A Simple Route to Chiral Synthesis

Asymmetric conjugate addition reactions of alkenylaluminums to enones
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Conversion of sugars to ethylene glycol with nickel tungsten carbide in a fed-batch reactor: high productivity and reaction network elucidation

Green Chem., 2013, Advance Article
DOI: 10.1039/C3GC41431K, Paper

Roselinde Ooms, Michiel Dusselier, Jan A. Geboers, Beau Op de Beeck, Rick Verhaeven,
Elena Gobechiya, Johan A. Martens, Andreas Redl, Bert F. Sels
Fed-batch reactor technology was used for the highly productive conversion of
concentrated sugar solutions into ethylene glycol using bifunctional nickel tungsten
carbide catalysts.

Conversion of sugars to ethylene glycol with nickel tungsten carbide

 in a fed-batch reactor: high productivity and reaction 

network elucidation

 

 http://pubs.rsc.org/en/Content/ArticleLanding/2013/GC/C3GC41431K?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+rss%2FGC+%28RSC+-+Green+Chem.+latest+articles%29#!divAbstract

 

 

 Bifunctional nickel tungsten carbide catalysis was used for the conversion of aqueous sugar

 solutions into short-chain polyols such as ethylene glycol. It is shown that very concentrated sugar 

solutions, viz. up to 0.2 kg L⁻¹, can be converted without loss of ethylene glycol selectivity 

by gradually feeding the sugar solution. Detailed investigation of the reaction network

 shows that, under the applied reaction conditions, glucose is converted via a retro-aldol

 reaction into glycol aldehyde, which is further transformed into ethylene glycol by hydrogenation. 

The main byproducts are sorbitol, erythritol, glycerol and 1,2-propanediol. 

They are formed through a series of unwanted side reactions including 

hydrogenation, isomerisation, hydrogenolysis and dehydration. 

Hydrogenolysis of sorbitol is only a minor source of ethylene glycol. To assess the 

relevance of the fed-batch system in biomass conversions, both the influence of the

 catalyst composition and the reactor setup parameters like temperature, pressure 

and glucose addition rate were optimized, culminating in ethylene glycol yields up to 66% and

 separately, volume productivities of nearly 300 g_EG L⁻¹ h⁻¹.

COLUMN CHROMATOGRAPHY

A chemist in the 1950s using column chromatography. The Erlenmeyer receptacles are on the floor.

Column chromatography in chemistry is a method used to purify individual chemical compounds from mixtures of compounds. It is often used for preparative applications on scales from micrograms up to kilograms. The main advantage of column chromatography is the relatively low cost and disposability of the stationary phase used in the process. The latter prevents cross-contamination and stationary phase degradation due to recycling.

The classical preparative chromatography column, is a glass tube with a diameter from 5 mm to 50 mm and a height of 5 cm to 1 m with a tap and some kind of a filter (a glass frit or glass wool plug – to prevent the loss of the stationary phase) at the bottom. Two methods are generally used to prepare a column: the dry method, and the wet method.

• For the dry method, the column is first filled with dry stationary phase powder, followed by the addition of mobile phase, which is flushed through the column until it is completely wet, and from this point is never allowed to run dry.
• For the wet method, a slurry is prepared of the eluent with the stationary phase powder and then carefully poured into the column. Care must be taken to avoid air bubbles. A solution of the organic material is pipetted on top of the stationary phase. This layer is usually topped with a small layer of sand or with cotton or glass wool to protect the shape of the organic layer from the velocity of newly added eluent. Eluent is slowly passed through the column to advance the organic material. Often a spherical eluent reservoir or an eluent-filled and stoppered separating funnel is put on top of the column.

The individual components are retained by the stationary phase differently and separate from each other while they are running at different speeds through the column with the eluent. At the end of the column they elute one at a time. During the entire chromatography process the eluent is collected in a series of fractions. Fractions can be collected automatically by means of fraction collectors. The productivity of chromatography can be increased by running several columns at a time. In this case multi stream collectors are used. The composition of the eluent flow can be monitored and each fraction is analyzed for dissolved compounds, e.g. by analytical chromatography, UV absorption, or fluorescence. Colored compounds (or fluorescent compounds with the aid of an UV lamp) can be seen through the glass wall as moving bands.

Overview

Stationary phase

The stationary phase or adsorbent in column chromatography is a solid. The most common stationary phase for column chromatography is silica gel, followed by alumina. Cellulosepowder has often been used in the past. Also possible are ion exchange chromatography, reversed-phase chromatography(RP), affinity chromatography or expanded bed adsorption(EBA). The stationary phases are usually finely ground powders or gels and/or are microporous for an increased surface, though in EBA a fluidized bed is used. There is an important ratio between the stationary phase weight and the dry weight of the analyte mixture that can be applied onto the column. For silica column chromatography, this ratio lies within 20:1 to 100:1, depending on how close to each other the analyte components are being eluted.

Mobile phase (eluent)

The mobile phase or eluent is either a pure solvent or a mixture of different solvents. It is chosen so that the retention factor value of the compound of interest is roughly around 0.2 - 0.3 in order to minimize the time and the amount of eluent to run the chromatography. The eluent has also been chosen so that the different compounds can be separated effectively. The eluent is optimized in small scale pretests, often using thin layer chromatography (TLC) with the same stationary phase.

There is an optimum flow rate for each particular separation. A faster flow rate of the eluent minimizes the time required to run a column and thereby minimizes diffusion, resulting in a better separation. However, the maximum flow rate is limited because a finite time is required for analyte to equilibrate between stationary phase and mobile phase, see Van Deemter's equation. A simple laboratory column runs by gravity flow. The flow rate of such a column can be increased by extending the fresh eluent filled column above the top of the stationary phase or decreased by the tap controls. Faster flow rates can be achieved by using a pump or by using compressed gas (e.g. air,nitrogen, or argon) to push the solvent through the column (flash column chromatography).

The particle size of the stationary phase is generally finer in flash column chromatography than in gravity column chromatography. For example, one of the most widely used silica gel grades in the former technique is mesh 230 – 400 (40 – 63 µm), while the latter technique typically requires mesh 70 – 230 (63 – 200 µm) silica gel.

A spreadsheet that assists in the successful development of flash columns has been developed. The spreadsheet estimates the retention volume and band volume of analytes, the fraction numbers expected to contain each analyte, and the resolution between adjacent peaks. This information allows users to select optimal parameters for preparative-scale separations before the flash column itself is attempted.

An automated ion chromatography system.

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Typical set up for manual column chromatography

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Boron vapour trail leads to heterofullerenes

The simple route to borafullerenes could open up an interesting new avenue of heterofullerene research © Wiley-VCH

http://www.rsc.org/chemistryworld/2012/12/boron-fullerene-heterofullerene-atom-exchange

A team of scientists has developed a simple way to synthesise heterofullerenes – fullerenes with atoms other than carbon in their structure – by exposing fullerenes to boron vapour during their growth. They found that atom exchange with a carbon takes place to form a derivative known as borafullerene. The team believes the process can be easily scaled up and applied to other all-carbon analogues including nanotubes or graphene.

read all at

http://www.rsc.org/chemistryworld/2012/12/boron-fullerene-heterofullerene-atom-exchange

Brevetoxin synthesis

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Anthony crasto brevetoxin synthesis from ANTHONY MELVIN CRASTO Ph.D

Nano-Technoloogy Makes Medicine Greener

The ultra small nanoreactors have walls made of lipids. During their fusion events volumes of one billionth of a billionth of a liter were transferred between nanoreactors allowing their cargos to mix and react chemically. We typically carried out a million of individual chemical reactions per cm2 in not more than a few minutes. (Credit: Image courtesy of University of Copenhagen)http://www.sciencedaily.com/releases/2011/11/111103132357.htm

 Researchers at the University of Copenhagen are behind the development of a new method that will make it possible to develop drugs faster and greener. Their work promises cheaper medicine for consumers.

Over the last 5 years the Bionano Group at the Nano-Science Center and the Department of Neuroscience and Pharmacology at the University of Copenhagen has been working hard to characterise and test how molecules react, combine together and form larger molecules, which can be used in the development of new medicine.http://www.sciencedaily.com/releases/2011/11/111103132357.htm