Lab+4+-+Preparation+of+Cyclohexene

Preparation of Cyclohexene __**﻿**__

__Introduction __

The dehydration of cyclohexanol via acid catalyst to create cyclohexene is a classic Organic Chemistry lab to observe the effects of elimination. It has traditionally been done with H 2 SO 4 . The greener (and safer) alternative uses H 3 PO 4 . Since no additional solvent is needed after the dehydration, this lab promotes the green concept of atom economy.



The reaction has multiple phases, aside from the inherent two-step elimination reaction that occurs. First, an acid-base reaction occurs which destabilizes the OH group to give it the energy needed to fall off by itself, leaving a carbocation. Since the strong acid becomes a weak base, it will not have the strength needed to rip off a beta hydrogen alone, implying an E1 elimination to form the cyclohexene. The byproduct of water, and not some other substance that is difficult to deal with, makes this reaction even more favorable for a safe and controlled laboratory setting. although, because the reaction is reversible, we have to get the water out of there in order to cause efficient conversion of reactant to products.

Nice introduction.

__Procedure __

The procedure for this experiment can be found at University of Oregon's Greener Education Materials for Chemists.

Chemicals used in the lab:


 * Name: Phosphoric Acid
 * <span style="font-family: Verdana,Geneva,sans-serif;">IUPAC Name: Phosphoric Acid
 * <span style="font-family: Verdana,Geneva,sans-serif;">Molecular Formula:H <span style="font-family: Verdana,Geneva,sans-serif; font-size: 80%; vertical-align: sub;">3 <span style="font-family: Verdana,Geneva,sans-serif;">PO <span style="font-family: Verdana,Geneva,sans-serif; font-size: 80%; vertical-align: sub;">4
 * <span style="font-family: Verdana,Geneva,sans-serif;">Structure:
 * [[image:160px-Phosphoric-acid-2D-dimensions.png width="166" height="104"]]


 * <span style="font-family: Verdana,Geneva,sans-serif;">Name: Cyclohexanol
 * <span style="font-family: Verdana,Geneva,sans-serif;">IUPAC Name: Cyclohexanol
 * <span style="font-family: Verdana,Geneva,sans-serif;">Molecular Formula:C <span style="font-family: Verdana,Geneva,sans-serif; font-size: 80%; vertical-align: sub;">6 <span style="font-family: Verdana,Geneva,sans-serif;">H <span style="font-family: Verdana,Geneva,sans-serif; font-size: 80%; vertical-align: sub;">12 <span style="font-family: Verdana,Geneva,sans-serif;">O
 * <span style="font-family: Verdana,Geneva,sans-serif;">Structure:
 * [[image:90px-Cyclohexanol.svg.png width="70" height="129"]]

__<span style="font-family: Verdana,Geneva,sans-serif; font-size: 20px;">Data __ <span style="font-family: Verdana,Geneva,sans-serif; line-height: 0px; overflow: hidden;">
 * <span style="font-family: Verdana,Geneva,sans-serif;">Reagents
 * <span style="font-family: Arial,Helvetica,sans-serif;">Cyclohexanol: liquid, clear and viscous, mass 7.466g
 * <span style="font-family: Arial,Helvetica,sans-serif;">H <span style="font-family: Verdana,Geneva,sans-serif; font-size: 80%; vertical-align: sub;">3 <span style="font-family: Arial,Helvetica,sans-serif;">PO <span style="font-family: Verdana,Geneva,sans-serif; font-size: 80%; vertical-align: sub;">4 <span style="font-family: Arial,Helvetica,sans-serif;">: liquid, clear and viscous, volume ≈10mL
 * <span style="font-family: Arial,Helvetica,sans-serif;">Products
 * <span style="font-family: Arial,Helvetica,sans-serif;">Cyclohexene: Clear, with a very distinct odor
 * <span style="font-family: Arial,Helvetica,sans-serif;">Water: Clear, odorless


 * <span style="font-family: Arial,Helvetica,sans-serif;">Observations
 * The distillation process began with the round bottom flask (rbf) situated in the sand bath (sans sand) we call those things "Thermowells." and the voltage output set at 20%. After about 10 minutes of heating the voltage output was set to 40% which worked well for the remainder of the reaction. The solution began to distill after about 20 minutes, vapor was clearly present and moving up the condensing tube. After distillation was complete the product solution was transferred into a separatory funnel and 5 mL of water was added to wash the solution. The bottom layer was taken off (water and impurities) and the final product was then poured out of the funnel into a pre-weighed vial.

Wow these look funny when you include all the room temperature readings up to the point of distillation. This graph makes quite an impression! If you use a graph in your report, I'd also like to get tables of the data. The graph alone contains less precise information than the tables, so as the reader gets curious about particular points (as I am right now) they are frustrated because they can't look up the exact temps.
 * <span style="font-family: Verdana,Geneva,sans-serif;">Below shows the temperature graph for the distillation
 * The infrared spectroscopy can be seen below along with a table of peak findings





__<span style="font-family: Verdana,Geneva,sans-serif; font-size: 20px;">Analysis __
 * Distillation Analysis:
 * The temperature peaked at near 80°C, which is very close to the listed boiling point of cyclohexene (83°C), and far below the listed boiling point of cyclohexanol (161°C), implying that the recovered product was primarily the desired product. What was the temperature when you began to see liquid distilling over?
 * IR Analysis:
 * Out of all of the peaks, there are only two that are important: be at . typo here The Peak at 2917.08 shows an sp 3 Carbon-Hydrogen bond, but that bond is found in most organic molecules. The peak at 3013.06, however, implies an sp 2 Carbon-Hydrogen bond, which is the biggest clue and the biggest difference, besides the lack of a broad Oxygen-Hydrogen bond signature in the 3200-3600 region, between the product and main reagent.
 * This, along with the distillation data, gives strong evidence that the recovered product is in fact, cyclohexene.


 * Name:Cyclohexene
 * <span style="font-family: Verdana,Geneva,sans-serif;">IUPAC Name:Cyclohexene
 * <span style="font-family: Verdana,Geneva,sans-serif;">CAS #: 110-83-8
 * <span style="font-family: Verdana,Geneva,sans-serif;">Molecular Formula:C <span style="font-family: Verdana,Geneva,sans-serif; font-size: 10px; vertical-align: sub;">6 <span style="font-family: Verdana,Geneva,sans-serif;">H <span style="font-family: Verdana,Geneva,sans-serif; font-size: 10px; vertical-align: sub;">10
 * <span style="font-family: Verdana,Geneva,sans-serif;">Structure:
 * [[image:240px-Cyclohexene.png height="99"]]

beautiful.

__<span style="font-family: Verdana,Geneva,sans-serif; font-size: 20px;">﻿Conclusion/Discussion __

Since the product recovered showed minimal signs of O-H bonding via IR spectroscopy, as well as the sp 2 -C bond present in cyclohexene, it can be concluded that the lab was successful in producing a significant quantity of the desired product. The purity of the recovered product was still reasonably high. It can be concluded that the reaction proceeded as predicted. The purity could have been increased even further with a second distillation that was not performed, which could have removed any other impurities such as leftover cyclohexanol or new random formations such as dicyclohexyl. What is the boiling point of this stuff? Would it be possible/reasonable to imagine it distilling over with your cyclohexene?

While the final product was identified as the desired one, the yield could have been greater. There were a few sources that could have led to a less-than-optimal harvest. The distillation could have been ended a bit prematurely, and by that not gleaning the maximum amount of distillate from the original container. <span style="font-family: Arial,Helvetica,sans-serif; letter-spacing: 0px;">The final product yield may have also been affected to by the precision of the toggling of separatory funnel's valve.

This lab gave a hands-on exposure to the concept of E1 elimination reactions, which are a fundamental part of understanding the substitution/elimination dynamic. The lab also did all of this, without forcing the participants to have to deal with the highly corrosive H<span style="font-family: Verdana,Geneva,sans-serif; font-size: 80%; vertical-align: sub;">2 SO<span style="font-family: Verdana,Geneva,sans-serif; font-size: 80%; vertical-align: sub;">4, and the extra complications that it brings, and thus goes along with the tenants of Green Chemistry. The reaction is clean, safe, and produces minimum waste.

__ POST LAB QUESTION __

<span style="font-family: Arial,Helvetica,sans-serif;">**Q:** Calculate the atom economy for this reaction. Atom economy is defined on Wikipedia, but essentially is the mass of the desired product divided by the mass of all reactants (don’t include catalysts or solvents in our reaction).


 * A:** Atom Economy = (82.143g ÷ 100.154) × 100 = 82.017%

__<span style="font-family: Verdana,Geneva,sans-serif; font-size: 20px;">Notes __

The chemical structures, formulas, and vital statistics of each compound was researched using [|Wolfram Alpha computational knowledge engine] and confirmed using the [|CRC Handbook of Chemistry and Physics [90th Edition.]]

This lab earned a 13.5/14. Lost 0.5 for the data section, see comments for details.