Piperazine (Pz) mixed with other amines is a proposed carbon capture solvent, but there is concern about the impact of Pz on air quality, including the potential to produce toxic products. Here, the • OH initiated oxidation of Pz has been studied by ab initio modelling and RRKM / master equation kinetic simulations. The Pz + • OH reaction is found to proceed at around the capture rate, consistent with experiment, with abstraction predominantly from C-H sites, forming an alkyl radical (PzC). The subsequent reaction kinetics of carbon centred Pz radicals with O2 are also studied, so as to determine the first-generation oxidation products. We find that the PzC radical predominantly reacts with O2 to produce a cyclic imine product + HO2 • under tropospheric conditions, with the stabilized peroxyl radical formed as a minor product. Subsequent reaction of the peroxyl radical with NO produces an alkoxyl radical that can react with O2 to yield a cyclic amide or undergo unimolecular ring opening followed by a second O2 addition / HO2 • elimination step to produce CH2=NCH2CH2NHCHO.