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David Bradley ISSUE #35
December 2003

The Virtual Rotarians

Rotary evaporators are ubiquitous in organic synthesis laboratories. They provide a means to remove solvent from a product mixture in the least time and without damaging the product. But, what exactly goes on inside such a device? That was the question asked by Paul Bartlett of the University of California at Berkeley. The answer comes from a Cambridge team in the form of a Java applet.

Jonathan Goodman  
Jonathan Goodman

Jonathan Goodman and student Craig Stewart, who has now graduated, at the University of Cambridge, have written a small piece of software that works on any operating system and can simulate exactly what is going on inside a rotary evaporator. "Chemists tend to assume that all the solvent evaporates and none of the product," explains Goodman in the chemistry department's newsletter, Chem@Cam. "But, leaving a rotary evaporator running to remove the last dregs of solvent while you go for a cup of tea can be disastrous for your yield," he adds.

Stewart's Java applet, available to use on the web at http://www.ch.cam.ac.uk/magnus/rotavap/, predicts the relative rates of evaporation of solvent and solute and offers a good, although not perfect, estimate of when you should switch off the rotary evaporator. The applet also shows that lower temperatures generally give slower evaporations but preserve more of the product. Chemists will, of course, necessarily balance time and energy against purity and yield, but the applet provides them with the means to do this more "scientifically".

"As they're on the Internet, our applets can be used anywhere in the world," says Goodman. "We've even got a user in Vatican City State!"

  Screengrab of rotavap applet in action
Screengrab of rotavap applet in action
Click image to magnify

The applet can also be used primary data which is often collected and then discarded such as changes in total weight and amount of solvent in a sample, adds Goodman. "This information can be used to give a crude estimate of the products boiling point. The precision of the boiling point estimate is not very high, but it is better than nothing, and provides an impetus not to throw away information which has been recorded and might later become useful," he told Reactive Reports.

Chem. Commun., 2003, 21, 2654 - 2655; http://dx.doi.org/10.1039/b309488j