all blogs

The on-solvent reaction

04 April 2014 - Physical chemistry

Never expected to one day see mercury listed as an organic solvent but it has happened. Here is how. Sela & Vigalok have been investigating the on water reaction and are reporting about it here. In this type of reaction, water is added to an ordinary organic reaction forming an emulsion and thereby greatly increasing the reaction rate. One possible explanation is hydrogen bonding taking place at the water-organic solvent interface. But what if water is replaced by an entirely different nonsolvent? Sela & Vigalok examined a specific Passerini reaction, well known to benefit from on-water conditions. To their surprise other solvents worked just as well. Perfluorooctane performs better than water, mercury is comparable to water. Both solvents were selected working under the assumption that organic reactions are accelerated by solvents with a very low or very high Hildebrand parameter. More puzzling data. Adding up to three equivalents of water in addition to the nonsolvent also increases the reaction rate. Hydrogen bonding does matter but a water - organic interface apparently does not.

This molecule must be in so much pain

02 April 2014 - Orgo

biphenylophane nobusue 2014.PNGThis molecule must be in so much sprain. In alkynes the bond angles are usually 180° but here the diacetylene unit makes an angle of 160°. It was synthesised in a simple intramolecular acetylene coupling with copper acetate in a 52% yield. Degradation starts at 70°, triggered by benzyne formation in an intramolecular alkyne - diacetylene 4+2 cycloaddition. The molecule was reported by Shunpei Nobusue et al. in Organic Letters (DOI).