2-CaffeinefromTEAbags1SS09 - Extraction: Isolation Caffeine...

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051109 Extraction: Isolation Caffeine from Tea 1 New techniques: Extraction and Sublimation Review: Vacuum Filtration and Acid/Base Chemistry Reading assignment: Fessenden, R.J., Fessenden, J.S., Feist, P. Organic Laboratory Techniques , 3 rd ed.; Brooks/Cole: Pacific Grove, 2001, pgs 49-66, 71-73. Introduction During the first week of lab we learned the process of recrystallization – a key purification technique used by organic chemists. Extraction is a separation technique in which one or more molecules from a mixture are selectively dissolved into an appropriate solvent. Extraction includes removal of soluble compounds from a solid, but most often involves the transfer of compounds from one liquid to another. The technique is based on the idea that “like dissolves like”. Polar molecules are likely to be soluble in water, a polar solvent. Non-polar molecules will be far less soluble in water and instead will dissolve in non-polar organic solvents like dichloromethane (CH 2 Cl 2 ) or diethyl ether (Et 2 O). When a non-polar organic solvent, such as ether, and water are combined two layers are formed – similar to oil and water. The solvents are said to be immiscible . If a mixture of compounds (such as sodium octanoate and anthracene, figure 1, is introduced to the mixture of solvents the compounds will migrate to the layer in which they are most soluble. The sodium octanoate is polar (what makes it polar?) and therefore most of it will move to the water layer. Alternatively, anthracene is non-polar and the majority of it will distribute itself into the ether layer. The ether and the water layers can be physically separated (with the help of a separatory funnel) and in the process most of the octanoate salt is separated from the anthracene. The efficiency of the separation is affected by the solubility of each compound in the solvent, the amount of solvent used, and the number of times the extraction is performed. anthracene CH 3 (CH 2 ) 6 O O Na + sodium octanoate Figure 1. Examples of polar (sodium octanoate) and non-polar (anthracene) organic molecules. In today’s lab we will learn the art of extraction by isolating caffeine from tea. Caffeine belongs to a class of important molecules called alkaloids . These molecules are plant-derived, contain a basic nitrogen, often have a bitter taste, and are commonly have physiological activity. Some examples of amines are shown below (Figure 2).
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051109 N N N N O O CH 3 H 3 C caffeine CH 3 N O Ph O H O OCH 2 CH 3 CH 3 cocaine N N CH 3 nicotine N MeO H HO N H quinine antimalarial Figure 2. Interesting alkaloids. The challenge of today’s experiment is to separate the caffeine from the other components of tea: 1. Cellulose: the major structural component of plants. A linear polysaccharide made up of thousands of glucose units. Water insoluble.
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This note was uploaded on 02/13/2010 for the course EGR 012 taught by Professor Witfield during the Spring '10 term at Aarhus Universitet.

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2-CaffeinefromTEAbags1SS09 - Extraction: Isolation Caffeine...

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