Green Chemistry Blog

A new porous co-ordination polymer has been synthesised in near-critical water which could broaden the synthetic strategies available for the environmentally friendly construction of metal-organic frameworks.

Metal-organic frameworks (MOFs) have received a lot of attention in recent years due to their potential applications in several areas, but in particular for hydrogen storage.  However, MOFs are often prepared using solvothermal routes typically involving significant quantities of toxic organic solvents. 

In this work Martyn Poliakoff and Martin Schröder and colleagues from the University of Nottingham and Diamond Light Source, UK, have developed a route to synthesise these Zn co-ordination polymers using near-critical water (300°C) as a cleaner alternative to organic solvents.  The zinc complex can be isolated without any water molecules bound to the Zn(II) centres, in contrast to solvothermal synthesis in DMF.  In addition, the use of water in this synthetic strategy potentially allows for the reuse and recovery of water from the reaction opening up possible industrial applications.

This article is free to access until the 20th December 2011!  Click on the link below to find out more…

Near-critical water, a cleaner solvent for the synthesis of a metal–organic framework, Ilich A. Ibarra, Peter A. Bayliss, Eduardo Pérez, Sihai Yang, Alexander J. Blake, Harriott Nowell, David R. Allan, Martyn Poliakoff and Martin Schröder, Green Chem., 2012, DOI: 10.1039/C1GC15726D

Hydrogen peroxide (H₂O₂) could be synthesized directly from molecular H₂ and O₂ using a supported heteropolyacid catalyst and water as solvent at ambient temperature.

Graham Hutchings and colleagues from Cardiff University, UK, prepared several Au-Pd exchanged supported Cs-heteropolyacid catalysts for application in the synthesis of H₂O₂.  Currently, H₂O₂ is prepared from alkyl anthraquinone but this process requires high capital investment and the production and transport of very concentrated H₂O₂ solutions.  By developing a direct synthesis process, these drawbacks could be avoided by giving small scale production of dilute H₂O₂ at the point of use.

In this work, the Au-Pd exchanged supported Cs-heteropolyacid catalysts developed by Hutchings showed excellent H₂O₂ synthesis activity and were considerably more effective in achieving high yields than previously reported catalysts.  By performing the reaction at ambient temperature in water in the absence of acid or halide additives, this method offers a potentially cleaner and more sustainable route to H₂O₂. 

This article is free to access until 15th December 2011!  Click the link below to find out more…

Direct synthesis of hydrogen peroxide using Au–Pd-exchanged and supported heteropolyacid catalysts at ambient temperature using water as solvent, Edwin N. Ntainjua, Marco Piccinini, Simon J. Freakley, James C. Pritchard, Jennifer K. Edwards, Albert F. Carley and Graham J. Hutchings, Green Chem., 2012, DOI: 10.1039/C1GC15863E

A recyclable Ru(II) complex has been found to be highly active for the aqueous phase nitrile hydration at 100°C in air.

Brian Frost and Wei-Chih Lee from the University of Nevada, USA, used the Ru complex [RuCl₂(PTA)₄] for the aqueous or biphasic hydration of nitriles.  Other approaches to this reaction suffer air-sensitive or non-recyclable catalysts as well as requiring organic solvents.  However, in the method developed by Frost, the reaction can be performed under an air atmosphere and the catalyst can be reused more than five times without significant loss of activity.  This reaction can convert aromatic, alkyl, and vinyl nitriles to their corresponding amides in near quantitative conversions.

This article has been made free to access until the 9th December 2011!  Click the link below to find out more…

Aqueous and biphasic nitrile hydration catalyzed by a recyclable Ru(II) complex under atmospheric conditions, Wei-Chih Lee and Brian J. Frost, Green Chem., 2012, DOI: 10.1039/C1GC15950J

Scientists from Italy have developed a new series of ionic liquids from renewable starting materials.

The team of scientists led by Cinzia Chiappe and Fabio Bellina synthesized a series of trialkyl(2,3-dihydroxypropyl)phosphonium salts prepared from 3-chloropropane-1,2-diol or (2,2-dimethyl-1,3-dioxolan-4-yl)methanol – two compounds that can be obtained easily from glycerol.  Phosphonium salts are emerging as promising alternatives to imidazolium analogues, as they are inert in basic reaction media and possess superior stability. Chiappe and Bellina have developed an efficient route to these compounds from cheap and commercially available starting materials.

This article is free to access until 9th December 2011!  To find out more, click on the link below…

Synthesis and properties of trialkyl(2,3-dihydroxypropyl)phosphonium salts, a new class of hydrophilic and hydrophobic glyceryl-functionalized Ils, Fabio Bellina, Cinzia Chiappe and Marco Lessi, Green Chem., 2011, DOI: 10.1039/C1GC16035D

Scientists from Germany have developed an efficient diastereoselective synthesis of 2,5-disubstituted tetrahydrofurans in three steps.

Magnus Rueping and Vilas Phapale used [IrCl(cod)]2 to catalyze the α-alkylation of substituted acetophenones with solketal (obtained from the protection of glycerol by actenone) as the hydrogen donor.  This route avoids the use of electrophilic alkylating agents like alkyl halides and as a result does not suffer from drawbacks such as salt or by-product formation.  The resulting products could then undergo reduction with NaBH4 to give the corresponding secondary alcohols, before subsequent acetyl deprotection and cyclisation by FeCl3 to give 2,5-disubstituted tetrahydrofurans. 

Furthermore, a one-pot, three-step version of this procedure could be performed which does not require chomatographic purification of any of the intermediates.

This article is free to access until the 22nd November 2011!  To read more, please click the link below…

Effective synthesis of 2,5-disubstituted tetrahydrofurans from glycerol by catalytic alkylation of ketones, Magnus Rueping and Vilas B. Phapale, Green Chem., 2011, DOI: 10.1039/C1GC15764G

Lipases immobilized onto biogenous iron oxide via an organic bridging group were applied to the kinetic resolution of secondary alcohols and could be used up to 5 times.

Immobilization of enzymes helps to achieve cost-effective, clean biocatalysis.  However, the method of immobilization employed can have a big impact on the catalytic activity, selectivity, thermostability and recyclability of enzymes. 

Scientists from Japan have used biogenous iron oxide (BIO) from iron-oxidising bacteria as a support for enzymes.  BIO was chemically modified with silane coupling agents to allow immobilization of the enzyme.  The supported catalyst was then applied to the resolution of secondary alcohols and could achieve a turnover frequency of 33 000 h^-1.  Heat treatment of BIO before chemical modification generated magnetic-BIO which was also employed as a support, and the immobilized enzymes could be recovered easily by using a magnet.

This article is free to access until 22nd November!  Click the link below to read more…

Highly active lipase immobilized on biogenous iron oxide via an organic bridging group: the dramatic effect of the immobilization support on enzymatic function, Tadashi Ema, Yuki Miyazaki, Izumi Kozuki, Takashi Sakai, Hideki Hashimoto and Jun Takada, Green Chem., 2011, DOI: 10.1039/C1GC15877E

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