The increasing use of carbon dioxide (CO2) as C1-synthon in organic chemistry is driven by the urge to avoid fossil resources and out-dated, dangerous synthetic procedures or reagents such as phosgene. Recently, mechanochemistry is experiencing growing popularity, and it has been employed for a plethora of organic and organometallic syntheses. Some major attributes of mechanochemical or ball milling approaches are reduced amounts of solvents, shorter reaction times through higher reaction rates, and alternative reaction pathways that are unavailable in solution. Specific ball milling setups allow the use of gases as reactants. While the mechanochemical hydrogenation or formation of CO2 as a by-product have been observed and addressed in several investigations, examples of mechanochemical carboxylative CO2 insertions are restricted to two studies: the transformation of aziridine into oxazolidinones using dry ice and the addition of gaseous CO2 to L-lysine forming its ecarbamate (Scheme 1, a and b). ___ then HCl Realizing the potential and challenges, we initiated a program to, first, prepare Grignard reagents in a ball mill, and, second, to react the expected organomagnesium reagents with CO2 under mechanochemical conditions. As equipment, we used a commercially available milling vessel with two gas valves suitable for adding gaseous reagents to solids or liquids. The Grignard carboxylations were conducted in three separate steps: First, magnesium turnings were milled to transform them into a fine powder. Then, the Grignard reagent was generated after adding an organobromide. Last, gaseous CO2 was introduced through the gas valves to serve as electrophile in the final milling step. After terminating the milling, dilute hydrochloric acid was added to support the removal of the product mixture from the milling device. Finally, extraction with ethyl acetate afforded the crude carboxylic acid.