The Green Oxidation of Cyclohexanol to Cyclohexanone - Lab Report Example

The Green Oxidation of Cyclohexanol to Cyclohexanone Summary: Cyclohexanone was synthesized from cyclohexanol usinga “green” reagent, sodium hypochlorite, as an oxidizing agent. In the first step, cyclohexanone was produced from cyclohexanol in a 34.82% yield using an oxidation reaction with sodium hypochlorite. In the second step, cyclohexanone was isolated from the cyclohexanone-water mixture in a salting out procedure using sodium chloride and ether. The extracted cyclohexanone had a refractive index (n20/D) of 1.467, which is close to the literature value of n20/D 1.450, indicating that the isolated cyclohexanone was of good purity. Introduction: KMnO4 and Cr (VI) compounds such as H2CrO4 have been widely used as oxidizing agents in the oxidation of alcohols to carbonyl compounds. However, each of these two reagents has its disadvantages, and chemists are increasingly using reagents containing chlorine in a positive oxidation state such as hypochlorite compounds. Sodium hypochlorite is the reagent chemists most commonly use for this purpose. Sodium hypochlorite has three crucial advantages over Cr (VI) compounds when used to oxidize cyclohexanol to cyclohexanone. Firstly, it has no hazardous waste products in contrast to Cr (VI) oxidations, which yield Cr (III) compounds, which are toxic to aquatic life. Secondly, sodium hypochlorite and its products have no skin or membrane irritation effects other than a negligible amount of chlorine gas, in contrast to Cr (VI) compounds, which are skin and membrane irritants. Thirdly, hypochlorite reagents are considerably cheaper than Cr (VI) compounds (Baird & Cann, 2008, p.67). Balanced equation Mechanism Figure 1: The oxidation of cyclohexanol to cyclohexanone by hypochlorite Experimental: A. Synthesis of Cyclohexanone 8 ml of cyclohexanol and 4 ml of glacial acetic acid were added to a 250 ml Erlenmeyer flask. A thermometer was placed into the flask and used to record the initial temperature. 115 ml of commercial bleach (NaOCl) was obtained in a beaker. The bleach was slowly added to the Erlenmeyer flask using a disposable pipette while slowly stirring the flask. The temperature was maintained between 40oC and 50o using an ice water bath large enough to hold the flask. After adding all the bleach, the mixture was allowed to sit for about 20 minutes. The mixture was continuously stirred during this period. The presence of the oxidizing agent was tested by adding a drop of the solution to a piece of starch-iodide paper. There was no color change indicating that hypochlorite was not present. 4 drops of thymol blue indicator were added to the reaction mixture. The solution turned yellow. 18.4 ml of 6 M sodium hydroxide was added to the reaction mixture until a neutral pH was obtained. This point was indicated by a color change to blue. A simple distillation apparatus was set up, with the receiving container being a 50 ml graduated cylinder. A 250 ml round-bottomed flask was used as the “still pot”. The mixture was distilled through steam distillation, and a mixture of cyclohexanone and water was obtained in a graduated cylinder. 40 ml of distillate was obtained. B. Isolation and Purification of Cyclohexanone The distillate mixture was placed in an Erlenmeyer flask. 6.8 g of NaCl was slowly added to the 34 ml aqueous layer with stirring in order to reduce the solubility of the cyclohexanone. This enabled it to be extracted completely using ether. The mixture was poured into a separatory funnel. Ether was added to the mixture until a 20 – 25 ml of organic layer was obtained. The separatory funnel was gently shaken with frequent venting. The aqueous and organic layers were left to separate. The aqueous layer was run off into a beaker labeled “aqueous waste”. The ether solution was poured from the separatory funnel into an Erlenmeyer flask. 3 M sodium hydroxide solution was added to the solution of ether, and the flask was gently shaken with frequent venting. The resulting aqueous layer was removed into the “aqueous waste” beaker. The ether solution was then poured out of the neck of the separatory funnel into a clean Erlenmeyer flask, and anhydrous sodium sulfate added to it to help in drying. The ether layer was decanted into a small weighed Erlenmeyer flask which was put in a water bath. All the ether was evaporated, and the flask with its contents was allowed to cool to room temperature. The product was weighed, and the percentage yield determined. C. Analysis and Characterization of Cyclohexanone The refractive index of cyclohexanone was measured at 24oC. Finally, an infrared spectrum of the product was taken. Results and Discussion: Refractive index of synthesized cyclohexanone was 1.467. The IR spectrum for cyclohexanone showed an intense absorption at 1703.8 cm-1. This compares to the literature values of the IR absorption range of the ketone group of cyclohexanone at 1715 cm-1. There was also an intense absorption at 2940.43 cm-1, corresponding to literature values of 3000 – 2800 cm-1 for cycloalkyl C – H bond. Sodium hydroxide was added to the reaction mixture to convert acetic acid to its anion so that it does not steam distil. Sodium chloride was added to the distillate so as to reduce the solubility of cyclohexanone which is fairly soluble in water. This made it possible to extract cyclohexanone completely using ether (Williamson, 1994, p.45) The amount of water in the collected distillate comprises 85% of the mixture. Therefore, volume of water in the distillate is: 40 ml X 0.85 = 34 ml of H2O The amount of NaCl required to salt out cyclohexanone from the mixture is: 34 ml X 0.2 g = 6.8g NaCl Weight of flask = 3.774 g Weight of flask + product = 37.9 g Weight of cyclohexanone = 37.9 g – 3.774 g = 34.126 Product percent yield = mass of actual yield/mass of theoretical yield X 100 Theoretical yield of product: C6H11OH + NaOCl C6H10O +H2O + NaCl R.M.M. of C2H10O = 12(6) + 10 + 16 = 98g Product percent yield = 34.126/98 X 100 = 34.82% Conclusion: Cyclohexanone was successfully synthesized from cyclohexanol using a hypochlorite ion as the oxidizing agent. The yield of synthesized cyclohexanone was fairly good, 78.4%. The refractive index of synthesized cyclohexanone, 1.467, only slightly differed from literature values, 1.450, indicating that it was fairly pure. The final product was obtained as a solid. The TLC showed that there was no complete conversion to the product, resulting in the partial yield obtained. Most of the unreacted cyclohexanol was not removed because its boiling point is slightly higher than that of cyclohexanone. Therefore, it would have contaminated the product. IR spectroscopic analysis showed that the product was cyclohexanone. Questions Q1: The refractive index of 1.467 shows that synthesized cyclohexanone was fairly pure since it compares to literature values of 1.450. Q2: The final product was free of water since there was no broad peak at approximately 3300 cm-1. Q3: The IR spectrum for cyclohexanone showed an intense absorption at 1703.8 cm-1. This compares to the literature values of the IR absorption range of the ketone group of cyclohexanone at 1715 cm-1. Q4: Sodium bisulfate is added to remove excess hypochlorite. OCl- + HSO3- Cl- + HSO4- References Baird C & Cann M 2008 Environmental Chemistry 4th ed. New York: W.H. Freeman and Company. Williamson K L 1994 Macroscale and Microscale Organic Experiments 2nd ed. Lexington, Ma: D. C. Heath and Company. Read More