The reaction between salicylic acid, acetyl chloride, and pyridine can be represented by the following equation:

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C7H6O3 (salicylic acid) + CH3COCl (acetyl chloride) + C5H5N (pyridine) → C9H8O4 (aspirin) + C5H5NHCl (pyridine hydrochloride)

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In this reaction, salicylic acid reacts with acetyl chloride in the presence of pyridine to form aspirin (acetylsalicylic acid) and pyridine hydrochloride as a byproduct. The reaction is typically carried out in a solvent such as chloroform or dichloromethane.