Resolving Asymmetric Epoxidations

An enantioselective route to form epoxides by using kinetic resolution techniques has been developed

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How to draft a patent

http://www.slideshare.net/webgoddesscathy/how-to-draft-a-patent

How to Draft a Patent from MaRS Discovery District

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Homogeneous catalyst made to act more like an enzyme

Homogeneous catalyst made to act more like an enzyme
	Supramolecular encapsulation imposes electronic and steric restrictions to make catalyst more selective http://www.rsc.org/chemistryworld/2013/08/homogeneous-catalyst-supramolecular-encapsulation

Sound solution to nanoparticle handling problems

Sound solution to nanoparticle handling problems
http://www.rsc.org/chemistryworld/2013/08/ultrasonic-technique-sticks-nanoparticles-catalytic-activity
	An unexpected discovery allows scientists to stick nanoparticles together using ultrasound without destroying their catalytic activity

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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EROS Best Reagent Award 2013

Huw Davis, Emory University, USA, has received the the Best Reagent Award for his widely used carbenoid precursor
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Organic Chemistry Becomes Multidisciplinary

18th European Symposium on Organic Chemistry (ESOC 2013) sees future trends in close connection to biology, physics, and materials science
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Jumping Crystals

Scientists from the United Arab Emirates and Russia examined light-induced jumping crystals by kinematic analysis
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The Sulfonamide Motif as a Synthetic Tool

Sulfonamides are well known motifs in medicinal chemistry, forming a large family of antibacterial agents as well as being found in numerous other drugs.  The chemistry of this functional group, however, is less well documented.  This review seeks to bring together the various applications and advantages of this motif in organic synthesis, which includes the sulfonamide as an activating group, protecting group, leaving group and as a molecular scaffold.

http://discovery.ucl.ac.uk/1301694/

http://www.ingentaconnect.com/content/stl/jcr/2010/00000034/00000010/art00001

 

Jonathan Wilden obtained his PhD from the University of Southampton in 2001 having worked on the total synthesis of the marine natural product pseudopterosin with Professor David Harrowven.  He then moved to the University of Sussex, Brighton, UK where his interest in sulfonamide chemistry began, working with Professor Steve Caddick.  In 2004 he was appointed lecturer at University College London where his research interests include the synthesis of medicinally important compounds and exploitation of the sulfonamide group in organic synthesis.

http://discovery.ucl.ac.uk/1301694/

http://www.ingentaconnect.com/content/stl/jcr/2010/00000034/00000010/art00001

Nickel-Catalyzed Suzuki–Miyaura Couplings in Green Solvents

Nickel-Catalyzed Suzuki–Miyaura Couplings in Green Solvents

Stephen D. Ramgren, Liana Hie, Yuxuan Ye, and Neil K. Garg

Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States

Org. Lett., Article ASAP

Publication Date (Web): July 23, 2013 (Letter)

DOI: 10.1021/ol401727y

http://pubs.acs.org/doi/abs/10.1021/ol401727y

The nickel-catalyzed Suzuki–Miyaura coupling of aryl halides and phenol-derived substrates with aryl boronic acids using green solvents, such as 2-Me-THF and tert-amyl alcohol, is reported. This methodology employs the commercially available and air-stable precatalyst, NiCl2(PCy3)2, and gives biaryl products in synthetically useful to excellent yields. Using this protocol, bis(heterocyclic) frameworks can be assembled efficiently.

Brevetoxin synthesis

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Anthony crasto brevetoxin synthesis from ANTHONY MELVIN CRASTO Ph.D

One-Pot Approach to α,β-Unsaturated Carboxylic Acids

 

One-Pot Approach to α,β-Unsaturated Carboxylic Acids

Carboxylation of alkynes with carbon dioxide in a one-pot approach could become a practical route to unsaturated carboxylic acids
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