Copper(I) and silver carbonyl catalysts were prepared in strong acids such as sulfuric acid, hydrogen fluoride, boron trifluoride-hydrate and fluoro sulfuric acid, Carboxylation of olefins, alcohols, dienes, diols, aldehydes and saturated hydrocarbons were carried out under atmospheric pressure and at room temperature by using copper(I) and silver carbonyl catalysts and tert.-alkanoic acids were obtained in high yields. if these catalysts were not used, carboxylation required high pressure and temperature.