Synthesis of aspirin تخليق الاسبرين
Synthesis of aspirin
Refine the lab procedures off the synthesis of acetylsalicylic acid
Incorporate some explanation off key concepts.
Equipment / Materials
Salicylic acid acetic anhydride sulphuric acid Ice-cold filter paper
water-bath
Introduction
Salicylic acid is a phenolic acid, indicating it has two functional groups on the benzene ring, an -OH group and a -COOH group. Aspirin and oil of wintergreen are esters of salicylic acid.
Aspirin is the ester of salicylic acid and acetic acid (acetyl salicylic acid), whereas oil of wintergreen is the ester of salicylic acid and methanol (methyl salicylate)
The chemical name for aspirin, acetyl salicylic acid, is not easily recognized as the name of an ester. However, the chemical name for oil of wintergreen, methyl salicylate, should readily be recognized as the name of an ester.
In the preparation of aspirin the -OH group of salicylic acid reacts with the acetyl group of acetic acid or acetic anhydride to form acetyl salicylic acid.
The formation of aspirin will proceed faster if acetic anhydride is used in place of acetic acid. However, acetic anhydride will hydrolyze in the presence of water to form acetic acid, slowing down the reaction. Hence, the reaction vessel must be very DRY to ensure a complete reaction.
Sulfuric acid, H2SO4, is used as a dehydrating agent. The aspirin will be isolated by filtration and washed several times with ice cold deionized water to remove the water soluble impurities (acetic acid and sulfuric acid).
Aspirin is quite insoluble in ice cold water, but is relatively soluble in warm water (1 g dissolves in 100 mL water at 37°C).
Methyl salicylate is a liquid at room temperature (mp = -9°C) and is relatively insoluble in water. It is also quite toxic (average lethal dose for adults is 30 mL). However, it is used in 36 small amounts as a flavoring agent and is used in topical analgesic balms for arthritis and aching muscles.
In this experiment you will prepare a very small amount of the methyl salicylate and characterize it by its aroma. It will not be isolated.
Preparation
Wight out ( 3.5 g ) of salicylic acid and transfer this to a conical flask . Record this mass on the report sheet
Using the graduated cylinder , measure out (8.3 ml ) of acetic Anhydride and add this to the flask
Carefully add( 15 ) drops of concentrated sulfuric acid ( 18 M H2SO4 ) a catalyst to the flask . Stir the mixer gently observing the rise in temperature to 70 – 80 while the salicylic acid dissolves
place the flask in the water bath and heat . After the begins to boil , heat for an additional 15 minutes
After heating , remove the flask from the water- bath and allow the flask and contents to cool on the lab bench for about 3 minutes
Add 15ml of room temperature to water to the flask to facilitate the decomposition of the excess acetic anhydride . Swirl the flask to mix the contents
Place it in an ice bath and cool until the crystallization of the aspirin appears complete , If crystals do not appear , you can scratch the walls of the flask with a stirring . rod to induce crystallization
Collect the solid aspirin using a Buchner funnel and filter paper ,be sure to seat the filter paper in the filter with a small amount of water
9 Rinse the flask twice with 3 ml of ice cold water to remove any residual crystals
Dry the crystals by pulling air through them for about 15 minutes , weight , and calculate the percentage yield
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