Green Chemistry Blog

Scientists from China have developed a way to intensify photocatalytic processes, and they have utilised it for efficient photoreactor design.

Currently, photocatalysis has few commercial or industrial applications because of the complex configuration of the photoreactor that would be required, and thus difficult engineering and scale-up issues.  However, Zhuhong Yang and co-workers from Nanjing University of Technology, China have developed a new photoreactor design which separates the process into two parts and has been inspired by photosynthesis in plants.

Photosynthesis can be considered as a tandem reaction consisting of the light reaction and the dark reaction. In the reactor designed by Yang, the first part of the reactor is the heterogeneous reaction, where surface-bound radical species are generated (the ‘light’ reaction) and the second part is the homogeneous reaction mediated by the radicals generated in part one (the ‘dark’ reaction).  The team used a static mixer which greatly improved the overall efficiency of the reaction by increasing radical mobility in the solution.

By separating the illumination and mixing parts of the photoreactor, scale-up and engineering applications will be made much easier.

For more information, please see the full article, free to read until 13th June:

Photosynthesis-inspired design approach of a liquid phase heterogeneous photoreactor, Dong Li, Kui Xiong, Kangzhong Shi, Zhuhong Yang, Chang Liu, Xin Feng and Xiaohua Lu, Green Chem., 2011, DOI: 10.1039/C1GC15082K.

Rapid screening of ionic liquids to determine their toxicity is now possible thanks to a modelling technique by scientists in Spain.

Ionic liquids (IL) – salts with low melting points – are being investigated as green alternatives to solvents, because their negligible vapour pressures result in minimal atmospheric contamination. However, their slight solubility in water poses a potential risk to aquatic ecosystems, as the toxicity of ILs is still relatively unknown.

Methods to predict the toxicity of unknown ILs would be very useful in IL research. Unfortunately, the only currently investigated method, quantitative structure-activity relationships, is labour intensive and time consuming.

The green fluorescent protein Vibrio fischeri in the background with ionic liquid structures

Now, Manuel Alvarez-Guerra and Angel Irabien at the University of Cantabria, in Santander, have devised a model to screen the toxicity of unknown ILs towards Vibrio fischeri, a standard bacterial assay for IL toxicity. 

The technique uses toxicity data from 64 known cations and 30 known anions that can be combined to theoretically make 1920 unique ionic liquids. By applying partial least squares-discriminant analysis and using the toxicity of toluene as a threshold value, the potential hazards of all the possible ILs can be predicted. After ‘training’ their model using a standard set of toxicity data, the team was able to confirm the model’s accuracy with a test set, obtaining a non-error rate of 93 per cent.

‘This tool could easily guide the design effort [of ILs] from the earliest steps of the process,’ says Alvarez-Guerra, ‘so we can direct the effort towards ionic liquids that we think will be less toxic than the conventional solvents that they may replace.’ 

Gloria Elliott, an expert in the biocompatibility of ionic liquids at the University of North Carolina at Charlotte, US, praises the novelty of the work. ‘Most of the [current] work has been looking at the structures and trying to deduce what functional groups or chain lengths would give rise to an enhanced toxicity,’ she explains. ‘But this takes the next step and starts to put it into computer language and enable more high-throughput processing,’ she adds.

However, she highlights that before the model can fulfil its potential, it needs to be tested against other datasets, such as toxicity data for cells of other species and higher organisms. Alvarez-Guerra agrees that this is the next step, but would rely on the availability of data.

Reproduced from a Chemistry World story written by Yuandi Li

Read the full article here:

Design of ionic liquids: an ecotoxicity (Vibrio fischeri) discrimination approach
Manuel Alvarez-Guerra and Angel Irabien, Green Chem., 2011
DOI: 10.1039/c0gc00921k

Chemical structures of the IL precursors used in this study: (a) 1-ethylpyridinium, (b) tributyl(2-hydroxyethyl)phosphonium and (c) bis(2-ethylhexyl)sulfosuccinate (docusate)

In this study Tony McNally and co-workers in Northern Ireland, Spain and the USA show that dual functional ionic liquids can uniquely provide both a plasticising effect for medical polymers, and exhibit antimicrobial and antibiofilm-forming activity to a range of antibiotic resistant bacteria.

Poly(vinyl chloride) (PVC) is widely used in the manufacture of a range of medical devices, including endotracheal tubes and catheters. The unique flexibility of PVC for use in such applications is derived from the use of phthalate esters as plasticisers. However, the possible carcinogenic and reprotoxic effects of phthalates has been a concern for some decades since their identification as an environmental contaminant.  Another problem with medical devices is the risk of infection of indwelling medical devices as bacteria can colonise and form a biofilm on the surface. As device-related infections are recalcitrant to conventional antimicrobial therapy and host defences, alternative agents for their treatment are required. Ionic liquids have been shown in separate experiments to have antimicrobial activity and a plasticising effect on polymeric materials.

This study reports the design of two dual functional ionic liquids which uniquely provide a plasticising effect, and exhibit antimicrobial and antibiofilm-forming activity to a range of antibiotic resistant bacteria. The design approach adopted will be useful in developing ionic liquids as multi-functional additives for polymers.

Interested in knowing more?  Read the full article here. Free until June 3rd.

Dual functional ionic liquids as plasticisers and antimicrobial agents for medical polymers
Seong Ying Choi, Héctor Rodríguez, Arsalan Mirjafari, Deirdre F. Gilpin, Stephanie McGrath, Karl R. Malcolm, Michael M. Tunney, Robin D. Rogers and Tony McNally
Green Chem., 2011, Advance Article
DOI: 10.1039/C1GC15132K

Carbon dioxide is used to promote the oxidation reactions of several cyclic alkenes

Carbon dioxide enhances the catalytic oxidation of cyclic alkenes, leading to higher conversions at low pressures, say researchers from South Korea. The system could be a step towards new technology for using CO₂ at low pressures.

Sang-Eon Park and coworkers from Inha University, Incheon, prepared carbon nitrides that contain surface groups to activate the CO₂, which was then used to promote the oxidation reactions of several cyclic alkenes.

CO₂ is being recognised as an alternative and economic resource for use in organic reactions and it has been used in catalytic reactions, either as a solvent or a reagent. However, in most cases, it is used in a dense phase or under supercritical conditions, which require high operating pressures and have low reaction rates. 

The team tested their system by oxidising different cyclic alkenes with various amounts of oxygen, with and without CO₂,  and compared the results. They found that the presence of the CO₂ increased the conversion percentage in all cases. The CO₂ acts as an oxygen source, which is inferred from the formation of carbon monoxide and surface carbamate. The team was also able to reuse the catalyst up to three times.

Chang-jun Liu from Tianjin University, China, an expert in catalysis and the use of greenhouse gases, says that using ‘high nitrogen containing carbon nitrides to enhance the oxidation of cyclic olefins with CO₂ as a soft oxidant’ is significant. Liu adds that the work could lead to an easy approach for CO₂ conversion with the production of highly-valued chemicals.

Park’s team now hopes to fully understand the reaction mechanism, explaining that this will help them to design a more appropriate catalyst. ‘Further spectroscopic and computational studies are in progress and hopefully, very soon, a complete insight over promotional aspects will be revealed,’ concludes Park.

Reproduced from a Chemistry World story written by Mary Badcock

Read the full article here:

CO₂ activation and promotional effect in the oxidation of cyclic olefins over mesoporous carbon nitrides
Mohd Bismillah Ansari, Byung-Hoon Min, Yong-Hwan Mo and Sang-Eon Park
Green Chem., 2011, Advance Article
DOI: 10.1039/C0GC00951B

Scientists from Bejing, China, have developed a highly selective supported Ru catalyst for the hydrogenation of benzene to cyclohexene – a compound which is very useful for nylon production. Until now, the Ru based catalysts used for this transformation deliver low selectivity and yield of the desired partial hydrogenation product, and often the use of additives is necessary. However, in this work by Buxing Han and co-workers, cyclohexene yields of 56% were achieved in water without the use of additives.

The selective hydrogenation of benzene to cyclohexene is challenging, as it is significantly more thermodynamically favorable for cyclohexane to be the primary product of the reaction. By using water as the reaction medium it is proposed that the hydrogenation of cyclohexene to cyclohexane is slowed because benezene is more soluable than cyclohexene in water under these conditions. This is also aided by the hydroxyl groups on the catalyst surface which disfavour the adsorption of cyclohexene onto the catalyst surface, thus preventing further hydrogenation. Synergistic effects between the zinc and zirconium in the catalyst support also play a crucial role in the efficiency and selectivity of the catalyst used in this work.

Read the full article for free until 22nd April by following the link below.

Highly selective benzene hydrogenation to cyclohexene over supported Ru catalyst without additives, Huizhen Liu, Tao Jiang, Buxing Han, Shuguang Liang, Weitao Wang, Tianbin Wu and Guanying Yang, Green Chem., 2011, DOI:10.1039/c0gc00959h

Spent coffee grounds have been turned into biodiesel by researchers from Portugal and Spain, who combined two separate processes to produce the biodiesel in one step.

Spent coffee grounds contain up to 20 weight per cent lipids, most of which are triglycerides that can be extracted and converted by transesterification into the fatty acid methyl esters that make up biodiesel. Pedro Simões from the New University of Lisbon and colleagues produced the esters in a 93 per cent yield, combining the extraction and transesterification processes in one step. 

The process combines extraction and transesterification in one step

Current commercial biodiesel production consists of an alkali-catalysed method to produce a mixture of fatty acid alkyl esters and glycerol. But, several purification processes are needed to remove the catalyst and by-products. Reactions in supercritical methanol without a catalyst have also been used – vegetable oils are more soluble in supercritical methanol than in normal methanol, leading to greater yields – but scientists need expensive equipment to produce the high temperatures and pressures required.

Simões’ team performed the reaction in supercritical methanol at 603K and 30MPa to obtain a fatty acid methyl ester in a yield of 85 per cent. To increase the yield further, they had to increase the temperature and pressure. But then they found that adding carbon dioxide to the mixture gave a higher yield – 93 per cent – at a reduced temperature of 573K and pressure of 10MPa.

The researchers explain that CO₂ may play a dual role in the reaction by increasing the extraction rate of oil from the spent coffee grounds and recovering the methyl esters from the reaction mixture. 

This work should pave the way for developing methods for new ways of processing waste food rather than composting and anaerobic digestion, says Rafael Luque, an expert on biofuels from the University of Cordoba, Spain. He adds that ‘there is a need to change the perception of waste as a problem – it should be perceived as a resource to produce valuable chemicals and biofuels.’

Reproduced from a Chemistry World story written by Anna Watson

Read the full article here:

Synthesis of fatty acid methyl esters via direct transesterification with methanol/carbon dioxide mixtures from spent coffee grounds feedstock
Filipe Calixto, João Fernandes, Ricardo Couto, Elvis J. Hernández, Vesna Najdanovic-Visak and Pedro C. Simões, Green Chem., 2011, DOI: 10.1039/c1gc15101k

Scientists from Germany have reported a simple and robust ionic liquid-based system for the selective decomposition of formic acid to hydrogen and carbon dioxide.

Formic acid has been proposed as an attractive hydrogen carrier substance as it can easily be stored and transported to be catalytically decomposed to release hydrogen (and CO₂) on demand.  Wasserscheid and his team have developed a simple and robust catalytic system involving the ionic liquid [EMMIM][OAc] and the ruthenium catalyst RuCl₃ which gave excellent yields of hydrogen from formic acid.  As ionic liquids have extremely low volatility, this avoids solvent contamination of the produced hydrogen stream. In addition, the system is very selective, with no carbon monoxide form during the decomposition, thereby avoiding complicated gas purification procedures later on.

However, one of the most striking features of the system reported by Wasserscheid is the recyclability of this ionic liquid-catalyst system.  The RuCl₃/[EMMIM][OAc] could was reused for at least another nine runs after its first use, with no decline in the selectivity or yields, illustrating the robust nature of this system.  This has clear implications for further development of this process and its application in industry.

To read more please see link below for the full journal article.  This article will be free to access until 2 May 2011.

Simple and recyclable ionic liquid based system for the selective decomposition of formic acid to hydrogen and carbon dioxide

M. E. M. Berger, D. Assenbaum, N. Taccardi, E. Spiecker and P. Wasserscheid, Green Chem., 2011, DOI: 10.1039/C0GC00829J,

Scientists at GlaxoSmithKline (GSK) have recently published a revised “solvent selection guide” which is designed to aid the decision-making process associated with choosing a solvent for a chemical transformation. The original solvent selection guide published in 1998 assessed the use of 47 solvents in organic chemistry reactions. The updated version of the solvent selection guide now includes 110 solvents (each with a life cycle score), thus providing a more comprehensive comparative and relative assessment of the solvents.

The guide also contains information on solvent recycling, environmental impact, health and flammability issues amongst others. The broad range of issues covered in the guide will enable scientists to make an objective decision on which solvents to use based on multiple paramenters – this will help truly assess which solvent is the most sustainable for a particular procedure.

Click the link below to read the article in full – free access until 21st April

Expanding GSK’s solvent selection guide – embedding sustainability into solvent selection starting at medicinal chemistry

Richard K. Henderson, Concepcion Jimenez-Gonzalez, David J. C. Constable, Sarah R. Alston, Graham G. A. Inglis, Gail Fisher, James Sherwood, Steve P. Binks and Alan D. Curzons, Green Chem., 2011, DOI: 10.1039/c0gc00918k

Polymer scientists from Aachen, Germany, have developed a novel and green method to produce biocompatible polyesters using Novozyme 435 as the catalyst.

The polyester poly(pentadecalactone) (PPDL) investigated in this work is a non-toxic, highly crystalline and hydrophobic material – similar to polyethylene. By copolymerizing pentadecalactone with functional e-caprolactones and macrolactones containing C=C double bonds, epoxide rings and amide functionalities, it was found that the properties of PPDL could be tuned and crystallinity was reduced – increasing the biocompatibility of the material which is necessary for applications in drug-delivery devices or scaffolds.

Using the Novozyme 435 enzyme catalyst, copolymerization of PDL with two 7-membered lactones leads to a near quantitative monomer conversion.

To find out more, click the link below to read the Green Chemistry article in full – free to access until 21st March 2011.

Tailor-made polyesters based on pentadecalactone via enzymatic catalysis by C. Vaida, H. Keul and M. Moeller
DOI: 10.1039/C1GC15044H

Scientists from the Netherlands and the UK have conducted a solvent screening study aimed at identifying greener alternatives for the commonly used solvent dichloromethane in N-oxy catalysed bleach oxidations of various alcohol substrates.

The team found that environmentally acceptable ester solvents, notably isopropyl acetate and methyl acetate, gave results comparable to or better than dichloromethane.

However, there was no apparent correlation between common solvent properties and performance.

A comparison of two co-catalysts, NaBr and borax, revealed that borax gave better results with cinnamyl alcohols whereas NaBr was generally better with the other alcohols.

The team also studied the effect of catalyst loading. In the oxidation of 3-phenyl-1-propanol the amount of N-oxy catalyst could be effectively reduced to a mere 0.1 mol%.

They concluded that due to the complex nature of these systems, there is not a single set of conditions that gives good results for all alcohols. However, by employing a simple screening approach to assess solvent, catalyst and co-catalyst combinations, similar or even better results can often be achieved in solvents other than dichloromethane.

Read more about this article:

Towards greener solvents for the bleach oxidation of alcohols catalysed by stable N-oxy radicals
M H A Janssen, J F Chesa Castellana, H Jackman, P J Dunn and R A Sheldon, Green Chem., 2011, DOI:10.1039/c0gc00684j