Aspirin Lab
Preparation of an Ester
Acetylsalicylic Acid (Aspirin)
OBJECTIVE:
To become familiar with the techniques and principle of esterification.
DISCUSSION:
Aspirin is a drug widely used as an antipyretic agent (to reduce fever), as an analgesic agent (to reduce pain), and/or as an anti-inflammatory agent (to reduce redness, heat or swelling in tissues). Chemically, aspirin is an ester. Esters are the products of reaction of acids with alcohols, as shown in the following equation using type formulas:
R – C – OH + R’ – OH R – C – O – R’ + H2O
ACID ALCOHOL ESTER WATER
The symbol R refers to the hydrocarbon portion (radical) of the molecules aside from the O functional group. In an organic acid, R – C – OH, the functional group is the carboxyl O group (-COOH) or –C-OH. The type of formula for an alcohol is R-OH, where the functional group is the hydroxyl group (-OH). The symbol R’ indicates that the two R-groups in the ester formula need not be the same. It has been shown by radioactive tracer methods that in the mechanism of the esterification reaction, the –OH group is split from the acid and the –H from the alcohol.
Aspirin can be made as follows:
C – OH C – OH
CH3 – C – OH + HO – CH3 – C – O– + H2O
Acetic acid Salicylic acid Aspirin (containing an (acetylsalicylic acid, -OH group) an ester)
The use of acetic anhydride instead of acetic acid, however, is a better preparative method, because the anhydride with the water to form acetic acid tends to drive the reaction to the right as shown below. An acid catalyst also is used to speed up the reaction.
Acetylsalicylic Acid (Aspirin)
OBJECTIVE:
To become familiar with the techniques and principle of esterification.
DISCUSSION:
Aspirin is a drug widely used as an antipyretic agent (to reduce fever), as an analgesic agent (to reduce pain), and/or as an anti-inflammatory agent (to reduce redness, heat or swelling in tissues). Chemically, aspirin is an ester. Esters are the products of reaction of acids with alcohols, as shown in the following equation using type formulas:
R – C – OH + R’ – OH R – C – O – R’ + H2O
ACID ALCOHOL ESTER WATER
The symbol R refers to the hydrocarbon portion (radical) of the molecules aside from the O functional group. In an organic acid, R – C – OH, the functional group is the carboxyl O group (-COOH) or –C-OH. The type of formula for an alcohol is R-OH, where the functional group is the hydroxyl group (-OH). The symbol R’ indicates that the two R-groups in the ester formula need not be the same. It has been shown by radioactive tracer methods that in the mechanism of the esterification reaction, the –OH group is split from the acid and the –H from the alcohol.
Aspirin can be made as follows:
C – OH C – OH
CH3 – C – OH + HO – CH3 – C – O– + H2O
Acetic acid Salicylic acid Aspirin (containing an (acetylsalicylic acid, -OH group) an ester)
The use of acetic anhydride instead of acetic acid, however, is a better preparative method, because the anhydride with the water to form acetic acid tends to drive the reaction to the right as shown below. An acid catalyst also is used to speed up the reaction.