1-3: Performing a Distillation
Distillation is a separation technique utilized by organic chemists. A distillation apparatus separates liquid compounds based on boiling points. The boiling point of each compound is determined by the intermolecular forces that exist in a solution of the compound.
In a standard distillation apparatus, the mixture of liquid compounds is held within a round bottom flask known as the distillation flask. A thermometer is used to measure the temperature of the liquid in the distillation flask, and the entrance point for the thermometer is sealed. The distillation flask is also connected to a condenser at a joint. The remaining open end of the condenser is connected to a second flask called the collection flask. Heat is applied to the distillation flask and the temperature is monitored via the thermometer. As the boiling point of one of the compounds is reached, the compound is vaporized and travels into the condenser. Cold water is run through the condenser, which causes the vapors to cool and condense on the inside of the condenser. The condensed vapors drip out of the condenser and into the collection flask. The collected liquid, called the distillate, is now separated from the other compounds in the distillation flask. Note that this is a sealed system and an inert gas must also be attached to provide pressure
relief and an inert environment for the distillate.
In this assignment, you will be guided through the steps of a Friedel-Crafts reaction (A
REACTION WE WILL GO OVER LATER, SO DON’T WORRY ABOUT THE MECHANISM
JUST YET) as a demonstration of how to use a distillation apparatus as a tool to separate products. This assignment will also serve as a tutorial to teach you how to utilize the various parts of the organic simulation that will be used in later assignments.
- Start Virtual ChemLab Organic and select Performing a Distillation from the list of assignments. The lab will open in the Synthesis laboratory, and you should see a lab bench containing reagents on the back of the bench, aqueous reagents on the right, an equipment rack containing necessary laboratory equipment, a red disposal bucket for cleaning up the lab, and the organic stockroom in the back. Other pieces of laboratory equipment will be used in other assignments.
- You will find a round bottom flask located on the stockroom counter. Select the starting materials for the reaction by first clicking on the bottle containing benzaldehyde and dragging
and dropping the syringe on the mouth of the flask. Now do the same for the other reactant – acetyl chloride – and for the solvent – ether. Note the bottle labels are small, but you can see the full name and structure of each starting material by hovering over the bottle. Now click on the flask and drag it to the stir plate on the lab bench. It should snap into place when you are at the right location.
- The round bottom flask containing the starting material should now be on the stir plate. The starting materials should be listed on the chalkboard, and hovering over a listed starting material will display its structure on the chalkboard. Help on using Virtual ChemLab Organic can be found by clicking on the bell on the stockroom counter.
- In order to perform the reaction, aluminum chloride (AlCl3) must be added. This is done by clicking on the Aluminum Trichloride bottle on the back of the lab bench and dragging the spatula to the round bottom flask. The reagent can also be added by double-clicking on the bottle. The chalkboard should now show that the reagent has been added to the reaction mixture.
- Before the reaction can be started, we must be able to heat the flask so the reaction can proceed at a suitable rate. This is done by adding a heating mantle to heat the reaction mixture, adding a condenser so the mixture can be refluxed, and then adding nitrogen gas to maintain an inert atmosphere and to prevent pressure buildup. Click on the Heating Mantle and drag it to the round bottom flask to place it on the stir plate. Now click on the Condenser from the equipment rack and drag it on top of the round bottom flask. Finally, click on the N2 Gas hose to the right of the stir plate and drag and drop it on top of the condenser. Now click on the Stir Plate button to start the reaction. You should see the reaction mixture stirring in the round bottom flask.
- Allow the reaction to proceed until the product begins to form, but do not let it go to completion. A reaction time of 3 minutes is sufficient. The reaction will proceed in real time. However, time can be sped up. The three blue buttons beneath the LED clock display can advance the time in 1 min, 10 min, and 1 hr intervals. This reaction occurs fairly quickly, so only advance the time in 1 min intervals (if at all). You will be able to monitor the progress of the reaction either by running TLC plates, by looking at the compounds on the blackboard, or both. The blackboard updates as the reaction proceeds, displaying the names of all compounds in the flask.
- After 3 minutes, the reaction mixture will contain both product and starting materials. Perform a separatory funnel extraction (see activity 1-2: Performing a Separatory Funnel Extraction). Add H2O by clicking on the large H2O container and dragging it to the separatory funnel. The separatory funnel should have two distinct layers of liquid. Remove and keep the organic layer, which contains your product. Do this by clicking on and dragging the organic layer to the cork ring, where it will be placed in a new round bottom flask. Notice that the organic layer contains the product and what remains of one of the starting materials.
What is the product that is in the organic layer?
What is the starting material that is in the organic layer?
- The aqueous layer in the separatory funnel can be discarded in the red bin, and the funnel can be returned to the equipment rack. Put the round bottom flask with the organic layer onto the stir plate. Bring the Distillation apparatus over from the equipment rack by clicking and dragging, placing it on top of the round bottom flask on the stir plate. It should snap in place. Hovering over the thermometer will show you the temperature of the apparatus. You can also hover over the collection flask, which will be filled with distilled compounds as you carry out the distillation.
- Attach the N2 Gas hose to the distillation apparatus to prevent pressure buildup. The distillation is started by clicking on the Stir Plate button. The apparatus takes 5–10 minutes to reach the boiling point of the compound with the lowest boiling point. You can monitor the temperature by hovering over the thermometer.
- The boiling point of one of the products is around 178 °C. As the distillation apparatus reaches this temperature, slowly advance the time until liquid begins to collect in the collection flask.
Which of the compounds has this lower boiling point and therefore begins to distill first (we will refer to this compound as Compound 1)?
- By hovering over the distillation flask, you will notice that some of Compound 1 remains mixed with the other compound. Continue to advance the time until all of Compound 1 is in the collection flask and none remains in the distillation flask.
What is the compound remaining in the distillation flask (Compound 2)?
- Draw the structures of Compounds 1 and 2.
- Intermolecular forces define the boiling points of compounds.
What type of intermolecular forces exist for Compounds 1 and 2?
Based on what you now know about the boiling points of Compounds 1 and 2, in which are intermolecular forces stronger? Why?
Distillation can be used to separate products from products, starting materials from products, or solvents from products through boiling point differences. Some lab activities in Virtual ChemLab Organic will require you to use the principles of distillation learned here to make necessary separations. KEEP READING! THERE’S MORE!!!
5-4: Alcohol Dehydration
For this assignment, the target compound that you should synthesize is cyclohexene. This is an
ELIMINATION REACTION. Assess the potential of the possible leaving groups (OR CAN
YOU MAKE ONE???). Keep in mind the mechanism and how that controls the outcome of the process. (WE TALK ABOUT FOUR FACTORS! WHAT DO YOU HAVE CONTROL OVER?)
- Start Virtual ChemLab Organic and select Alcohol Dehydration from the list of assignments. After entering the synthesis laboratory, Use the available reagents on the stockroom shelf and identify the appropriate starting materials required to synthesize the target compound and add them to the round bottom flask. Select the appropriate solvent and drag the flask to the Stir Plate on the lab bench.
- The round bottom flask containing the starting materials should now be on the stir plate, and the contents of the flask should be visible on the chalkboard. From the group of reagents found on the lab bench, select the correct reagent to synthesize the target compound and add it to the flask on the stir plate.
- Start the reaction by clicking on the Stir button on the front of the stir plate. You should be able to observe the reaction mixture stirring in the flask. Monitor the progress of the reaction using TLC measurements as necessary until the product has formed and the starting materials have been consumed. You can advance the laboratory time using the clock on the wall. With the electronic lab book open (click on the lab book on the stockroom counter), you can also save your TLC plates by clicking Save on the TLC window.
- When the reaction is complete, “work up” your reaction by doing a separatory funnel extraction. Drag and drop the separatory funnel on the flask and then add the appropriate solvent to the funnel. Either the organic or the aqueous layer can be removed by clicking and dragging it to the bench. Your target compound should be in one of these layers. The other layer can be discarded into the red bin.
- The layer in the round bottom flask may contain multiple products. To separate them, you must carry out a distillation. Drag the flask back to the stir plate. Drag and drop the distillation apparatus onto the flask and attach flowing N2. Start the distillation by clicking on the Stir button. The temperature of the distillation flask can be monitored by hovering your mouse over the thermometer. As the temperature increases, products will evaporate and then distill into the collection flask at the back of the apparatus according to their boiling points. Products that are not needed can be discarded until the desired product is isolated.
List the starting materials, solvent, reagent, and products formed:
How long did it take to finish the reaction?
What are the TLC values (Rf) for (a) Starting Materials: (b) Products:
Write a mechanism for this reaction:
FTIR and NMR Spectra
After completing a reaction and working up the products, it is still necessary to confirm that the correct product was formed. The most common tools used for this analysis are Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy. In the virtual laboratory, 1H and 13C NMR spectra are available. Details on interpreting FTIR and NMR spectra are found in your textbook. Your instructor may or may not ask you to perform this section depending on how your class is structured.
- To collect an FTIR spectrum of your product, click on the FTIR spectrometer located to the right of the lab bench and drag the salt plate icon to the flask on the lab bench. A window containing the FTIR spectrum for your product should now open. Identify the relevant peaks in the FTIR spectrum and record the position and associated functional group for each in the FTIR table below. The FTIR spectrum can also be saved to the lab book for later analysis.
FTIR List position (cm-1) & functional group
- To collect a 1H NMR spectrum of your product, click on the NMR magnet and drag the NMR sample tube to the flask on the lab bench. A window containing the NMR spectrum for your product should now open. You can zoom into various portions of the NMR spectrum by clicking and dragging over the desired area. The Zoom Out button is used to zoom back out to view the full spectrum. Identify all of the peaks in the NMR spectrum and record the chemical shift, the splitting, and the number of hydrogens for each peak in the NMR table below. The NMR spectrum can also be saved to the lab book for later analysis. If necessary to confirm the structure of your product, you can measure the 13C NMR for the product and record the chemical shifts for the peaks. Mass spectrometry is also available if needed.
PLEASE PUT THE MULTIPLICITY AS IT SHOULD BE, NOT AS IT LOOKS!!! AND ONLY USE MULTIPLET IF IT IS ABOVE A SEPTET!
† Specify the multiplicity as a singlet (s), doublet (d), triplet (t), quartet (q), or multiplet (m). ‡ Specify the number of hydrogens associated with each peak.
8. Do the FTIR and NMR spectra you measured and recorded in the tables above confirm that you synthesized the assigned target compound? Explain. IN DETAIL!!! DON’T JUST SAY
YES! PROVE TO YOURSELF (AND ME) THAT THE PEAKS ARE AS THEY