Process for preparing a solution L 1 <115> of a sodium alkoxide NaOR in the alcohol ROH in an electrolysis cell E <100>, wherein E <100> comprises at least one anode chamber K A <101>, at least one cathode chamber K K <102> and at least one interposed middle chamber K M <103>, wherein K A <101> comprises an anodic electrode E A <104> and an outlet A KA <106>, wherein K K <102> comprises a cathodic electrode E K <105>, an inlet Z KK <107> and an outlet A KK <109>, wherein K M <103> comprises an inlet Z KM <108> and a gas outlet G <120>, is separated from K A <101> by a diffusion barrier D <110> and is separated from K K <102> by a sodium cation-conducting solid-state electrolyte F K <111>, wherein K A <101> and K M <103> are connected to one another by a connection V AM <112> through which liquid can be routed from K M <103> into K A <101>, wherein the process comprises the following steps (a), (b) and (c) that proceed simultaneously: (a) a solution L 2 <113> comprising the alcohol ROH is routed through K K <102>, (b) a neutral or alkaline, aqueous solution L 3 <114> comprising NaCl and at least one salt S selected from hydrogencarbonate and carbonate is routed through K M <103>, then via V AM <112>, then through K A <101>, (c) voltage is applied between E A <104> and E K <105>, which affords the solution L 1 <115> at the outlet A KK <109>, wherein the concentration of NaOR in L 1 <115> is higher than in L 2 <113>, and which affords an aqueous solution L 4 <116> of NaCl at the outlet A KA <106>, wherein the concentration of NaCl in L 4 <116> is lower than in L 3 <114>, and wherein the total concentration of all salts S in L 4 <116> is lower than in L 3 <114>, and which forms CO 2 <121> in the middle chamber K M <103>, which is removed from the middle chamber K M <103> via the gas outlet G <120>, wherein R is an alkyl radical having 1 to 4 carbon atoms. wherein E <100> comprises at least one anode chamber K A <101>, at least one cathode chamber K K <102> and at least one interposed middle chamber K M <103>, wherein K A <101> comprises an anodic electrode E A <104> and an outlet A KA <106>, wherein K K <102> comprises a cathodic electrode E K <105>, an inlet Z KK <107> and an outlet A KK <109>, wherein K M <103> comprises an inlet Z KM <108> and a gas outlet G <120>, is separated from K A <101> by a diffusion barrier D <110> and is separated from K K <102> by a sodium cation-conducting solid-state electrolyte F K <111>, wherein K A <101> and K M <103> are connected to one another by a connection V AM <112> through which liquid can be routed from K M <103> into K A <101>, wherein the process comprises the following steps (a), (b) and (c) that proceed simultaneously: (a) a solution L 2 <113> comprising the alcohol ROH is routed through K K <102>, (b) a neutral or alkaline, aqueous solution L 3 <114> comprising NaCl and at least one salt S selected from hydrogencarbonate and carbonate is routed through K M <103>, then via V AM <112>, then through K A <101>, (c) voltage is applied between E A <104> and E K <105>, which affords the solution L 1 <115> at the outlet A KK <109>, wherein the concentration of NaOR in L 1 <115> is higher than in L 2 <113>, (a) a solution L 2 <113> comprising the alcohol ROH is routed through K K <102>, (b) a neutral or alkaline, aqueous solution L 3 <114> comprising NaCl and at least one salt S selected from hydrogencarbonate and carbonate is routed through K M <103>, then via V AM <112>, then through K A <101>, (c) voltage is applied between E A <104> and E K <105>, which affords the solution L 1 <115> at the outlet A KK <109>, wherein the concentration of NaOR in L 1 <115> is higher than in L 2 <113>, and which affords an aqueous solution L 4 <116> of NaCl at the outlet A KA <106>, wherein the concentration of NaCl in L 4 <116> is lower than in L 3 <114>, and wherein the total concentration of all salts S in L 4 <116> is lower than in L 3 <114>, and which forms CO 2 <121> in the middle chamber K M <103>, which is removed from the middle chamber K M <103> via the gas outlet G <120>, wherein R is an alkyl radical having 1 to 4 carbon atoms.