synthesis of aspirin | Schemes and Mind Maps Chemistry

Los Angeles City College Chemistry 51 Fall 2005

3093

Experiment 11

Synthesis and Analysis of Aspirin

INTRODUCTION

Aspirin is most widely sold over-the-counter drug. It has the ability to reduce fever (an antipyretic), to

reduce pain (an analgesic), and to reduce swelling, soreness, and redness (an anti-inflammatory agent). One of

the first recorded accounts for the discovery of aspirin appeared in England, in 1763, crediting the bark of

willow trees with a beneficial effect in alleviating distress due to fevers, aches, and pains. Later, the compound

salicylic acid (named for the Latin word for willow, salix) was isolated from willow bark. It proved to be the

active ingredient. By 1860, organic chemists were able to synthesize salicylic acid from basic starting materials,

this furthered the therapeutic use of the substance, but there were problems. Salicylic acid proved to be irritating

to the membranes of the throat, mouth, and stomach. These problems are directly associated with the high

acidity of the compound, but a simple remedy was discovered, namely, replacement of the acidic phenolic

hydrogen atom with an acetyl group.

When interpreting the structures of the above organic compounds, note the following characteristics of these

molecules. Organic molecules are complex compounds of carbon. Carbon always shares four pairs of electrons

in bonds with other molecular groups or atoms. When the structure of an organic molecule is drawn using the

condensed method, carbon rings are represented with simple geometric shapes, such as a hexagon. Each corner

of the hexagon represents a carbon atom and the number of hydrogen atoms required to share 4 pairs of

electrons with the carbon. If the “corner” has no other marks, that means there is a carbon atom bonded to 2

other carbon atoms (in the ring) plus 2 hydrogen atoms. The hydrogen atoms are implied, not show. If a carbon

to carbon double bond (C =C) is present and the carbons are attached in a ring, each of the two carbon atoms is

bonded to two others with 6 pairs of electrons, and only one hydrogen is attached to each of these carbons give

the full compliment of four bonds. If a triple bond is present then only one other atom may be attached. Check

the structures below to see that each carbon has four and only four bonds. Oxygen, on the other hand, will bond

covalently to only two atoms, and hydrogen bonds to only one.

A useful synthesis of acetylsalicylic acid was developed in 1893, patented in 1899, marketed under the trade

name of “aspirin” by the Bayer Company in Germany. The name aspirin was invented by the chemist, Felix

Hofmann, who originally synthesized acetylsalicylic acid for Bayer. More than 50 million 5-grain tablets of

aspirin are consumed daily in the United States. In Part I of this experiment, you will prepare aspirin by reaction

of salicylic acid with acetic anhydride, using concentrated sulfuric acid as a catalyst.

synthesis of aspirin, Schemes and Mind Maps of Chemistry