Synthesis Of Cyclohexene In Chemistry And Organic Matter PDF

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Course was instructed by Dr. Rajani Srinivasan at Tarleton State University for a 6 week summer course....

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Synthesis of cyclohexene by Isabella Manlapaz [email protected] CHEM 2423 Section 520 Experiment 7 June 20, 2018 Executive Summary The purpose of this experiment is to generate cyclohexene from the acid catalyzed dehydration of cyclohexanol. Dehydration reactions are a type of elimination reaction in which water is eliminated from an alcohol. In an E1 reaction mechanism, the source of the proton comes from H3PO4. The alkene is then distilled off during the course of the reaction shifting equilibrium to the product side.

Introduction During an E1 reaction, alcohols undergo dehydration to form an alkene when heated with a strong acid. The acid-catalyzed dehydration of an alcohol is an important method for the preparation of an alkene. It is also an example of an elimination reaction, which proceeds by a first order mechanism via an intermediate carbocation. In this experiment, cyclohexanol is dehydrated to cyclohexene in the presence of phosphoric acid: Distillation is employed in this experiment to synthesize and purify cyclohexene.

Name

M.W.

M.P.

B.P.

Density

Cyclohexanol

100.158 g/mol 25.4℃

161.8℃

0.962 g/mL

Phosphoric Acid

97.995 g/mol

42.4℃

407℃

1.685 g/mL

Sulfuric Acid

98.072 g/mol

10℃

337℃

1.84 g/mL

Calcium Chloride

110.98 g/mol

773℃

1,670℃

2.20 g/cm3

Cyclohexene

82.143 g/mol

-104℃

83℃

0.81 g/mL

Chemicals to be used:

Procedure  In a 10 mL round-bottom flask, weight out 3 mL of cyclohexanol.

Structure

 Add 4 mL of 85% H3PO4 and 5 drops of concentrated H2SO4 while swirling the solution.  Attach flask distillation head, thermometer/adapter, condenser, vacuum adapter, and receiving flask.  Turn on the heating mantle, distill the reaction mixture, and collect the distillate until no more liquid distills or the temperature rises above 85℃.  Remove receiving flasks and transfer distillate to centrifuge tube.  As the temperature cools, two layers should form. Using a Pasteur pipette, remove the bottom layer and place in a container labeled “Recovered Acid Layer.”  Dry the top organic layer by adding anhydrous CaCl2.  With a Pasteur pipette, remove the liquid and transfer to a tarred flask.  Weight and determine the percent yield of the product. Following the synthesis of cyclohexene from cyclohexanol, you should determine whether the product cyclohexene was or was not formed during the procedure.  Take 5-6 drops of the product formed in a small test tube.  Add 1-2 drops of potassium permanganate (KMnO4) to the product.  Solution turns colorless  Take 5-6 drops of the starting product.  Add 1-2 drops of potassium permanganate (KMnO4) to the starting product.  Solution retains the color

Table of Observation: Calculation

Cyclohexanol

H3PO4 (85%)

Cyclohexene

Molecular weight

100.158 g/mol

97.995 g/mol

82.143 g/mol

(g/mol) Amount in mL Amount in (g) Density (g/mL) Moles

3 mL 2.89 g 0.9624 g/mL 0.028 moles

4 mL 6.74 g 1.685 g/mL 0.068 moles

-0.709 g 0.81 g/mL --

% yield = mass of product (experimental)/theoretical yield of product in (g) x100 0.709 g of cyclohexene/2.30 g of cyclohexanol x100 = 30.8% recovery

E1 Mechanism is shown below:

Reference Mohrig, J. R. Laboratory Techniques in Organic Chemistry: Supporting inquiry-driven experiments; W.H. Freeman and Company: New York, 2014 https://pubchem.ncbi.nlm.nih.gov/

https://www.sigmaaldrich.com/united-states.html

Post-lab questions: 1. What would be the major product obtained from the E1 dehydration of 2methylcyclohexanol?

The major product obtained from the E1 dehydration of 2-methylcyclohexanol would be 1methylcyclohex-2-ene.

2. Outline a mechanism for the dehydration of 1-methylcyclohexanol. Would it be faster or slower than the reaction you performed?

1-methylcyclohexanol undergoes a faster dehydration due to the formation of a stable tertiary carbocation. Whereas in the dehydration of 2-methylcyclohexanol, a secondary carbocation is produced and is therefore less stable.

3. The product decolorizes Br2 in CH2Cl2. What product is being formed as a result of the reaction of bromine with your product?...