Current Green Chemistry - Volume 6, Issue 1, 2019

Potassium alum (KAl(SO4)2.12H2O), commonly known as ‘alum’, has recently drawn the attention of synthetic chemists as an efficient, safe and eco-friendly acid catalyst in implementing a large number of organic transformations, thereby generating interesting molecular frameworks. The present review article offers an overview of the potent catalytic applications of this commercially available and low-cost inorganic sulfate salt in organic reactions reported during the period of 2014 to 2018.

The reduction of carbon dioxide has gained much attention due to increasing environmental concerns about global warming associated with carbon emissions from industrial effluents and public transport etc. In this regard, considerable attention has been devoted to the chemical conversion of carbon dioxide, and its incorporation into synthetic organic molecules under mild and “green” conditions. In recent years, significant effort has been dedicated to studying the fixation of carbon dioxide with aziridines to afford oxazolidinones, which is an environmental friendly and atom economical process. In this review, we discuss the efficiency of different catalytic systems, by comparing and analyzing each reaction parameter such as pressure, temperature, substrate scope and product selectivity.

Biomass, as the most abundant and renewable organic carbon source, can be upgraded into various value-added platform molecules. To implement more sustainable and economic catalytic biomass valorization, reusable heterogeneous catalysts would be one of the preferable choices. In this work, a series of phosphotungstic acid-based solid hybrids were produced by assembly of phosphotungstic acid with different pyridines using a facile solvothermal method. The obtained 3- phenylpyridine-phosphotungstate hybrid displayed superior catalytic performance in the upgrade of fructose to methyl levulinate with 71.2% yield and 83.2% fructose conversion at 140 ºC for 8 h in methanol, a bio-based and environmentally friendly solvent, which was probably due to its relatively large pore size and high hydrophobicity. This low-cost and eco-friendly catalytic process could be simply operated in a single pot without cumbersome separation steps. In addition, the 3- phenylpyridine-phosphotungstate catalyst was able to be reused for four times with little deactivation.

A green and environmental–friendly method for the removal of the hazardous bromothymol blue from aqueous solution was considered applying a hydrophilic, biocompatible and biodegradable natural sorbent of Latvian sphagnum peat moss, applying shaking-dispersive solid-phase extraction. First, the influence of shaking speed was evaluated at 300, 600, 900 U. Furthermore, the optimum conditions of dye-adsorption, such as pH, adsorption-equilibrium contact time, adsorbent mass, and adsorbate initial concentration were investigated. In addition, the adsorption equilibrium isotherms, thermodynamics, and kinetics were studied. Thus, the optimum removal of bromothymol blue was concluded at a shaking speed of 600 U. Regarding the dye adsorption at different pH, bromothymol blue showed two removal maxima at acidic (pH 2.5) and almost neutral (pH 7.5) media, reaching dye % removal of 80.8 and 88.2 %, respectively, in 120 min of adsorption equilibrium contact time. Moreover, the dye removal improved reasonably by increasing the concentration and the sphagnum dose. Additionally, the equilibrium isotherm plot correlated comparably to Langmuir's and Freundlich's models. Also, the adsorption kinetic study demonstrated a better correlation to pseudo-secondorder plot than to pseudo-first-order one. Finally, excellent reproducibility in % removal was demonstrated with RSD values of 2.2 and 2.7% at pH of 7.5 and 2.5, respectively.

We describe herein the use of glycerol as an efficient and sustainable approach for the synthesis of 2-amino-1, 8-naphthyridine-3-carbonitriles and 2-amino-3-quinolinecarbonitriles. The catalyst- free reactions occur straightforwardly using biodegradable and non-hazardous solvent. It is a strategy to address mounting environmental concerns with current approach includes the use of environmentally benign solvent, simple workup procedure, economic viability, shorter reaction time and providing good to excellent yield.

Polyaniline supported palladium catalyst was applied in the reductive degradation of organic dyes such as Methylene Blue, Rhodamine B, and Methyl Orange in presence of sodium borohydride as an environmental-friendly approach. Role of pH, catalyst amount, and catalyst support were investigated thoroughly to achieve complete and efficient degradation within few minutes under ambient condition. Heterogeneous nature of the catalyst allowed easy recovery by centrifugation and the catalyst was recycled for five cycles with slightly reduced activity. Recovered catalyst was characterized by ICP-AES and TEM and a slight decrease in the activity of the catalyst was attributed to the agglomeration of the palladium nanoparticles.