Green Chemistry Blog

Cheap and readily available photovoltaic cells have been used to conduct electrochemical oxidation reactions by Kevin D Moeller and co-workers from the Washington University in St Louis.

Connecting the dots

Oxidation reactions are among the most powerful tools available to synthetic chemists because they increase the level of functionality in a molecule.  This study demonstrates that the energy efficiency of sunlight-driven reactions can be combined with the versatility of electrochemistry to create new, sustainable methods for conducting oxidation reactions.

Interested in knowing more?  Read the full article here.

Connecting the dots: using sunlight to drive electrochemical oxidations
Laura A. Anderson, Alison Redden and Kevin D. Moeller
Green Chem., 2011, Advance Article
DOI: 10.1039/C1GC15207F

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