Abstract: Objective To establish a method for monitoring synthesis systems of acetylsalicylic acid with citric acid as the catalyst by second derivative spectrometry.Methods Respectively, standard work curve of acetyl salicylic acid and salicylic acid were established with second derivative value against concentration at the wavelengths of 289nm and 308nm. Under different temperatures, the real-time content of acetyl salicylic acid and salicylic acid in synthesis reaction system were monitored. Results When the reaction temperature is 70 ℃,80 ℃,90 ℃ and 95 ℃, the complete reaction times were about 80 min, 50 min, 20 min and 15 min individually. Conclusion The second derivative spectrometry method can be achieved on the monitoring and judging acetylsalicylic acid synthesis reaction endpoint.

Key words: acetyl salicylic acid, citric acid, ultraviolet spectrum, derivative spectrum