The purpose of this experiment is to calculate the yield percent of caffeine that was isolated from tea leaves by several processes. Tea is a popular beverage that contains caffeine and widely used in the world. Caffeine is one of the main substances that extracted from the tea. When caffeine is isolated it appears as a white crystalline solid. Caffeine also can be found in natural and manufactured substances. Caffeine stimulates the central nervous system, increases the alertness and relaxes certain muscles.
The solubility of caffeine is poor in cold water and very high in hot water. Caffeine dissolves in water due to its amine functional group which that can form hydrogen bonds with water molecules. While the hot water was added to 25.032 g of tea and was let to brew, 2.001g of calcium hydroxide & 48.364g of sodium chloride were added to the tea mixture and were stirred for 1 min. By adding calcium hydroxide which is base, it converts the tannins into sodium salts which are not soluble in dichloromethane while tannins are very soluble in water. Therefore, it helps to keep the tannins in the aqueous layer. And by adding sodium chloride (salt) to the tea mixture it decreases the solubility of caffeine, where the water will be saturated with NaCl. Also, salt forces the caffeine into the dichloromethane. After filtering the tea mixture, the solution was transferred to the separating funnel and 20 ml of DCM was added. The stopper was placed, the mixture was inverted and gently swirled, and the pressure was released by opening the tap. Then it was let to stabilize and DCM was collected. This step was repeated 3 times. The organic solution became in the bottom layer, this is due to the density of DCM which is 1.33 g/cm³ which is heavier than water 1 g/cm³. After the DCM layer was collected, drying agent (magnesium sulfate) was added to the DCM layer to make sure no water is left in the solution. Then it was filtered into the round-bottom flask that has a mass of 57.882g and was sublimated by rotary evaporation. Dichloromethane can be easily evaporated by rotary evaporation. After the sublimation step, the round-bottom flask with crude caffeine was weighted out and has a mass of 57.930g, therefore, the mass of the caffeine is 0.048g. Caffeine constitutes 3% of the tea leaves weight and the yield percent that was calculated is 0.192%. The reason behind this low percentage it could be some of the caffeine still in the tea leaves or in the filter paper.