Objective: The purpose of this lab is to obtain lycopene from tomato paste using methods of extraction and purification. We will then test the purity of our compounds using TLC and UV/vis. In this lab, we will be expected to create our own experimental procedure through conducting a literature search using the provided materials, using the understanding we have gained from previous experiments, and relying on our knowledge of chemical compounds and their properties. 

Experimental:

• Weighed 12 grams of tomato paste in a beaker

• Add 40 mL of 3:2 (25 mL:15 mL) ratio hexane/ethyl acetate, stirred solution using a stirring rod.

•  Transferred solution into a round bottom flask. 

• The solution was then set up for a refluxing procedure according to the image shown below. The solution was heated at 60 until the solution began to boil and then the power was decreased to 30.

• The solution began to boil after approximately 7 minutes.

• By minute 37 the solution went from a deep red to a lighter, more orange color. 

• Periodically inserted a glass thermometer into the reflux system to ensure the system was below 65 degrees Celsius. The highest recorded temperature was 57 degrees Celsius.

• Allowed the solution to reflux for 1 hour and 1 minute. The solution appeared to be a bright, red-orange color.

• After allowing the solution to cool to room temperature, the solution was vacuum-filtered to remove excess solid tomato paste.

• The solution was then transferred into a separatory funnel.

• Allow the solution to sit until two distinct layers appear within the funnel.  Two distinct lawyers formed within the separatory funnel, the bottom layer appeared a clear, watery color, while the top appeared a bright, red-orange color. 

• Add 10 mL of DI water to fully extract the compound into the non-polar organic layer.

• Inverted the funnel 10 times, venting every 5th inversion.

• Washed with an additional 10 mL of DI water.

• Allowed the funnel to sit until the two distinct layers again reappeared within the separatory funnel. The bottom layer appeared more yellow in color, while the top layer remained a bright, red-orange color.

Drained the layers to extract the non-polar organic layer (the bottom layer should be the polar layer while the top should be the non-polar or organic layer with the compound of interest).

• Magnisium sulfate was added to the organic layer until the mixture began to swirl.

• Removed the anhydrous salt from the solution under vacuum filtration. 

• Evaporated the solution on low heat until a solid was formed. The solid appeared red in color. and smelled strongly of tomatoes.

• Analyze the compound using TLC 

• Prepared the compound for analysis under UV/vis by adding 3 ml of reagent alcohol to the solid and transferred the new solution into a cuvette. The new solution appeared a pale yellow color. 

• Obtained the results of three other lab groups for comparison to be completed. 

Discussion: The presence of two spots on my TLC plate indicates the presence of at least two distinct chemicals within the compound that I extracted during the laboratory procedure today. This indicates that the lycopene I obtained was an impure sample, despite the melting point obtained for this experiment (170.8–173.0°C) falling within the lower end of the literature value range for lycopene.

The TLC result for my experiment also indicates that a different solvent should have been used for analysis as my sample reached the edge of my solvent front, which likely negatively impacted the results of my analysis and caused my Rf values (0.63 and 0.34) to differ from those of my laboratory partners (0.56 and 0.52). The results of Violet and Sebastian's TLC and Emmalee and Gilua's TLC were similar, as their obtained Rf values only differed by 0.2, which further indicates a need for me to use a stronger ratio of a nonpolar solvent in my analysis by having a greater ratio of hexane within my solvent.

The expected yield for this experiment was approximately 0.2 grams of wet lycopene. I obtained 0.18 grams of the final product, which is close to the expected outcome. The yield for this experiment was somewhat good when compared to other lab groups, sitting at 1.50% when compared to 1.60%, which indicates that the methods used in this experiment could be effective at isolating lycopene, but something about my experimental procedure needs to be adjusted to allow for a pure product to be obtained.

UV/Vis indicated small peaks in the 400–500 range. This indicates the presence of lycopene in the sample, although it is minimal. The further on the left you travel, the graph for UV/Vis eventually cuts off. After doing some online research it appears that this trendline indicates that my sample was too dilute (Libretexts, 2023).  I was unable to create a second cuvette for repeat testing due to not enough product being obtained in the lab. At the time of writing my discussion, no other labs have uploaded their UV/Vis results, therefore, no comparisons can be drawn form them at this time. 

The mass spec revealed a molar mass of 536.17 g/mol. Due to the Westminster mass spec machine giving results with an M+1 value, we would expect the results of mass speech to be the literature value of pure lycopene (536.87 g/mol) with a +1 result, giving us a result of 536.87. The result obtained in the lab indicates that a small amount of pure lycopene was obtained but that 1 hydrogen was lost in the process of mass spec analysis

SOURCES:

Libretexts. (2023, October 8). 14.8: Interpreting ultraviolet spectra- the effect of conjugation. Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/14%3A_Conjugated_Compounds_and_Ultraviolet_Spectroscopy/14.08%3A_Interpreting_Ultraviolet_Spectra-_The_Effect_of_Conjugation