Alkene Fron an Alcohol: Cyclohexene Synthesis from Cyclohexanol

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Cyclohexene Synthesis by Dehydration Reaction of Cyclohexanol Gjulia Vokrri 02-15-2013

Alkenes can be produced by heating and dehydrating an alcohol in the presence of a strong acid. The purpose of this experiment was to synthesize cyclohexene by dehydration of cyclohexanol and to detect the presence of a double bond in the alkene. The dehydration reaction using distillation was performed using two acid catalysts, 85% phosphoric acid and sulfuric acid. Tests for unsaturation were performed adding drops of bromine in tetrachloride and potassium permanganate to four test tubes, two containing 5 drops of cyclohexanol(control), and two containing cyclohexene(prepared product. 3 drops of bromine solution changed the product from red to clear within in 5 seconds. The control remained red after 5 drops of bromine were added. Likewise, 3 drops of potassium permanganate changed the product from purple to brown within 3 seconds. The control remained purple after 5 drops were added. These positive results both theoretically and experimentally confirmed the presence of a double bond by comparing the control and the product to their changes or lack of changes in color.

Alkenes are unsaturated hydrocarbons that contain at least one double bond (Brown et al. 2012). The presence of the double bond allows alkenes to react in a variety of ways. Economically they are very important (Thornley 2011). They are used in the petrochemical industry to refine and process petroleum, which are many of the fuels used in airplanes and cars and machinery. They can polymerize to form polymers, which form many different types of plastics such as rigid water pipes, plastic bottles, elastic rubber, and many household items. One way to synthesize an alkene is to perform an alcohol dehydration reaction using acid catalysts. The goal of this experiment was to synthesize cyclohexene by distillation and dehydration of cyclohexanol using strong acid catalysts, sulfuric and phosphoric acid(Figure1). In a dehydration reaction, the compounds with large differences in boiling points, cyclohexanol ( BP 161C) and cyclohexene(BP 83C) , are able to be distilled using a simple distillation apparatus and heating mantle(Pavia et al. 2011).The alkene product vapors condense through a water cooled condenser and are collected into a receiving flask semi-submerged in an ice bath.

Table 1
CompoundsC6H12O(l)85% H3PO4(l)H2SO4(l)C6H10(l)H2O(l)
Mol Weight101g/mol98g/mol98g/mol82g/mol18g/mol
V used (mL)7.502.000.40
Boiling Point161 C83 C100 C

Apparatus Assembly
7.5mL of cyclohexanol was measured in a tared 50-mL round-bottom flask and reweighed to determine weight of alcohol. 2.0mL of 85% phosphoric acid and 30 drops (0.40mL) concentrated sulfuric acid were added to the flask. Liquids were mixed thoroughly with a glass stirring rod. Simple distillation apparatus assembled, omitting condenser . Heating mantle was used as source of heat.

Dehydration took place for approximately 30 minutes while rate of distillation was approximately 1 drop per 2 seconds. Distillation apparatus was turned off after rate of distillation dramatically decreased , approximately 30 minutes. Distillate was allowed to cool to room temperature. Isolation and Drying of Product

Distillate transferred to centrifuge tube via help of 2mL sodium chloride solution. Layers allowed to separate. Bottom aqueous layer was removed with Pasteur pipet. Second dry Pasteur pipet was used to transfer organic layer to 125mL Erlenmeyer flask. Approximately 2.0 g anhydrous sodium sulfate was put in flask. Stopper was placed on the flask and set aside for 15 minutes for drying. Unsaturation Tests

Approximately 5 drops of cyclohexanol was placed in two test tubes. In two separate...
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