Current Green Chemistry - Volume 7, Issue 2, 2020

One of the organocatalysts 1,4-diazabicyclo[2.2.2]octane (DABCO) is an excellent solid catalyst in a number of reactions. It is also a good nucleophile and a base in numerous reactions for the synthesis of heterocycles. DABCO catalyzes many reactions like cycloaddition reactions, coupling reactions, Baylis-Hillman reaction, Henry reaction, ring opening reactions, etc. One more advanced feature of these reactions is that they proceed through environmental friendly pathway. DABCO has more advantages than other organic catalysts because it is an inexpensive, non-toxic base, an ecofriendly and a highly reactive catalyst for building of organic frameworks, which produce the desired products in excellent yields with high selectivity. Many catalytic applications of DABCO have been reported for the synthesis of an organic framework which has been discussed in this review.

Non-steroidal anti-inflammatory drugs (NSAIDs) act as a major class of therapeutic agents. The biological activity of NSAIDs is due to the suppression of prostaglandin biosynthesis by inhibiting cyclooxygenase (COX) enzyme. COX is an endogenous enzyme, which catalyzes the conversion of arachidonic acid into prostaglandins. But the significant side effect by NSAIDs is the formation of gastric ulcers, irritation and GI bleeding. Therefore, alternative drugs that can overcome these limitations are necessary. Towards the goal, oxadiazole derivatives are designed and synthesized following a green chemistry approach. This method helps to reduce environmental pollution and the formation of by-products so that the yield of products is increased in less reaction time. It is observed that the anti- inflammatory activity of oxadiazoles is based on dual mechanisms, such as the inhibition of both COX and LOX (lipoxygenase) enzyme thereby reducing gastric ulceration. On this basis, research is carried out to develop efficient anti-inflammatory agents with minimal side effects by incorporating the oxadiazole moiety.

Deep Eutectic Solvent (DES) as a “green solvent” has been used as an alternative to replace Volatile Organic Compounds (VOCs) and traditional Ionic Liquids (ILs). In recent years, DES has gained much attention due to its excellent properties such as low cost, easy preparation, high viscosity, low vapor pressure, low volatility, high thermal stability, biodegradability and non-toxicity, among others. Other classes of compounds with increased interest are organosulfur compounds due to their applicability as synthetic intermediates in organic reactions and their high importance in pharmaceutical and agrochemical industries. This review describes the recent advances in the preparation of organosulfur compounds using DES as an alternative solvent, focusing on several types of organic reactions, including aromatic substitution reactions (SNAr), condensation, cyclocondensation, cyclization, ring-opening, thia-Michael addition, one-pot reactions and heterocyclodehydrations.

This review highlights the achievements in the synthesis of organic thiocyanates (OTCs) over the past five years (late 2015 to mid-2019) and is intended as a follow-up on our tutorial review published in Chemical Society Reviews in 2016. The discussion places a special emphasis on sustainable synthetic approaches involving thiocyanation or sulfur-cyanation. The large number of contributions within this short period of time clearly indicates that the chemistry of OTCs provides a growing interest and a rapid evolution.

A one-pot three-component reaction promoted by choline chloride: zinc(II) chloride deepeutectic solvent (ChCl-ZnCl2 DES) in an aqueous medium for the synthesis of several merocyanin dyes based on isoxazol-5(4H)-ones is presented. This three-component approach is efficient, clean, experimentally simple, convenient, safe, and environmentally friendly. This reaction was performed at room temperature without using energy sources such as heat, microwave and ultrasound waves. Nonuse of toxic solvents, available materials, one-vessel, no wasted reagents, simple preparation, and recyclability of DES are other important points of this method that is significant from the perspective of green chemistry.

The potentialities of condensation of α-ketophosphonates with primary amines for direct synthesis of α-iminophosphonates have been revealed. Diesters of α-ketophosphonic acids react with the primary amines by two competitive pathways: with a formation of α-iminophosphonates or a C-P bond cleavage resulting in a hydrogen phosphonate and an acylated amine. In many cases, the latter undesirable pathway is dominant, especially for more nucleophilic alkyl amines. Using metallic salts of α-ketophosphonates avoids the C-P bond cleavage, allowing direct preparation of α-phosphorylated imines by the reaction with primary amines. This strategy provides an atom economy single-stage synthesis of iminophosphonates – precursors of bio relevant phosphorus analogs of α-amino acids. Methyl sodium iminophosphonates, bearing aryl or heteryl substituents at the imino carbon atom exist in solutions at room temperature as an equilibrium mixture of Z- and E-isomers. A configuration of the C=N bond can be controlled by the solvent: changing the aprotic dipolar solvent DMSO-d6 by water or alcohols leads to the change from a predominant Z-isomer to almost an exclusive E-form. In contrast, diesters of the respective iminophosphonates exist in non-protic solvents predominantly in Econfiguration. The solvent effect on E-Z stereochemistry is demonstrated by DFT calculations.

Black soldier fly (Hermetia illucens) larvae are a new source of high-quality bio-based materials that can be implemented for technical applications. Black soldier fly larvae can be bred in high numbers in small areas and organic waste streams, making large scale industrial breeding possible. Fats from the black soldier fly are very rich in lauric acid, and the fatty acid profile resembles that of palm kernel and coconut oil. Therefore, black soldier fly fats could be envisaged to have similar applications to these plant-derived oils. The aims of this work were (1) to use black soldier fly fat, palm kernel and coconut oil to synthesize a glycine-acyl surfactant by means of a Schotten-Baumann reaction; (2) to determine the yield and purity of the reaction products; and (3) to determine solubility, foaming capacity, surface tension and critical micelle concentration of the surfactants in comparison to a commercially-available glycinecoconut oil surfactant, Amilite GCS-11®. The average yield of each reaction was satisfactory (70% or higher). The in-house synthesized surfactants had a fatty acid profile similar to the fatty acid profile of the initial fat/oil. All in-house synthesized surfactants showed similar properties, regardless of the source of the fat/oil, but they performed slightly less well regarding foaming capacity compared to the commercial surfactant. It is concluded that black soldier fly fats are a suitable alternative to coconut or palm kernel oil for the preparation of glycine-acyl surfactants.

N,N-Bis(trimethylsilyl)-9-aminoanthracene (Si9AA) was synthesized by deprotonation of 9-aminoanthracne (9AA) with n-BuLi followed by the addition of trimethylsilyl chloride (TMSCl). Under ultraviolet, Si9AA showed blue fluorescence originated from the anthracene skeleton due to orthogonal relation between anthracene skeleton and bis(trimethylsilyl)amino group, which was determined by X-ray crystallographic analysis, while 9AA, in which conjugation exists between the anthracene and the amino group, showed green fluorescence. In a THF solution, Si9AA was converted to 9AA by desilylation of bis(trimethylsilyl)amino group with fluoride ion, which was contained in tetrabutylammonium fluoride (TBAF) or KF-18-crown-6 complex, resulting in fluorescence color change from blue to green. Si9AA was found to utilize as a sensor to detect fluoride ion in THF solution or on a thin layer chromatography (TLC) via the fluorescence color change without any metals, regarding a metal free fluorescence fluoride sensor in green chemistry.