Rotary Evaporator Theory

The rotary evaporator is used for extraction because of its excellent distillation. They have been designed to work on solvents that have different boiling points, especially during organic synthesis. The theory of rotary evaporator revolves around the extraction of compounds.

rotary evaporator theory

Rotary Evaporator Theory

Evaporation Principle

Ideally, the rotary evaporator utilizes the evaporation principle where mixtures are subjected to temperatures which will make the mixture to evaporate. The substance to be extracted will be extracted when its boiling point reaches. This is determined by the volatility of the substance which is collected in the fractional parts of the apparatus. Separation is done through a thin film of the solvent which accumulates around the flask as the process continues. The condensation will take place to ensure the extract can be collected eventually.

The Applications of Rotation and Heat

Therefore, theoretically, the two main aspects that come into play are the application of rotation and application of heat to boil the substances. Once the required temperature has been applied there will need to regulate pressure since the mixture is exposed into an airtight condition. Therefore, vacuuming is used to regulate the pressure that will be caused by elevated temperatures. This ensures the apparatus works optimally without any mechanical damages.

That is why when the mixture boils and rises to the brim of the neck it is advisable to loosen the cork to vent off the excess pressure that has been trapped in the flask. Under normal pressure the there are more air particulars against the liquid molecules. When the pressure is reduced through the vacuum the air molecules will reduce hence there will be fewer struggles for the liquid molecules to gain dominance.

Increase the Surface of Solvents

Additionally, this apparatus as the name suggest utilizes rotation. This ensures the thin film of the solvent trapped in the flask is spread all over the flask to increase the surface area so that more extracts can be trapped during evaporation. This mainly involves the motor which will be used to regulate the speed. Therefore, as evaporation takes place the molecules will be trapped in the flask as a thin film which will be cooled and collected at the end of the processes.


Temperature is also a crucial element during these processes. It influences the pressure and the boiling points of the mixture.

Therefore, water-bath is used to regulate the temperature of the flask which is immersed in the bath. Rotation also helps in temperature distribution which reduces bumping that can be dangerous when it gets out of hand.

Be Careful

The rate at which the substances evaporate is regulated by the speed of rotation, size of the flask, the temperature of the bath and the pressure of the vacuum.

Centrifugal to evaporation is good for many samples and there are developments to make the apparatus allow extraction of hydrogen bond substances that require high temperature.

The use of a rotary evaporator requires users to take caution when handling the apparatus. Some corrosive mixtures should be handled with care. It is also good to be vigilant when dealing with unknown mixtures.


This theoretical approach is to help in understanding how to extract mixtures in a complex combination that requires critical evaporation during the entire process.