Exp 6 - Dehydration Of Cyclohexanol 5p5i2

OBJECTIVES: This experiment aims to: - Produce cyclohexene through the acid catalyzed elimination of water from cyclohexanol - Successfully use the distillation process for the dehydration of cyclohexanol - Understand mechanism involved in the reaction - Successfully distill the cyclohexene as soon as it forms to prevent the reverting back to alcohol INTRODUCTION: The dehydration of an alcohol is one way to synthesize alkenes. In the dehydration of cyclohexanol using phosphoric acid as a catalyst, cyclohexene, an alkene molecule highly useful in the synthesis of other organic molecules, is produced. This dehydration process is considered an elimination reaction, when a base attacks the proton on the adjacent carbon atom of a carbocation to form an alkene. Elimination reaction is further promoted by heating which allows the reaction to move to an E 1 mechanism. On the other hand, the substitution reaction occurs when a nucleophile attacks the carbocation. This reaction is used in the substitution of alcohols and is favored with the use of weakly basic nucleophiles. For this experiment, we will be using the elimination reaction since the reaction medium is acidic. PRELAB QUESTIONS: 1. What are the possible side products in the dehydration of cyclohexanol? How is the formation of these side products minimized/prevented?  The dehydration of cyclohexanol can form the following side products: dicyclohexyl ethers, polymers, mono and dicyclohexyl sulfate. These side products can be prevented from forming once the cyclohexene is protonated with an acid. The distillation process also removes the alkene from with the sulfuric acid, thus acting as the first stage of purification of the alkene. 2. How is the yield of the reaction maximized? Explain.  The maximization of the yield is done through the removal of the resulting alkene as soon as it is formed. This is done to prevent the alkene from reverting back to its alcohol form. Distillation aids in this process since alkenes have lower boiling points than alcohols or water. It is also possible to get a good yield if the substitution reaction is suppressed. This is done through the use of strong acids, a high reaction temperature that favors elimination, and distillation of cyclohexene from reaction mixture as it is formed. 3. What is the use of phosphoric acid? Can it be substituted with other acids such as sulfuric acid or hydrochloric acid? Explain.  Phosphoric acid acts as the catalyst in the E1 dehydration of cyclohexanol. It protonates the alkene and forms a carbocation which will be attacked by water in order to form an alcohol. Other strong acids may also be used but phosphoric acid, since it is an oxidizing agent, os preferred because it minimizes the loss of the organic compound and the product is not contaminated with volatile decomposition products. 4. What steps are undertaken to prevent cyclohexene from reverting back to cyclohexanol? How do these steps prevent reversal from taking place?  The removal of the cyclohexene as soon as it forms prevents the reverting back to cyclohexanol. This removal displaces the reaction to the right (Le Chatelier’s principle) (Pahlavan, n.d.). 5. What are the qualitative tests to the presence of cyclohexene and cyclohexanol? What constitutes a positive test result?  The presence of cyclohexene can be determined through a solubility test, an ignition test, and a Baeyer test. The Baeyer test must form a reddishbrown precipitate to confirm the presence of cyclohexene. Meanwhile a solubility test, a Lucas test, and a Chromic Acid test can be done to

determine the presence of cyclohexanol. The Lucas test must have the formation of a second phase while the Chromic Acid test must form a bluegreen precipitate.

REAGENTS: REAGENTS Cyclohexanol (IUPAC) [C6H12O]

PHYSICAL AND CHEMICAL PROPERTIES Molecular Weight: 100.161 g/mol Boiling Point: 161.84oC Melting Point: 25.93oC Density: 0.96 g/cm3 Solubility: 42,000 mg/L (10oC) in water Appearance: Colorless needles or viscous liquid with a camphorlike odor

Phosphoric Acid (IUPAC) [H3O4P]

Molecular Weight: 97.994 g/mol Boiling Point: 407oC Melting Point: 42.4oC Density: 1.6850 g/cm3 Solubility: Miscible in water Appearance: Thick, colorless, odorless, crystalline solid

Sodium Hydroxide (IUPAC) [NaOH]

Molecular Weight: 39.997 g/mol Boiling Point: 1388oC Melting Point: 323oC Density: 2.13 g/cm3 Solubility: 109 g/100mL (20oC) in water Appearance: Colorless to white solid, colorless liquid, odorless

Sodium Chloride (IUPAC) [ClNa]

Molecular Weight: 58.44 g/mol Boiling Point: 1465oC Melting Point: 800.7oC Density: 2.17 g/cm3 Solubility: 36.0 g/100g (25oC) of water Appearance: Colorless to white crystalline solid, salty taste

SAFETY PRECAUTIONS Has caused adverse reproductive and fetal effects in animals Potential cancer hazard Skin and eye irritant: flush with water for at least 15 mins. then get medical assistance Ingestion (hazardous): do not induce vomiting unless instructed by medical personnel Inhalation (hazardous): to fresh air, give oxygen, seek medical assistance Combustible Skin and eye irritant: flush with water if Serious skin : Wash with disinfectant soap and cover contaminated skin with antibacterial cream. Seek medical aid Ingestion (hazardous): do not induce vomiting unless instructed by medical personnel Inhalation (hazardous): remove to fresh air, give oxygen, seek medical assistance Skin and eye irritant: flush with water if Serious skin (very hazardous): Wash with disinfectant soap and cover contaminated skin with antibacterial cream. Seek medical aid Ingestion: do not induce vomiting unless instructed by medical personnel Inhalation: remove to fresh air, give oxygen, seek medical assistance Corrosive – causes 3rd degree burn Skin and eye irritant: flush with water if Serious skin : Wash with disinfectant soap and cover contaminated skin with antibacterial cream. Seek medical aid Ingestion: do not induce vomiting unless instructed by medical personnel Inhalation: remove to fresh air, give oxygen, seek medical

Disodium Sulfate (IUPAC) [Na2SO4]

Molecular Weight: 142.04 g/mol Melting Point: 888oC Density: 2.67 g/cm3 Appearance: White powder or orthorhombic bipyramidal crystals, odorless, bitter saline taste

assistance Skin and eye irritant (hazardous): flush with water if Serious skin : Wash with disinfectant soap and cover contaminated skin with antibacterial cream. Seek medical aid Ingestion: do not induce vomiting unless instructed by medical personnel Inhalation: remove to fresh air, give oxygen, seek medical assistance

REFERENCES: Guidote AM, del Rosario DR, Abuzo AL. Experiencing Organic Chemistry. Quezon City: Office of Research and  Publications, Ateneo de Manila University; 2005. [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2004 September 16 [updated 2017 March 11; cited 2017 March 12]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/cyclohexanol  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9923625  [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2004 September 16 [updated 2017 March 11; cited 2017 March 12]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/phosphoric_acid  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9927393  [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2005 March 26 [updated 2017 March 11; cited 2017 March 12]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/sodium_hydroxide  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9924998  [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2005 March 25 [updated 2017 March 11 cited 2017 March 12]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/sodium_chloride  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9927593  [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2004 September 16 [updated 2017 March 11; cited 2017 March 12]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/sodium_sulfate  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 12]. Available from: http://www.sciencelab.com/msds.php?msdsId=9927278  Pahlavan. Chem2423 Cyclohexene Synthesis. [Unknown Publication]; [Unknown Publication Date] [cited 2017 March  12]. Available from: http://swc2.hccs.edu/pahlavan/2423L9.pdf  -

PROCEDURES:  Set up simple distillation apparatus. Cover receiving flask with aluminum foil and immerse flask in ice-water bath.

Place 8g of cyclohexanol, 2mL phosphoric acid, and boiling chips into RBF. Heat mixture and maintain temperature between 85-95oC. Distill until 2-3mL is left in RBF.

Pour distillate into separatory funnel and wash it with 5mL of 3 M NaOH saturated with NaCl.

Continue washing organic layer until aqueous layer is basic then discard aqueous layers. Decant organic layer into Erlenmeyer flask and dry it over sodium sulfate.

Clean distillation setup with acetone and let dry. Distill organic layer at a temp. not more than 5oC above boiling point of cyclohexene.

Perform qualitative tests and store product in scintillating vial.

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Cyclohexane is very flammable. Keep away from direct heat. Evaporates easily, diffuses through cork and dissolves in rubber. Store in tightly covered screw-cap vials and keep refrigerated.