Title: Dehydration Of An Alcohol: Cyclohexene From Cyclohexanol
Objective:
To produce cyclohexene through the acid catalyzed elimination of water from cyclohexanol. To understand mechanism involved in the reaction. To learn the technique of distillation.
Introduction:
A secondary alcohol, such as cyclohexanol, undergoes dehydration by an E1 mechanism. The key intermediate in the mechanism is a cyclohexyl cation, which can undergo substitution as well as elimination. To prepare a cyclohexene (olefin) in good yield, it is necessary to suppress the substitution reaction. In this experiment, the substitution reaction is suppressed by: (1) the use of strong acids with anions that are relatively poor nucleophiles ; (2) a high reaction temperature,
…show more content…
Specifically, the side products are dicyclohexyl ether, polymer, mono and dicyclohexyl sulphate, and degradation products such as carbon, sulphur dioxide and carbon dioxide.
The dehydration of cyclohexanol is carried out in such a way that the product, cyclohexene, distils from the reaction mixture as it is formed, the distillation technique serves to remove the olefin from contact with the sulphuric acid before polymerization can set in and it also serves as a first stage in the eventual purification of the olefin. The products and side products fall three categories: (a) gases, composed of sulphur dioxide and carbon dioxide and carbon dioxide, (b) distillate, composed of cyclohexene, un-reacted cyclohexanol, water and traces of sulphurous acid; and (c) residue, composed of high-boiling or non-volatile substances such as dicyclohexyl ether, mono- and dicyclohexyl sulphate, polymer and
…show more content…
Experimental Procedure: 10.0 g of cyclohexanol and 2 mL of conc.(85%) phosphoric acid were placed in a 50 mL ST round bottomed flask and the two were mixed by swirling. Several carborundum porcelain or anthracite boiling chips (do not use marble chips) were added, the flask was clamped to a ring stand at Bunsen burner height, and a take-off distillation adapter was attached, a thermometer, a condenser, and a small receiving flask. The reaction mixture was heated so that it boils gently and distillate boiling in the range 85-90 ℃ was obtained. When the distillate was exhausted, the heat was increasing gradually. The same receiver was using; the distillate boiling was collected in the range of 90-100℃. The two liquid layers were tested in the receiving flask to see which the aqueous layer was. With the aid of a 9-in disposable pipette, the aqueous layer was drawn off and discarded the aqueous layer. The organic layer remaining in the receiving flask was dried by adding to it 0.1-0.2g of anhydrous magnesium
In a small reaction tube, the tetraphenylcyclopentadienone (0.110 g, 0.28 mmol) was added into the dimethyl acetylene dicarboxylate (0.1 mL) and nitrobenzene (1 mL) along with a boiling stick. The color of the mixed solution was purple. The solution was then heated to reflux until it turned into a tan color. After the color change has occurred, ethanol (3 mL) was stirred into the small reaction tube. After that, the small reaction tube was placed in an ice bath until the solid was formed at the bottom of the tube. Then, the solution with the precipitate was filtered through vacuum filtration and washed with ethanol. The precipitate then was dried and weighed. The final product was dimethyl tertraphenylpthalate (0.086 g, 0.172mmol, 61.42%).
Alcohol, which is the nucleophile, attacks the acid, H2SO4, which is the catalyst, forming oxonium. However, the oxonium leaves due to the positive charge on oxygen, which makes it unstable. A stable secondary carbocation is formed. The electrons from the conjugate base attack the proton, henceforth, forming an alkene. Through this attack, the regeneration of the catalyst is formed with the product, 4-methylcyclohexene, before it oxidizes with KMnO4. In simpler terms, protonation of oxygen and the elimination of H+ with formation of alkene occurs.
When the liquid level is above the calibration line on the pipette, remove the bulb quickly and put your thumb or index finger over the pipette. Carefully “roll” finger to the side and allow the liquid to drop until the meniscus is level with the mark. Then hold the pipette over the flask to receive the liquid and remove the finger. Allow the liquid to drain out.
Once the mixture had been completely dissolved, the solution was transferred to a separatory funnel. The solution was then extracted twice using 5.0 mL of 1 M
The product was recrystallized to purify it and the unknown filtrate and nucleophile was determined by taking the melting points and performing TLC. Nucleophilic substitution reactions have a nucleophile (electron pair donor) and an sp3 electrophile (electron pair acceptor) with an attached leaving group. This experiment was a Williamson ether synthesis usually SN2, with an alkoxide and an alkyl halide. Conditions are favored with a strong nucleophile, good leaving group, and a polar aprotic solvent.
The first procedure requires one 10mL volumetric pipette, one 50mL buret, two small beakers, one labeled “vinegar” and the other labeled “NaOH”, three 250mL Erlenmeyer flasks, labeled one, two and three, and one large beaker for waste collection. Collect 50mL of vinegar in the beaker labeled “vinegar” and record the brand and listed concentration of vinegar. Then collect about 60mL of NaOH in the beaker labeled “NaOH” and record its concentration.
Moisture is heavy, and thus it can change the results of the experiment, as we only want the weight of magnesium and the magnesium oxide.
The three butene products have been verified to elute in the following order: 1-butene, trans-2-butene, and cis-2-butene. Theory: The dehydration of 2-butanol, a secondary alcohol, progresses readily in the presence of a strong acid like concentrated sulfuric acid (H2SO4). The reaction is completed via the E1 mechanism. Initially, the hydroxyl group is a poor leaving group, but that is remedied by its protonation by the acid catalyst (H2SO4) converting it to a better leaving group, H2O. The loss of this water molecule results in a secondary carbocation intermediate that continues to form an alkene in an E1 elimination.
Variables --------- During the experiments, the water will be heated using different spirit burners containing different alcohols. I will be able to change different parts of the experiment. These are the. Volume of water heated:
Plan 1. Collect 4 different sized beakers 2. Boil some water in the kettle 3. Pour 50ml into each beaker 4. After 1 minute check temperature 5.
2. In the large beaker, put water and boil it completely. After that, remove the beaker from heat. 3. Sample tubes (A-D) should be labeled and capped tightly.
The experiment required that a 250 mL beaker be filled with 75-85 mL of distilled water. Then between 25-30 grams of borax was weighed out using the electric analytical balance and added into the beaker of distilled water. To ensure that all of the borax was transferred from the weigh boat, it was washed with distilled water a few times and also added into the beaker. The beaker was place on to the hot plate and the stir bar was put inside the beaker. The thermometer was then place into the beaker close to its side; making sure it was not touching the bottom. The stirrer was turned on low and the borax was allowed to dissolve and reach saturation. After about five minutes, the stirrer was turned off to allow the solid to settle at the bottom of the beaker. The temperature of the borax solution was then recorded. A glass rod was used to carefully pour 5-7 mL of the solution from the beaker into a dry, clean 10mL graduated cylinder. The volume of the aliquot was recorded then poured into a 125 mL Erlenmeyer flask. To make sure all of the solution was successfully ...
The first step taken within the experiment was to obtain and label three 400 mL beakers with the numbers 1 through 3 using a wax pencil. Once labeled, each beaker needed to be filled with a corresponding solution. The beaker marked with a “1” was filled with 200 mL of distilled water and