Synthesis of Cyclohexene via Dehydration of Cyclohexanol Lab

Synthesis of Cyclohexene via Dehydration of Cyclohexanol Purpose The purpose of this experiment was to synthesize cyclohexene from cyclohexanol using dehydration, using 85% phosphoric acid and gas chromatography will be carried out to an obtain the purity of a substance. Reaction Scheme Experimental Procedure 1. Synthesis of Cyclohexene To the round bottomed flask, the following were added: boiling chips, cyclohexanol (2.004g), and 0.5 mL of 85% phosphoric acid (0.5 mL). The solution was then distilled into a vial using a fractional distillation apparatus, during which the range of temperature of the drops were recorded until 10% of the volume remained. The contents of the vial were then pipetted into a test tube, adding water (1 mL) and washed, removing the lower aqueous layer. The contents of the test tube were washed with brine (1-2 mL aq. NaCl), the the lower aqueous layer was extracted. The upper layer was transferred to a clean dry vial where spheres of CaCl were 2 added. The dry product was then transferred to a clean tared vial without the calcium chloride. The final product was weighed and underwent gas chromatography and IR spectroscopy. 2. Chemical Tests Bromine in Dichloromethane: In a test tube, cyclohexene (0.5 mL) was added. To another test tube, cyclohexane (0.5 mL) was added. To each test tube, 3% bromine in dichloromethane (3-4 drops) was added and changes in color were observed. Potassium Permanganate: In a test tube, cyclohexene (0.5 mL) was added. To another test tube, cyclohexane (0.5 mL) was added. To each tube, 1% potassium permanganate and 10% sulfuric acid (2-3 drops) was added and any changes in color were observed. Results and Discussion Figure 1: Weight of Product Product Weight (grams) BP Range (from Distillation) Percent Yield Cyclohexene 0.792 g 66-70 ℃ 48% Figure 2: Percent Yield of Product with Gas Chromatography Percent Yield Cyclohexene RT (retention time) % Pure Cyclohexene from Gas Chromatography 48% .397 min 100% Figure 3: IR Spectroscopy Analysis Peak 1 3043.54 cm (some OH leftover) Peak 2 3023.5 cm (sp carbon) Peak 3 2926.12 cm (sp carbon) -1 -1 Figure 4: Chemical Tests 2 -1 3 Compound Bromine in Dichloromethane Potassium Permanganate Cyclohexene Drop 1: colorless Drop 2: colorless Drop 3: colorless Drop 1: clear + brown layer Drop 2: clear + brown layer Drop 3: clear + brown layer Cyclohexane Drop 1: reddish-brown Drop 2: reddish-brown Drop 3: reddish-brown Drop 1: purple Drop 2: purple Drop 3: purple + clear layers The starting materials cyclohexanol (2.004g) and 85 % phosphoric acid was reacted using dehydration to synthesize cyclohexene and the product was obtained in 48% yield at the conclusion of this experiment. Once the reaction occurred, gas chromatography measured the sample resulting in 100% cyclohexene due to only one peak and a retention time of .397 minutes. The product was also observed using Ir spectroscopy, which provides information on what bonds are present in a compound depending on absorption peaks. Overall three peaks appeared. The absorption location of 3374-3403 cm showed that there was O-H bonds remaining, the peak at -1 location 3023.5 cm confirmed that there were C=C bonds (presence of sp carbon). Absorptions -1 2 at 2926.12 cm showed that there were C-C bonds present (sp carbon). -1 3 The percent yield of cyclohexene was low: 48%. This can be contributed towards having to lose some product during distillation because ~10% volume was left behind in the round bottomed flask for safety reasons. In addition, some product could have been pipetted out by mistake when washing the solution after distillation. The identity and purity of the product was assessed. In IR spectroscopy, only one peak appeared which showed that the solution was 100% pure. However the results of the gas chromatography disagreed with this, showing a peak for alcohol functional groups still present. This could be due to distillation running to quickly, and prevented by the rate of drops being drop per 20-30 seconds. When cyclohexene and cyclohexane solutions were tested with 3% bromine in dichloromethane, the cyclohexylene solution turned a clear color while the cyclohexane test tube remained reddish-brown. When cyclohexene and cyclohexane solutions were tested with potassium permanganate, the cyclohexene solution turned clear with brown precipitate forming, where the cyclohexane solution remained purple with a cloudy clear layer.