Green Chemistry Blog

An new and innovative method of free enzyme recycling from a reaction mixture has been developed which relies only on the physical properties of the reaction medium.

Biotechnology is gaining an increasing role in industrial processes, but various factors including poor industrial availability of free enzymes and efficient recycling procedures limit utilization.  Common methods for enzyme recycling include immobilization of the enzyme onto a suitable support material or by encapsulation in aqueous gels.  However, disadvantages of these methods include leeching of enzymes and loss of activity.

Arno Behr and his team from the Technical University of Dortmund, Germany, have provided a new solution to the problem of enzyme recycling.  They used a mixture of three solvents (water, methanol and hexanol) which are immiscible at room temperature.  When heated to the reaction temperature, the solvents form one phase which allows the reaction to proceed with no mass-transfer limitations.  Cooling the mixture to below the critical solution temperature leads to a biphasic system, resulting in the product phase being simply separated from the phase containing the catalyst, which can then be reused.  The catalyst could be used again over 5 sequential runs with only a 2% loss in maximum yield.

This article is free to access until the 17th November 2011!  Click the link below to read more…

A liquid immobilisation concept for enzymes by thermomorphic solvent systems, Arno Behr, Leif Johnen and Bastian Daniel, Green Chem., 2011, DOI: 10.1039/C1GC15802C

A new technique has been developed to deposit dyes onto metal oxide surfaces using supercritical carbon dioxide (scCO₂), resulting in efficient photovoltaic performance.

Dye sensitized solar cells (DSSCs) have become a very promising option as a cheap, non-silicon based devise to harness solar energy.  At present a range of organic solvents are used to deposit the dye component onto the metal oxide surface.  However, the approach is still very empirical and may not be ideal for industrial processes as manufacturing parameters, such as scale, flammability, waste disposal, dye recovery and cost, need to be considered.

In this work scientist from the UK and Australia led by Gavin Collis have employed scCO₂ as the solvent for dye deposition.  As well as eliminating the need for hazardous organic solvents and waste solvents generated during the process, it also allows the unreacted dye to be recovered easily in solid form after venting the carbon dioxide.  This technique now allows dye deposition to be completed in 2 hours, a dramatic decrease from the 15 hours it took using organic solvents.

This article is free to access until 10th November 2011!  Click the links below to read more…..

Supercritical carbon dioxide as a solvent for deposition of a tailored dye in dye sensitized solar cells, Subashani Maniam, Andrew B. Holmes, Julia Krstina, Gary A. Leeke and Gavin E. Collis, Green Chem., 2011, DOI: 10.1039/C1GC15864C

Scientists from New Zealand have used food additive-derived ionic liquids for extracting wood lignin.

Wood cellulose, the most abundant biopolymer on earth, has great potential as a renewable feedstock, but in order to ‘unlock’ this potential, the various components of wood cellulose need to separated and processes individually.  The three main components are cellulose, hemicellulose and lignin.  However, current methods used to separate these components, for example Kraft pulping, have many draw backs such as high operating temperatures and pressures and many sequential steps. 

In this work, André Pinkert and his team used food additive-derived ionic liquids for seperating wood lignin and looked at the influence of selected parameters on the process.  In one gentle step, an extraction efficiency of e= 0.43 of wood lignin was achieved which increased to e= 0.60 in the presence of a co-solvent.  The gentle conditions employed here did not decrease the crystallinity of the wood sample, and resulted in lignin with both a larger molar mass and a more uniform molar mass distribution compared to commercially available Kraft lignin.

Click the links below to read more.  This article is free to access until the 18th November 2011!

Extracting wood lignin without dissolving or degrading cellulose: investigations on the use of food additive-derived ionic liquids, André Pinkert, Dagmar F. Goeke, Kenneth N. Marsh and Shusheng Pang, Green Chem., 2011, DOI: 10.1039/C1GC15671C

A strategy to utilize corncobs to generate porous carbonaceous materials has been reported by scientists from Spain and the Philippines, which were then used to generate biodiesel from waste oils.

There has been increased focus on reducing organic wastes in industry and for providing and utilizing renewable chemicals and fuels.  Waste valorisation is attracting considerable attention, providing an alternative to the disposal of a range of waste materials in landfill sites.  In particular, the valorisation of food wastes is considered to be very promising. 

In this work, researchers led by Rick Arneil Arancon and Rafael Luque utilized corncobs, which are a common food waste, and generated microporous carbonaceous material.  The material was then subsequently sulfonated to give a solid acid catalyst which exhibited excellent activity in the simultaneous esterification/transesterification of waste oils. 

This article is free to access until 1st November 2011!  To read more, please click on the link below:

Valorisation of corncob residues to functionalised porous carbonaceous materials for the simultaneous esterification/transesterification of waste oils, Rick Arneil Arancon, Higinio R. Barros Jr, Alina M. Balu, Carolina Vargas and Rafael Luque, Green Chem., 2011, DOI: 10.1039/C1GC15908A

French scientists report a new method to generate the oxidative homocoupling of N-phenylpyrazole using  Ru(OAc)₂(p-cymene) catalyst.

Traditionally, the transition metal-catalysed Heck reaction has proven to be a useful method to synthesize unsaturated molecules and conjugated materials viacross-coupling and C-C bond formation.  However, a potentially more efficient, greener route to the same family of compounds is through the catalytic oxidative alkenylation of aromatic C-H bonds.  This process would avoid the prehalogenation of the substrate as in the Heck reaction and therefore would be more atom economical.

The team of scientists here, led by Christian Bruneau and Pierre Dixneuf, report the direct dehydrogenative alkenylation of N-aryl pyrazoles with styrene and alkyl acrylates, catalysed by Ru(OAc)₂(p-cymene) in the presence of Cu(OAc)₂·H₂O and acetic acid in air.  The authors show that the acetic acid plays an important role, and believe its action lies in C-H bond cleavage as an autocatalytic process.

This article is free to access until the 20th October 2011!  To read more, just click below:

Ruthenium diacetate-catalysed oxidative alkenylation of C–H bonds in air: synthesis of alkenyl N-arylpyrazoles, Percia B. Arockiam, Cedric Fischmeister, Christian Bruneau and Pierre H. Dixneuf, Green Chem., 2011, DOI: 10.1039/C1GC15875A

A new recyclable copper catalyst has been developed which could be reused 20 times in the Diels-Alder reaction in ionic liquids without any obvious loss of activity or enantioselectivity.

Homogeneous metal-catalysed reactions are widely employed in organic synthesis.  However, because most catalysts are expensive and because the metal and the ligand can often higly toxic to the environment, the recycling of the these catalysts is very important. 

Zhi-Ming Zhou and colleagues from China report a series of imidazolium-tagged C2-symmetric bis(oxazoline) copper catalysts.  These catalysts were applied to the Diels-Alder reaction and achieved high levels of activity and enantioselectivity.  Due to the nature of the ligand, these catalysts were soluble in ionic liquids, including the hydrophobic [Bmim]NTf2, which enabled good recyclability.  In fact, these catalysts could be recycled at least 20 times without showing an obvious loss in activity or enantioselectivity.

To read more, please click on the link below:

Recyclable copper catalysts based on imidazolium-tagged C₂-symmetric bis(oxazoline) and their application in D–A reactions in ionic liquids, Zhi-Ming Zhou, Zhi-Huai Li, Xiao-Yan Hao, Xiao Dong, Xin Li, Li Dai, Ying-Qiang Liu, Jun Zhang, Hai-feng Huang, Xia Li and Jin-liang Wang, Green Chem., 2011, DOI: 10.1039/C1GC15788D

This article is free to access until the 14th October!

A four-component reaction catalysed by L-proline has been developed to efficiently synthesize a series of complex ortho-quinones.

Quinoline-detrived ortho-quinones are very important biological compounds and play crucial roles as cofactors, being involved in several biochemical reactions.  Therefore there is interest in providing economical routes to these compounds.  One strategy that could be employed are multi-comnponent reactions.  However, little attention has been focused on the development of these reactions in aqueous conditions. 

Scientists from India and Spain have now developed a L-proline catalysed four-component sequential reaction performed “on water” for the synthesis of 7-(aryl)-8-methyl-10-phenyl-5H-benzo[h]pyrazolo-[3,4-b]quinoline-5,6(10H)-diones.  This procedure gives high atom economy and leads to the generation of two rings together with two C-C, one C-N and two C=N bonds in a single operation.  Together with the short reaction times, excellent yields, easy work-up and without the need for chromatography purification, this methods show several environmental advantages over other protocols.

To read more, please click on the click below:

L-Proline-catalysed sequential four-component “on water” protocol for the synthesis of structurally complex heterocyclic ortho-quinones, Stephen Michael Rajesh, Balasubramanian Devi Bala, Subbu Perumal and J. Carlos Menéndez, Green Chem., 2011, DOI: 10.1039/C1GC15794A

This article is free to access until the 14th October 2011!