Cyclohexene+from+cyclohexanol

=Preparation and Distillation of Cyclohexene=

=Introduction:= The purpose of this laboratory experiment is to conduct an elimination reaction (E1), which involves synthesis of cyclohexene by an alcohol dehydration or distillation reaction of cyclohexene (cyclohexanol). This process is more of a greener reaction, focusing on the use of milder less corrosive Phosphoric Acid (85%) H3PO4 ,instead of the more corrosive Sulfuric Acid which has been know to cause problematic side reactions when used as a catalyst during this experiment. __Elimination (E1) Reaction__ Step one- the phosphoric acid donates a Hydrogen to the Hydroxyl on the Cyclohexanol, this then creates a H20 which is a good leaving group, the water then leaves the Cyclohexane to create a Cyclohexane carbocation. Step two- The H20 acts as a base stripping a proton from the Beta-Hydrogen making it possible for the electron to form a Pi bond making the Cyclohexane to become Cyclohexene and H20, refer to figure below.



=Procedure:= Procedure provided by Professor Carol Higginbotham, link provided: [|__http://greenchem.uoregon.edu/Pages/Overview.php?CategoryIDString=&FullTextSearchKeywords=cyclohexene&CategoriesToSearch=&NumberOfMainCategories=7&AnyAll=Any&ID=70__]

Picture below taken of Apparatus of dehydration of cyclohexanol ==

=Data:= Calculations: 1.75 mL of 85% H3PO4 at 98.00 g/mol, and 1.685 g/ml. 0.074 moles of cyclohexanol converted to grams for procedure molar mass of C6H12O=100 g/mol 0.074 moles C6H12O*(100 g/mol **/** 1 mol C6H12O)= 7.41 g C6H12O Calculation okay but watch sig figs! You've only got TWO.





The atom economy calculations for the reaction above. Molecular weight of products: Cyclohexene = 82.158 g/mol x 0.074 mol = 6.079 g Molecular weight of reactants: Cyclohexanol = 100.158 g/mol x 0.074 mol =7.411 g 6.079 g / 7.411 g = 82% Economy Theoretical yield Calculation OK. Experimental yield: 3.941g recovered product. 3.941g/6.079g = 65% actual yield calculated OK Analysis: The vapor from distillation reached the top of the column after 32min of heating. The temperature readings jumped to 77°C and slowly dropped to 68°C throughout the distillations progress. The time from first drop of condensate collected to finish was 14 minutes. The distillate was clear with no visible impurities in the flask. After transferring the product to the separatory funnel and washing with 5 mL of water the product formed a clear layer on top and was easily separated from the water. The product was very strong in odor and the slightest exposure to the room air filled the entire laboratory with its pungent smell. Identifying the purity of the starting cyclohexene could be identified by monitoring the distillation temperature. By observing and refering to the temperature graph you can identrify the distillation being between 77°C and 68°C aaccording to the text book information Cyclohexene boiling point is 82.98°C therefore we can clarify that the distilled cyclohexene was not pure and contained impurities and the range of boiling point was much wider than expected. It's a bit odd that your temps went down during the distillation. I think if you had distilled more slowly (difficult to do when this is the first time, we're just getting a feel for how the equipment works, and the lab time is limited) you would have seen temperatures more in line with the expected temps, and a slow but gradual increase in temp as the distillation occurred. IR Spectroscopy: The first strong transmittance is at 3021.99 and is indication of the presence of water in the sample. Nope! This is the C-H stretch on the alkene! Alcohol is a big swoop, deep and wide. The next transmittance (Trans) is at 2927.64. This is the largest peak and is indication of the aromatic benzene ring structure stretching the carbon hydrogen bonds. No; at wavenumbers below 3000 we are not seeing this. 2927 is the C-H stretch on sp3 hybridized carbons. Besides, cyclohexene is not aromatic. The two smaller Trans indications at 2856.67 and 2837.34 are also the carbon hydrogen bond stretch. Only these two points are more indicative of a hydrogen stretch with a carbon involved in a double bond. The peaks at 2350.64 and 2340.86 show the presence of sulfur that was used as the drying agent. The indication at 1448.79 is that of the carbon to carbon double bond in the hexene ring. The several smaller peaks around 1067.79 are the carbon to hydrogen bond stretches of the equatorial H orbital’s involved in the benzene ring. Conclusion: The experiment performed was a dehydration of cyclohexanol to cyclohexene using an acid. The acid for this experiment was phosphoric acid H3PO4. H3PO4 is a strong acid and easily donates a proton to the alcohol group of cycloexanol thus converting it into an excellent leaving group and creating cycloexene and H2O in the reaction. The percentage yield was reasonable at 65% for a theoretical reaction economy of only 82%. The decent percentage indicates few operator errors. IR analysis of the final product is strong evidence that the products that were intended for the reaction were indeed formed, and also the results show the purity of the product with probable identities of the contaminates. The errors for this experiment mostly involved the measurement of reactants and the transfer of products to different containers for analysis and weighing. Some containers could have not been properly cleaned before use and moisture from the previous lab group is always a factor. Also blow drying the wet glassware by using the compressed air ports in the lab could also have introduced foreign materials into the experiment. There are some misunderstandings of the infrared data. The reaction appears to have gone well, but your explanation of how you know this is, unfortunately, flawed.

=Post-lab Questions:= 1) Calculate the atom economy of the reaction-mass of a desired product / by the mass of the reactants not including the solvents or the catalyst of the reaction. The particular reason to calculate atom economy can benefit in the aspect of a green reaction utilizing all the products and not bypassing the products in a chemical reaction.

2)Infrared Spectrum - First strong transmittance 3021.99-Water, 2927.64-aromatic benzene ring structure stretching the carbon hydrogen bonds. The two smaller Trans indications at 2856.67 and 2837.34 are also the carbon hydrogen bond stretch. Only these two points are more indicative of a hydrogen stretch with a carbon involved in a double bond. The peaks at 2350.64 and 2340.86 show the presence of sulfur that was used as the drying agent. The indication at 1448.79 is that of the carbon to carbon double bond in the hexene ring. The several smaller peaks around 1067.79 are the carbon to hydrogen bond stretches of the equatorial H orbital’s involved in the benzene ring.

=Reference:= Doxsee, K. M. ;Hutchison, J.E. Green Organic Chemistry-Strategies, Tools, and Laboratory Experiments, Print 2004; pp 129-134 Provided by Professor Carol Higginbotham Central Oregon Community College CH-242/335 Organic Chemistry II Winter Term 2012.