The invention relates to the production of carbamates in a single reactor (one-pot) using solid catalysts, involving the reaction between at least one nitro compound, an organic carbonate of formula (OR)(OR')C=O, a gas selected from hydrogen gas and a mixture of gases containing hydrogen and hydrogen precursor compounds, and a catalyst that has at least one metallic oxide and can also contain an element of groups 8, 9, 10 and 11 of the periodical table. The carbonates obtained can be transformed into their corresponding isocyanates.