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!
Virginia Nykänen and colleagues at Aalto University, Finland have transformed rice starch into a temporally stable, optically transparent, biodegradable plastic with a high degree of mechanical strength and good thermal resistance.
This important step towards bioplastics made from simple and sustainable resources has potential applications in food packaging and biomedical materials.
Read the full article here in Chemistry World.
This paper is free to access until 8 September, so download it now:
V P S Nykänen et al, Green Chemistry, 2014, DOI: 10.1039/c4gc00794h
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.
Check out the full article – online now!
Direct self-condensation of bio-alcohols in the aqueous phase
A wide variety of metal complexes act as efficient catalysts for the synthesis of cyclic carbonates from carbon dioxide and epoxides; organic bases, such as pyridine, are often useful co-catalysts in the reaction. Metal-free catalyst systems are also effective, and polymers having abundant hydroxyl groups, such as cellulose, are known to catalyze cycloaddition when combined with an alkali metal halide. Building upon these findings, researchers from the Chinese Academy of Sciences have developed a metal-free and halide-free catalyst system using a combination of a superbase and a hydrogen bond donor.
Among the bases and hydrogen bond donors investigated, a cellulose-DBU catalyst system exhibited the highest conversion to propylene carbonate. Optimization of the reaction conditions led to a further study using an array of terminal epoxides; the highest yield and selectivity was observed for ethylene oxide, with lower yields for more sterically hindered substrates. The catalyst system also proved to be recyclable for up to four trials without an appreciable loss of activity or selectivity.
Read the full article now:
Superbase/cellulose: an environmentally benign catalyst for chemical fixation of carbon dioxide into cyclic carbonates
Jian Sun, Weiguo Cheng, Zifeng Yang, Jinquan Wang, Tingting Xu, Jiayu Xin and Suojiang Zhang
Green Chem. 2014, Advance Article, DOI: 10.1039/C3GC41850B
Jenna Flogeras obtained her B.Sc. and M.Sc. in Chemistry from the University of New Brunswick (Fredericton), Canada. Currently a Ph.D. student at Memorial University of Newfoundland, she is excited to spend some time outside the laboratory this summer to explore Thailand and Southeast Asia.
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.
L. Chen et al., Green Chem., 2014. DOI: 10.1039/C4GC00016A
http://pubs.rsc.org/en/content/articlelanding/2014/gc/c4gc00016a#!divAbstract
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