Green Chemistry Blog

Pentose-based surfactants could be obtained enzymatically from hydrothermally pretreated wheat bran.

Wheat is an important agricultural cereal in Europe and the waste generated annually from this industry could produce 115 billion litres of bioethanol.  In view of this there is a lot of interest in producing fine chemicals from this lignocellulosic biomass. 

In this work, Caroline Rémond and colleagues from France, report the enzymatic synthesis of pentyl and octyl-β-D-xylosides and oligoxylosides first from xylan and then from hydrothermally pretreated wheat bran.  As well as thoroughly investigating the various parameters that affect the nature and yield of the final product, the pentyl and octyl oligoxylosides obtained from the hydrothermally pretreated wheat bran exhibited good surface properties, demonstrating that the production of green surfactants can be envisaged from renewable resources using biotechnological methodologies.

This article is free to access until 5th October!  To read more, click on the links below:

Enzymatic synthesis of alkyl β-D-xylosides and oligoxylosides from xylans and from hydrothermally pretreated wheat bran, Marjorie Ochs, Murielle Muzard, Richard Plantier–Royon, Boris Estrine and Caroline Rémond, Green Chem., 2011, 13, 2380-2388

UK scientists have conducted a study to show how waste carbon dioxide can become an exploitable resource. The work could kick idle supercritical processing plants back into life.

High pressure supercritical carbon dioxide (scCO₂) can be an effective solvent for a range of catalytic reactions, but the cost of compressing CO₂ is high. Martyn Poliakoff, Mike George and Trevor Drage have been collaborating at the University of Nottingham to assess the possibility of using scCO₂ from carbon capture and storage (CCS) – in which considerable quantities of pressurised liquid CO₂ will be available – in the hope of turning a waste product into a resource. 

It is hoped that CCS will achieve large reductions in CO₂ emissions from power plants, but as the cost of compression is incurred at the plant, using this captured CO₂ as a source of scCO₂ for chemistry would be a cheaper and greener route. ‘The first scCO₂ chemical plant used less than 0.5 ton of scCO₂ per hour, but a power station running at full blast produces more than 0.5 ton of CO₂ per second, so you could produce enough high pressure CO₂ during a football match to run the plant for a year without needing to recycle the CO₂,’ says Poliakoff.

However, one of the concerns is that captured CO₂ will contain impurities. So, the team investigated what effects these impurities might have on a reaction that has previously been carried out commercially in scCO₂ – the hydrogenation of isophorone to trimethylcyclohexanone catalysed by Pd on SiO₂/Al₂O₃. They used an automated continuous reactor and monitored the products using gas liquid chromatography. They found that none of the impurities caused problems that couldn’t be overcome.

‘I’m delighted to see some encouraging science that may bring supercritical processing back towards commercial reality,’ says Harry Swan, managing director of Thomas Swan & Co. Ltd, who built the world’s only continuous phase scCO₂ reactor in 2002. But, owing to economic challenges and lack of legislation to reduce the use of volatile organic solvents, which would have created demand for scCO₂ as an environmentally friendly alternative, the plant is sitting idle. ‘This work brings us a step closer to my long term objective of getting our plant back up and running,’ he adds.

‘The obvious next step is to try other reactions,’ says Poliakoff. ‘Although hydrogenations are interesting reactions, it may well be that the real future of CO₂ lies in oxidation reactions that are dangerous in conventional solvents’.

Reproduced from a Chemistry World story written by Tegan Thomas.

Could the energy cost of using supercritical fluids be mitigated by using CO₂ from carbon capture and storage (CCS)? James G. Stevens, Pilar Gómez, Richard A. Bourne, Trevor C. Drage, Michael W. George and Martyn Poliakoff, Green Chem., 2011, DOI: 10.1039/c1gc15503b

A facile and green method to generate reduced graphene oxide nanosheets in supercritical alcohols had been developed.

Graphene has attracted much attention as a potential material for a wide range of applications due to its superior electrical, optical, chemical, mechanical, thermal and catalytic properties.  In view of this, a large scale and cost effective method for the production of graphene is necessary in order for it to be used in industry. There are currently four different methods to synthesize graphene, the most promising of which is the chemical reduction route – but this method still has several limitations which hinder its use in commercial implementation. 

Jaehoon Kim and coworkers from the Republic of Korea have developed a method to produce reduced graphene oxide (RGO) in supercritical fluids.  This fast, facile and green route results in RGO with a high carbon-to-oxygen ratio, high electronic conductivity and high lithium storage capacity.  This process is applicable for large scale production of RGO using a continuous flow-type reactor, providing opportunities for its production on industrial scale.

This article is free to access until the 30th September 2011!  To read more, please see:

Facile synthesis of reduced graphene oxide in supercritical alcohols and its lithium storage capacity, Eduardus Budi Nursanto, Agung Nugroho, Seung-Ah Hong, Su Jin Kim, Kyung Yoon Chung and Jaehoon Kim, Green Chem., 2011, DOI: 10.1039/C1GC15678K

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!