Merissa+ReWrite+Winter+2011+Preparation+and+Distillation+of+Cyclohexene

Merissa Honey Re-Write Winter 2011: Preparation and Distillation of Cyclohexene

**__Introduction:__**

Cyclohexene can be prepared from cyclohexanol through the acid catalyzed dehydration of alcohol and acid; In this lab, an E1 reaction occurs and thus the alcohol will be dehydrated. A strong acid, such as H3PO4 will be used so that the alochol will be protonated and a hydronium ion may be eliminated. A distillation technique will be incorporated so that the anticipated products will achieve a high level of purity and then will be able to be analyzed using an Infrared Spectrum. The rate expression for an E1 reaction shows that the only determining step involves the electrophile. This step allows the for water, instead of a hydroxide ion (a poor leaving group), to leave. This happens because the acid is used to protonate the alcohol to form a better leaving group.After the leaving group has left, a stable carbocation forms. The primary reason that this experiment results an E1 reaction is the fact that the carbocation is stable. In this experiment the cyclohexanol is being “eliminated” of its alcohol and a double bond is formed. This lab also demonstrates the ability to view how an E1 reaction will occur in place of an SN1 reaction. Another indicator of an elimination reaction is the addition of heat to the reactants that can be observed in this lab. The atom economy, that is solved at the end of the experiment, will show how efficient the reaction was aswell as how wasteful it might be. The role of boiling points comes into play because it is desired that the cyclcohexene will be distilled into another new vessel and leave behind the cyclohexanol. The fact that the cyclohexanol has a higher boiling point (161 degrees C) is a good thing in that it will not boil off before or at the same time as the cyclohexene which has a boiling point of 83 degrees C.



Thanks for adding in the reaction mechanism.

**__Procedure:__** > Decant/pipette the organic liquid away from the drying agent and place it in a clean, dry round-bottom flask. This will be the distillation flask for the next step.
 * 1) Add 0.074 moles of cyclohexanol and 1.75 mL of 85% H3PO4 to a 50 mL round-bottom flask containing a magnetic stir bar (or boiling stone). Use gentle swirling to mix the two layers.
 * 2) Fit the flask with a fractionating column, a distillation adapter, a thermocouple (or thermometer), a condenser, and a vacuum adapter as for fractional distillation. A rubber septum should be used to provide a seal between the thermocouple or thermometer and the glassware.
 * 3) Heat the reaction mixture first at a gentle reflux for about 5 minutes, then heat the flask more strongly in order to distill the mixture into the collection flask. Keep distilling until the volume remaining in the distillation flask has been reduced to approximately 1 mL.
 * 4) Transfer the distillate to a separatory funnel and wash with approximately 5 mL of water. Carefully separate the layers and transfer the organic layer into a small, dry Erlenmeyer flask. If any water droplets are visible, remove t hem before adding the drying agent (sodium sulfate). Add a small amount of anhydrous sodium sulfate to the flask. Let the mixture stand for 5 minutes, occasionally swirling it gently. If the drying agent completely clumps together, its capacity to remove water has been exceeded and a little more sodium sulfate should be added. If you have successfully removed the water, the liquid should be clear, and a little of the drying agent should remain free flowing.
 * 1) Transfer the distilled cyclohexene to a clean, dry, pre-weighed sample vial and determine the mass of the product. Record an infrared spectrum of the distilled product.

Source: //Strategies, Tools, and Laboratory Experiments// by K.M. Doxsee and J.E. Hutchison, Thempson Brooks/Cole, 2004; pp 129-134.



__**Data:**__ Cyclohexene Product Mass: 4.446g Cyclohexanol Initial Mass: 7.399g Phosphoric Acid: 1.75mL

Heat Time of Distillation to achieve approximately 1.0mL of reactants: 1hr 13min.

//Product Appearance////:// clear liquid with low viscosity (like water)

//Boiling points:// Cylcohexene = 83° C Cyclohexanol = 161° C Water = 100° C

//Percent Recovery:// 4.446g cyclohexene/7.399g cyclohexanol = 0.6008 X 100% = **60.08% =Percent Recovery** Calculation OK, Sig Figs OK __**IR Spectra:**__

The spectrum labeled “heathercyclohexene” displays this lab's experimental results. The peaks correspond to the the structure of the substance. The small amount of water is evident in the far left, small peak to the left of the 3000 mark. The alkene, Csp2-H (present at 3013) and alkane Csp3-H (present at 2923) are also evident in the spectrum leading to the conclusion of cyclohexene as the product. The lab's results indicate that only through an elimination of alcohol on cyclohexanol could result in cyclohexene.


 * __Conclusion:__**

An elimination, E1 reaction was anticipated due to the heat and strong acid (weak base). The dehydration of cyclohexanol to cyclohexene was confirmed by Infrared spectrosopy and is seen in the data section chart. The alkene peak was clear on the spectrum (cyclohexene) and the alcohol (cyclohexanol) was not evident on the spectrum also leading to the conclusion that an elimination reaction had occurred.

The yield of the product is an important consideration, especially when completing this reaction in an industrial setting in which efficiency and quantity of the production of cyclohexene affects the cost to profit ratio. It is known, through calculation of atom economy, that 82.01% of the mass is the maximum that can be recovered. In this experiment, the yield of the product was measured using percent yield and resulted in 60.08%. The yield seemed to be lower than desired which was a result of several factors. Possible sources of error could include that the thermometer may have touched the inside of the distillation tube, loss of product when using the separatory funnel as well as adding too much or not enough anhydrous sodium sulfate. The possible sources of error were found in the distillation process as well as in the washing of the product after distillation was complete. During distillation, it was likely that some of the cyclohexene remained in the pot and the heating of the pot did not occur for long enough to vaporize all of the desired product, resulting in a low percent yeild.The heat loss was reduced during reflux due to the aluminum foil wrapper. The reflux that occurred during the lab was observed when the reactants started to boil but was reduced with a small increase in temperature and an additional layer of aluminum foil wrapped around the fractionating column to reduce heat loss.

The peaks of importance on the spectrum are at wavenumbers 3013.62, 2923.72 the label on these numbers is "reciprocal centimeters," or "cm-1" which indicate the presence of a C,C double bond (alkene) and C,C single bonds (alkane), respectively. This matches the structural formula of cyclohexene in that it contains one double bond and five single bonds. There is an extra peak in the IR spectrum from this experiment, as compared to the spectrum from the IR database, which appears at wavenumbers between 2000 and 2500.This indicates an impurity in the sample that was collected, however it is unclear what may have cause this impurity. What can you say about the distillation temperatures? They can help you understand the purity, and identity, of your product also.


 * __Post lab question:__**

Atom Ecomony - conversion efficiency of a chemical process in terms of atoms involved. //Calculate % Atom Economy// __Molecular Mass of Desired Product__ X 100% Molecular Mass of ALL Reactants __82.14 g cyclohexene__ X 100% = **82.01 %** 100.156 g cyclohexanol Phosphoric acid is present as a catalyst which promotes the reaction but is not consumed in it.

http://www.google.com/imgres?imgurl=http://journeytoforever.org/biofuel_library/ethanol_manual/z-image/fig11-1.jpg&imgrefurl=http://journeytoforever.org/biofuel_library/ethanol_manual/manual11.html&h=436&w=300&sz=38&tbnid=DQBCH3rTtFyAkM:&tbnh=126&tbnw=87&prev=/images%3Fq%3Ddistillation%2Bapparatus&zoom=1&q=distillation+apparatus&usg=__DZ2vflg9VYqGulSSFgjNsFv5-Xo=&sa=X&ei=0n9wTZagNtKDtgeJmqCEDw&ved=0CCUQ9QEwBQ
 * Sources:**

http://msds.chem.ox.ac.uk/CY/cyclohexene.html