Green Chemistry Blog

Scientists in Canada and China have shown that the effectiveness of commercial sunscreens can be enhanced by the addition of lignin and, as an unprecedented bonus; sunlight exposure may help them work even better!

To read the full article written about this work visit Chemistry World.

The original research article is free to access until 14 November 2014.

Download it here: Y Qian, X Qiu and S Zhu, Green Chem., 2014, DOI: 10.1039/c4gc01333f

The separation of lignocellulosic biomass into its three component polymers; cellulose, hemicellulose, and lignin, is an important field of research relevant to biorefineries and the production of bio-based products. The chemical valorisation of polysaccaharides (to bio-ethanol for example) and the paper industries leave the lignin behind as waste.

Rich in aromatic functionality, it is unfortunate that because of the poor solubility of lignin up to 40% of lignocellulosic biomass feedstock is consigned to low value applications.

The use of ammonia as a solvent for lignin has now been revisited by a team of Dutch scientists in order to resolve this solubilisation bottleneck. Ammonia was shown to readily dissolve most varieties of lignin at room temperature and 7-11 bar, and can be removed simply by releasing the pressure.

The mild conditions make ammonia an attractive solvent for biorefineries looking to maximise lignocellulosic biomass utilisation. Furthermore the necessary apparatus is already incorporated into biorefineries for the ammonia fibre explosion (AFEX) process.

This article is open access and available to everyone to read for free:

Lignin solubilisation and gentle fractionation in liquid ammonia

Zea Strassberger, Pepijn Prinsen, Frits van der Klis, Daan S. van Es, Stefania Tanasea and Gadi Rothenberg

Green Chem., 2014, Advance Article. DOI: 10.1039/C4GC01143K

Researchers from Iowa State University have recently developed a route to non-solvated aluminum trihydride (alane), free of metallic aluminum. The reaction occurs at room temperature by the mechanical milling of lithium aluminum hydride and aluminum chloride and a nearly complete conversion can be achieved in 30–60 mins. The formation of aluminum can be entirely avoided above a certain critical pressure, which depends on the nature of the gas and the milling parameters. An intermediate was identified in the process, which reacts to produce alane and lithium chloride.

Due to the impractical conditions required for the direct hydrogenation of aluminum, alternative routes that allow for the large-scale preparation of alane are essential, for example the one described in this paper. The authors have also recently introduced a mechanochemical synthesis of alane using lithium hydride as a starting material, which directly leads to adduct-free alane.

Check out the original article online now:

Solvent-free mechanochemical synthesis of alane, AlH₃: effect of pressure on the reaction pathway
S. Gupta, T. Kobayashi, I. Z. Hlova, J. F. Goldston, M. Pruski, and V. K. Pecharsky
Green Chem. 2014, 16, 4378.
DOI: 10.1039/C4GC00998C

Jenna Flogeras obtained her B.Sc. and M.Sc. in Chemistry from the University of New Brunswick (Fredericton), Canada. She is currently a Ph.D. student at Memorial University in Newfoundland, where she studies aluminum-based catalysts under the supervision of Dr. Francesca Kerton.

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!