An experimental study, monitored by FTIR spectroscopy, of the spontaneous reaction of C3O2 with HCI on the acid hydrate surface has been performed at low temperature. The first appearing reaction product at 85 K was assigned to chloroformylketene while the second, appearing at 145 K, to malonyl dichloride by comparison with previously reported data in matrix isolation spectroscopy. C3O2 was deposited at 80 K over an amorphous surface of HCl hydrates mainly formed from ionic species (H3O+(H2O)(n-1)Cl-; n = 1-3, 4, 6), prepared by codeposition of a H2O:HCl gaseous mixture at 80 K. The reactions were promoted by warming the substrate from 80 to 200 K. Experiments showed that monohydrate H3O+Cl- was more reactive than higher hydrates by easier C3O2 protonation. Reactions are described by an ionic mechanism catalyzed by ice water and occurring on the surface. Spectral evidence of HCl amorphous hydrates, chloroformylketene, and malonyl dichloride are reported.