Microreactors tame osmium tetroxide | Chemistry World

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Researchers in South Korea and India have made microfluidic reactors that safely harness the synthetically powerful but noxious catalyst osmium tetroxide.

Dong-Pyo Kim at POSTECH in Pohang, South Korea, and colleagues trapped OsO4 in poly(4-vinylpyridine) (P4VP) ‘nanobrushes’ on the inner walls of silicone microreactors. Their reactors catalysed dihydroxylation and oxidative cleavage – steps important in natural product, pharmaceutical and fine chemical synthesis – of 10mmol of various olefins with yields of more than 90%. Only 50µg of OsO4 was needed, making the microreactor catalyst 50 times more efficient than bulk supported systems.

OsO4 powers reactions like the chemistry Nobel prize winning Sharpless asymmetric dihydroxylation, but is toxic and unusually volatile, and therefore produces deadly fumes. ‘Many researchers have tried to stabilise or immobilise it on a polymer or inorganic substrate,’ Kim tells Chemistry World. ‘But leaching and exposure to the environment is inevitable in a bulk reaction system.’

So Kim’s team sought to trap OsO4 in microreactors by moulding two pieces of silicone holding mirror image nano-sized channels using soft lithography. As silicone normally swells in organic solvents they spin-coated the channels with protective polyvinylsilazane (PVSZ) layers, which they then bonded PV4P nanobrushes to. After putting the two halves of silicone together, the researchers infused the microreactor with aqueous OsO4.

Initially, catalytic activity disappeared after just a day. To boost the reactor’s stability, the team reduced OsO4 to a dark blue oxoosmium(VI) complex by feeding tetrahydrofuran through it after catalyst loading. In testing on biomass-based olefins, dihydroxylation reactions exceeded 98% conversion in 10 minutes, and oxidative cleavage reached similar levels in seven minutes. But the reactor’s volume limits it to around 1mmol of product per hour.

Reactor performance did not change significantly after 10 hours’ continuous use, or three months’ storage. Reaction mixtures contained just 30–50ppb osmium, around 100 times lower than other reported systems, Kim says. ‘We are now working on scale-up of our reactor system for possible industrial application and further developing microchemical systems for hazardous heterogeneous catalysts,’ he adds.

Paul Watts, who researches microfluidic continuous flow chemistry at Nelson Mandela Metropolitan University in Port Elizabeth, South Africa, notes the increasing interest in such reactors’ safety potential. He says Kim’s team’s reactor ‘provides a very elegant way to use OsO4 within research’. ‘I envisage the methodology being of significant use to other organic chemists,’ he adds.

SOURCE:  http://www.rsc.org/chemistryworld/2013/04/microreactors-tame-poisonois-osmium-tetroxide


Chemistry Framework using Common Component Architecture | Ames Laboratory

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The development of emerging technologies such as molecular computing, nanotechnology, and next generation catalysts will continue to place increasing demands on chemical simulation software, requiring more capabilities and more sophisticated simulation environments.  Such software will be too complex for a single group, or even a single discipline to develop independently.  Coupling multiple physical models in one domain and coupling simulations across multiple time and length-scales will become the norm rather than the exception. These simulations will also run on more complicated and diverse hardware platforms, potentially with hundreds of thousands of processors and performance exceeding one petaFLOP/s.  This evolution will transform the way chemists must think about scientific problems, models and algorithms, software lifecycle and the use of computational resources.  Advances in chemical science critical to DOE and national challenges require adoption of new approaches for large-scale collaborative development and a flexible, community-based architecture. We propose to employ the infrastructure of the Common Component Architecture to develop interfaces among three of the most important computational chemistry codes in the world: General Atomic and Molecular Electronic Structure System (GAMESS), the Massively Parallel Quantum Chemistry program (MPQC) and Northwest Chem (NWChem).

SOURCE:  https://www.ameslab.gov/amcs/fwp/chemistry-framework

The Six Types of Chemical Reaction | Brinkster

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All chemical reactions can be placed into one of six categories.  Here they are, in no particular order:

1) Combustion: A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:

C10H8 + 12 O2 —> 10 CO2 + 4 H2O

2) Synthesis: A synthesis reaction is when two or more simple compounds combine to form a more complicated one. These reactions come in the general form of:

A + B —> AB

One example of a synthesis reaction is the combination of iron and sulfur to form iron (II) sulfide:

8 Fe + S8 —> 8 FeS

3) Decomposition: A decomposition reaction is the opposite of a synthesis reaction – a complex molecule breaks down to make simpler ones. These reactions come in the general form:

AB —> A + B

One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas:

2 H2O —> 2 H2 + O2

4) Single displacement: This is when one element trades places with another element in a compound. These reactions come in the general form of:

A + BC —> AC + B

One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:

Mg + 2 H2O —> Mg(OH)2 + H2

5) Double displacement: This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:

AB + CD —> AD + CB

One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:

Pb(NO3)2 + 2 KI —> PbI2 + 2 KNO3

6) Acid-base: This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water:

HA + BOH —> H2O + BA

One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide:

HBr + NaOH —> NaBr + H2O

SOURCE:  http://misterguch.brinkster.net/6typesofchemicalrxn.html