Green Chemistry Blog

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

Albert Matlack, one of the founding educators of green chemistry and author of the book ‘Introduction to Green Chemistry’, selects his favourite papers in Green Chemistry this month…

Mechanical depolymerisation of acidulated cellulose: understanding the solubility of high molecular weight oligomers, Abhijit Shrotri, Lynette Kay Lambert, Akshat Tanksale and Jorge Beltramini, Green Chem., 2013, 15, 2761–2768, DOI: 10.1039/c3gc40945g

In this work, cellulose was milled with sulfuric acid to produce oligomers which were hydrogenated over a Ni/Pt/aluminium oxide catalyst 200 °C for an hour to produce 90% of sorbitol and mannitol. This yield is better than the efforts of others to do the job. Sorbitol can be converted to isosorbide, then to high melting point biopolymers. Further work is needed to get more than the 34.6% of the starting cellulose to dissolve.

Continuous flow nanocatalysis: reaction pathways in the conversion of levulinic acid to valuable chemicals, Jose M. Bermudez, J. Angel Menéndez, Antonio A. Romero, Elena Serrano, Javier Garcia-Martinez and Rafael Luque, Green Chem., 2013, 15, 2786–2792, DOI: 10.1039/c3gc41022f

This work shows the advantages of a continuous flow system to produce biomass platform chemicals. The authors use a ThalesNano H-Cube of levulinic acid to produce 60% methyltetrohydrofuran and 40% 1,4-pentanediol in one minute at 150 °C, which shows the value of the system over a batch method.

“Release and catch” catalytic systems, Michelangelo Gruttadauria, Francesco Giacalone and Renato Noto, Green Chem., 2013, 15, 2608–2618, DOI: 10.1039/c3gc41132j

This review covers catch and release systems which do not use covalent bonding to a support. The concept is good in the sense that a homogeneous catalyst may have a single active site, whereas a heterogeneous catalyst may have several types of active sites. The systems work with a variety of metal catalysts, but activity decreases on repeating cycles. Metal leaching may be taking place. Further work is needed to make such systems practical for widespread use.