Chromium-substituted aluminophosphate-5 (CrAPO-5) is a heterogeneous, recyclable catalyst for the liquid phase autoxidation of hydrocarbons. CrAPO-5 catalyzed the autoxidation of cyclohexane at 115-130 degrees C and 5 bar O-2, 20 bar air in the presence of a small amount of an alkyl hydroperoxide initiator, to afford cyclohexanone as the major product. Similarly, tetralin and indane were selectively oxidized to 1-tetralone and 1-indanone, respectively, at 100 degrees C and 1 bar O-2 Ethylbenzene was selectively converted to acetophenone, in the presence of sodium-exchanged CrAPO-5, at 130 degrees C and 1 bar O-2. The CrAPO-5 catalyst was recycled four times without loss of activity or selectivity in the decomposition of cyclohexyl hydroperoxide. Evidence is presented to support a mechanism involving initial free radical autoxidation of the hydrocarbons followed by selective CrAPO-5-catalyzed intramolecular, heterolytic decomposition of the secondary alkyl hydroperoxide intermediate to the corresponding ketone and water.