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Synthesis of antimalarial trioxanes via continuous photo-oxidation

UK scientists have developed a continuous photo-oxidation procedure of an allylic alcohol in supercritical carbon dioxide.

Malaria is one of the most infectious diseases in the world.  Some strains of malaria are becoming resistant to the traditionally used quinine based antimalarials, and so there is a need to develop new antimalarial drugs.  Synthesis of spirobicyclic trioxanesA common feature of some newly developed antimalarial compounds is the trioxane moiety, and a convenient way to introduce this group is via photochemically generated singlet oxygen species (1O2).  However the highlight reactive nature of this species can introduce problems when trying to scale-up the synthesis of these groups for industrial production, particularly in terms of identifying acceptable solvents (non-flammable and in-efficient 1O2 quenchers).

In this work, Martyn Poliakoff, Michael George and colleagues from the University of Nottingham, UK, have developed a continuous process for the sustainable synthesis of trioxones with  1O2in supercritical CO2.  The team also examined the remaining two steps in the synthesis of antimalarial trioxanes from readily available starting materials, and hope that this approach could lead to the exploration of libraries of different trioxanes as potential antimalarial agents.

Read the full article for free until the 9th January 2013!

Synthesis of antimalarial trioxanes via continuous photo-oxidation with 1O2 in supercritical CO2, Jessica F. B. Hall, Richard A. Bourne, Xue Han, James H. Earley, Martyn Poliakoff and Michael W. George, Green Chem., 2013, DOI: 10.1039/C2GC36711D

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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, 13, 2727-2733

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Stopping endocrine disruptors in their tracks

The endocrine system

The endocrine system

US scientists have come up with a system to assess whether chemists’ latest synthetic product is an endocrine disruptor – a chemical that interferes with hormone regulation in animals and humans.

As industry seeks replacements for endocrine disrupting chemicals (EDCs), such as bisphenol A and some flame retardants, it often discovers that the replacements are no better, and sometimes worse, than what is being replaced. This is because the replacements have been designed using the same flawed tools as their parent chemicals and because of the lack of adequate EDC testing, say the scientists. Now, a team led by Pete Myers, chief executive and chief scientist at Environmental Health Sciences, Virginia, has come up with a way to address this using a system they call TiPED (tiered protocol for endocrine disruption).

Read the full article in Chemistry World!

Tweet: RT @ChemistryWorld Stopping endocrine disruptors in their tracks http://rsc.li/TUxb2q 

Link to journal article
Designing endocrine disruption out of the next generation of chemicals
T. T. Schug,  R. Abagyan, B. Blumberg, T. J. Collins, D. Crews, P. L. DeFur, S. M. Dickerson, T. M. Edwards, A. C. Gore, L. J. Guillette, T. Hayes, J. J. Heindel, A. Moores, H. B. Patisaul, T. L. Tal, K. A. Thayer, L. N. Vandenberg, J. C. Warner, C. S. Watson, F. S. vom Saal, R. T. Zoeller, K. P. O’Brien and J. P. Myers
Green Chem., 2013, Advance Article
DOI: 10.1039/C2GC35055F

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Enantioselective reduction of sparingly water-soluble ketones

Biocatalysis is becoming an increasingly attractive method to achieve enantiopure chemicals, in a cleaner and more environmentally sustainable way.  This is in part due to the fact that in most of these reactions, water is used as the solvent primarily because the enzyme catalysts are most stable in this medium.  However, some substrates are insoluble or only sparingly soluble in water which can limit the use of these enzymes.

Graphical abstract of C2GC36558HIn this work, Lasse Greiner and colleagues from Germany have developed a procedure whereby sparingly water-soluble long-chain ketones can be reduced in a continuous process.  The authors used an ionic liquid as a detergent to increase the solubility of these substrates and products, and ultrafiltration in an enzyme membrane reactor was employed to increase the enzyme utilization.  A cascade of two enzyme membrane reactors was configured which could run for more than 1000 hours with high turnover numbers and 99.9% enantioselectivity.

Finally, downstream adsorption of the resulting alcohols allowed 90% recycling of the aqueous buffer solution, reducing the E-factor of the process to 13.

This article is currently free to access until the 3rd January 2013!

Enantioselective reduction of sparingly water-soluble ketones: continuous process and recycle of the aqueous buffer system, Susanne Leuchs, Shukrallah Na’amnieh and Lasse Greiner, Green Chem., 2013, DOI: 10.1039/C2GC36558H

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Utilising hardly-water soluble substrates as a second phase enables the straightforward synthesis of chiral alcohols, Christina Kohlmann, Nora Robertz, Susanne Leuchs, Lasse Greiner and Shukralla Na’amnieh, Green Chem., 2011, 13, 3093-3095

Continuous biocatalytic synthesis of (R)-2-octanol with integrated product separation, Christina Kohlmann, Susanne Leuchs, Lasse Greiner and Walter Leitner, Green Chem., 2011, 13, 1430-1436

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Mechanochemical degradation of lignin and wood

Scientists from Germany employed a mechanochemical approach to cleave β-O-4-linkages in lignin.

In recent years, plant biomass has come to the fore due to it’s potential to replace fossil-fuel derived chemicals.  Lignin is one of the three main constituents of biomass, but it’s use is hampered by its poor solubility and structural complexity. The β-O-4-linkage is the most abundant linkage found in lignin, and attempts to cleave them currently employ harsh reaction conditions.

Graphical abstrct for C2GC36456E showing the resulting compounds produced after ball milling lignin and beech woodHere, Carsten Bolm and colleagues have developed a base-assisted ball milling process for the degradation of lignin and wood.  The process is transition metal- and solvent-free and is tolerant of standard reagent impurities and water.  The authors hope that further work into optimising this reaction can reduce the current quantities of base required.

Read this article for free until the 3rd January!

Mechanochemical degradation of lignin and wood by solvent-free grinding in a reactive medium, Tillmann Kleine, Julien Buendia and Carsten Bolm, Green Chem., 2013, DOI: 10.1039/C2GC36456E

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Mechanocatalysis for biomass-derived chemicals and fuels, Sandra M. Hick, Carolin Griebel, David T. Restrepo, Joshua H. Truitt, Eric J. Buker, Caroline Bylda and Richard G. Blair, Green Chem., 2010, 12, 468-474

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Issue 12 of Green Chemistry now published online

The last issue of 2012 of Green Chemistry is now published online.

Green Chemistry issue 12, 2012, front coverThe front cover of this months’ issue features work by Amit Naskar and colleagues from Oak Ridge National Laboratory, USA, who report the development of lignin-based thermoplastics.  Lignin is one of the most abundant natural polymers, and represents an valuable renewable resource.  Previous work into applications of this material found that it could be combined with flexible polymers to produce a variety of co-polymer materials.  However, these materials tended to be thermoset plastics and brittle materials and therefore are barely recyclable.  Here the team managed to create lignin-based co-polymer thermoplastics, which would be recyclable and potentially biodegradable as well.

Turning renewable resources into value-added polymer: development of lignin-based thermoplastic, Tomonori Saito, Rebecca H. Brown, Marcus A. Hunt, Deanna L. Pickel, Joseph M. Pickel, Jamie M. Messman, Frederick S. Baker, Martin Keller and Amit K. Naskar, Green Chem., 2012, 14, 3295-3303

The inside front cover highlights work by Yu Fan, Xiaojun Bao and colleagues from the China University of Petroleum (China) and the University of British Columbia (Canada) who report the synthesis of zeolite Y from natural aluminosilicate minerals for application in fluid catalytic cracking.  Modern industrial synthesis of zeolite Y involves chemicals that are derived from natural bauxite, but this requires an huge amount of energy and generates a lot of waste.  Here, zeolite Y could be synthesised directly from natural aluminosilicate minerals, avoiding the need of additional inorganic chemicals and relying instead on natural raw materials.  The resulting zeolite exhibited outstanding catalytic cracking performance.

Synthesis of zeolite Y from natural aluminosilicate minerals for fluid catalytic cracking application, Tiesen Li, Haiyan Liu, Yu Fan, Pei Yuan, Gang Shi, Xiaotao T. Bi and Xiaojun Bao, Green Chem., 2012, 14, 3255-3259

Read these articles for free for 6 weeks!

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C-H activation: an article collection

Picture showing several chemical reaction schemes and moleculesOne of the simplest and most utilised chemical reactions is the burning of hydrocarbons and while combustion is an excellent way to exploit the energy content of this naturally occurring resource, there is a lot more we can do with the ‘inert’ C-H bond.

C-H activation allows us to convert cheaper hydrocarbon starting materials into more valuable and versatile products; leading to the development of a wide range of reagents and catalysts that activate C-H bonds. To keep you up to date with the latest developments in the field we have created this article collection, where all articles are free to download until 15th December.

Click here fore the full list of free articles

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Copper-catalyzed C–C bond cleavage and intramolecular cyclization

Chinese scientists have developed a new approach to synthesize acridones viacopper-catalyzed C–C bond cleavage and intramolecular cyclization.

Graphical abstract for C2GC36502BC–C and C–H bond cleavage/activation has become a very important area of research in recent years due to the variety of possible applications.  Presently, the cleavage of C–C bonds generally involves the use of noble metal catalysts such as Rh, Ry, Pd and Pt among others.  However, there are very few examples in the current literature of cheaper metals such as copper or iron being employed in these transformations.

In this work, Wang Zhou and colleagues from Xiangtan University, China, used a copper catalyst and air as the oxidant to synthesize acridones through a C–C bond cleavage and intramolecular cyclization, under neutral conditions.  This reaction provides an alternative strategy for C–C cleavage.

Read the full article for free until the 11th December 2012:

Copper-catalyzed C–C bond cleavage and intramolecular cyclization: an approach toward acridones, Wang Zhou, Youqing Yang, Yong Liu and Guo-Jun Deng, Green Chem., 2012, DOI: 10.1039/C2GC36502B

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Copper(II) catalysis provides cyclohexanone-derived propargylamines free of solvent or excess starting materials: sole by-product is water, Conor J. Pierce and Catharine H. Larsen, Green Chem., 2012, 14, 2672-2676

An efficient copper-catalyzed formation of highly substituted pyrazoles using molecular oxygen as the oxidant, Mamta Suri, Thierry Jousseaume, Julia J. Neumann and Frank Glorius, Green Chem., 2012, 14, 2193-2196

A highly efficient Cu-catalyst system for N-arylation of azoles in water, Deping Wang, Fuxing Zhang, Daizhi Kuang, Jiangxi Yu and Junhua Li, Green Chem., 2012, 14, 1268-1271

Microwave-assisted solvent- and ligand-free copper-catalysed cross-coupling between halopyridines and nitrogen nucleophiles, Zhen-Jiang Liu, Jean-Pierre Vors, Ernst R. F. Gesing and Carsten Bolm, Green Chem., 2011, 13, 42-45

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Meet our Authors: François Jérôme

Picture of François JérômeFrançois Jérôme is a research director at the CNRS University of Poitiers, France.  His research is focused on the catalytic activation of biomass and the subsequent conversion of the products to value-added chemicals.  François took a few moments to chat to Green Chemistry to talk about the challenges facing this field of research…

Who or what initially inspired you to become a chemist?

When I was a kid, I was very curious and I always wanted to have a rational explanation on many natural phenomena such as volcanoes, earthquakes, storms, space, etc… Later, when I entered the University, I had the chance to attend the courses of Prof. Pierre Dixneuf. During three consecutive years, he taught me with enthusiasm and passion catalysis and organometallic chemistry. His courses really gave me the taste of chemistry.

What has been the motivation behind your recent research?

The depletion of fossil carbon reserves together with the continuous increase of the barrel price requires the society to imagine and design new and innovative strategies. In this context, fascinating works have recently been proposed that now open new fields to be explored in chemistry. In particular, the synthesis of fine chemicals and chemical platforms from non-edible resources has become a fascinating topic. Beside the green aspect of this approach, the biggest challenge faced by chemists consists in designing bio-based chemicals with superior performances than fossil-derived chemicals while respecting the essential requirements of economic competitiveness and social progress. The concept of green chemistry has dramatically changed the way we work and driven us to think about chemistry differently. In particular, the design of an atom economical or energy-saving process is not self-satisfied anymore and major other issues of green chemistry need to be addressed such as supply of renewable raw materials, structural variability of biomass, which plants for which markets, biodiversity, resource management (water, metal, carbon) and environmental impact of processes. All of these considerations are really motivating mainly because the successful design of a “green process” obviously requires close collaborations between researchers with different scientific horizons.

What do you see as the main challenges facing research in this area?

Click here to read the full interview

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“All-water” chemistry for synthesis of N-arylmethyl-2-substituted benzimidazoles

Scientists from India have developed a tandem N-alkylation-reduction-condensation route to synthesize N-arylmethyl-2-substituted benzimidazoles.

1,2-Disubstituted benzimidazoles exhibit a broad range of biological activities, which make them a very popular synthetic target.  The regio-specific synthesis of these compounds is the main synthetic challenge, with the desired regioselectivity of the final compounds determined at the aryl-amination stage.  However, this traditionally requires a transition metal catalyst, expensive ligands and an appropriate base.

Graphical abstract for C2GC36377AIn this work, Asit Chakraborti and colleagues from the National Institute of Pharmaceutical Education and Research, Punjab, India, present a one-pot strategy to produce N-arylmethyl-2-substituted benzimidazoles in water.  The procedure does not require a transition metal catalyst or base, with water directing the regioselectivity of the reaction through hydrogen bond mediated ‘electrophile-nucleophile dual activation’.

Read the full article for free until the 4th December 2012!

“All-water” chemistry of tandem N-alkylation–reduction–condensation for synthesis of N-arylmethyl-2-substituted benzimidazoles, Damodara N. Kommi, Dinesh Kumar, Rohit Bansal, Rajesh Chebolu and Asit K. Chakraborti, Green Chem., 2012, DOI: 10.1039/C2GC36377A

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Catalytic procedures for multicomponent synthesis of imidazoles: selectivity control during the competitive formation of tri- and tetrasubstituted imidazoles, Dinesh Kumar, Damodara N. Kommi, Narendra Bollineni, Alpesh R. Patel and Asit K. Chakraborti, Green Chem., 2012, 14, 2038-2049

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Selective oxidation of alcohols and aldehydes over supported metal nanoparticles

Oxidation represents one of the most important reactions in organic synthesis and looks to have a significant role on the development and synthesis of value-added chemicals from biomass.  Efforts to make oxidation reactions more sustainable have led to the development of heterogeneous catalysts and the use of molecular oxygen an alternative to traditional, toxic chemical oxidants.

Graphical abstract of C2GC36441GIn this Critical Review, Robert Davis and colleagues from the University of Virginia, USA, evaluate the literature surrounding the use of supported metal nanoparticle catalysts for the selective oxidation of alcohols and aldehydes.  Davis compares the performances of the catalysts studied in this review by categorising reaction rates based on the turnover frequency as a common, consistent denominator.   The authors also look at factors that can affect the evaluation of reaction kinetics, such as catalyst deactivation, and give suggestions regarding how to obtain the best data.

Read this article for free until the 29th November 2012!

Selective oxidation of alcohols and aldehydes over supported metal nanoparticles, Sara E. Davis, Matthew S. Ide and Robert J. Davis, Green Chem., 2012, DOI: 10.1039/C2GC36441G

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On the mechanism of selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over supported Pt and Au catalysts, Sara E. Davis, Bhushan N. Zope and Robert J. Davis, Green Chem., 2012, 14, 143-147

Inhibition of gold and platinum catalysts by reactive intermediates produced in the selective oxidation of alcohols in liquid water, Bhushan N. Zope and Robert J. Davis, Green Chem., 2011, 13, 3484-3491

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