Green Chemistry Blog

A collaboration between scientists at Frankfurt’s DECHEMA Research Institute and the Delft University of Technology has established a biocatalytic route to make bio-based antiseptics from carvacrol and thymol. Halogenation of monoterpenes yields interesting antimicrobial compounds, some with anti-tumour activity and other desirable medicinal properties. As more is discovered about enzymatic halogenation (and significant progress on this front is only recent) it becomes increasingly viable as a benign technology for the synthesis of these important molecules.

A chloroperoxidase enzyme was used to form hypochloride from sodium chloride and hydrogen peroxide, with later experiments exploring combined electrochemical enzymatic halogenation, producing the hydrogen peroxide in situ from oxygen. The hypochloride then reacts with carvacrol or thymol to produce their respective monochloro-derivatives. For example, an ortho-chlorothymol to para-chlorothymol molar ratio of 70:30 was achieved, with yields exceeding 80% under optimised conditions.

The greenness of this methodology is apparent upon comparison to the typical reaction conditions, as highlighted by Getrey et al. and found here. In contrast to the application of copper(II) chloride as a catalyst in the chlorination of phenol derivatives with oxygen and lithium chloride, this new enzymatic process operates at a lower temperature with less catalyst, and does not require an organic solvent.

By James Sherwood

Click below to read the full article. Free to access until 8th January.

Enzymatic halogenation of the phenolic monoterpenes thymol and carvacrol with chloroperoxidase, Laura Getrey, Thomas Krieg, Frank Hollmann, Jens Schrader and Dirk Holtmann, Green Chemistry, 2014, DOI: 10.1039/C3GC42269K

The 10 most-accessed Green Chemistry articles between July and September 2013 were as follows:

Synthesis of thioesters through copper-catalyzed coupling of aldehydes with thiols in water
Chih-Lun Yi, Yu-Ting Huang and Chin-Fa Lee  
Green Chem., 2013,15, 2476-2484, DOI: 10.1039/C3GC40946E, Paper

Highly efficient iron(0) nanoparticle-catalyzed hydrogenation in water in flow
Reuben Hudson, Go Hamasaka, Takao Osako, Yoichi M. A. Yamada, Chao-Jun Li, Yasuhiro Uozumi and Audrey Moores  
Green Chem., 2013,15, 2141-2148, DOI: 10.1039/C3GC40789F, Paper 

Iodine-mediated arylation of benzoxazoles with aldehydes
Yew Chin Teo, Siti Nurhanna Riduan and Yugen Zhang  
Green Chem., 2013,15, 2365-2368, DOI: 10.1039/C3GC41027G, Communication

Polymer anchored Cu(II) complex: an efficient and recyclable catalytic system for the one-pot synthesis of 1,4-disubstituted 1,2,3-triazoles starting from anilines in water
Susmita Roy, Tanmay Chatterjee and Sk. Manirul Islam  
Green Chem., 2013,15, 2532-2539, DOI: 10.1039/C3GC41114A, Paper

 Multicomponent reactions in unconventional solvents: state of the art
Yanlong Gu  
Green Chem., 2012,14, 2091-2128, DOI: 10.1039/C2GC35635J, Critical Review

Photocatalysis on supported gold and silver nanoparticles under ultraviolet and visible light irradiation
Sarina Sarina, Eric R. Waclawik and Huaiyong Zhu  
Green Chem., 2013,15, 1814-1833, DOI: 10.1039/C3GC40450A, Tutorial Review

Characterization and comparison of hydrophilic and hydrophobic room temperature ionic liquids incorporating the imidazolium cation
Jonathan G. Huddleston, Ann E. Visser, W. Matthew Reichert, Heather D. Willauer, Grant A. Broker and Robin D. Rogers  
Green Chem., 2001,3, 156-164, DOI: 10.1039/B103275P, Paper

Deconstruction of lignocellulosic biomass with ionic liquids
Agnieszka Brandt, John Gräsvik, Jason P. Hallett and Tom Welton  
Green Chem., 2013,15, 550-583, DOI: 10.1039/C2GC36364J, Critical Review

Hydrolysis of cellulose to glucose by solid acid catalysts
Yao-Bing Huang and Yao Fu  
Green Chem., 2013,15, 1095-1111, DOI: 10.1039/C3GC40136G, Tutorial Review

Catalytic conversion of biomass to biofuels
David Martin Alonso, Jesse Q. Bond and James A. Dumesic  
Green Chem., 2010,12, 1493-1513, DOI: 10.1039/C004654J, Critical Review

Take a look at the articles and then let us know your thoughts and comments below.

Fancy submitting your own work to Green Chemistry? You can submit online today, or email us with your ideas and suggestions.

Issue 12 of Green Chemistry is now available to read online.

The front cover this month (pictured left) features work by Peter C. K. Lau and co-workers from Quebec, Canada. In their work they engineer sinapic acid decarboxylaseas an alternative to chemistry-based or thermal decarboxylation to produce canolol from canola meal.

Read the full article:
Antioxidant canolol production from a renewable feedstock via an engineered decarboxylase
Krista L. Morley, Stephan Grosse, Hannes Leisch and Peter C. K. Lau  
Green Chem., 2013, 15, 3312-3317, DOI: 10.1039/C3GC40748A

The inside front cover this month (pictured right) features work by Joerg Schrittwieser, Frank Hollmann and co-workers from Deltf, The Netherlands. In their work they show how the one-pot combination of alcohol dehydrogenase (ADH) and palladium nanoparticle (Pd-NP) catalysis provides access to aromatic 1,2-amino alcohols in high yields and excellent optical purities.

Read the full article:
One-pot combination of enzyme and Pd nanoparticle catalysis for the synthesis of enantiomerically pure 1,2-amino alcohols
Joerg H. Schrittwieser, Francesca Coccia, Selin Kara, Barbara Grischek, Wolfgang Kroutil, Nicola d’Alessandro and Frank Hollmann  
Green Chem., 2013, 15, 3318-3331, DOI: 10.1039/C3GC41666F

Both of these articles are free to access for 6 weeks!

Keep up-to-date-with the latest content in Green Chemistry by registering for our free table of contents alerts.

Olefin metathesis is a route to the formation of new C=C bonds, and is, thus, ubiquitous in organic chemistry. Reactions of this type include cross metathesis (CM) and ring-closing metathesis (RCP), among others, where Grubbs-type ruthenium (Ru) complexes bearing N-heterocyclic carbene (NHCs) ligands are commonly used commercial catalysts. Traditionally, chlorinated and aromatic solvents, e.g., DCM and toluene, are employed; their use, however, is accompanied by health and environmental concerns. Less hazardous reaction media, including water and ionic liquids (ILs), have been previously investigated, but special reaction conditions, or catalysts that are not readily available, are required for their success.

In this paper, the authors sought to evaluate the performance of several types of commercial metathesis catalysts in non-traditional solvents, viz., MeOH, i-PrOH, EtOAc, DMC, CPME, and 2-MeTHF. These solvents were chosen based on their adherence to “green” solvent selection criteria. A series of ten Ru-based catalysts with varied (NHC) ligand architecture was chosen for this study. The most effective solvent/catalyst combinations for ROP of dienes and CM of esters were first determined using model compounds. A number of substrates, having motifs prevalent in natural products, were subsequently tested in the best performing solvent, i.e., EtOAc. The results indicated that the catalyst systems, when used in ester solvents at 70 °C, produced similar yields and selectivites to analogous reactions in toluene and DCM. These results were obtained in air rather than under an inert gas. Moreover, the reactions were carried out in solvents that had not been degassed or distilled, as is typically the case. This presents a valuable alternative to the less sustainable conditions commonly used in industry and academia.

By Jenna Flogeras

To read the full article, please click the link below. The paper is free to access for 4 weeks!

In an attempt to provide green solvent selection guide for olefin metathesis, Tomasz Krzysztof Olszewski, Krzysztof Skowerski, Andrzej Tracz and Jacek Bialecki, Green Chem., 2013, DOI: 10.1039/C3GC41943F

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

Mimicking mineral neogenesis for the clean synthesis of metal–organic materials from mineral feedstocks: coordination polymers, MOFs and metal oxide separation
Feng Qi, Robin S. Stein and Tomislav Friščić  
Green Chem., 2013, Advance Article. DOI: 10.1039/C3GC41370E

One-pot combination of enzyme and Pd nanoparticle catalysis for the synthesis of enantiomerically pure 1,2-amino alcohols
Joerg H. Schrittwieser, Francesca Coccia, Selin Kara, Barbara Grischek, Wolfgang Kroutil, Nicola d’Alessandro and Frank Hollmann  
Green Chem., 2013, Advance Article, DOI: 10.1039/C3GC41666F

Sunlight, electrochemistry, and sustainable oxidation reactions
Bichlien H. Nguyen, Alison Redden and Kevin D. Moeller  
Green Chem., 2013, Advance Article, DOI: 10.1039/C3GC41650J

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

Cross coupling reactions are immensely useful in the construction of organic molecules, a fact recognised with the award of the 2010 Nobel Prize in chemistry to Akira Suzuki, Richard Heck, and Ei-ichi Negishi. Now scientists in Beijing have discovered that adding common salts like sodium chloride, in a large excess, to Pd/C catalysed Suzuki-Miyaura reactions can more than double the achievable yield. This use of cheap and abundant materials would appear to be an excellent way to improve the productivity of the reaction without drastically increasing its burden on the environment.

It is known that Suzuki-Miyaura reactions can be conducted without any catalyst specifically being added to the reaction. Instead, the reaction is catalysed by trace amounts of palladium in the inorganic base. The authors of this present work report that the inorganic salts are not catalytic themselves, but enhance the activity of the true catalyst. The nature of this synergetic effect was deduced from infra-red and X-ray photoelectron spectroscopy studies, showing evidence of the auxiliary salt interacting with both the bromoarene reactant and the palladium catalyst. The polarisation of the reactive C-Br bond, and the increased electron density placed on the metal catalyst, is said to enhance the rate determining oxidative addition step of the reaction.

By James Sherwood

Click below to read the full article, free until December 1st:

Acceleration of Suzuki coupling reaction by abundant and non-toxic salt particles, Binbin Zhang, Jinliang Song, Huizhen Liu, Jinghua Shi, Jun Ma, Honglei Fan, Weitao Wang, Peng Zhang and Buxing Han, Green Chem., 2013, DOI: 10.1039/C3GC42088D

Chlorophyll formation was enhanced when algae were grown in a flask surrounded by a solution of gold and silver nanoparticles

Scientists in Australia have developed a nanoparticle light filter system that only lets through wavelengths favourable for microalgae growth. The system could make producing algal biofuels more efficient.

Photosynthetic systems, particularly microalgae, are at the forefront of the search for new renewable fuels and feedstock chemicals. The speed and efficiency at which microalgae grow is currently limiting them from becoming a commercially viable product so optimising their production is obviously a priority.

Colin Raston from Flinders University and his co-workers at the University of Western Australia have developed a new technique to enhance the formation and accumulation of photopigments, namely chlorophyll, in algae. They cultured Chlorella vulgaris in flasks that were surrounded by a solution of gold and silver nanoparticles. Tweaking the composition and size of the nanoparticles alters the wavelengths of light allowed through to the algae.

Read the full article in Chemistry World»

Read the original journal article in Green Chemistry:
Enhanced accumulation of microalgal pigments using metal nanoparticle solutions as light filtering devices
Ela Eroglu, Paul K. Eggers, Matthew Winslade, Steven M. Smith and Colin L. Raston  
Green Chem., 2013, 15, 3155-3159, DOI: 10.1039/C3GC41291A