Preparation of Tea Solution:
We started out experiment by weighing out 5.023g of tealeaves and 2.008g of calcium carbonate powder. These two substances were mixed with 50ml of water and heated under gentle reflux in a round-bottom flask using a condenser apparatus. The hot solution was then filtered and the filtrate was collected and cooled. Extraction and Drying:
Using a separatory funnel, the cooled filtrate was extracted with 10ml of methylene chloride. After shaking our mixture, we broke and dried our emulsion by slowing passing the lower layer through a cotton ball layered with anhydrous magnesium sulfate. The extraction process was repeated 2 more times for maximum collection of the organic layer.
Distillation:
The extracts were poured into a 50ml round bottle flask and connected to a simple distillation apparatus. To obtain the caffeine, the methylene chloride was removed from the extract, leaving us with our solid caffeine residue.
Sublimation:
We purified our solid caffeine through sublimation. By constructing a side-arm test tube apparatus, we vaporized and condensed the caffeine using a Bunsen burner. Upon cooling, the apparatus was carefully disassembled and the sublimed caffeine was scraped off of the test-tube collection surface and weighed. The melting point range was then determined by utilizing a melting point apparatus.
RESULTS
Final Product Weight: .024g
Melting Pointing Range: 165-200°C
DISCUSSION
In this experiment, caffeine was isolated from tealeaves through extraction, distillation and sublimation. Caffeine (also known as Guaranine, Methyltheobromine, and Thein) is defined as a naturally occurring chemical stimulant of the central nervous system that occurs in beans, leaves, fruit, and beverages such as tea, coffee and soda.
REFLUX:
Before beginning the isolation process, it must be understood that caffeine is amongst several other natural substances and does not exist in tea alone. With that said, our first step in the experiment is to thoroughly separate caffeine from these substances. In order to achieve separation, we use a method known as liquid-liquid extraction. This is the process of transferring a solute from one solvent into another solvent in which the solute is more miscible. To do this we prepared our initial solution by using a condenser apparatus to heat the tea mixture under reflux. This is an important apparatus because it allows prolonged heating of our aqueous tea solution at its constant boiling point of 100C with minimal evaporation. A solution will be refluxed at its own particular boiling point. For example, the boiling point of ether is 37C, therefore it will be refluxed at that temperature. As shown below in figure 1a, our mixture appeared to have a “muddy” brown color.
EXTRACTION:
After filtrating and cooling the refluxed mixture, it was time to separate the caffeine from the other natural substances contained in our solvent. To do this, we use liquid-liquid extraction by adding the water immiscible solvent, methylene chloride, to our aqueous tea solvent. Using a separatory funnel to shake the two solvents together caused separation of the two layers, otherwise known as an emulsion. The non-polar methylene chloride
is able to attract and dissolve the non-polar caffeine (like dissolves like), therefore separating it from the polar water filtrate. Methylene chloride has a density of 1.330 g/mL, making it denser than water; therefore causing it to separate into the bottom layer of the seperatory funnel. By draining this bottom layer into an Erlenmeyer flask, we have successfully obtained our caffeine extract.
Some other extraction solvents and their densities include,
Ligroin.67-.69 g/mL
Diethyl Ether.71 g/mL
Toluene.87 g/mL
Unlike Methylene Chloride, these solvents have densities lower than that of water, which will cause them to emulsify into the top layer of the seperatory funnel as opposed to the bottom layer like the extraction solvent used in this experiment. It is also worth mentioning that there is more than one type of extraction apparatus as well. As seperatory funnels are ideal for larger quantities of material, while centrifuge tubes are used for quantities up to 10mL and conical vials are used for quantities of less than 4mL.
DISTILLATION:
Just as we used extraction to separate the caffeine from the water solvent, we then used distillation to separate our dissolved caffeine from its methylene chloride solvent. Distillation is the process of vaporizing a liquid, condensing the vapor, and collecting the condensate in another container. A distillation apparatus was constructed and our caffeine extract was placed inside of the distilling flask attached to a thermometer and cooling condenser. As the extract was heated, the liquid methylene chloride was being evaporated. The vapor rose past the thermometer and was condensed back into liquid by going through the cooling condenser, leading to its collection in the receiving flask. Figure is a picture of the distillation process. On the left side of the photo, the extract was being heated inside of the distillation flask, while the condensed methylene chloride was collected in the receiving flask on the right side.
SUBLIMATION:
Being left with a dried caffeine residue after distillation allowed us to utilize sublimation as a method to purify the product. For our purposes, sublimation is considered a better alternative to crystallization because it yields faster results since it doesn’t require the addition of a solvent that will eventually need to be removed. Securing a small test tube with ice water inside of a sidearm test tube containing the crude caffeine assembled our sidearm test tube apparatus.
Delving deeper into the process occurring above in figure 3a, the sidearm test tube was attached to a vacuum for the purpose of lowering the pressure within the apparatus. Solids sublime when the atmospheric pressure is less than their vapor pressure at their melting point. In respect to our crude caffeine, this means that we must apply heat through a Bunsen burner while “cranking up” the vacuum to significantly reduce the pressure. By doing this, we are essentially skipping the solid-liquid-gas transition phases and going straight from solid to gas. As shown in figure , the gaseous caffeine condenses back to solid on the cold surface of the ice-water test tube. We collected .024g of caffeine as a final product.
MELTING POINT RANGE:
Using a melting point apparatus, the melting point range of the purified caffeine was determined to be 190-220°C. Our measurement has shown to be somewhat consistent with the actual melting point of caffeine, which has been documented as 236°C.
ADDITIONAL INFORMATION ON CAFFEINE:
STRUCTURAL
As learned in lecture, the fashions in which we draw chemical structures are not 100% accurate. Drawing a single picture of a chemical molecule does not show the electronic positions and chemical bonds occurring at any given moment. In order to come closer to depicting the most accurate picture, we draw multiple structures. Resonance Structures are multiple structures of
an aromatic compound drawn to display electron flow around the molecule. As shown below, we can draw two resonance structures to efficiently illustrate electron distribution in the caffeine molecule.
PHYSIOLOGICAL
In our fast-paced modern society, caffeine has become a dietary staple in many people’s lives. Its stimulatory effects give individuals the energy they need to complete their daily activities. Caffeine affects the body by changing the chemical actions of the brain. It achieves this by blocking the natural brain chemical responsible for sleep, adenosine. This chemical is produced throughout the day through physical activity. To state simply, the more you do, the tired you’ll be. Lets take a closer look at the two structures.
As seen above, caffeine has a similar structure to adenosine. When caffeine is ingested into the body, cells that would bind to adenosine (adenosine receptors) mistakenly bind to caffeine instead. This ultimately blocks the binding of adenosine molecules and the cells speed up as opposed to speeding down. This change in activity ultimately causes the pituitary gland to release hormones that spark the release of adrenaline from the adrenal gland. These events lead to the feeling of high energy that we experience when we drink coffee or any other caffeine containing foods or beverages.
