A rotary evaporator (or rotavap/rotovap) is actually a device found in chemical laboratories for the effective and gentle removal of solvents from samples by evaporation. When referenced in the chemistry research literature, description of the usage of this method and equipment can include the phrase “rotary evaporator”, though use is often rather signaled by other language (e.g., “the sample was evaporated under reduced pressure”).
Rotary evaporators will also be found in molecular cooking for the preparation of distillates and extracts. A rotary evaporator was introduced by Lyman C. Craig. It was initially 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 frequent form is the 1L bench-top unit, whereas large scale (e.g., 20L-50L) versions are employed 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 this is the axis for sample rotation, and is also a vacuum-tight conduit for the vapor being drawn from the sample.
A vacuum system, to substantially lessen 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 a “cold finger” into which coolant mixtures such as dry ice and acetone are placed.
A condensate-collecting flask at the bottom of the condenser, to catch the distilling solvent after it re-condenses.
A mechanical or motorized mechanism to quickly lift the evaporation flask through the heating bath.
The rotovap parts used with rotary evaporators may be as simple being a water aspirator with a trap immersed in a cold bath (for non-toxic solvents), or as complex being a regulated mechanical vacuum pump with refrigerated trap. Glassware used in the vapor stream and condenser may be simple or complex, based upon the goals of the evaporation, as well as any propensities the dissolved compounds might share with the mix (e.g., to foam or “bump”). Commercial instruments can be found that include the essential features, and other traps are produced to insert involving the evaporation flask as well as the vapor duct. Modern equipment often adds features such as digital control over vacuum, digital display of temperature and rotational speed, and vapor temperature sensing.
Vacuum evaporators being a class function because reducing the pressure above a bulk liquid lowers the boiling points in the component liquids inside it. Generally, the component liquids of interest in uses of rotary evaporation are research solvents that a person desires to remove from a sample after an extraction, like following a natural product isolation or a element of an organic synthesis. Liquid solvents can be removed without excessive heating of the items are often complex and sensitive solvent-solute combinations.
Rotary evaporation is frequently and conveniently applied to separate “low boiling” solvents such a n-hexane or ethyl acetate from compounds that are solid at room temperature and pressure. However, careful application also allows removing of a solvent from a sample containing a liquid compound when there is minimal co-evaporation (azeotropic behavior), and 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 in the same), or dimethyl sulfoxide (DMSO, 189 °C at the same), can be evaporated in the event the unit’s vacuum system can do sufficiently low pressure. (For example, both DMF and DMSO will boil below 50 °C when 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 such cases (e.g., evaporation while centrifuging or vortexing at high speeds). Rotary evaporation for top boiling hydrogen bond-forming solvents like water can be a last recourse, as other evaporation methods or freeze-drying (lyophilization) can be purchased. This is partly simply because that such solvents, the tendency to “bump” is accentuated. The modern centrifugal evaporation technologies are particularly useful when one has many samples to do in parallel, as in medium- to high-throughput synthesis now expanding in industry and academia.
Evaporation under vacuum can also, in principle, be done using standard organic distillation glassware – i.e., without rotation from the sample. The true secret advantages being used of the rotary evaporator are
that the centrifugal force as well as the frictional force between the wall in the rotating flask and the liquid sample resulted in formation of the thin film of warm solvent being spread more than a large surface.
the forces developed by the rotation suppress bumping. The combination of those characteristics and the conveniences built into modern rotary evaporators permit 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., over a Schlenk line or in a vacuum oven).
A vital disadvantage in rotary evaporations, besides its single sample nature, is the chance of some sample types to bump, e.g. ethanol and water, which can lead to loss of a area of the material supposed to have been retained. Even professionals experience periodic mishaps during evaporation, especially bumping, though experienced users discover the propensity of some mixtures to bump or foam, and apply precautions that assist in order to avoid most such events. Specifically, bumping is often prevented by taking homogeneous phases into the evaporation, by carefully regulating the potency of the vacuum (or even the bath temperature) to supply for an even rate of evaporation, or, in rare cases, through use of added agents including boiling chips (to help make the nucleation step of evaporation more uniform). Rotary evaporators can be designed with further special traps and condenser arrays that are suitable to particular difficult sample types, including those with the tendency to foam or bump.
There are hazards associated despite simple operations such as evaporation. Such as implosions as a result of utilization of glassware which 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 must take precautions to avoid exposure to 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 must also be applied to operations with air reactive materials, especially when under vacuum. A leak can draw air in to the apparatus along with a violent reaction can take place.