Autoxidative processes in HCI may be influenced by reactions of the organic peroxy intermediates, or of H,O,, with the medium. These reactions with HCI led to the evolution of O2 and also of CI, under certain conditions. The question whether HCI is oxidized by an organic peroxy intermediate or by H,O, could be answered.Organic compounds may be chlorinated by H,O,-HCI in high yields. The experiments strongly support the idea that aromatic chlorination is then effected by the species HOCl and/or HOOCI which are produced in situ.