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The Rotary Evaporator

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A glass-blower bytrade, Walter Buchi made a name for himself when he released his rotaryevaporator in the late nineteen-fifties. Scientists C.C. Draig and M.E. Volkwere pioneers in developing the modern-day concept, but Buchi developed thefirst manufactured rotary evaporator, patented in 1957.

A rotary evaporator(often called a ?rotovap? by scientists) is a device by which solvents can beremoved from reaction mixtures via evaporation. Put very simply, a liquidmixture is heated, and the solvent evaporates and gets collected.

A vacuum is a keycomponent of this device, and is used to aid in the evaporation of the solvent.A vacuum will lower the air pressure in the space above a liquid, therebylowering the boiling point of the liquid being heated. Often the mixture isvery sensitive and highly reactive so excessive heating would not be ideal. Thevacuum allows the user to temporarily alter the physical properties of thesample so that solvents can be extracted from a variety of mixtures that wouldotherwise be impossible. The simplest type of vacuum used on a rotaryevaporator is a water aspirator. Picture a tube that is wider at the top andnarrows as it goes down, with an opening at the side. When water is channeleddownwards, it increases speed, and the pressure is lowered - creating a vacuumeffect through the opening at the side. A more complex method would involve aregulated mechanical vacuum pump.

Rotation is notabsolutely necessary for the evaporation process to take place. However, thecentrifugal forces allow the solvent to rise and be spread thinly over a largersurface, which make sit easier to extract. Also, the rotation helps reduce?bumping.? Bumping is what happens when two substances come together, likewater and ethanol, and the total amount is reduced. (This is due the differencein the size of the molecules. For example, if you took one cup of grapes andcombined it with one cup of apples, the result would be less than the assumedtwo cups, because the grapes would fill in the space left by the apples.)

The rotary evaporatorhas evolved over the years to become more and more advanced, and while featuresand capabilities of different models vary widely, modern rotary evaporatorsstill consist of seven primary components:

?  Themotor that rotates the sample (contained in either a flask or vial)

?  Hotwater bath to heat the sample

?  Thevacuum used to lower the pressure

?  Avapor duct to capture the solvent

?  Condenserthat cools the solvent

?  Flaskto collect the solvent after it condenses

?  Amechanism to quickly remove the sample from the hot water bath

Thename Buchi now represents a corporation run in part by descendants of WalterBuchi. Buchi develops, produces, and distributes laboratory equipment andanalytical instruments for R&D laboratories, as well as for qualitycontrol. They support chemical, pharmaceutical and food industries worldwide.Today, the continues to be the most widely used rotary evaporator usedby research laboratories around the world.

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