Green Chemistry Blog

Olefin metathesis is a route to the formation of new C=C bonds, and is, thus, ubiquitous in organic chemistry. Reactions of this type include cross metathesis (CM) and ring-closing metathesis (RCP), among others, where Grubbs-type ruthenium (Ru) complexes bearing N-heterocyclic carbene (NHCs) ligands are commonly used commercial catalysts. Traditionally, chlorinated and aromatic solvents, e.g., DCM and toluene, are employed; their use, however, is accompanied by health and environmental concerns. Less hazardous reaction media, including water and ionic liquids (ILs), have been previously investigated, but special reaction conditions, or catalysts that are not readily available, are required for their success.

In this paper, the authors sought to evaluate the performance of several types of commercial metathesis catalysts in non-traditional solvents, viz., MeOH, i-PrOH, EtOAc, DMC, CPME, and 2-MeTHF. These solvents were chosen based on their adherence to “green” solvent selection criteria. A series of ten Ru-based catalysts with varied (NHC) ligand architecture was chosen for this study. The most effective solvent/catalyst combinations for ROP of dienes and CM of esters were first determined using model compounds. A number of substrates, having motifs prevalent in natural products, were subsequently tested in the best performing solvent, i.e., EtOAc. The results indicated that the catalyst systems, when used in ester solvents at 70 °C, produced similar yields and selectivites to analogous reactions in toluene and DCM. These results were obtained in air rather than under an inert gas. Moreover, the reactions were carried out in solvents that had not been degassed or distilled, as is typically the case. This presents a valuable alternative to the less sustainable conditions commonly used in industry and academia.

By Jenna Flogeras

To read the full article, please click the link below. The paper is free to access for 4 weeks!

In an attempt to provide green solvent selection guide for olefin metathesis, Tomasz Krzysztof Olszewski, Krzysztof Skowerski, Andrzej Tracz and Jacek Bialecki, Green Chem., 2013, DOI: 10.1039/C3GC41943F

Here are the latest HOT papers published in Green Chemistry, as recommended by the referees:

Mimicking mineral neogenesis for the clean synthesis of metal–organic materials from mineral feedstocks: coordination polymers, MOFs and metal oxide separation
Feng Qi, Robin S. Stein and Tomislav Friščić  
Green Chem., 2013, Advance Article. DOI: 10.1039/C3GC41370E

One-pot combination of enzyme and Pd nanoparticle catalysis for the synthesis of enantiomerically pure 1,2-amino alcohols
Joerg H. Schrittwieser, Francesca Coccia, Selin Kara, Barbara Grischek, Wolfgang Kroutil, Nicola d’Alessandro and Frank Hollmann  
Green Chem., 2013, Advance Article, DOI: 10.1039/C3GC41666F

Sunlight, electrochemistry, and sustainable oxidation reactions
Bichlien H. Nguyen, Alison Redden and Kevin D. Moeller  
Green Chem., 2013, Advance Article, DOI: 10.1039/C3GC41650J

All the papers listed above are free to access for the next 4 weeks!

Cross coupling reactions are immensely useful in the construction of organic molecules, a fact recognised with the award of the 2010 Nobel Prize in chemistry to Akira Suzuki, Richard Heck, and Ei-ichi Negishi. Now scientists in Beijing have discovered that adding common salts like sodium chloride, in a large excess, to Pd/C catalysed Suzuki-Miyaura reactions can more than double the achievable yield. This use of cheap and abundant materials would appear to be an excellent way to improve the productivity of the reaction without drastically increasing its burden on the environment.

It is known that Suzuki-Miyaura reactions can be conducted without any catalyst specifically being added to the reaction. Instead, the reaction is catalysed by trace amounts of palladium in the inorganic base. The authors of this present work report that the inorganic salts are not catalytic themselves, but enhance the activity of the true catalyst. The nature of this synergetic effect was deduced from infra-red and X-ray photoelectron spectroscopy studies, showing evidence of the auxiliary salt interacting with both the bromoarene reactant and the palladium catalyst. The polarisation of the reactive C-Br bond, and the increased electron density placed on the metal catalyst, is said to enhance the rate determining oxidative addition step of the reaction.

By James Sherwood

Click below to read the full article, free until December 1st:

Acceleration of Suzuki coupling reaction by abundant and non-toxic salt particles, Binbin Zhang, Jinliang Song, Huizhen Liu, Jinghua Shi, Jun Ma, Honglei Fan, Weitao Wang, Peng Zhang and Buxing Han, Green Chem., 2013, DOI: 10.1039/C3GC42088D

Chlorophyll formation was enhanced when algae were grown in a flask surrounded by a solution of gold and silver nanoparticles

Scientists in Australia have developed a nanoparticle light filter system that only lets through wavelengths favourable for microalgae growth. The system could make producing algal biofuels more efficient.

Photosynthetic systems, particularly microalgae, are at the forefront of the search for new renewable fuels and feedstock chemicals. The speed and efficiency at which microalgae grow is currently limiting them from becoming a commercially viable product so optimising their production is obviously a priority.

Colin Raston from Flinders University and his co-workers at the University of Western Australia have developed a new technique to enhance the formation and accumulation of photopigments, namely chlorophyll, in algae. They cultured Chlorella vulgaris in flasks that were surrounded by a solution of gold and silver nanoparticles. Tweaking the composition and size of the nanoparticles alters the wavelengths of light allowed through to the algae.

Read the full article in Chemistry World»

Read the original journal article in Green Chemistry:
Enhanced accumulation of microalgal pigments using metal nanoparticle solutions as light filtering devices
Ela Eroglu, Paul K. Eggers, Matthew Winslade, Steven M. Smith and Colin L. Raston  
Green Chem., 2013, 15, 3155-3159, DOI: 10.1039/C3GC41291A

Issue 11 of Green Chemistry is now available to read online. 

The front cover this month (pictured left) features work by Wouter De Soute and co-workers from Ghent, Belgium. In their work, they show that shifting from batch to continuous pharmaceutical tablet manufacturing results in a significant reduction in natural resource extraction. 

Read the full article:
Exergetic sustainability assessment of batch versus continuous wet granulation based pharmaceutical tablet manufacturing: a cohesive analysis at three different levels
Wouter De Soete, Jo Dewulf, Philippe Cappuyns, Geert Van der Vorst, Bert Heirman, Wim Aelterman, Kris Schoeters and Herman Van Langenhove  
Green Chem., 2013, 15, 3039-3048, DOI: 10.1039/C3GC41185K 

The inside front cover this month (pictured right) features work by Davit Zargarian and co-workers from Quebec, Canada. In their work they reveal a new one-pot method for the efficient and atom-economical synthesis of POCOP-type pincer complexes of divalent nickel that serve as pre-catalysts for various catalytic transformations.

Read the full article:
Direct, one-pot synthesis of POCOP-type pincer complexes from metallic nickel
Boris Vabre, Fabien Lindeperg and Davit Zargarian  
Green Chem., 2013, 15, 3188-3194, DOI: 10.1039/C3GC40968F 

Both of these articles are free to access for 6 weeks! 

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Diarylsulphides are popular motifs for the basis of drug design and materials, but their synthesis is usually dependant on inherently wasteful cross coupling reactions that require metals such as palladium, copper, and indium. Now iodine has been discovered to be an effective catalyst for the synthesis of diarylsulphides from thiophenols and cyclohexanone derivatives. Researchers from Xiangtan in China have shown that the desired reaction is achievable when an oxygen atmosphere is used to regenerate the catalyst. A large number of pendant functional groups are tolerated, with yields of up to 80% observed.

The use of iodine to replace metal containing catalysts is hugely beneficial in securing the long term sustainability of this synthetic protocol. The vulnerability of scarce metal resources is a vital consideration often overlooked when designing new organic syntheses supposedly within the remit of green chemistry. Unlike C-S cross coupling procedures that result in stoichiometric halide containing wastes, this new protocol produces only water as a by-product, whilst also circumventing the need for an auxiliary base or an expensive metal catalyst. Unfortunately the only satisfactory solvent that could be found was NMP, which will need to be improved upon if this procedure is to be considered as a green process. Otherwise this synthetic method is a welcome advance in the development of sustainable catalytic chemistries.

By James Sherwood

Read the article in full – free to access for 4 weeks!

Iodine-catalyzed efficient 2-arylsulfanylphenol formation from thiols and cyclohexanones, Yunfeng Liao, Pengcheng Jiang, Shanping Chen, Hongrui Qi and Guo-Jun Deng, Green Chem., 2013, DOI: 10.1039/c3gc41671b

Lignin, a component of plant cell walls, gives plants the strength to grow tall but this strength is a barrier to turning plants into biofuels. So researchers in the UK have devised an efficient way to make complex model compounds of lignin to help them figure out the best way to break lignin down.

Lignin is a complex and random polymer. This representative substructure shows some of the common linkages in lignin

Unlike cellulose, a plant cell wall component with a repeating polymer structure, lignin is a complex and random polymer. The chemical units are linked by different connectivities, so one single process cannot attack all of these bonds. Previously, monomers and dimers were used to model chemical linkages of lignin, but were too simple for the study of lignin itself. More complex trimers, tetramers and hexamers have been synthesised, but with inefficient, low-yielding methods.

Work undertaken in Gary Sheldrake’s group at Queen’s University Belfast looks set to significantly advance the study of lignin with the development of a new scalable synthetic route for complex model lignin oligomers that produces several grams of product, and can easily be performed in a standard lab. ‘The ultimate aim was to get a synthesis that worked, but we tried as far as possible to avoid ungreen solvents and harsh conditions,’ notes Sheldrake.

Read the full article in Chemistry World»

Read the original journal article in Green Chemistry:
An efficient and flexible synthesis of model lignin oligomers
W. Graham Forsythe, Mark D. Garrett, Christopher Hardacre, Mark Nieuwenhuyzen and Gary N. Sheldrake  
Green Chem., 2013, DOI: 10.1039/C3GC41110A, Paper

Scientists in France have developed a computer-assisted organic synthesis program to design sustainable solvents from bio-based building blocks.

The GRASS software has a green chemistry-focussed approach to solvent design

Finding clean, sustainable alternatives to petroleum-derived solvents and chemicals is a matter of increasing urgency in the chemical industry worldwide. Concerns over health, safety, economic and legal issues, together with a need to minimise the environmental impact of industrial processes have led to increased interest in developing new solvents, particularly those derived from biomass. While a number of computer-aided organic synthesis tools have been developed to aid molecular design and synthetic planning over the past few decades, they have not found widespread application in commodity chemical synthesis.

Traditional synthesis planning combines specialist chemical knowledge and careful literature analysis. GRASS, short for GeneratoR of Agro-based Sustainable Solvents, the software developed by Jean-Marie Aubry at the University of Lille Nord de France and co-workers, challenges this tradition and provides a wholly green chemistry-focussed approach to solvent design on an industrial scale.

Read the full article in Chemistry World»

Read the original journal article in Green Chemistry:
In silico design of bio-based commodity chemicals: application to itaconic acid based solvents
Laurianne Moity, Valérie Molinier, Adrien Benazzouz, René Barone, Philippe Marion and Jean-Marie Aubry  
Green Chem., 2013, DOI: 10.1039/C3GC41442F, Paper