The invention pertains to a compound generating an acid of the formula I or II, for instance corresponding sulfonium and iodonium salts, as well as corresponding sulfonyloximes wherein X is CH2 or CO; Y is O, NR4, S, O(CO), O(CO)O, O(CO)NR4, OSO2, O(CS), or O(CS)NR4; R1 is for example C1-C18alkyl, C1-C10haloalkyl, C2-C12alkenyl, C4-C30cycloalkenyl, phenyl-C1-C3-alkyl, C3-C30cycloalkyl, C3-C30cycloalkyl-C1-C18alkyl, interrupted C2-C18alkyl, interrupted C3-C30cycloalkyl, interrupted C3-C30cycloalkyl-C1-C18alkyl, interrupted C4-C30cycloalkenyl, phenyl, naphthyl, anthracyl, phenanthryl, biphenylyl, fluorenyl or heteroaryl, all unsubstituted or are substituted; or R1 is NR12R13; R2 and R3 are for example C3-C30cycloalkylene, C3-C30cycloalkyl-C1-C18alkylene, C1-C18alkylene, C1-C10haloalkylene, C2-C12alkenylene, C4-C30cycloalkenylene, phenylene, naphthylene, anthracylene, phenanthrylene, biphenylene or heteroarylene; all unsubstituted or substituted; R4 is for example C3-C30cycloalkyl, C3-C30cycloalkyl-C1-C18alkyl, C1-C18alkyl, C1-C10haloalkyl, C2-C12alkenyl, C4-C30cycloalkenyl, phenyl-C1-C3-alkyl; R12 and R13 are for example C3-C30cycloalkyl, C3-C30cycloalkyl-C1-C18alkyl, C1-C18alkyl, C1-C10haloalkyl, C2-C12alkenyl, C4-C30cycloalkenyl, phenyl-C1-C3-alkyl, Ar, (CO)R15, (CO)OR15 or SO2R15; and Ar is phenyl, biphenylyl, fluorenyl, naphthyl, anthracyl, phenanthryl or heteroaryl, all unsubstituted or substituted.