A rotary evaporator (or rotavap/rotovap) is a device utilized in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation. When referenced in the chemistry research literature, description of the usage of this technique and equipment can include the phrase “rotary evaporator”, though use is frequently rather signaled by other language (e.g., “the sample was evaporated under reduced pressure”).
Rotary evaporators can also be used in molecular cooking for that preparation of distillates and extracts. A rotary evaporator was invented by Lyman C. Craig. It was first commercialized through the Swiss company Büchi in 1957. Other common evaporator brands are EYELA, Heidolph, IKA, KNF, LabFirst, LabTech, Hydrion Scientific, SENCO, Shanghai HJ Lab Instruments, and Stuart Equipment. In research the most typical form is the 1L bench-top unit, whereas large scale (e.g., 20L-50L) versions are used in pilot plants in commercial chemical operations.
A motor unit that rotates the evaporation flask or vial containing the user’s sample.
A vapor duct which is the axis for sample rotation, and it is a vacuum-tight conduit for the vapor being drawn off the sample.
A vacuum system, to substantially decrease the pressure within the evaporator system.
A heated fluid bath (generally water) to heat the sample.
A condenser with either a coil passing coolant, or even a “cold finger” into which coolant mixtures including dry ice and acetone are placed.
A condensate-collecting flask in the bottom in the condenser, to catch the distilling solvent after it re-condenses.
A mechanical or motorized mechanism to quickly lift the evaporation flask from the heating bath.
The rotovap parts used with rotary evaporators could be as simple as a water aspirator having a trap immersed in a cold bath (for non-toxic solvents), or as complex as a regulated mechanical vacuum pump with refrigerated trap. Glassware utilized in the vapor stream and condenser can be simple or complex, depending upon the goals in the evaporation, and any propensities the dissolved compounds might give the mixture (e.g., to foam or “bump”). Commercial instruments can be found including the fundamental features, and other traps are manufactured to insert in between the evaporation flask and also the vapor duct. Modern equipment often adds features including digital charge of vacuum, digital display of temperature and rotational speed, and vapor temperature sensing.
Theory
Vacuum evaporators as a class function because decreasing the pressure above a bulk liquid lowers the boiling points of the component liquids within it. Generally, the component liquids of interest in applications of rotary evaporation are research solvents that a person desires to eliminate coming from a sample after an extraction, including following a natural product isolation or perhaps a step in an organic synthesis. Liquid solvents can be taken off without excessive heating of the things tend to be complex and sensitive solvent-solute combinations.
Rotary evaporation is frequently and conveniently put on separate “low boiling” solvents this type of n-hexane or ethyl acetate from compounds which can be solid at room temperature and pressure. However, careful application also allows removing of a solvent from the sample containing a liquid compound if there is minimal co-evaporation (azeotropic behavior), along with a sufficient difference in boiling points on the chosen temperature and reduced pressure.
Solvents with higher boiling points like water (100 °C at standard atmospheric pressure, 760 torr or 1 bar), dimethylformamide (DMF, 153 °C on the same), or dimethyl sulfoxide (DMSO, 189 °C in the same), may also be evaporated when the unit’s vacuum system is capable of doing sufficiently low pressure. (As an example, both DMF and DMSO will boil below 50 °C in the event the vacuum is reduced from 760 torr to 5 torr [from 1 bar to 6.6 mbar]) However, more modern developments are frequently applied in these instances (e.g., evaporation while centrifuging or vortexing at high speeds). Rotary evaporation for high boiling hydrogen bond-forming solvents like water can be a last recourse, as other evaporation methods or freeze-drying (lyophilization) are available. This is partly simply because that in these solvents, the tendency to “bump” is accentuated. The modern centrifugal evaporation technologies are particularly useful when one has numerous samples to do in parallel, as with medium- to high-throughput synthesis now expanding in industry and academia.
Evaporation under vacuum can also, in principle, be practiced using standard organic distillation glassware – i.e., without rotation of the sample. The key advantages being used of the rotary evaporator are
that the centrifugal force and the frictional force involving the wall in the rotating flask and the liquid sample result in the formation of the thin film of warm solvent being spread spanning a large surface.
the forces produced by the rotation suppress bumping. The mixture of those characteristics as well as the conveniences built into modern rotary evaporators enable quick, gentle evaporation of solvents from most samples, even at the disposal of relatively inexperienced users. Solvent remaining after rotary evaporation can be taken off by exposing the sample to even deeper vacuum, on how to use rotovap, at ambient or higher temperature (e.g., on a Schlenk line or in a vacuum oven).
A key disadvantage in rotary evaporations, besides its single sample nature, is the potential for some sample types to bump, e.g. ethanol and water, which can result in loss in a area of the material supposed to have been retained. Even professionals experience periodic mishaps during evaporation, especially bumping, though experienced users start seeing the propensity of some mixtures to bump or foam, and apply precautions which help in order to avoid most such events. Particularly, bumping is often prevented through taking homogeneous phases into the evaporation, by carefully regulating the strength of the vacuum (or the bath temperature) to offer to have an even rate of evaporation, or, in rare cases, through use of added agents like boiling chips (to help make the nucleation step of evaporation more uniform). Rotary evaporators may also be equipped with further special traps and condenser arrays which are best suited to particular difficult sample types, including those that have the tendency to foam or bump.
Safety
There are hazards associated even with simple operations such as evaporation. These include implosions as a result of use of glassware that contains flaws, such as star-cracks. Explosions may occur from concentrating unstable impurities during evaporation, for instance when rotavapping an ethereal solution containing peroxides. This could also occur when taking tlpgsj unstable compounds, including organic azides and acetylides, nitro-containing compounds, molecules with strain energy, etc. to dryness.
Users of rotary evaporation equipment have to take precautions to avoid contact with rotating parts, particularly entanglement of loose clothing, hair, or necklaces. In these situations, the winding action in the rotating parts can draw you to the apparatus resulting in breakage of glassware, burns, and chemical exposure. Extra caution should also be employed to operations with air reactive materials, specially when under vacuum. A leak can draw air into the apparatus as well as a violent reaction can happen.