Current Green Chemistry (v.1, #2)

The first three-component synthesis of phosphane sulfides from diphenylphosphane, elemental sulfur, and α,β-unsaturated carbonyl compounds is presented. Reactions proceed under solvent-free conditions in the absence of catalyst,providing the expected β-diphenylphosphorothioyl-functionalised products in moderate-to-high yields. Different experimentsrevealed that the process takes place through the in situ formation of diphenylphosphane sulfide and subsequent1,4-addition to the substrate.

Tribromoisocyanuric Acid: A Green and Versatile Reagent by Leonardo S. de Almeida, Pierre M. Esteves, Marcio C. S. de Mattos (94-107).
The present review summarizes the synthetic application of tribromoisocyanuric acid [1,3,5-tribromo-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione] in organic synthesis and focuses on its green aspects. It is a safe, stable and easily preparedsolid. Electrophilic bromination reactions involving alkenes, arenes, dicarbonyl compounds and the bromodecarboxylationof cinnamic acids (Hunsdiecker reaction), as well as benzylic bromination and some oxidations involving tribromoisocyanuricacid are presented and discussed. In accordance with green chemistry principles, the use of tribromoisocyanuricacid enables bromination without bromine or other harmful or dangerous reagents.

According to the current literature, a dramatic increase in new published data or some-like "renaissance“ in thesynthesis and fabrication of zeolitic and other industrial adsorbents, in a broad sence porous adsorption materials, has beenreported over the last quarter of the century. Some of them are expected to be very useful and perspective adsorbents alsoin environmental control and remediation processes. Zeolites synthetic as well as natural, based on their beneficial propertiesand economic value, represent for a long time recognized industrial commodities. Advances in nanoscale science andengineering and development of novel functional materials, nanostructured membranes, bioactive nanoparticles and othersurface engineered materials, microstructure of which has been recognized from evolutionary unique anatomy in natureare providing another unprecedent opportunity to develop more cost effective and environmentally acceptable adsorptionmaterials of today.

Glycerol as Renewable Resource in the Synthesis of Thioethers Using KF/Al2O3 by Gelson Perin, Elton L. Borges, Jose E. G. Duarte, Rodrigo Webber, Raquel G. Jacob, Eder J. Lenardao (115-120).
The title compounds were synthesized starting from tosyl ether derivative of glycerol using KF/Al2O3 andPEG-400 as solvent. The reactions were performed under mild conditions with a range of aliphatic and aromatic thiols andthe catalytic system was reused without previous treatment and with comparable activity for one additional reaction.

Bis-allyl ruthenium(IV) complexes containing N-heterocyclic ligands [Ru(η33-C10H16)Cl21-N-L)] (L =pyrazole (1a), benzimidazole (1b)) are active catalysts in the redox isomerization of allylic alcohols into saturated carbonylcompounds using the ionic liquid [BMIM][BF4] (BMIM = 1-butyl-3-methylimidazolium) as a non-conventional reactionmedia in the absence of additional base. Complex 1b has been found to be the most efficient catalyst for the isomerizationof a series of primary and secondary allylic alcohols (9 substrates). In addition, we have studied the effect ofthe counter anion in the ionic liquid finding that non coordinating anions (BF4-, PF6- and SbF6-) led to the best reactionstimes and conversion, when compared with the coordinating chloride anion (Cl-). It is important to note that the catalyticsystem could be recovered through seven catalytic cycles with only partial loss of the initial activity in the first five cycles.Since this catalytic system: i) shows high efficiency and selectivity, ii) involves no presence of phosphines or anybase as co-catalyst, iii) proceeds without the formation of by-products (atom economy), and iii) is readily recovered, it canbe considered as a genuine example of a Green chemical process.

A Catalytic System for the Estragole to Anethole Isomerization Based on [{RuCl(µ-Cl)(η6-p-cymene)}2] by Lucia Menendez-Rodriguez, Pascale Crochet, Victorio Cadierno (128-135).
An efficient, inexpensive and selective catalytic system for the industrially relevant isomerization of estragoleto trans-anethole has been developed using the arene-ruthenium(II) dimer [{RuCl(µ-Cl)(η6-p-cymene)}2] in combinationwith P(OMe)3. As an example, using 100 mg of this complex and 38 µL of P(OMe)3 (1 equiv. per Ru), 10 mL of estragolecould be quantitatively converted into anethole (98% trans-selectivity) after heating the mixture at 80°C for 24 h. In addition,after separation of the anethole product by distillation, the catalytic system could be reused without loss of efficiencyand selectivity.

Niobic Acid as a Recyclable Heterogeneous Catalyst for the Solvent-Free Synthesis of Substituted Benzimidazoles by Beatriz M. Vieira, Angelita M. Barcellos, Ricardo F. Schumacher, Eder J. Lenardao, Diego da Silva Alves (136-144).
We describe here a simple method for the synthesis of several substituted benzimidazoles using niobic acidNb2O5.5H2O as heterogeneous catalyst and under solvent-free conditions. This new protocol is general and a range ofaromatic and aliphatic aldehydes were condensed with o-phenylenediamine furnishing the corresponding 1,2-disubstitutedbenzimidazoles selectively in good yields. The catalyst was reused up four times giving the respective products in goodyields but with a little decreasing in the selectivity.

A Green Approach for Producing Solvent-free Anisyl Acetate by Enzymecatalyzed Direct Esterification in Sponge-like Ionic Liquids Under Conventional and Microwave Heating by Pedro Lozano, Juana M. Bernal, Almudena Lajarin, Daniel Romera, Eduardo Garcia-Verdugo, Gregorio Sanchez-Gomez, Mathieu Pucheault, Michel Vaultier, M. Isabel Burguete, Santiago V. Luis (145-154).
The biocatalytic synthesis of anisyl acetate fragrance was carried out by direct esterification of acetic acid withanisyl alcohol in sponge-like ionic liquids (SLILs), e.g. N,N,N,N-hexadecyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([C16tma][NTf2], N,N,N,N-octadecyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([C18tma] [NTf2]),etc. as reaction/separation media under conventional and microwave (MW) heating. These SLILs are temperatureswitchableionic liquid/solid phases that behave as sponges. As liquid phases, they are excellent monophasic reaction mediafor the lipase-catalyzed synthesis of anisyl acetate, the product yield being improved up to 100% for 2 hour reactionunder the appropriate reaction conditions (i.e. SLIL concentration, alcohol: acid molar ratio, enzyme amount, dehydratingmolecular sieves, temperature and MW heating). As a function of the phase behaviour of different SLIL/anisyl acetatemixtures, a new clean separation protocol based on the centrifugation of the solid IL/flavour ester through nylon membraneswas proposed, which provided a nearly full separation of the solid SLIL and the easy recovery of the reaction mixture.The enzymatic synthesis of anisyl acetate in [C16tma] [NTf2] under MW assistance, followed by the separation stepof the solid SLIL, provided a nearly solvent-free fragrance product with up to 0.89 g/mL concentration. The catalytic activityof the enzyme / SLIL system remained unchanged for ten consecutive operational cycles. This work reports astraightforward and sustainable approach for producing anisyl acetate as a natural flavour and demonstrates to be suitablefor scaling-up, providing a high potential for practical application.

Biocatalysis in the Pharmaceutical Industry. A Greener Future by Pilar Hoyos, Vittorio Pace, María J. Hernaiz, Andres R. Alcantara (155-181).
The use of biocatalyzed processes is increasingly becoming recognized as a very important part inside GreenChemistry, because those synthetic routes mediated by enzymes or cells are generally conducted under mild reaction conditions,at ambient temperature and can use water as reaction medium in many cases. Their high selectivity avoids theneed of functional group activation and protection/deprotection steps usually required in traditional organic synthesis.Thus, biocatalysis provides processes which are shorter, produce less waste and reduce manufacturing costs and environmentalimpact. These features are even more significant in drug synthesis, because it is well known that Pharma Industryis the most waste-producers. In this review some biocatalyzed protocols for the preparation of bioactive molecule and/orchiral building blocks for drug synthesis will be presented, focusing only in those used for treatment of noncommunicablediseases (NCDs).

The possibilities for the deoxygenation of 3-methyl-1-phenyl-3-phospholene 1-oxide were investigated usingdifferent silanes. Cl3SiH and PhSiH3 were efficient, but they have disadvantages regarding user-friendliness and price,respectively. Tetramethyldisiloxane and polymethylhydrosiloxane that are cheap and user-friendly, but are of lowerreactivity could be applied at 110 °C in toluene solution, without the use of any catalyst successfully. Then, thedeoxygenation was extended to other 1-phenylphospholene oxides and phospholane oxides. The cyclic phosphines usefulas ligands in transition metal complexes were identified as their sulfides and boranes. The catalyst-free method elaboratedseems to be of more general value.