Isolating Limonene and Comparing the Purity of Organic and Regular Navel OrangesIntroduction: In all living organisms, natural products are produced. Recently, scientists have been exploring using these natural products for pharmaceutical drugs. Since I have lived in Florida for all of my life, I obviously enjoy oranges. Also since I am interested in going into medicine after college, this experiment applies to me since the products produced from oranges may be able to be used as a pharmaceutical drug. In this experiment, I will isolate the limonene from three large regular and three large organic navel oranges and then compare the purity to a neat sample of R – (+) – limonene using a polarimeter. By measuring the rotation of linearly polarized light by a sample, a polarimeter can help determine the identity of the specific chemical compound being tested. If a specific chemical compound is tested, then it will have the same specific rotation under the same experimental conditions. By using Biot’s law, the specific rotation can be determined:= l c is the observed rotation in degrees, is the specific rotation in degrees, l is the length of the of the cell in dm, and c is the sample concentration in units of grams per mL. In order to isolate the R – (+) – limonene from the stem, leaves, and peels, many commercial oil operations utilize steam distillation, solvent extraction and hydro diffusion (Andrews 1). Since Limonene is a high-boiling liquid (bp763 = 175.5-176 °C), it decomposes under the high heat that is needed to boil the sample; therefore, steam distillation provides a simple and safe way to procure the R – (+) – limonene from the samples. To properly measure the purity of each sample, microdistillation and an epoxidation reaction must occur. However, with the materials given, it is possible to compare the purities of R – (+) – limonene produced by the organic and regular oranges by soley using the isolated distillate. To calculate the optical purity of the sample, use the following formula:% optical purity = Research Question: How does the purity in the isolated R – (+) – limonene in large organic navel oranges compare to the purity in the isolated R – (+) – limonene in large regular navel oranges? Hypothesis:If I isolate the limonene from both organic and regular oranges, then the organic oranges will have the purest form of limonene because organic oranges have less harmful toxins than regular oranges. Variables:Independent Variable: The type of Navel Orange – organic or regular orangeDependent Variable: The optical purity percentage Controlled Variables: The room temperature for all trials was 23.7? Three large oranges were used for each trialThe same distiller was used for each trialMaterials: LabQuest or computer interface Fractional distillation apparatusLabQuest App or Logger Pro Heating mantleWide-Range Temperature Probe Aluminum panVernier Polarimeter SandPolarimeter Sample Cell 125 mL separatory funnel Zester and six large oranges (3 organic and 3 regular) Orange Oil500 mL round bottom flask Safety:R – (+) – limonene is a flammable liquid and vapor. It can cause respiratory problems such as respiratory tract irritation. It is a skin and eye irritant. If inhaled, swallowed or absorbed through the skin, R – (+) – limonene can be harmful. HMIS Classification: Health Hazard-2, Flammability-2, Physical Hazard-0 (Sigma Aldrich Co. 1). To take precaution, use goggles and aprons when near chemicals. Also use gloves to handle hot materials.Method:Part I: Isolation Wear goggles, apron and gloves when handling hot glasswareIsolation of R -(+)- limonene from oranges Completely remove the zest from three large regular oranges by using a zester. Weigh the amount of zest produced to .1 g and record it. Add the zest and 100 mL of distilled water to a 500 mL flask and set up for distillation.Using a heating mantle, bring the mixture to a vigorous boil and collect distillate until no further oily liquid appears (it should be about 25 mL).Using a 125 mL separatory funnel, separate the limonene from the aqueous distillate.Connect the Wide-Range Temperature Probe to LabQuest or a computer interface. Set data collection program duration to at least 60 min.Repeat step two twice more with 3 large regular oranges each so there are three trials total for the regular orangesRepeat step 2 three times with 3 large organic oranges each so there are three trials total for the organic orangesMeasure and record how much distillate is collected in each trial.Part II: Measure the Optical Activity of LimoneneConnect the two Vernier Polarimeter cables to the respective points on your Vernier interface. Start the data collection program and choose New from the File menu.Calibrate the Polarimeter Now add the optically active sample into the Polarimeter cell. Pour your sample in the Polarimeter cell. Start data collection and slowly rotate the analyzer clockwise or counterclockwise for about 15 seconds (until data collection stops)Record the first angle above 0° where the illumination is at a maximum for the optically active sample. Repeat steps 3-5 for each sample that you have, including a sample of orange oil Qualitative Observations: Once the zest was brought to a vigorous boil during the distilling process, the zest and water were a murky brown inside of the flask being heated. All of the distillates collected were clear. It was quite difficult to see the difference between the limonene and the water. After being separated, the limonene was still clear. The orange oil, however, was bright yellow. Discussion:In my experiment, I found that the Organic Navel Orange Samples have a higher Specific Rotation than the Specific Rotation of the Orange Oil and the Regular Navel Orange Samples. The % Optical Purity of the Organic Samples were much closer to the % Optical Purity of the Orange Oil, the neat sample. It was expected that the Organic samples would be closer in all aspects to the neat sample than the Regular samplesIn my data collection, I did not have many anomalous results. The random and systematic errors may have made the results to each sample slightly different to each other; however, no major anomalies occurred in the collected data. Evaluation:Throughout my experiment, there were severals errors made. While preparing the distillation, I was unable to use some of the zest that had been made due to it being stuck in an unreachable place inside the flask that would be boiled during distillation. This random error would increase the uncertainty of the overall data collected. To reduce this random error, I used three trials to average out the data. Later, while distilling the samples, the glassware I was using to heat the flask during distillation (before I switched to the Aluminum pan) exploded due to overheating. This systematic error would increase the uncertainty of the data collected as well. The solution to this was to switch to the aluminum pan to heat the flask for distillation. Another systematic error was when I was heating the flask for distillation. While heating, the glassware holding the sand got overheated again and welded itself to the heating mantle. This error would also have increased the uncertainty of the data collected. The solution to this was to switch to the aluminum pan. Conclusion: In conclusion, the Organic Navel Oranges had a higher % Optical Purity than the Regular Navel Oranges. Also the Organic samples had a much higher Specific Rotation than the Regular samples as well as the neat sample (the orange oil). Comparing the two, Organic Oranges have a more pure form of limonene than the Regular Oranges. Further Investigations: To further this investigation, microdistillation and epoxidation can take place. I did not microdistill the oil collected due to the lab not having all the necessary items. Microdistillation would have a better effect on extracting the oil; however, the simple distillation and separating worked well in my experiment. To get a more accurate result, microdistillation would be necessary. Another possibility would be to test the effects of epoxidation on the amount of limonene extracted.