A method of conducting a chemical reaction in a flow reactor comprises the steps of pumping at least one liquid reaction plug bounded at both ends by liquid spacer plugs along a reaction channel of the reactor; and conducting the chemical reaction in the reaction plug inside the reaction channel, wherein the liquid reaction plug comprises one or more reagents dispersed in a reaction solvent, the liquid spacer plugs are immiscible in the reaction solvent, and the reagents are substantially insoluble in the spacer plugs; and wherein the aspect ratio of the at least one reaction plug is at least about 10.