organic solvent selected from the group consisting of alkanol ketone chlorinated hydrocarbon ester and nitrile the preferred alkanol is methanol ethanol propanol isopropanol butanol 2 butanol and pentanol the preferred ketone is acetone and methyl ethyl ketone the preferred chlorinated hydrocarbon is dichloromethane the preferred ester is ethyl acetate and isopropyl acetate and the preferred nitrile is acetonitrile wherein the volume of organic solvent used is 5 to 20 times preferably 10 to 15 times of the mirabegron the preferred alkanol of the present invention is a mixture of isopropanol and methanol wherein the ratio of methanol to isopropanol volume volume is 1 8 preferably the ratio is 1 4 in step b an antioxidant and or a chelating agent are added to the reaction mixture obtained in step a the antioxidant is selected from group consisting of hydrogen donating antioxidants such as phenolic antioxidants more preferably butylated hydroxy toluene bht butylated hydroxy anisole bha u03b1 tocopherol tocopheryl acetate and a mixture thereof the preferred antioxidant of the present invention is butylated hydroxy anisole in a preferred aspect of the invention the chelating agent is ethylenediamine tetra acetic acid or a salt thereof in step c the reaction mixture of step b is heated to about 40 u00b0 c to about 90 u00b0 c preferably to about 50 u00b0 c to about 80 u00b0 c more preferably to about 60 u00b0 c to about 75 u00b0 c to obtain the solution of step c the solution of step c is optionally micron filtered to make it clear free of unwanted particles the solution obtained in step c is cooled to about.