The activity of titanium silicalite (TS-1) and the reaction pathway for the ammoximation of cyclohexanone to produce cyclohexanone oxime were studied using acetic acid as a solvent at 60 degrees C. The effect of solvent, sources of nitrogen, water content and the active site stability were also evaluated. It was found that, in the reaction using acetic acid as a solvent, the ammoximation of cyclohexanone proceeded mainly via the oxidation of imine, which was primarily formed in situ by the condensation of ketone with ammonia. In addition, the ammonium salts of weak acids, such as acetate, citrate and carbonate, can be used as nitrogen sources for the ammoximation in acetic acid. Water was shown to inhibit the formation of imine, and also prevent the side reactions. Moreover, TS-1 possessed an excellent stability, and can be reused without significant loss of activity. (c) 2005 Elsevier B.V. All rights reserved.