The hydrolysis kinetics of aspirin in microemulsion system for cetyltrimethyl-ammonium bromide (CTAB)/n-butanol/25% n-octane/water was studied by using UV method, and the mechanism of the hydrolysis was discussed. The results show that the hydrolysis was affected by the structure and the structural transition of microemulsions. The hydrolysis rates are higher in W/O microemulsion media and decrease with the addition of water, they increase with that in B. C., and they decrease with that in O/W. The transition points of the hydrolysis rates occur at the points of the structural transition from W/O to B. C., and B. C. to O/W, and this was considered to be caused by the different hydrolysis mechanism and the change of polarity in interfacial films.

Key words: ULTRAVIOLET SPECTROPHOTOMETRY, REACTION MECHANISM, WATER, HYDROLYSIS, ACETYLSALICYLICUM ACID, NORMAL OCTANE, N-BUTANOL, KINETIC STUDY, MICROEMUSION