A rotary evaporator (or rotavap/rotovap) is a device used in chemical laboratories for the effective and gentle elimination 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 are also found in molecular cooking for the 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 will be the 1L bench-top unit, whereas massive (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 that is the axis for sample rotation, and it is a vacuum-tight conduit for your vapor being drawn off of 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 perhaps a “cold finger” into which coolant mixtures like dry ice and acetone are placed.
A condensate-collecting flask at the bottom from the condenser, to capture the distilling solvent after it re-condenses.
A mechanical or motorized mechanism to quickly lift the evaporation flask from your heating bath.
The rotovap parts combined 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 as a regulated mechanical vacuum pump with refrigerated trap. Glassware utilized in the vapor stream and condenser may be simple or complex, based on the goals in the evaporation, as well as any propensities the dissolved compounds might give the mixture (e.g., to foam or “bump”). Commercial instruments can be found which include the fundamental features, and other traps are produced to insert between the evaporation flask and also the vapor duct. Modern equipment often adds features such as digital charge of 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 of the component liquids in it. Generally, the component liquids of interest in applications of rotary evaporation are research solvents that one desires to get rid of coming from a sample after an extraction, like using a natural product isolation or perhaps a step in an organic synthesis. Liquid solvents can be removed without excessive heating of the things tend to be complex and sensitive solvent-solute combinations.
Rotary evaporation is frequently and conveniently placed on 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 elimination of a solvent from the sample containing a liquid compound if 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), may also be evaporated when the unit’s vacuum system can do sufficiently low pressure. (For instance, both DMF and DMSO will boil below 50 °C if the vacuum is reduced from 760 torr to 5 torr [from 1 bar to 6.6 mbar]) However, more modern developments are often applied in these cases (e.g., evaporation while centrifuging or vortexing at high speeds). Rotary evaporation for high boiling hydrogen bond-forming solvents such as water can be a last recourse, as other evaporation methods or freeze-drying (lyophilization) are available. This can be partly simply because that in these solvents, the tendency to “bump” is accentuated. The present day centrifugal evaporation technologies are particularly useful when one has several samples to accomplish in parallel, as in medium- to high-throughput synthesis now expanding in industry and academia.
Evaporation under vacuum could also, in principle, be practiced using standard organic distillation glassware – i.e., without rotation from the sample. The true secret advantages in use of a rotary evaporator are
the centrifugal force and the frictional force between the wall of the rotating flask and also the liquid sample result in the formation of the thin film of warm solvent being spread over a large surface.
the forces created by the rotation suppress bumping. The mixture of those characteristics and the conveniences that are part of modern rotary evaporators permit quick, gentle evaporation of solvents from most samples, even in the hands of relatively inexperienced users. Solvent remaining after rotary evaporation are easy to remove by exposing the sample to even deeper vacuum, on how to use rotovap, at ambient or higher temperature (e.g., on the 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 result in loss of a part of the material intended to be 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 to avoid most such events. Particularly, bumping is often prevented if you take homogeneous phases in to the evaporation, by carefully regulating the effectiveness of the vacuum (or perhaps the bath temperature) to supply to have an even rate of evaporation, or, in rare cases, through utilization of added agents like boiling chips (to create the nucleation step of evaporation more uniform). Rotary evaporators may also be designed with further special traps and condenser arrays which can be best suited to particular difficult sample types, including those with the tendency to foam or bump.
You can find hazards associated even with simple operations including evaporation. Included in this are implosions caused by usage of glassware which has flaws, like star-cracks. Explosions may occur from concentrating unstable impurities during evaporation, for instance when rotavapping an ethereal solution containing peroxides. This can also occur when taking tlpgsj unstable compounds, such as organic azides and acetylides, nitro-containing compounds, molecules with strain energy, etc. to dryness.
Users of rotary evaporation equipment have to take precautions in order to avoid exposure to rotating parts, particularly entanglement of loose clothing, hair, or necklaces. In these situations, the winding action of the rotating parts can draw the users into the apparatus causing breakage of glassware, burns, and chemical exposure. Extra caution should also be applied to operations with air reactive materials, specially when under vacuum. A leak can draw air to the apparatus and a violent reaction can happen.