help to improve the sensory quality, the food safety and stability as well as technological aspects of food manufacturing. The chemical and potential physiological characteristics of the most critical (so-called Top 10) food additives are also summarized and some regulatory aspects and questions of application of additives in food systems are submitted. Conclusion: The main focus of the optimization in application of food additives should be a win-win effect for the benefit of consumer and producers.

Background: Ionic liquids could be used as a potential solvent to dissolve rubber wood. This is one the most successful methods for the dissolution of rubber wood. Methods: In this study, various imidazolium-based ionic liquids with different anions, e.g acetate, chloride, dycanimide and ethylphosphonate were used to dissolve rubber wood and showed that 1-ethyl-3- methyl imidazolium acetate ([Emim][OAc]) could be recycled four times. There was a small decrease in the cellulose and lignin mass regenerated of the rubber wood using recycled ionic liquids compared to fresh ionic liquids. This method had achieved a recovery ionic liquid efficiency of 90% and the Fourier Transform Infrared (FTIR) and X-Ray Diffraction (XRD) showed that the crystallinity of the cellulose through the recycled ionic liquid has significantly decreased. The yield of the conversion of cellulose to glucose increased as the number of ionic liquid cycles increased, especially at the fourth instance of recycling. On the other hand, Thermogravimetric Analysis (TGA) and 1H NMR (nuclear magnetic resonance) spectroscopy showed no structural changes in the recovered ionic liquids. Conclusion: This work proves that [Emim][OAc] has an excellent reusability.

Background: Pharmaceutical industry is one of the most popular sectors known for spreading of pollution. Here the association with various bases belonging to either organic or inorganic for the enhancement of different transformation is a routine practice for manufacturing of active pharmaceutical ingredients and their intermediates. This results in the destruction of environment directly or indirectly because such bases are non-recoverable and non-recyclable. Methods: Present investigation has focused on the advantage of application of century old hydrotalcite as a green catalyst, which is recoverable and recyclable, in various organic transformations useful for the synthesis of some active pharmaceutical ingredients and their intermediates. Here the authors have identified research gap and disclosed novel green synthetic procedures catalyzed by hydrotalcite. Hydrolysis, oxidation, S-Alkylation, Knovengel condensation and peptide bonding transformations were tested in this protocol resulting in efficient, cost effective, eco-benign and industrially advantageous outcome. Conclusion: This methodology was assessed by Reaction Mass Efficiency, one of the green metrics, proving it to be eco-friendly as well as describing its financial importance which comes under green and sustainable practices.

Background: Flavanones are known to exhibit numerous biological properties, such as antimicrobial, antitumor, antioxidant and anti-inflammation. Synthesis of these flavanones has attracted much attention in the past few decades. Although some catalyst systems have been developed to synthesize flavanones, some disadvantages of those methods still exist, including harsh reaction conditions, tedious work-up, a lot of unfriendly reaction solvents used. Some paper reported that the reaction could proceed in aqueous solution, however, it was hard to achieve the results as they reported that some methods lacked good repeatability. Methods: We used tap water as the reaction medium and used KOH (0.1 equiv.) as the catalyst. The reaction conditions were systematically investigated. Nine chalcones were tested which could be converted into the corresponding flavanones at 50 °C or 80 °C with moderate to good yield. Results: Nine flavanones were successfully synthesized in basic water solution at 50 °C or 80 °C. Especially, seven of them were obtained as pure products simply after filtration without additional workup. All of the products were confirmed by 1H NMR and 13C NMR. Conclusion: We have developed an efficient and reliable catalytic system for the cyclization of chalcones to flavanones in tap water. The method was characterized by rapidity, accuracy and good replication. In addition, the simple work up procedure makes the current reaction practically useful.

Background: A clean and environmentally benign route to 4H-benzo[h]chromene-3- carbonitriles has been developed via three-component condensation reaction of various benzyl alcohols, malononitrile and 1-naphthol using DBU-hydrobromide-perbromide as an efficient oxidizing reagent at room temperature. Methodology: The present methodology offers several advantages such as solvent-free conditions, excellent yields, simple procedure, mild conditions and reduced environmental consequences. Conclusion: All of synthesized compounds were characterized by IR, NMR and elemental analyses.

Background: The aryldiazonium salts (ArN2+X-) are useful intermediates in organic synthesis. Although well stablished, the generation of ArN2+X- from anilines usually requires the use of corrosive and hazardous strong acids (HCl, H2SO4 or HBF4). The use of weak acids from a renewable source for diazotization reaction is infrequent and not well investigated. Methods: The goal of this work is to verify if vinegar, an easily available solution of acetic acid can act both as a acid source and as a solvent to promote the diazotation reaction. The reactivity of the aryldiazonium acetates was evaluated by addition of KI (Sandemeyer reaction) or furan (Gomberg-Bachmann reaction). Results: Using 1 equivalent of KI and 1.2 equivalents of NaNO2, substituted iodoarenes were obtained with poor to good yields. We observed in this two-step iodination protocol, the anilines that contained electron withdrawing groups performed better than those with electron donating groups. For the arylation reaction, higher amounts of furan and NaNO2 were required. In this case, the corresponding substituted arylfurans were also obtained with poor to good yields. Similar to the diazotization-iodination reaction, this arylation of furan with anilines containing electron withdrawing groups (Br, NO2) performed better than the same reaction with anilines containing electron donating groups. Conclusion: Substituted iodoarenes and arylfurans can be synthesized directly from anilines in vinegar, without the use of metals, additives or catalysts. The dual role of vinegar (acting as a solvent and acid source) combined with the green aspects (low cost, low toxicity, renewable) and the simplicity makes this method attractive.