8. Using Dehydration Reaction to Convert an Alcohol to an Alkene PDF

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lab report 8...

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Using Dehydration Reaction to Convert an Alcohol to an Alkene

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_____________________________ Purpose: The goal of this experiment is to gain chemical knowledge of dehydration reactions through the creation of cyclohexene from cyclohexanol. Chemical Structures/Reactions:

Calculations:

Results  

Isolated product: Cyclohexene Appearance: colorless, clear liquid

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Mass of flask: 30.2956 grams Mass of flask & product: 31.0325 grams Amount of product obtained: .7369 grams Measured boiling point: 80-82°C Percent yield: 9.3% Bromine test results: When bromine was dropped into our distilled cyclohexene, the yellow bromine gas immediately turned clear. This is different from the bromine test results for cyclohexanol—the bromine gas did not change color and remained yellow.

IR spectrum data

Bond

Characteristic Functional Group/Bond Frequencies

Actual Frequency (cm-1), transmittance (%)

Cyclohexanol

O-H stretch C-O stretch -C-H stretch

3400-3350 1240-1080 2950-2880

3325.67, 80.84% 1064.80, 42.68% 2928.52, 2854.04 46.42%, 60.03%

Cyclohexene

=C-H stretch C=C stretch

3080-3010 1600-1680

3022.31, 85.75% 1652.69, 95.44%

Discussion Questions 1) Our percent yield was 9.3%, which is low. The low percent yield may have been caused by us not running the distillation long enough therefore not being able to get all the products that we wanted. 2)

3) The accepted boiling point range for cyclohexene is 83-85°C. The range that we found experimentally was 80-83°C. Our product’s boiling point range differed from the known boiling point range by ~ 1°C which indicates that our sample was not completely pure. This may have been caused by human error in distilling the solution.

4) The IR spectrum of the cyclohexanol and the cyclohexane is very similar to each other. However, since the cyclohexanol has an additional O-H group, there was an additional OH stretch peak at 3325.67 cm-1 that showed up in the IR spectrum. Also, in the cyclohexene, there is an alkene bond stretch peak at 1652.69 cm-1 that the cyclohexane IR spectrum does not have. 5) When bromine was dropped into our distilled cyclohexene, the yellow bromine gas immediately turned clear. This is different from the bromine test results for cyclohexanol —the bromine gas did not change color and remained yellow. These results suggest that our distilled product had more cyclohexene present than impurities. Since the bromine turned clear once added to the product, it shows that there is an alkene in the product. Conclusion: From this experiment we obtained a 9.3% percentage yield of cyclohexene that appeared as a colorless clear liquid, had a boiling range of 80-82°C, and bromine that turned from yellow to clear when dropped into cyclohexene. The product’s IR spectrum had a =C-H- stretch at 30803010 and a C=C stretch at 1600-1680. Based on our experimental data from the bromine test, IR spectrum, and appearance, we believe that we obtained the expected outcome of the experiment which was to synthesize cyclohexene from cyclohexanol using a dehydration reaction. The boiling point range of our product differed from the actual boiling point range by ~1°C, which suggests that our product had some impurities. Some ways we can improve this experiment is to make sure to collect all possible products through distillation, make sure that the boiling point does not exceed 85 degrees Celsius, and make sure that the distillation setup is at the correct angle so that all the product that is being collected will be in the receiving flask....