Overview:
For this experiment, we would have to extract caffeine from tea. Büchner filtration, solvent extraction and distillation using a rotary evaporator. These techniques will be used during this experiment to extract the caffeine from beverages.
What is caffeine?
Caffeine(C₈H₁₀N₄O₂) is a type of alkaloid which is found in tea, coffee and kola nuts.
What is alkaloid?
It is an organic weak base which is 'alkali-like'. It is a nitrogenous substance which is found naturally in plants. Cocaine, strychnine (poison), morphine, piperine (found in black pepper) and quinine (used to treat malaria and added to tonic) are a few examples of an alkaloid. This shows that some alkaloids are beneficial while some are very harmful.
What is an alkali?
It is a soluble base which contains and releases hydroxide ions(OH¯)quantitatively.
What is the difference between panadol and panadol extra?
Panadol extra has a higher amount of caffeine compared to panadol.
What is solvent extraction?
One of the methods to judge solubility is "like dissolves like". Organic compounds have a high chance to be soluble in organic solvents. Polar materials are usually more soluble in polar solvents. An example of a polar material is salt.
It is also known as liquid-liquid extraction and partitioning. This method is used to separate compounds based on their relative solubilities in two different immiscible(unable to be form a mixture when added together) liquids. It is usually water and an organic solvent. It extracts a substance from one liquid phase into another liquid phase.
What is a polar solvent(solvent extraction)?
It contains molecules whose electric charge are unequally distributed. Thus leaving one end of the molecule more positive than the other. It usually has O¯H bond. Some examples are water and acetic acid(CH₃COOH).
What is a non-polar solvent(solvent extraction)?
It contains molecules whose electric charge are equally distributed. It is not miscible with water. An example would be benzene(C₆H₆).
How to separate organic compound and inorganic salt(solvent extraction)?
When a mixture of 1, 4-dimethoxybenzene and lithium chloride is dissolved in a mixture of diethyl ether and water, both will be dissolved. The mixture will then separate into two clear layers because organic and inorganic solvents are immiscible.
The "organic layer" will contain 1, 4-dimethoxybenzene. The aqueous layer(inorganic layer) will contain lithium chloride. However, if the organic layer is separated from the aqueous layer, dried to remove traces of water and evaporated pure 1, 4-dimethoxybenzene will be obtained.
∗Tips/Tricks: Extraction must be done at least two times. This would ensure that all traces if the phase are removed. On top of that, organic extracts must be dried after being separated from the aqueous layer(inorganic layer). This is necessary because organic solvents will contain a small amount of dissolved water. A "drying agent" such as anhydrous magnesium sulfate or anhydrous sodium sulfate will be used to dry the organic extracts. These "drying agent" absorbs the water from the organic solution.
People often put in too much effort into extractions by shaking the separatory funnel vigorously to mix the two layers. However, this is what we should not do. The vigorous shaking/mixing can cause an emulsion(intimate and inseparable mixture of the two layers) to form. Emulsions can be broken but it is not easy. An example of an emulsion is milk. Swirling the separatory funnel is a better technique and what we should be doing.
What is rotary evaporator?
It increases the speed of evaporation of the solvent that the chemical compound in the experiment is solubilized in. It is something like a mini-distillery. It composes of hot water bath and a rotating glass tube connected to a condenser and a vacuum. The hot water bath is used to heat up the chemical compound. The vacuum reduces the pressure within the evaporator system. The condenser is used to cool down the chemical compound.
First, spin and heat the rotating glass tube. Next, place the tube under a vacuum. The solvent from the tube would evaporate into gas before condensing into a liquid.
Example of a Rotary Evaporator (http://docs.google.com/viewer?a=v&q=cache:5qRJC5h7PtwJ:www.geosc.psu.edu/courses/Geosc518/4_Sample_Prep/Chapter_4/4_6_Sulfur/4_6_1_SO2/4_6_1_3_Elemental_S/Papers/Roto_vap.pdf+Rotary+Evaporator&hl=en&gl=sg&pid=bl&srcid=ADGEESj4xA78USHCeawcM9dvw899cD06_P7m0G21Fsp9KscZ1yGXvXyFK8zY-ukaGn6qiX0sL5w9j-1rfipzhnUCytMuIKK1A1yHUvrgGkS8pXyC5TykNC-hiFXk6P5sJUPdkl7VhjzO&sig=AHIEtbQ0Mv5QWRcGOfcvdoF66sAZfyiRVQ&pli=1)
Why do we rotate the flask while it is heating in water?
It is to ensure a consistent dissolution between the caffeine and the solvent. It also ensures that the solvent is evaporated smoothly.
Why do we need a condenser?
It is to change the gaseous state of the solvent to a liquid state.
What is the benefit to work under vacuum?
Under a vacuum condition, lowering the pressure in the condenser will lower the boiling point of the solvent. Hence, the solvent in the round bottom flask will evaporate at a lower temperature. Also, it will condense at a lower temperature.
What is Büchner filtration?
It is used when a solid needs to be isolated from a solution. It is usually done at a reduced pressure using a Büchner flask/funnel.
The Büchner flask is known as a vacuum flask. It is a thick-walled Erlenmeyer flask with a hose barb and short glass tube protruding around an inch from the neck of the flask. The tube and hose acts as an adapter which the end of a thick-walled flexible hose can be fitted to form a connection to the flask. The other end of the hose can be connected to source of the vacuum. The thick wall of the Büchner flask allows it to withstand the difference in pressure while holding a vacuum inside. It is usually used with a Büchner funnel.
The Büchner funnel is used in suction filtration. On top of the funnel-shapped part, a cylinder with a perforated plate is found which separates it from the funnel. Normally, a filter paper is place on the plate and is moistened with a solvent to prevent any leakage. The liquid that needs to be filtered is poured into the cylinder and drawn through the perforated plate by vacuum suction.
This is an example of a setup of a Büchner filtration. (http://en.wikipedia.org/wiki/File:Embudo_B%C3%BCchner.jpeg)
To take note:
Solvent extraction is used extensively in synthetic chemistry as a way of purifying reaction mixtures. It is based on the different solubility of compounds in different types of solvent. At room temperature, caffeine is more soluble in dichloromethane than water.
http://www.biology-online.org/dictionary/Alkaloid
http://en.wikipedia.org/wiki/Base_%28chemistry%29
http://www.nps.org.au/consumers/publications/medicine_update/issues/paracetamol_with_caffeine
http://en.wikipedia.org/wiki/Liquid-liquid_extraction
http://www.chemicalland21.com/info/SOLVENTS.htm
http://www.chem-ilp.net/labTechniques/BuchnerFiltration.htm
http://en.wikipedia.org/wiki/B%C3%BCchner_flask
http://en.wikipedia.org/wiki/B%C3%BCchner_funnel
http://docs.google.com/viewer?a=v&q=cache:5qRJC5h7PtwJ:www.geosc.psu.edu/courses/Geosc518/4_Sample_Prep/Chapter_4/4_6_Sulfur/4_6_1_SO2/4_6_1_3_Elemental_S/Papers/Roto_vap.pdf+Rotary+Evaporator&hl=en&gl=sg&pid=bl&srcid=ADGEESj4xA78USHCeawcM9dvw899cD06_P7m0G21Fsp9KscZ1yGXvXyFK8zY-ukaGn6qiX0sL5w9j-1rfipzhnUCytMuIKK1A1yHUvrgGkS8pXyC5TykNC-hiFXk6P5sJUPdkl7VhjzO&sig=AHIEtbQ0Mv5QWRcGOfcvdoF66sAZfyiRVQ&pli=1
