Cassie is sharing research she's done on the synthesis of cyclohexanone.
Cyclohexanol to Cyclohexanone
The purpose of this lab is to synthesize cyclohexanone. Cyclohexanone is used as a precursor for nylon. This makes it one of the largest mass-produced chemicals in the industry. Billions of kilograms of cyclohexanone are produced each year for the making of nylon . The synthesis of cyclohexanone is simple. First, sodium hypochlorite and acetic acid are reacted to yield hypochlorous acid. Second, hypochlorous acid is added to cyclohexanol to synthesize cyclohexanone via the Chapman-Stevens oxidation reaction. The following picture depicts what possibly could be happening for the Chapman-Stevens oxidation of cyclohexanol . The mechanism has not been fully established at this time.
After cyclohexanone is synthesized, it must be separated out from by-products. In order for it to be separated out, sodium chloride is added to the mixture. The sodium chloride will salt out the cyclohexanone from the aqueous layer. Now the aqueous layer and the cyclohexanone must be separated. Dichloromethane is added to the mixture. Next, the cyclohexanone and dichloromethane are separated from the aqueous layer by liquid-liquid separation. The top layer should be the aqueous layer, while the bottom layer should be organic and contain the final product, cyclohexanone. Last, the dichloromethane is boiled off to leave only the final product. The final product should be characterized by using IR. A reference IR of cyclohexanol should be taken. The IR allows for analysis of the structures of both the final product and cyclohexanol . This is done by identifying functional groups after the 1500 cm-1 frequency.
Chemicals can be dangerous, and the right precautions should be taken to avoid harm. Lab coat, goggles, and gloves should be worn at ALL TIMES . One chemical hazard to be aware of is that acetic acid is extremely irritating, and skin contact and inhalation should be avoided. Also, cyclohexanol and cyclohexanone are toxic and irritating. Caution should always be used when handling all chemicals. If any chemicals come in contact with the skin, wash the infected area with cold water for at least fifteen minutes. Please consult the MSDS sheet for further information on any of the chemicals used in the experiment. Another consideration should be for disposal of the chemicals. All liquid waste should be disposed of in the designated hazardous container. All aqueous solutions produced should be disposed of in the aqueous waste container. Organic waste goes in the non-halogenated waste container. Solid waste goes in the solid waste container .
- First, a 500 mL 3-neck round bottom flask was secured to a ring stand with all joints tightly connected. A thermometer was attached to one of the necks of the round bottom flask.
- Next, 3.65 mL of acetic acid was added to a 125 mL separatory funnel.
- After the acetic acid was added 79.00 mL of sodium hypochlorite was transferred into the same separatory funnel. The separatory funnel was set aside for later use.
- A small magnetic stir bar was added to the 3-neck round bottom flask. In the hood, 5.3 mL of cyclohexanol was measured and then transferred into the 3-neck round bottom flask.
- The separatory funnel was then attached to one of the necks on the 3-neck round bottom flask.
- The acetic acid and sodium hypochlorite, which is now hypochlorous acid, is slowly dripped into the round bottom flask. The temperature was closely monitored to stay between 40-50 °C.
- After the addition of the hypochlorous acid was complete, the mixture was stirred with the magnetic stir bar for 15 minutes.
- Once the stirring was complete, sodium carbonate was slowly added until the bubbling stopped.
- The mixture was then transferred into a 100 mL beaker and 2.0 g of sodium chloride was added, 0.2g of sodium chloride was added per milliliter of water.
- The mixture was then transferred again to a clean 125 mL separatory funnel.
- To the same separatory funnel, 10 mL of dichloromethane was added.
- The top was stoppered, and the funnel was shaken and vented. The separatory funnel was vented often to make sure that pressure did not build up. The separatory funnel was then set upright to allow layers to separate.
- The bottom organic layer was then drained from the funnel and set aside. This was repeated two more times with two 10 mL portions of dichloromethane. Once again, caution was taken to not allow the pressure to build up within the separatory funnel.
- The organic layer was then transferred into an Erlenmeyer flask and dried with anhydrous sodium sulfate.
- Next, a 100 mL beaker was pre-weighed. Then, a piece of filter paper was folded and put into the100 mL beaker for gravity filtration.
- The contents of the Erlenmeyer flask were poured into the filter paper. Once the filtration was done, the beaker was placed in the hood on a steam bath to boil off the dichloromethane. It was boiled for approximately fifteen minutes.
- It was placed on the steam bath until it was no longer boiling. The beaker was then weighed .
- Lastly, the final product, cyclohexanone, was characterized. An IR spectrum was taken of both cyclohexanol and cyclohexanone. Also, percent yield was calculated. The following picture is the balanced reaction of the reactants and products .
Results and Observations
- The first observation that was seen during the reaction was the temperature change. The temperature was below 30 °C while adding the mixture of sodium hypochlorite and acetic acid, which is also known as hypochlorous acid. Then while the hypochlorous acid and cyclohexanol were being stirred, the temperature began to rise. The temperature only rose to 38°C.
- The next observation was that the solution turned a cloudy white and was not yellow. This meant that the sodium bisulfate step could be skipped because it was not yellow. If the mixture was yellow in color, it contained too much hypochlorous acid. Next, bubbling was seen when sodium carbonate was added. The bubbling was CO2 gas being created by the neutralizing of acetic acid. The mixture was the transferred to a beaker where two layers were seen. One of the layers was the aqueous layer and contained some of the cyclohexanone, so 2.0 g of sodium chloride was added. This salted out the cyclohexanone for the aqueous layer. The mixture was then transferred to a separatory funnel where two layers were once again seen. The top layer was the aqueous, which was obvious due to the salt crystals that could be seen. This made the bottom layer the organic layer that contained the final product. The bottom layer was drained and more dichloromethane was added to wash the aqueous layer in case any cyclohexanone remained. Two layers formed again and the bottom one was drained. This was repeated twice before the organic layers were combined and dried with anhydrous sodium sulfate. The sodium sulfate clumped at first meaning there was some water still in it, but after three spatulas of sodium sulfate, it began to be free-flowing. This meant there was no more water in the organic layer. While one the steam bath boiling was seen because the dichloromethane was being boiled off.
- The final observation was of our final product. The final product was yellowish in color and a liquid. The yield of the final product was 2.5 g which makes the percent yield 51%. Two IR spectrums were taken, one of cyclohexanol and one of cyclohexanone. The IR of cyclohexanol was taken for reference. The expected peaks for the cyclohexanol were an O-H peak between 3600-3200 cm-1 and a C-H alkane peak between 3000-2850 cm-1 . The observed peaks for cyclohexanol were an O-H peak at 3400-3200 cm-1 and a C-H alkane peak at 3950-3850 cm-1. The expected peaks for cyclohexanone were a C=O peak between 1810-1640 cm-1 and a C-H alkane peak between 3000-2850 cm-1 . The observed peaks for cyclohexanone were a C=O peak at 1700-1600 cm-1, a C-H alkane bond at 2950-2800 cm-1, and an O-H peak at 3550-3400 cm-1. The O-H bond was unexpected because it is not a part of cyclohexanone. The unexpected peak reveals that there was still some of our starting product, cyclohexanol.
This procedure was chosen for three reasons. For one, it was the simplest and easiest procedure. Secondly, it contained all reagents that would be available in the lab for use. And lastly, it contained all techniques that had previously been used and mastered.
One advantage of choosing this procedure was that it contained all previously used techniques. If a procedure that had techniques that had never been used was chosen, it could have created more problems.
One major disadvantage to choosing this procedure was having to keep the temperature between 40-50 °C. This disadvantage caused a problem at the beginning of the lab that could have caused a low percent yield. This problem could have easily been fixed by putting the round bottom flask in a hot water bath.
One possible reason for a low yield is that the temperature did not reach above 40°C. This could have caused the reaction to not go to completion, giving a much lower yield. The product that was lost could not be later recovered. In the IR of cyclohexanone, an O-H peak appeared. This shows that some of the leftover cyclohexanol was in the final product. This could be due to not adding enough bleach. The reaction is reversible and therefore will proceed to go to the left if not driven towards the right. If too little bleach was added, some of the product could have been converted back to cyclohexanol. This means that our purity was not perfect.
The Lesson Learned
The synthesis of cyclohexanone is a simple procedure that uses Acetic acid, sodium hypochlorite, hypochlorous acid, ether, sodium chloride, sodium carbonate and cyclohexanol. The reaction is a Chapman-Stevens oxidation. The synthesis is done by simply adding the acetic acid and sodium hypochlorite, which is also known as hypochlorous acid, to cyclohexanol and then separating the final product from the by-products. The final results of the synthesis of cyclohexanone are that we had a 51% yield and that it was not 100% pure. This can be concluded from the IR of cyclohexanone because it contained an O-H peak.
The key lesson learned is that temperature plays a key role in the synthesis of cyclohexanone. It can give you a low yield, which is not what you want.
1.L. Huynh, C. Henck, A. Jadhav, and D.S. Burz. Organic Chemistry II: Laboratory manual. Infrared (IR) Spectroscopy: A Practical Approach, 22
2.University of Colorado, Boulder, Dept of Chem and Biochem . Experiment 3: Oxidation of Alcohols: Preparation of Cyclohexanone,2004, 22 http://chemistry.mdma.ch/hiveboard/picproxie_docs/000522396-OxAlcoholsLM41Su04.pdf
3.Experiment 8 :Preparation of Cyclohexanone by Hypochlorite Oxidation, 1-5 http://myweb.brooklyn.liu.edu/swatson/Site/Laboratory_Manuals_files/Exp8.pdf
4.Experiment 9: Oxidation of Cyclohexanol to Cyclohexanone, 1 http://www.brynmawr.edu/chemistry/Chem/mnerzsto/Labs/Experiment_9.pdf
Kevin on March 23, 2017:
Carlos is right, you did make cyclohexanone. You just switched up the spectras.
Carlos on September 29, 2016:
Hi, I think you changed the spectra order. The first one may be cyclohexanone because the vibration in 1705 be relate with ketone and the deformation near of 3500 be relate with hydroxyl of alcohol. Greetings from Brazil.
L on August 02, 2016:
How did you get the 51 % yield?
scotch on September 12, 2015:
wow wow wow but were is the mechanism of the reaction
Fred Arnold from Clearwater, FL on August 15, 2014:
I tell you what! I took some chemistry in college, but not enough for majority of this to make an impression on me! Haha. Reminded me of my 7-9PM chemistry lab class I took a few years ago.