Current Green Chemistry - Volume 1, Issue 1, 2014

One criterion of green chemistry is efficiency that may be fulfilled by selecting atomic efficient reactions, and among others, utilizing the microwave (MW) or the phase transfer catalytic techniques, rationalizing the use of solvents and optimizing the syntheses. The use of green chemical tools is exemplified via a wide range of organophosphorus reactions including additions/cycloadditions (Michael additions, carbonyl additions and Diels-Alder cycloadditions), substitutions/ couplings (acylations, alkylations, the Arbuzov reaction) and 3-component condensations (the Kabachnik–Fields reaction). An efficient optimization is shown via the synthesis of dronic acids or their sodium salt (dronates) from substituted acetic acid derivatives and tervalent P-reactants (PCl3 and P(OH)3). The optimum conditions were explored on a rational basis.

During past decades, significant advancement in the field of ultrasound assisted processes revealed that this method is broadly applicable to a variety of research fields allied to organic synthesis. Emblematically, employing this technique as key step, a great number of multicomponent reactions have been developed for the creation of an assortment of heterocyclic compounds. In this review, we attempt to give an overview about the use of multicomponent reaction under ultrasound irradiation for synthesis of various heterocyclic compounds.

The purpose of this review is to provide appropriate details concerning the application of green methods in polymers synthesis. Phosphorus-containing polymers were synthesized by a simple and green synthetic method, namely vapor-liquid polycondensation. Solvent and catalysts were not required in this technique. Another green method for the polyphosphonate synthesis is the solid-phase polycondensation using ultrasound. Solid-liquid phase transfer catalysis also was used as eco-friendly and economical procedure for phosphorus-containing polymers, by using potassium phosphate in order to suppress the side reactions. In order to increase segmental motion and to aid the ion transport and ionic conductivity at ambient temperatures of polymer membranes for batteries, linear polymers composed of phosphonate (4- chlorophenyldichlorophosphonate) as a linking agent with poly(ethylene glycol) were synthesized using “green” conditions. An important area in the development of green chemical technology is the control of chemical reactions by the “tuning” of the reaction medium. The influence of the structure and the nature of ionic liquids on the efficiency of polymerization of white phosphorus is presented. Phosphorus-containing styrene derivatives (dimethyl-p-vinylbenzylphosphonate and diphenyl styryl phosphine oxide) were used as comonomers in the cationic copolymerization of soybean oil, styrene and divinylbenzene. Poly(oxyethylene hydrogen phosphonate) with an average molecular weight of 3100 Da was synthesized under microwaves method for 55 min.

Owing to its biodegradable and non-toxic nature, glycerol, the main byproduct in the production of biodiesel fuel, is being actively investigated as a green reaction medium for synthetic organic chemistry. A huge number of synthetic transformations have been conducted in glycerol in recent years, showing most of them having similar or even superior efficiency and selectivity than those performed in conventional petroleum-based organic solvents. Herein, an overview on the most recent advances reached in the field is presented.

The synthesis of (S)-2-hydroxy-(3-phenoxyphenyl)acetonitrile derivatives (components of pyrethroid insecticides) by the asymmetric addition of three different cyanide sources to 3-phenoxybenzaldehyde is investigated. Titanium and vanadium(salen) complexes are used as asymmetric catalysts and the processes are analyzed on the basis of both degree of asymmetric induction and relative cost to determine the commercially most viable synthesis. This provides a greener route to pyrethroid insecticides since the enantiomers of synthetic pyrethroids have different insecticidal activity, toxicity and environmental persistence. Thus, by producing only the stereoisomer with the most desirable properties, the production of waste and material with inferior effects on biological organisms and the environment can be avoided.

Chemoselective acylation of amines has been carried out in water under open air using acyclic or cyclic anhydrides or benzoyl chloride in the absence of any acid or base catalyst or a surfactant. The alkyl or aryl amines including primary or secondary amines, amino acids, diamines etc afforded the corresponding N-acyl derivatives in good yields. The selective N-acylation was observed in the presence of -OH, -SH, -COOH or -COOEt group. Being a practical alternative to the existing methods for selective acylation of amines the present methodology may find applications.

A novel methodology for the synthesis of privileged medicinal scaffolds 1,5-benzothiazepine derivatives using amberlyst-15 as a heterogeneous catalyst in ionic liquid as solvent is reported. In this report, substituted 2- aminothiophenols react with 3-pyrazolidinyl-2H-indol-2-one generated in situ from indole-2,3-dione and 3-methyl-1- phenylpyrazoline-5-one to furnish spiro azathiaheterocycles. The catalytic system can be easily recycled and reused for at least four times without significant loss of yields and reactivity. Interestingly, title compounds were not achieved, when the reactions were carried out conventionally using volatile organic solvents.