How To Use Rotary Evaporator – You Will Need To Understand This..

A rotary evaporator (or rotavap/rotovap) is a device used in chemical laboratories for the efficient and gentle elimination of solvents from samples by evaporation. When referenced in the chemistry research literature, description of using this method and equipment can include the phrase “rotary evaporator”, though use is usually rather signaled by other language (e.g., “the sample was evaporated under reduced pressure”).

Rotary evaporators will also be used in molecular cooking for that preparation of distillates and extracts. A rotary evaporators for sale was introduced by Lyman C. Craig. It was initially commercialized by 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 common form is definitely 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 that is the axis for sample rotation, and is also a vacuum-tight conduit for that vapor being drawn off of the sample.

A vacuum system, to substantially reduce the pressure inside 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 like dry ice and acetone are positioned.

A condensate-collecting flask at the bottom of the condenser, to trap 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 can be as simple as a water aspirator having a trap immersed in a cold bath (for non-toxic solvents), or as complex as being a regulated mechanical vacuum pump with refrigerated trap. Glassware found in the vapor stream and condenser may be simple or complex, based upon the goals in the evaporation, and any propensities the dissolved compounds might share with the mixture (e.g., to foam or “bump”). Commercial instruments can be found including the basic features, and various traps are made to insert involving the evaporation flask and 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.

Theory

Vacuum evaporators as being a class function because decreasing the pressure above a bulk liquid lowers the boiling points in the component liquids in it. Generally, the component liquids of interest in uses of rotary evaporation are research solvents that a person desires to get rid of from the sample after an extraction, such as after a natural product isolation or even a step in 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 most often and conveniently applied to separate “low boiling” solvents this kind of n-hexane or ethyl acetate from compounds which are solid at room temperature and pressure. However, careful application also allows elimination of a solvent coming from a sample containing a liquid compound when there is minimal co-evaporation (azeotropic behavior), and a sufficient difference in boiling points at the chosen temperature and reduced pressure.

Solvents with higher boiling points including water (100 °C at standard atmospheric pressure, 760 torr or 1 bar), dimethylformamide (DMF, 153 °C at the same), or dimethyl sulfoxide (DMSO, 189 °C on the same), can also be evaporated when the unit’s vacuum system is capable of 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 top boiling hydrogen bond-forming solvents like water is usually a last recourse, as other evaporation methods or freeze-drying (lyophilization) are available. This really is partly due to the fact that such solvents, the tendency to “bump” is accentuated. The present day centrifugal evaporation technologies are particularly useful when one has numerous samples to accomplish in parallel, like medium- to high-throughput synthesis now expanding in industry and academia.

Evaporation under vacuum may also, in principle, be done using standard organic distillation glassware – i.e., without rotation from the sample. The true secret advantages in use of the rotary evaporator are

that the centrifugal force as well as the frictional force in between the wall of the rotating flask and also the liquid sample resulted in formation of a thin film of warm solvent being spread over a large surface.

the forces produced by the rotation suppress bumping. The mixture of those characteristics as well as the conveniences included in modern rotary evaporators enable quick, gentle evaporation of solvents from most samples, even in the hands of relatively inexperienced users. Solvent remaining after rotary evaporation can be removed by exposing the sample to even deeper vacuum, on how to use rotary evaporator, 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 chance of some sample types to bump, e.g. ethanol and water, which can lead to loss of a part 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 help to avoid most such events. In particular, bumping can be prevented through taking homogeneous phases into the evaporation, by carefully regulating the effectiveness of the vacuum (or the bath temperature) to offer to have an even rate of evaporation, or, in rare cases, through usage of added agents such as boiling chips (to make the nucleation step of evaporation more uniform). Rotary evaporators can be built with further special traps and condenser arrays which can be best suited to particular difficult sample types, including those that have the tendency to foam or bump.

Safety

There are hazards associated despite simple operations like evaporation. Included in this are implosions caused by utilization of glassware which has flaws, like star-cracks. Explosions may occur from concentrating unstable impurities during evaporation, for example when rotavapping an ethereal solution containing peroxides. This may 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 must take precautions to prevent contact with rotating parts, particularly entanglement of loose clothing, hair, or necklaces. Under these circumstances, the winding action from the rotating parts can draw the users into the apparatus causing breakage of glassware, burns, and chemical exposure. Extra caution also must be used to operations with air reactive materials, particularly when under vacuum. A leak can draw air into the apparatus as well as a violent reaction can take place.