The oxidative carbonylation of methane to acetic acid was investigated using Pt(II) cations as the catalyst and sulfuric acid as the solvent. The reactions were carried out at 180 degrees C in a sealed batch reactor containing either fuming or concentrated (96 wt%) sulfuric acid (3 ml) and PtCl2 (20 mM) in the liquid-phase, and pressurized with CH4 (400 psi) and CO (400 psi). In the absence of CO, the only product is methyl bisulfate, but in the presence of CO, this product undergoes carbonylation to acetic acid. CO also serves as a reducing agent and can reduce the catalytically active Pt(II) to Pt(0), which is inactive. The catalyst activity can be increased by promoting the re-oxidation using co-catalyst, such as CuCl2 and 0, Thus, a balance must be maintained between oxidizing and reducing conditions in order to minimize or avoid the loss of Pt(II). (c) 2006 Elsevier B.V. All rights reserved.