Friday, 27 December 2013

A Chemical Tripod


Tripod immobilization of ligands is a simple and flexible strategy for creating new heterogeneous catalysts

A Chemical Tripod

Friday, 20 December 2013

Saturday, 14 December 2013

Baeyer-Villiger oxidation

Baeyer-Villiger oxidation

Also known as: Baeyer-Villiger rearrangement

Schematic of the Baeyer-Villiger oxidation. Reagents: ketone, peroxyacid. Product: ester. Comments: The more electron rich group migrates to the oxygen.
The Baeyer-Villiger oxidation is an organic reaction used to convert a ketone to an ester using a peroxyacid (such as mCPBA). The reaction of the ketone with the acid results in a tetrahedral intermediate, with an alkyl migration following to release a carboxylic acid. The more electron rich R group migrates to the oxygen in this concerted process, allowing for accurate prediction of the stereochemistry of the product.[1]
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Mechanism

Mechanism of the Baeyer-Villiger oxidation. Attack with another molecule of peroxyacid followed by deprotonation. As a positive charge is forming on the labeled oxygen (as the carbonyl group abstracts a proton from the acid), the more electron rich R group migrates to the oxygen to stabilize it.

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References:

1.
Baeyer, A.; Villiger, V. Ber. Dtsch. Chem. Ges. 189932, 3625–3633.

Tuesday, 10 December 2013

Supercritical Carbon Dioxide: A Promoter of Carbon–Halogen Bond Heterolysis


Thumbnail image of graphical abstract

Angewandte Chemie International Edition

Volume 52Issue 50pages 13298–13301December 9, 2013

Thais Delgado-Abad, Dr. Jaime Martínez-Ferrer, Prof. Dr. Ana Caballero, Dr. Andrea Olmos, Prof. Dr. Rossella Mello, Prof. Dr. María Elena González-Núñez, Prof. Dr. Pedro J. Pérez and Prof. Dr. Gregorio Asensio
Article first published online: 15 OCT 2013 | DOI: 10.1002/anie.201303819

Amazing reaction medium: Supercritical carbon dioxide, with zero dipole moment, lower dielectric constant than pentane, and non-hydrogen-bonding behavior, ionizes carbon–halogen bonds, dissociates the resulting ion pairs, and escapes from capture by the carbocation intermediates at temperatures above 40 °C. These properties allow the observation of carbocation chemistry in the absence of acids.