Green Chemistry Blog

The asymmetric, enzymatic reduction of ketones has been enhanced with a graphene derived light harvesting photocatalyst. Typically the use of reducing enzymes for specialty chemical synthesis is restricted by the cost of the redox cofactor. In this example the enzyme cofactor is recycled via a rhodium complex. The energy needed to do this is delivered by the chlorophyll mimicking graphene. Enantioselectivity to the resulting alcohols is high, and applicable to both aliphatic and aromatic ketones.

The scientists from KRICT responsible for this research believe that artificial photosynthesis using functionalised graphene shows promise for energy generation and sustainable chemical production in the near future, with applications including carbon dioxide sequestering reactions already proven as viable.

Check out the full article – online now!

Fermentation strategies for the production of bio-fuels will continue to grow in importance, and as they do, problems with retrieving the products from dilute fermentation broths and the low energy content of short-chain alcohols will be magnified. A partnership between the energy company Shell and the Qingdao Institute of Bioenergy and Bioprocess Technology is addressing this challenge by using catalysis to condense bio-ethanol or bio-butanol via the Guerbet reaction to give improved, higher-alcohol biofuels.

An immobilised iridium catalyst was successful in converting 1-butanol in aqueous solution to 2-ethyl-1-hexanol with >85% selectivity over five consecutive reactions. The upgrading of ethanol was less selective to a single product: In addition to 1-butanol, 2-ethyl-1-butanol and even traces of 1-octanol were observed. A phenanthroline ligand is required to facilitate the aqueous phase reaction, conditions that mimic the environment of a fermentation broth. This approach also negates the usual requirement of hydrogen gas to reduce the β-unsaturated aldehyde intermediate, with the reaction proceeding under air.

These results all indicate that this reaction shows great potential for producing biofuels, as well as many other useful chemicals, in a cheaper and more efficient way.

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Ionic liquids have been touted as green solvents since even before the definition of green chemistry was presented in Anastas and Warner’s seminal text. Academic research on ionic liquids, across many varied applications, is a strong and still growing area of interest. Despite this, the commercialisation of ionic liquid products, and their utilisation as solvents in manufacturing processes, has been limited because of their high costs.

In this latest work from Jason Hallett and colleagues from Imperial College London, the economic feasibility of two ionic liquids synthesized by acid–base neutralization has been assessed. It was found that process intensification dramatically reduces the end cost of these ionic liquids, and is recommended in this latest work as a means of reducing the cost of ionic liquids so that their potential in commercial applications may be realised.

The prices of triethylammonium hydrogen sulfate and 1-methylimidazolium hydrogen sulfate produced with optimised manufacturing methods are estimated to be as little as $1.24 kg⁻¹ and $2.96 kg⁻¹ respectively, which are largely dictated by the raw material costs. These prices are similar to conventional organic solvents such as acetone, while at present typical ionic liquid prices can be two orders of magnitude greater than this. The authors conclude that  more effort should be dedicated to developing new ionic liquids that can be synthesised from affordable raw materials in very few steps.

http://pubs.rsc.org/en/content/articlelanding/2014/gc/c4gc00016a#!divAbstract

The European Commission has established a target for EU member states to obtain 20% of their energy from renewable sources by the year 2020. Although production of electricity from solar energy and hydropower are crucial technologies in achieving this goal, liquid hydrocarbon fuels are seemingly irreplaceable in certain heavy transportation sectors (specifically sea freight and aviation).

Scientific advances are now being made in the use of non-food crops to produce liquid hydrocarbon fuels, complementing the established oxygenated biofuels made of ethanol and bio-diesel. The latest research demonstrates that pine wood can be successfully converted into a mixture of liquid hydrocarbons. The resulting fuel has a similar calorific value to diesel, and contains less than 5% oxygen.

The necessary catalyst is made through a simple wet impregnation technique to give copper and ruthenium supported on phosphotungstic acid, which is then calcined. The transformation of the lignocellulosic biomass is conducted under hydrogen at an elevated temperature to produce the liquid fuel (30 wt%), which separates from an aqueous phase and any residual solid. The organic liquid was found to contain a number of mostly cyclic aliphatic hydrocarbons and also aromatic compounds, and thus is an attractive option as a next generation biofuel.

Direct thermocatalytic transformation of pine wood into low oxygenated biofuel
Walid Al Maksoud, Cherif Larabi, Anthony Garron, Kai C. Szeto, Jean J. Walter and Catherine C. Santini
Green Chem., 2014, Advance Article, DOI: 10.1039/C3GC42596G

Research by French scientists has identified 18 vanillin derived chemicals for application in the synthesis of bio-based polymers. Vanillin is interesting as a chemical intermediate because of its different functional groups, and because it is manufactured in different ways. Extraction of natural vanillin and fermentation of bio-based ferulic acid are high cost options compared to the petroleum derived synthesis from guaiacol. An alternative route to vanillin has recently been proposed starting from p-cresol, but this approach is also based on non-renewable feedstocks. Another procedure that presently has a minority share of global vanillin production is the valorisation of lignin. This process had fallen out of favour somewhat, but cleaner technologies have revitalised research into vanillin derived from Kraft lignin, benefiting from the growing interest in producing chemicals from lignin more generally.

Polymers of vanillin are known, but are not often significantly diversified from the parent molecule. This latest work lead by Sylvain Caillol has resulted in the synthesis of difunctionalised epoxides, carbonates, alkenes, alcohols, amines and carboxylic acids, all with obvious potential as monomers for bio-based polymers. Different polymer types have been targeted, including epoxy resins, polyesters and polyurethanes. Through this research a number of opportunities for new and interesting renewable polymers have been opened up, which utilise the abundant resource of lignin via the important chemical intermediate vanillin.

Vanillin, a promising biobased building-block for monomer synthesis
Maxence Fache, Emilie Darroman, Vincent Besse, Auvergne Rémi, Sylvain Caillol and Bernard Boutevin
Green Chem., 2014, Advance Article, DOI: 10.1039/C3GC42613K

Jennifer Lee and George Kraus of Iowa State University have published a new method of producing dimethyl terephthalate, a precursor to polyethylene terephthalate (PET), from renewable sources. In this new work the reaction between methyl coumalate (the esterified dimer of malic acid) and methyl pyruvate (the ester of pyruvic acid) is optimised to provide dimethyl terephthalate in 95% yield.

This is the latest of several approaches currently being developed to supplant the current manufacturing process that produces PET from finite fossil resources. These include the valorisation of citrus waste and the reaction of ethylene with 2,5-dimethylfuran. As is true for the zeolite catalysed fast pyrolysis of certain bio-based resources, these other green methods produce an intermediate aromatic compound, p-xylene or sometimes p-cymene, which must later be oxidised to terephthalic acid. This oxidation reaction is present in the conventional petroleum derived synthesis of PET. The new uncatalysed, solvent-free method of Lee and Kraus circumvents the oxidation stage, and by doing so shortens the synthetic procedure and avoids the use of cobalt or manganese oxidation catalysts, which from an elemental sustainability perspective are vulnerable to depletion.

Free to access until 4th March:

One-pot formal synthesis of biorenewable terephthalic acid from methyl coumalate and methyl pyruvate, J. J. Lee and G. A. Kraus, Green Chemistry, DOI: 10.1039/C3GC42487A