Acetylsalicylic acid benzene rings

Only four years after Kekule proposed the ring structure for benzene, and before the configuration of salicylic acid was established, Kraut concluded on the basis of sound chemical evidence that the products obtained on heating acetylsalicylic acid possess chain structures formed through intermolecular esterification. He assigned the dimeric and tetrameric formulas... 

Phenol acids are phenols in which there is also a carboxylic acid group attached to the benzene ring. They include salicylic acid (ortho-hydroxybenzoic acid) and para-hydroxy-benzoic acid (Figure 25.8). Acetylsalicylic acid (aspirin) and sodium salicylate are derivatives of salicylic acid. Like phenol, they have antipyretic and analgesic properties. The methyl, ethyl and propyl esters of para-hydroxybenzoic acid (parabens) are used as preservatives in pharmaceuticals, cosmetics and foodstuffs. 

Acetylsalicylic acid. Red atoms are oxygen white atoms are hydrogen and black atoms are carbon. Striped sticks indicate a benzene ring, publishers... 

In this reaction, the hydroxyl group (—OH) on the benzene ring in salicylic acid reacts with acetic anhydride to form an ester functional group. Thus, the formation of acetylsalicylic acid is referred to as an esterification reaction. This reaction requires the presence of an acid catalyst, indicated by the above the equilibrium... 

The most likely impurity in the final product is salicylic acid itself, which can arise from incomplete reaction of the starting materials or from hydrolysis (reaction with water) of the product during the isolation steps. The hydrolysis reaction of acetylsalicylic add produces salicylic acid. Salicylic add and other compounds that contain a hydroxyl group on the benzene ring are referred to as phenols. Phenols form a highly colored complex with ferric chloride (Fe + ion). Aspirin is not a phenol, because it does not possess a hydroxyl group directly attached to the ring. 

As time passed, chemists found or synthesized many compounds with benzene rings that had no odor, such as benzoic acid and acetylsalicylic acid (aspirin). 

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