R-Limonene Lab Report PDF

Preview

Summary

R-Limonene Lab Report...

Description

R-Limonene Lab Report Purpose: The purpose of this experiment was to extract R-Limonene from a sample of orange or grapefruit using steam distillation and use the extract to determine the optical rotation of our sample; the optical rotation will then allow us to calculate the enantiomeric excess of R-Limonene in our distillate, as compared to a racemic mixture of R-Limonene and L-Limonene. Results: 1. Percent Weight or R-Limonene in Peel = (Mass of R-Limonene/Mass of Peel)*100 = [(0.66g)/(42.35g)]*100 = 1.56% R-Limonene in my orange peel. 2. Rotation of Limonene: Bf = 195.83 B0 = 193.61 Mass of Limonene = 0.66g Volume of Test Tube = 10.2 cm = 1.02 dm = 23.97 mL Path Length = 10.2 cm = 1.02 dm [ɑ] = ɑ / (c*l), where c is the concentration in g/mL and l is the path length in dm = (Bf-B0)/(c*l) = (2.22)/(1.02 dm * (0.66 g/23.97 mL)) = 79.05 degrees Discussion: 1. The literature value of the optical rotation of R-Limonene was at 115.5 +/- 1.0 (1). The value of the specific rotation we obtained was 79.05 degrees. Assuming that our sample is entirely limonene, we can calculate the enantiomeric excess as follows: EE = ([ɑ]/Literature Value)*100 = (79.05/115.5)*100 = 68.44% Enantiomeric Excess 2. Two other ways we can isolate R-limonene are using a soxhlet extractor (2) and a cold press (3). The soxhlet extraction is similar to distillation, but it feeds the condensed vapors into a “thimble” of packed filtering substances (like a filter paper). Once it passes through the filtering thimble and the chamber is full, it drains back into the round bottom flask from whence it came to be filtered again if desired (2).

The cold press method is very simple. By “squeezing” the orange peels in a container (such as pressing them against a sieve), crude oil will actually emerge from the peel. You can then take this crude sample and use a number of purification methods, like a centrifuge, separatory funnel, or column chromatography to purify the crude sample by separating the oil from the aqueous solution (3). 3. Distillation does not change the enantiomeric excess simply because enantiomers share physical properties such as boiling point, melting point, etc. As a result, we are unlikely to separate the enantiomers using physical separation methods. Their main difference is their optical rotation (4). Therefore when we steam distill our orange puree, we are only separating contents based on these physical properties, which would mean both enantiomers (whenever present) would be condensed into our collecting beaker in the same ratio they were present in the orange. 4. Myrcene will not have an optical rotation. Upon observation, myrcene is achiral, as it has a plane of symmetry. Beta-pinene, however, is an achiral molecule that will lower the optical rotation of our sample because it has an optical rotation of -21 degrees (5), which will subtract linearly (6) with our positive optical rotation for limonene and result in a lower than literature value. Optical rotations of molecules affect the specific rotation in a solution simply based on their concentration in the solution and their isolated rotation. This is why we can calculate enantiomeric excess by using our observed rotation and the literature rotation values of the enantiomers. The presence of myrcene may be one source of explanation for why my experimental value is lower than the literature value; since it has a negative rotation, its presence in the solution may cause lowering of our observed rotation. Sources Cited: 1. “(R)-(+)-Limonene 62118.” Sigma Aldrich, Drugs, www.sigmaaldrich.com/catalog/product/sial/62118?lang=en®ion=US. 2. “Soxhlet Extraction.” Royal Society of Chemistry - Advancing Excellence in the Chemical Sciences, www.rsc.org/publishing/journals/prospect/ontology.asp?id=CMO%3A0001609&MSID=b82300c. 3. “Quantitative Composition of Cold-Pressed Orange Oils.” ACS Publications, pubs.acs.org/doi/abs/10.1021/jf60195a039. 4. “The University of Chicago Organic Chemistry Laboratory Manual: Experimental Procedure—Distillation of R-Limonene”,  Great River Learning, May 2018. 5. “(−)-β-Pinene 112089.” H2NC6H4CO2C2H5, Drugs, www.sigmaaldrich.com/catalog/product/aldrich/112089?lang=en®ion=US. 6. “Polarimetry - Optical Rotation Vs Specific Rotation Definition.” Rudolph Research Analytical, 14 Oct. 2014, rudolphresearch.com/polarimeters-and-polarimetry/....