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OPRD solvent survey

28 March 2015 - Data mining

A group of researchers from Pfizer and GlaxoSmithKline have been datamining the journal Organic Process Research & Development for solvents and report about it here. The chemistry detailed in this journal may be typical of what is happening in chemistry industry with procedures in the 1 to 100 Kg scale and therefore highly relevant. Here are the key findings based on 388 publications starting from 1997. The good news: chlorinated solvents are in decline. The bad news: overall the solvents with environmental issues are continued to be used. One of them dioxane is actual on the increase due to its popularity in Suzuki and Buchwald reactions. In the dipolar aprotic solvent section most popular are ugly acetonitrile, DMF and DMSO on account of their utility in nucleophilic substitution reactions. Greener alternatives such as acetone, 2-methyltetrahydrofuran or phase transfer catalysts are ignored?

Limitless power by water droplets

27 March 2015 - Alternative energy

droplet power generator.PNGIn the latest of fantastic endless renewable energy schemes: energy harvested from falling raindrops on a surface (think roof tile and gutter) as devised by Yajuan Sun, Xu Huang and Siowling Soh (DOI) from the National University of Singapore (annual precipitation: 2,340 mm). The basics: water droplets sliding down a surface become positively charged and hence become a potential energy source. Based on the age-old triboelectric series the ideal surface is teflon. The scientific explanation according to no other than George M. Whitesides is that hydroxide ions in the water migrate out of the water onto the surface of the solid. When the droplet eventually becomes detached from the surface, it is permanently positively charged. The charge accumulation can be measured in another age-old concept: the Faraday cup. The scientists cleverly call their invention SLIDE as in Solid-Liquid Interface for Developing Electrification. Downside: salts dissolved in the water droplet diminish the effect. More data: more power with a smaller diameter teflon tube, no increase in power with a tube in excess of 30 cm. Power decreases when flow rate in excess of 100 mL/min.

Premium power at 170 microwatts and 3 to 4% efficiency. Interesting question: at one point the surface is saturated with negative charge. By experiment a water droplet is found to accumulate 20 nC of positive charge while all the teflon surface has to show for is a measly 2 nC. So where does all the negative charge go to? According to the researchers it all goes up to air, as ionised atmospheric molecules. It would nicely explain the power decrease at higher flow rates because surface exposure to the atmosphere also decreases.

On Frank Weinhold

20 March 2015 - Controversy

Frank Weinhold is Professor Emeritus at the University of Wisconsin. A chemist with a talent for attracting controversy so it seems. He recently found himself in hot scientific debate on two occasions. Last year together with Roger Klein, Weinhold introduced the concept of the "anti-electrostatic hydrogen Bond" (AEHB) (DOI). Is the well-known hydrogen-bond purely based on an electrostatic attraction? (accepted theory) or is something else going on? The alternative AEHB theory claims that a short-range donor-acceptor covalent interaction between two atoms of same charge outperforms the long-range electrostatic repulsion between them. This theory was tested by Weinhold on a hypothetical hydrogen bond between a fluoride (donor) and a bicarbonate anion (acceptor) and calculations did confirm an attractive interaction. According to Weinhold The AEHB bond can be found in other ionic interactions.

Controversial?. Frenking and Caramori represent the members of the opposition. In their comment (DOI) they argue that "it takes much chutzpah to use an energy-minimum structure with a well depth of 0.05(!) kcal per mol" to identify a bond and "it takes a still higher degree of flippancy when the electrostatic interactions between the fragments are estimated with a formula that was proven already in 1927 not to be suitable for calculating Coulombic forces between atoms at shorter region". They are not done yet when they write that "coulombic interactions are calculated with the correct formula for electronic charges rather than using hand-waiving arguments and a wrong equation". What the dispute of course boils down to is that Weinhold is a natural bond orbital guy and that Frenking lives by energy decomposition analysis

The other debate Weinhold has dragged himself into is all about rabbit ears. In 2014 ( DOI) he argued that the two lone pairs on water are not symmetrical (as per conventional theory, resembling rabbit ears, backed by NBO) but asymmetrical with different degrees of s-p mixing based on symmetry arguments. Not an entirely novel idea , others went before him, so where is the controversy you may ask. Here it is: in a recent comment Hiberty et al. counter that notion (DOI) but in an unusual way. Their research in their words "shows that the equivalent lone-pair picture is an equivalent and a valid alternative to the nonequivalent one; neither is superior to the other or anachronistic with respect to the other". This is totally unconvincing: it is like the Pope and Galilei happily agreeing that "the sun may revolve around earth or earth may revolve around the sun, both views are equally valid". What makes Hiberty say such a thing? Hiberty lives by localized molecular orbitals.

And so who is right? and who is wrong? Depends on your computational beliefs. I do not have any but I do know retired professors are usually right.