Extraction or isolation

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A method of separate an organic compound from a mixture of compounds.

It is a process that selectively dissolves one or more of the mixture compounds into an appropriate solvent.

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Extraction processes include removal of soluble compounds from a solid matrix, then transfer the compounds from one liquid solvent to another liquid solvent.

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Extraction is a particularly effective means of separating organic compounds if one compound in the mixture can be chemically converted to an ionic form. The ionic form is soluble in an aqueous layer( polar layer) and can be extracted into it.

Other non-ionized organic compounds in the mixture will remain dissolved in the non-polar solvent layer. Separation of the two layers results in the separation of the dissolved compounds.

Example: The addition of sodium carbonate to the tea and coffee in the extraction process of caffeine.

1-the tannins are acidic and sodium carbonate is a base, so when sodium carbonate is added to the tea water mixture, the acids are converted to their sodium salts which are highly soluble in water.

ArOH + Na2CO3 → tannins soluble in water and chloroform

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ArO¯ Na⁺ + HCO3 ¯ tannins salts soluble in water and insoluble in chloroform

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2-Caffeine is an alkaloid, an organic base.

Sodium carbonate also a base, and it is added in the first extraction to make sure that the caffeine remains in the free base form (to prevent it from reacting with any acids that may be present).

Solvent selection: (Likes dissolve likes) Solvents differ in their extraction capabilities depending on their own and the solute’s chemical structure.

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1-Immiscible or poorly miscible with the main solution. e.g., water/ether. water/ chloroform 2-The target compound dissolves well in the solvent.

3- have low boiling point (reasonably volatile).

distribution coefficient (partition coefficient) K: the ratio of the concentration of a single solute in two immiscible solvents.

Concentration in extractant

Concentration in source solution

Partition functions with larger values result in more efficient extractions.

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Example: a solute that has a solubility of 8g /100mL of ether, and 2g /100mL of water.

Proplem1: If 100 mL of an aqueous solution containing 1.0 g of caffeine is extracted with 10 mL of chloroform at room temperature, 0.5 g of caffeine is transferred to the chloroform layer. Calculate the distribution coefficient of caffeine between chloroform and water at room temperature.

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Caffeine belongs to a group of compounds known as alkaloids. Alkaloids are a group of compounds that are found primarily in plants and contain basic nitrogen atom(s).

-The major sources for caffeine are the seeds of the coffee plant , cola nuts, and Tea leaves.

-Caffeine acts as a stimulant. It stimulates the heart, respiration, the central nervous system, and is a vasodilator (relaxes the blood vessels) as well as a diuretic (increases urination).

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1fluid ounce (oz)=28.4ml

1. Cellulose − the major structural material of all plant cells. Since cellulose is virtually insoluble in water it presents no problems in the isolation procedure.

2. Caffeine − one of the major water soluble substances present in tea leaves. Caffeine comprises as much as 5% by weight of the leaf material in tea plants.

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3. Tannins − high molecular weight, water soluble

compounds that are responsible for the color of tea. The term "tannin" does not refer to a single compound or even to substances having similar chemical structure.

Rather, "tannin" refers to a class of compounds that have certain properties in common. They contain phenol groups and are acidic.

4. Flavonoid Pigments − water soluble colored compounds that are widely distributed in plant life.

Procedure: 1-Place 30 g of the tea leaves or tea bags in a 1000 ml beaker. Add 300 ml of distilled water and 5 g of sodium carbonate and stir the contents of the beaker with a glass rod.

Or place 20g of coffee in 500ml beaker. Add 200ml distalled water and 5g sodium carbonate.

2- Boil the beaker over direct flame or hot plate for 20 minutes.

3- Cool the solution at room temperature.

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4-Ensure separating funnel valve shut. Using an ordinary funnel, pour the solution into the separating funnel.

5- Extract the caffeine with four successive 25 ml portions of chloroform. Do not shake the separating funnel vigorously.

6-Remove the lower layer from the separating funnel into 250 ml beaker through an ordinary funnel lined with filter paper and a drying reagent such as anhydrous sodium sulphate.

7- Evaporate the combined chloroform extract to obtain a crud product .

8-With a spatula, remove the solid left behind and mass it. This solid is principally caffeine.

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Chloroform phase

Percentage of caffeine in tea or coffee:

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Melting point of a solid is the temperature at which the solid and liquid phases are in equilibrium.

The purity compound is measured by melting point.

Always record a range of temperature, where it starts melting and where it is completely melted.

Impurities will change the melting point.

Pure caffeine melts at 238 째 C.

Place a VERY SMALL quantity of the solid of interest on glass capillary, and use a stirring rod to grind the solid to a powder. Use a spatula to gather the powder into a small pile. Stick the open end of a melting point capillary into the pile to a depth of about 1 mm, then invert the capillary and tap the sealed end on the bench to encourage the solid to drop to the bottom. The height of solid in the capillary should be no more than 1-2 mm.

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place the capillary into one of the 3 sample wells of the Mel-Temp apparatus . Turn the Mel-Temp power switch on .

While the sample is heating, watch it through the magnifying window, while frequently checking the temperature reading of the thermometer. Observe the sample as the temperature rises.

To measure the melting point of a substance, it is necessary to gradually heat a small sample of the substance while monitoring its temperature with a thermometer.

The temperature at which liquid is first seen is the lower end of the melting point range. The temperature at which the last solid disappears is the upper end of the melting point range.

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turn off the Mel-Temp and remove your capillary. CAREFUL--DO NOT TOUCH THE END THAT WAS HEATED! Let the capillary cool, then discard it in the glass waste .

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