Green Chemistry Blog

A magnetically separable nanomaterial has been developed which showed good photocatalytic activity under visible light in the selective transformation of malic acid in aqueous solution.

Titanium dioxide (TiO₂) is well known as a photocatalyst, but its application in various processes is hindered due to several limitations.  The most important of these limitations is its lack of photocatalytic activity under visible light.  In addition, efficient separation of the catalyst once the reaction is complete can be difficult, with additional filtration steps and/or a tedious work-up required. 

However, in this work scientists from Spain and the USA led by Rafael Luque and Rajender Varma have developed a novel nanomaterial which overcomes these problems.  The TiO₂-guanidine-(Ni,Co)Fe₂O₄nanomaterial was shown to have good activity in the selective transformation of malic acid.  Not only did the reaction proceed well under visible light, the material was also shown to have superior activity over the commercial catalyst Degussa P25.  The catalyst could be separated from the reaction mixture simply by using a magnet and the catalyst could be reused several times, preserving most of its activity.

To read more, please click on the link below.  This article is free to access until the 30th September 2011!

Magnetically separable nanocomposites with photocatalytic activity under visible light for the selective transformation of biomass-derived platform molecules, Alina M. Balu, Babita Baruwati, Elena Serrano, Jaume Cot, Javier Garcia-Martinez, Rajender S. Varma and Rafael Luque, Green Chem., 2011, DOI: 10.1039/C1GC15692F

Click here to read Anna Simpson’s recent interview with Rafael Luque!

Ionic liquids containing methyl sulfate, hydrogen sulfate and methanesulfonate anions were used to pretreat lignocellulose in the presence of water.

Ionic liquids (ILs) are salts which are liquid at room or slightly elevated temperatures, and the majority have negligible vapour pressures.  One of the applications of ILs is in the pretreatment and processing of biomass (e.g. cellulose and lignocellulose).  However, the presence of water in these processes reduces the solubility of the biomass in the ILs and therefore the effectiveness of the pretreatment.  ILs currently have to be dried before use which requires heat and vacuum, but as biomass contains significant quantities of water, it would be far more beneficial to have an IL pretreatment process that tolerates moisture.

In this work, Welton and co-workers from Imperial College London have used IL and water mixtures of 1-butyl-3-methylimidazolium methyl sulfate and 1-butyl-3-methylimidazolium hydrogen sulfate to pretreat ground lignocellulosic biomass.  These ILs were shown to work effectively in the presence of significant quantities of water thereby eliminating the need for anhydrous conditions during the process.

To find out more, please click on the link below:

Ionic liquid pretreatment of lignocellulosic biomass with ionic liquid–water mixtures, Agnieszka Brandt, Michael J. Ray, Trang Q. To, David J. Leak, Richard J. Murphy and Tom Welton, Green Chem., 2011, DOI: 10.1039/C1GC15374A

This article is free to access until the 21st September 2011

The photocatalyst ZnIn₄S₄was synthesized hydrothermally and applied to the conversion of hydrogen sulfide to hydrogen under solar light.

Scientists from India have demonstrated that a zinc nanostructured photocatalyst could be used to decompose hydrogen sulfide (H₂S) into hydrogen (H₂).  H₂S is commonly converted into water and sulfur using the Claus process. However this process is not considered to be environmentally viable due to its high cost and the fact that it usually creates further environmental problems.  This has switched interest into converting H₂S into H₂ in order to try and avoid these issues.

Kale and colleagues report here the controlled synthesis of ZnIn₄S₄by a hydrothermal method and its application to H₂S conversion to H₂ using solar energy.  The H₂ evolution rate obtained is much higher compared to earlier reported photocatalysts.

To read more, just click on the link below.  This article is free to access until the 21st September 2011!

Ecofriendly hydrogen production from abundant hydrogen sulfide using solar light-driven hierarchical nanostructured ZnIn₂S₄photocatalyst, Nilima S. Chaudhari, Ashwini P. Bhirud, Ravindra S. Sonawane, Latesh K. Nikam, Sambhaji S. Warule, Vilas H. Rane and Bharat B. Kale, Green Chem., 2011, DOI: 10.1039/C1GC15515F

A series of novel ionic liquids have been synthesized and applied to the dissolution of cellulose materials without causing considerable degradation of the polymer.

Hummel and co-workers from Finland and Austria have prepared by a facile route, a series of novel ionic liquids (ILs) which comprise of two asymmetric anions – dimethyl phosphorothioate and dimethyl phosphoroselenoate – and several imidazolium and non-imidazolium cations.  The principle of the work was to design an ionic liquid with reduced viscosity, while preserving its ability to dissolve lignocellulosic material, by altering the anion.

Hummel tested these new ionic liquids in the dissolution of cellulose, and the dimethyl phosphorothioate ionic liquids were able to dissolve cellulose with a high degree of polymerization but without extensive degradation.

To read more, please click on the link below.  This article is free to access until the 14th September 2011!

Dimethyl phosphorothioate and phosphoroselenoate ionic liquids as solvent media for cellulosic materials, Michael Hummel, Carmen Froschauer, Gerhard Laus, Thomas Röder, Holger Kopacka, Lauri K. J. Hauru, Hedda K. Weber, Herbert Sixta and Herwig Schottenberger, Green Chem., 2011, DOI: 10.1039/C1GC15407A

A variety of β-nitro ketones have been synthesised at room temperature using a supported nitrite.

Scientists from Italy have developed a more eco-friendly route to synthesize β-nitro ketones.  Nitroalkanes are an important class of organic substrates as the nitro group can be converted into many other functionalities, which makes them key starting materials for many fine chemicals.  Currently, the main method to make these compounds is by a Miyakoshi procedure – however, the method is limited to simple α,β-unsaturated ketone starting materials, gives only moderate yields and requires the presence of volatile organic solvents.

However, in this work, β-nitro ketones could be synthesized from a variety of α,β-unsaturated ketones using a solid supported nitrite, acetic acid and cyclopentyl methyl ether (CPME), an emerging ‘green solvent’.  This method works well with complex starting materials and it is able to preserve other functionalities, thereby minimizing work-up procedures (simple filtration and evapouration of the acetic acid and solvent) and decreasing the E-factor.

To read more, please click the link below:

Eco-friendly synthesis of β-nitro ketones from conjugated enones: an important improvement of the Miyakoshi procedure, Serena Gabrielli, Alessandro Palmieri, Alvise Perosa, Maurizio Selva and Roberto Ballini,  Green Chem., 2011, 13, 2026-2028, DOI: 10.1039/C1GC15616K

This article is free to access until 14th September!

Recyclable mesoporous silica-supported chiral ruthenium-(NHC)NN-pincer catalysts for asymmetric reactions.  Scientists from Spain have reported two new stable chiral Ru-pincer complexes with a pendant silyloxy group, which were grafted onto a mesoporous silica (MCM-41).  These supported complexes were shown to be highly active and recyclable catalysts for the asymmetric hydrogenation of alkenes and the cyclopropanation of styrenes.  These catalysts avoid the draw-backs associated with homogeneous catalysts such as high catalyst loadings and difficulties in catalyst recovery.  The supported catalysts reported here showed no deactivation after repeated recycling. (Green Chem., 2011, DOI 10.1039/c1gc15412e)

C-H bond functionalisation with [RuH(codyl)₂]BF₄ catalyst precursor.  Scientists from the CNRS-University of Rennes, France have employed a ruthenium catalyst, assisted by a coordinating base, for the direct diarylation of arenes with (hetero)arylhalides.  This reaction under these conditions is milder that the classical organometallic cross-coupling reactions.  The coordinating ligand/base has an important role by promoting the initial cleavage of the C-H bond.  The efficiency of the system strongly depends on the nature of both the assisting ligand/base and the (hetero)aryl halides. (Green Chem., 2011, DOI: 10.1039/c1gc15642j)

These articles are free to access until September 9th!