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G.Patton

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Rotary evaporator.

A rotary evaporator (rotovap) is a device which is used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation as well as for the separation of liquids. When referenced in the chemistry research literature, description of the use of this technique and equipment may include the phrase "rotary evaporator", though use is often rather signaled by other language (e.g., "the sample was evaporated under reduced pressure").
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Rotary Evaporator Applications.

A rotary vacuum evaporator should be used to evaporate the solvent from the reaction mixture, as well as to distill the solvent before synthesis.
For example, in the amphetamine synthesis the solvents should be distilled. To purify acetone from contaminants (other solvents), the first distilled solvent fraction and the last distilled solvent fraction are removed during distillation. To evaporate isopropyl alcohol containing free amphetamine base. For the synthesis of other phenylethylamines, such as 2C-B, DOM, MDA, MESCALINE, TMA, where distillation, sublimation and removal of the solvent from the reaction mixture to obtain the intermediate is necessary. MDMA synthesis also requires solvent removal to produce free base oil. The synthesis of other substances is not without the use of evaporation stages. For example, the preparation of DMT also requires removal of the solvent under vacuum to obtain an oily free base from the reaction mass.

Crystallization technique on the rotary evaporator (always produces a fine fraction).
Mefedrone is dissolved in a solvent in the proportion of 1 g per 1 ml. The solution is placed in the flask of the rotary evaporator and the distillation begins. The deeper the vacuum, the lower the boiling point of the solution. Large amounts of fine crystals can be obtained quickly in this way.

Purification of mephedrone solution in dichloromethane.
Dissolve mephedrone in the proportion of 1 g per 1 ml of water (+30 ºC), add 0.5 volume of dichloromethane and stir the solution well for a few minutes. Allow to stand and observe the separation into two fractions: the upper aqueous layer - the mephedrone solution, the bottom layer - dichloromethane with impurities. We separate the upper layer, dispose of the lower one. The mephedrone aqueous solution can be evaporated to powder in a rotary evaporator under vacuum, or it can be used to grow crystals. Washing the mephedrone solution can be done several times until the solution becomes colorless.

The Step #1 3-(1-naphthoyl)indole of obtaining JWH-018 requires the use of a vacuum evaporator. The organic phase was dried over Na2SO4 and concentrated at reduced pressure to give the 3- (1-naphthoyl) indole as a crystalline solid.

Principle of operation.

Vacuum evaporators as a class function because lowering 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 remove from a sample after an extraction, such as following a natural product isolation or a step in an organic synthesis. Liquid solvents can be removed without excessive heating of what are often complex and sensitive solvent-solute combinations.

Rotary evaporation is most often and conveniently applied to separate "low boiling" solvents such an n-hexane or ethyl acetate from compounds which are solid at room temperature and pressure. However, careful application also allows removal of a solvent from a sample containing a liquid compound if 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, such as 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 at the same), can also be evaporated, if 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 recent 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 is often a last recourse, as other evaporation methods or freeze-drying (lyophilization) are available. This is partly due to the fact, that in such solvents, the tendency to "bump" is accentuated.

The main components of a rotary evaporator are:
  1. A motor unit that rotates the evaporation flask or vial containing the user's sample.
  2. A vapor duct that is the axis for sample rotation, and is a vacuum-tight conduit for the vapor being drawn off the sample.
  3. A vacuum system, to substantially reduce the pressure within the evaporator system.
  4. A heated fluid bath (generally water and oil) to heat the sample.
  5. A condenser with either a coil passing coolant, or a "cold finger" into which coolant mixtures, such as dry ice and acetone are placed. It is used to generate a localized cold surface; it is a type of cold trap.
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  6. A condensate-collecting flask at the bottom of the condenser, to catch the distilling solvent after it re-condenses.
  7. A mechanical or motorized mechanism to quickly lift the evaporation flask from the heating bath.
In the vast majority of cases, a water bath is sufficient for laboratory purposes, but an oil bath is used to evaporate high boiling liquids. Special oil compositions serve as a heat carrier. The devices are used to work in a wide range of temperatures - from +5 to +360 °C. The best heat-carrier for oil baths is a colorless silicone oil (mixture of organosilicon compounds) that can withstand a long time heating up to 300 - 360 °C without noticeable change in color and viscosity. Sometimes during prolonged heating at the maximum permissible temperature, the oil in the bath bursts into flames. To extinguish the fire, the bath is covered with asbestos cloth. Neither water nor sand can be used to extinguish burning oil.
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The rotary evaporator consists of a glass tube with a slit, to which a round bottom flask A is connected, which is heated by a water bath B. A motor C drives the flask in rotation, and the solvent vapor enters the reflux condenser F, where it is cooled and condenses, flowing into the condensate-collecting flask G. Parts of the rotary evaporator can be additionally fastened using tripod D and foot E. For a quick vacuum release a valve H is provided in the system, which is also often used for introducing inert gas (argon or nitrogen) into the system.

The operation of the rotary evaporator is based on lowering the boiling point of the solvent by creating a reduced pressure in its system using a water jet or vacuum pump. This approach makes it possible to remove the solvent from the solution at a lower temperature, avoiding the side reactions that can occur when the mixture is heated.

What does a Chiller for a Rotovap?

In the simplest of explanations, Rotovaps require cooling and ideally a recirculating chiller supplies that cooling. A chiller is used to ensure that the rotovap has sufficient cooling at the precise temperature. For the solvent to vaporize properly in the rotary evaporator, cooling must be added because during evaporation, the solvent evaporated is warm. Typically, a chiller will pump cool fluid (typically water or a water/glycol mixture) to the process to remove the heat and the warm fluid returns to the chiller. Chiller connects to reflux condenser. This unit should be used instead of running water to cool the reflux condenser.
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Accessory vacuum pumps.

For most volatile solvent, a water jet pump as in a picture below. The strength of the vacuum produced depends on the velocity and shape of the fluid jet and the shape of the constriction and mixing sections, but if a liquid is used as the working fluid the strength of the vacuum produced is limited by the vapor pressure of the liquid (for water, 3.2 kPa or 0.46 psi or 32 mbar at 25 °C or 77 °F). If a gas is used, however, this restriction does not exist. If not considering the source of the working fluid, vacuum ejectors can be significantly more compact than a self-powered vacuum pump of the same capacity. Cost from ~25-30$.
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Also, you can use vacuum diaphragm pump, which do not take a water stream and easy to use. This type of pump may produce to 1.5 mbar vacuum. Main disadvantage is a produced noise to 50-60 dB and necessity of periodic maintenance (replacement of oil and membranes). Moreover, diaphragm pumps cost from ~450-500$ and takes to ~200-250 W.
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General rules for usage of a rotary evaporator.

1. The solvent collection flask of the unit should always be emptied prior to use to prevent accidentally mixing of incompatible chemicals.

2. The flask with the solution is placed on the rotary evaporator. The use of a bump trap prevents the solution from accidentally splashing into the condenser (and being contaminated). It is highly advisable to start with a clean bump bulb in case something bumps over after all! This would allow the experimenter to recover the solution or solid.
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3. A metal or Keck clip is used to secure the flask and the bump trap. The green one shown below fits 24/40 ground glass joints. Similar blue clips fit 19/22 joints and the yellow ones fit 14/20 joints, which will most likely used in the lab.

4. The dial on the motor is used for speed control of the flask rotation. A typical rotavap uses a variable speed sparkless induction motor that spins at 0-220 rpm and provides high constant torque. A good setting here is 7-8.

5. The aspirator vacuum is turned on. On most models, the vacuum on/off control is managed by turning a stopcock at the top of the condenser (left side of the above diagram). This stopcock is later also used to vent the setup after the solvent is removed (see point H on scheme).

6. The flask A is lowered into the water bath or the water bath is raised to immerse the flask in the warm water. On most models, a convenient handle (with height locking mechanism) moves the entire condenser/motor/flask assembly up and down. Often the tilt of the condenser assembly can also be adjusted. The water bath temperature should not exceed the boiling point of the solvent!! For small amounts of common solvents, the bath heater is not needed.

7. The solvent should start collecting on the condenser F and drip into the receiving flask G. Some solvents (such as diethyl ether or dichloromethane) are so volatile that they will also evaporate from the receiving flask and be discharged down the drain. OPTIONALLY: To prevent this, a cooling bath on the receiver or (on some models) use a dry-ice condenser can be used. In addition, an additional trap (with dry-ice or liquid nitrogen) can be placed between the vacuum source and the condenser unit. This is particularly important as a membrane pump is used as vacuum source. There is a rotary evaporator with dry ice cooler for low boiling solvents such as diethyl ether.
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8. Once all the solvent evaporated (or whatever is desired at this point), the vacuum is released very slowly (to prevent explosion and destruction of glass). The flask is raised out of the water bath and the spinning is discontinued.

9. The bump trap has to be cleaned and the receiving flask is emptied upon completion of the evaporation.

Tips and Tricks.
Distilled water should be used in the heating bath to minimize the scale build up in the bath, which coats the thermistor and heating coils. It is very difficult to remove and reduces the efficiency of the bath. In addition, regular tap water will promote the growth of spectacularly disgusting algae colonies, particularly during the summer months. The best protocol is a regular exchange of the water.

To remove algae gunk from the inside of a coiled water condenser, the condenser has to be removed from the rotavap and the coil is soaked in a dilute nitric acid solution for a few hours. After carefully rinsing the insides, the rotavap is reassembled. All standard safety precautions should be followed when working with nitric acid!

The ground glass joint holding the flask does not need to be greased, but on rare occasions it (or the bump bulb) may get "frozen". Some companies sell special joint clips that can free frozen joints simply by screwing them in one direction. If you are not lucky enough to have these and cannot release the joint, you can try yo move it from one side to another gently.

If a mechanical pump is used instead of an aspirator to produce a vacuum, a secondary trap has to be used to prevent that the solvent destroys the membrane or is absorbed in the oil.

Additional equipment.
There are different nozzles, such as spiders with several flasks. They are place after a bump trap on the rotary evaporator neck!

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Safety.
Possible hazards include implosions resulting from use of glassware that contains flaws, such as star-cracks. Explosions may occur from concentrating unstable impurities during evaporation, for example when rotavapping an ethereal solution containing peroxides. This can also occur when taking certain 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 avoid contact with rotating parts, particularly entanglement of loose clothing, hair, or necklaces. Under these circumstances, the winding action of the rotating parts can draw the users into 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 into the apparatus and a violent reaction can occur.

Suppliers.

There are a lot of companies, which produce and sell this equipment. Your choice depends on your budget. I have a wide experience of using different kind of them and I want to say that they do not have big difference.
List of popular suppliers:
There is a price list for rotary evaporators with small (50 ml-3l) and large (up to 30 l) load from the above suppliers. All prices are valid as of 11.2021.
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madmoney69

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Does Chiller is a must for rotovap in drug making?
What is your advice on it?
 

G.Patton

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Does Chiller is a must for rotovap in drug making?
What is your advice on it?
madmoney69Chiller does not necessary in case of having good pressure of cold water. In case of low boiling temperature solvent evaporation, necessary to drop temperature of cooling water to avoid solvent volatilization to atmosphere. You can use chiller, but this equipment optional.
 

tucoXxX

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I can't wait to try it. Rotovap+cooling protection device+vacuum pump. in a device. since it will be my first synthesis and I am not a chemist, I hope it will make it easier to make amphetamine. and of course I want the best possible quality.
 

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Does such device efficient for base distillation? If meth, mdma, amph etc base put in the main flask, and vacuum source is strong enough will it distill product fast and pure?
As I remember all these bases have boiling points around 200-220C.
What vacuum pressure and capacity shall be reached to reduce it down to 80-100C and how fast is the process?
Or v/v what boiling point and what yeld per 1 hour shall be expected if medium capacity pump 10-15L 0.07-0.08 (low noise pump considered) is used?
 

G.Patton

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Does such device efficient for base distillation? If meth, mdma, amph etc base put in the main flask, and vacuum source is strong enough will it distill product fast and pure?
As I remember all these bases have boiling points around 200-220C.
What vacuum pressure and capacity shall be reached to reduce it down to 80-100C and how fast is the process?
Or v/v what boiling point and what yeld per 1 hour shall be expected if medium capacity pump 10-15L 0.07-0.08 (low noise pump considered) is used?
Mr Good CatIt's not a good idea to carry out vacuum distillation by rotovap. Moreover, amph and meth should be steam distilled.
What vacuum pressure and capacity shall be reached to reduce it down to 80-100C and how fast is the process?
Depends on a substance, use calculator for this https://www.sigmaaldrich.com/FI/en/...essure-temperature-nomograph-interactive-tool
Or v/v what boiling point and what yeld per 1 hour shall be expected if medium capacity pump 10-15L 0.07-0.08 (low noise pump considered) is used?
How can I answer you, man? Are you seriously? There are a lot of factors, which have influence on this: vacuum pressure, bp of substance, volume of apparatus, stability of the temperature maintaining. If anyone would know all of them, they won't answer you because it's not a calculated value. You need to try by yourself.
 

Mr Good Cat

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It's not a good idea to carry out vacuum distillation by rotovap. Moreover, amph and meth should be steam distilled.

Depends on a substance, use calculator for this https://www.sigmaaldrich.com/FI/en/...essure-temperature-nomograph-interactive-tool

How can I answer you, man? Are you seriously? There are a lot of factors, which have influence on this: vacuum pressure, bp of substance, volume of apparatus, stability of the temperature maintaining. If anyone would know all of them, they won't answer you because it's not a calculated value. You need to try by yourself.
G.PattonYes, thank you. I forgot it is easy to calculate with Clausius Clapeyron equation.

Second question was to those, who already tried to do this. I guess some already tried.

Any way, thank you for reminding me basic things.
 

G.Patton

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Yes, thank you. I forgot it is easy to calculate with Clausius Clapeyron equation.

Second question was to those, who already tried to do this. I guess some already tried.

Any way, thank you for reminding me basic things.
Mr Good CatIt's possible to carry out vacuum distillation by rotovap but not for these substances. Welcome!
 
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