Iron complexes [Fe-II(OPPh(3))(4)(2+), Fe-II(bpy)(2),(2+), Fe-II(OH2)(6)(2+), and (FeCl3)-Cl-III] catalytically activate 1:1 HOOH/HCl combinations for the efficient chlorohydroxylation of olefins. The reactive intermediate 7 is not HOCl, but appears to be formed via a Fenton process Fe(II)L(x)(2+) reversible arrow (B) [L(x)(+)Fe(II)OOH(BH+)] (1) --> (HCl) [L(x)Fe(IV)(OH)Cl] (7) + H2O). Although the major product from the reaction of 7 with olefin substrates (e.g., cyclohexene, c-C6H10) is the chlorohydroxo derivative [c-C6H10 + HOOH + HCl --> (Fe(II)L(x)) c-C6H10(OH)Cl + H2O], significant amounts of the dihydroxo [c-C6H10(OH)2] and traces of the dichloro [c-C6H10Cl2] derivatives are produced. The reaction efficiency with respect to HOOH/HCl ranges from 51% for norbornene to 31% for cyclohexene to 10% for l-hexene. The presence of dioxygen (O-2) With c-C6H10 results in the production of some ketone [c-C6H8(O)] via oxygenated Fenton chemistry, but does not inhibit the chlorohydroxylation process. The catalyzed process is equally efficient and selective in a biphasic H2O/substrate solution as in acetonitrile. With cis-stilbene (cis-PhCH=CRPh) the major product is the epoxide (> 80%); the reaction efficiency is 63% relative to HOOH/HCl. These systems chlorinate saturated hydrocarbons (c-C6H12 --> c-C6H11Cl) and hydroxylate benzene (PhH --> PhOH). Because 7 chlorohydroxylates olefins and chlorinates hydrocarbons in aqueous media much more efficiently than HOCl, its in-vivo analogue may be a reasonably reactive intermediate for "oxy-radical" damage in biological systems.