How to be a Successful Organic Chemist

13 standard for any crude material, because the success of any recrystallization depends on the identities of the other constituents and their respective solubilities, but in general the crude material should contain about 80% of the desired compound. The crude material is transferred to a suitable crystallization vessel. The crude material is dissolved in a solvent, and gently heated. The solution is allowed to gently and slowly cool down. Notice the crystals growing in the solution. The solution is cooled to room temperature, leading to the formation of large crystals. 2.2 Distillation Distillation is a purification technique for a liquid or a mixture of liquids. We utilize the difference in boiling points of liquids as a basis of separation. The core of a distillation process, is selective evaporation and condensation of particular components. Our overall goal is to evaporate and condense only one component from a mixture, but to attain this goal, we must allow many, many cycles of evaporation and condensation to take place. This process gradually enriches the vapor phase in favor of the most volatile component. After a sufficient number of evaporation and condensation cycles have taken place, the final condensate contains a liquid that is en- riched in the more volatile component. Distillation is easier to understand if we envision a spesific mixture of two liquids, say diethyl ether and ethanol. The boil- ing points of the two liquids are 36 ° C and 78 ° C, respective- ly. When we boil this mixture, we observe the following: the entire mixture (both compounds) boils, but the vapor phase is enriched in the more volatile component (diethyl ether). As this vapor mixture rises, cools, and condenses, the resulting liquid is enriched in diethyl ether too. If we attach a column to the flask so that the vapor enters this column, the condensing liquid will be heated by rising vapors, and it will boil again producing a vapor that is even more enriched in diethyl ether. The higher the column, the more times this cycle of evaporation-conden- sation can be repeated, and the higher up we sample the vapor, the more enriched the vapor phase will be in the more volatile component (diethyl ether). Ideally, with a long enough column, one could obtain a vapor that is nearly pure diethyl ether, and leave behind a liquid that is nearly pure ethanol, the less volatile component. Let us discuss a typical distillation apparatus (shown above) We start with a flask containing the solution (often called a still pot), which is heated. You can see from our discussion above, that a key feature of a distillation apparatus must be a column, where many cycles of condensation and evaporation can take place. The column can be just a short tube (an “unpacked” col- umn), which is the basis of a simple distillation.This is typically less efficient. The column can be packed with an inert material, which is the basis of a fractional distillation, and typically con- stitutes a more efficient distillation. The inert material, such as Figure 2.2. A simple distillation apparatus. The round bottom flask (or still pot) is attached to an unpacked condenser. The condenser is attached to a three way adapter that contains the thermome- ter, and a water jacketed condenser with cold wa- ter running through it. Figure 2.3. A fractional distillation apparatus. The round bottom flask (or still pot) is attached to a condenser packed with copper sponge. The sponge gives a large surface area for the vapor to condense on, leading to a more efficient distillation.