Green Chemistry Blog

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.

Charles Wyman and colleagues have demonstrated a highly effective lignocellulosic bio-refinery model, producing unrivalled quantities of furfural, 5-hydroxymethylfurfural (HMF), and levulinic acid as products. Proposed as a basis for the production of renewable fuels, the furan derivatives generated by this process are also a promising platform onto many other intriguing bio-based molecules. Additionally, more than 90% of the lignin contained within the maple wood feedstock was reclaimed, making the process as a whole exceptionally appealing.

Instead of the typical acidified aqueous media often used, the hydrolysis of the lignocellulose feedstock (and subsequent sugar dehydration) was enhanced with the addition of the potentially renewable solvent tetrahydrofuran. The organic solvent increased yields of HMF by an order of magnitude over what could be obtained otherwise in a one-pot reaction conducted at 170 °C. Under these optimised conditions, 87% of the total pentose (C5) sugar content was accountable in the form of furfural, while the hexose (C6) sugar content was converted from cellulose into HMF (in up to yields of 21% of the theoretical maximum), levulinic acid (up to 40%), and free sugars. The authors believe this represents a key step towards achieving commercial viability for sustainable, sugar derived bio-fuels.

By James Sherwood

This article is free to access for 4 weeks! Click the link below to read more:

THF co-solvent enhances hydrocarbon fuel precursor yields from lignocellulosic biomass, Charles M. Cai, Taiying Zhang, Rajeev Kumar and Charles E. Wyman, Green Chem., 2013, DOI: 10.1039/c3gc41214h

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

Pharmaceutical Green Chemistry process changes – how long does it take to obtain regulatory approval?
Peter J. Dunn  
Green Chem., 2013, Advance Article, DOI: 10.1039/C3GC41376D

Preparation of waterborne functional polymers using a bifunctional coupler
Subrata Chattopadhyay, Helmut Keul and Martin Moeller  
Green Chem., 2013, Advance Article, DOI: 10.1039/C3GC41406J

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, Advance Article, DOI: 10.1039/C3GC41110A

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